// What is this module called?
module syncEngine;

// What does this module require to function?
import core.stdc.stdlib: EXIT_SUCCESS, EXIT_FAILURE, exit;
import core.thread;
import core.time;
import std.algorithm;
import std.array;
import std.concurrency;
import std.container.rbtree;
import std.conv;
import std.datetime;
import std.encoding;
import std.exception;
import std.file;
import std.json;
import std.parallelism;
import std.path;
import std.range;
import std.regex;
import std.stdio;
import std.string;
import std.uni;
import std.uri;
import std.utf;

// What other modules that we have created do we need to import?
import config;
import log;
import util;
import onedrive;
import itemdb;
import clientSideFiltering;
import progress;

class posixException: Exception {
	@safe pure this(string localTargetName, string remoteTargetName) {
		string msg = format("POSIX 'case-insensitive match' between '%s' (local) and '%s' (online) which violates the Microsoft OneDrive API namespace convention", localTargetName, remoteTargetName);
		super(msg);
	}	
}

class accountDetailsException: Exception {
	@safe pure this() {
		string msg = format("Unable to query OneDrive API to obtain required account details");
		super(msg);
	}	
}

class SyncException: Exception {
    @nogc @safe pure nothrow this(string msg, string file = __FILE__, size_t line = __LINE__) {
        super(msg, file, line);
    }
}

class SyncEngine {
	// Class Variables
	ApplicationConfig appConfig;
	OneDriveApi oneDriveApiInstance;
	ItemDatabase itemDB;
	ClientSideFiltering selectiveSync;

	// Array of directory databaseItem.id to skip while applying the changes.
	// These are the 'parent path' id's that are being excluded, so if the parent id is in here, the child needs to be skipped as well
	RedBlackTree!string skippedItems = redBlackTree!string();
	// Array of databaseItem.id to delete after the changes have been downloaded
	string[2][] idsToDelete;
	// Array of JSON items which are files or directories that are not 'root', skipped or to be deleted, that need to be processed
	JSONValue[] jsonItemsToProcess;
	// Array of JSON items which are files that are not 'root', skipped or to be deleted, that need to be downloaded
	JSONValue[] fileJSONItemsToDownload;
	// Array of paths that failed to download
	string[] fileDownloadFailures;
	// Array of all OneDrive driveId's that have been seen
	string[] driveIDsArray;
	// List of items we fake created when using --dry-run
	string[2][] idsFaked;
	// List of paths we fake deleted when using --dry-run
	string[] pathFakeDeletedArray;
	// Array of database Parent Item ID, Item ID & Local Path where the content has changed and needs to be uploaded
	string[3][] databaseItemsWhereContentHasChanged;
	// Array of local file paths that need to be uploaded as new itemts to OneDrive
	string[] newLocalFilesToUploadToOneDrive;
	// Array of local file paths that failed to be uploaded to OneDrive
	string[] fileUploadFailures;
	// List of path names changed online, but not changed locally when using --dry-run
	string[] pathsRenamed;
	// List of paths that were a POSIX case-insensitive match, thus could not be created online
	string[] posixViolationPaths;
	// List of local paths, that, when using the OneDrive Business Shared Folders feature, then diabling it, folder still exists locally and online
	// This list of local paths need to be skipped
	string[] businessSharedFoldersOnlineToSkip;
	// List of interrupted uploads session files that need to be resumed
	string[] interruptedUploadsSessionFiles;
	// List of validated interrupted uploads session JSON items to resume
	JSONValue[] jsonItemsToResumeUpload;
		
	// Flag that there were upload or download failures listed
	bool syncFailures = false;
	// Is sync_list configured
	bool syncListConfigured = false;
	// Was --dry-run used?
	bool dryRun = false;
	// Was --upload-only used?
	bool uploadOnly = false;
	// Was --remove-source-files used?
	// Flag to set whether the local file should be deleted once it is successfully uploaded to OneDrive
	bool localDeleteAfterUpload = false;
	
	// Do we configure to disable the download validation routine due to --disable-download-validation
	// We will always validate our downloads
	// However, when downloading files from SharePoint, the OneDrive API will not advise the correct file size 
	// which means that the application thinks the file download has failed as the size is different / hash is different
	// See: https://github.com/abraunegg/onedrive/discussions/1667
    bool disableDownloadValidation = false;
	
	// Do we configure to disable the upload validation routine due to --disable-upload-validation
	// We will always validate our uploads
	// However, when uploading a file that can contain metadata SharePoint will associate some 
	// metadata from the library the file is uploaded to directly in the file which breaks this validation. 
	// See: https://github.com/abraunegg/onedrive/issues/205
	// See: https://github.com/OneDrive/onedrive-api-docs/issues/935
	bool disableUploadValidation = false;
	
	// Do we perform a local cleanup of files that are 'extra' on the local file system, when using --download-only
	bool cleanupLocalFiles = false;
	// Are we performing a --single-directory sync ?
	bool singleDirectoryScope = false;
	string singleDirectoryScopeDriveId;
	string singleDirectoryScopeItemId;
	// Is National Cloud Deployments configured ?
	bool nationalCloudDeployment = false;
	// Do we configure not to perform a remote file delete if --upload-only & --no-remote-delete configured
	bool noRemoteDelete = false;
	// Is bypass_data_preservation set via config file
	// Local data loss MAY occur in this scenario
	bool bypassDataPreservation = false;
	// Maximum file size upload
	//  https://support.microsoft.com/en-us/office/invalid-file-names-and-file-types-in-onedrive-and-sharepoint-64883a5d-228e-48f5-b3d2-eb39e07630fa?ui=en-us&rs=en-us&ad=us
	//	July 2020, maximum file size for all accounts is 100GB
	//  January 2021, maximum file size for all accounts is 250GB
	ulong maxUploadFileSize = 268435456000; // 250GB
	// Threshold after which files will be uploaded using an upload session
	ulong sessionThresholdFileSize = 4 * 2^^20; // 4 MiB
	// File size limit for file operations that the user has configured
	ulong fileSizeLimit;
	// Total data to upload
	ulong totalDataToUpload;
	// How many items have been processed for the active operation
	ulong processedCount;
	// Are we creating a simulated /delta response? This is critically important in terms of how we 'update' the database
	bool generateSimulatedDeltaResponse = false;
	// Store the latest DeltaLink
	string latestDeltaLink;
	
	// Configure this class instance
	this(ApplicationConfig appConfig, ItemDatabase itemDB, ClientSideFiltering selectiveSync) {
		// Configure the class varaible to consume the application configuration
		this.appConfig = appConfig;
		// Configure the class varaible to consume the database configuration
		this.itemDB = itemDB;
		// Configure the class variable to consume the selective sync (skip_dir, skip_file and sync_list) configuration
		this.selectiveSync = selectiveSync;
		
		// Configure the dryRun flag to capture if --dry-run was used
		// Application startup already flagged we are also in a --dry-run state, so no need to output anything else here
		this.dryRun = appConfig.getValueBool("dry_run");
		
		// Configure file size limit
		if (appConfig.getValueLong("skip_size") != 0) {
			fileSizeLimit = appConfig.getValueLong("skip_size") * 2^^20;
			fileSizeLimit = (fileSizeLimit == 0) ? ulong.max : fileSizeLimit;
		}
		
		// Is there a sync_list file present?
		if (exists(appConfig.syncListFilePath)) this.syncListConfigured = true;
		
		// Configure the uploadOnly flag to capture if --upload-only was used
		if (appConfig.getValueBool("upload_only")) {
			log.vdebug("Configuring uploadOnly flag to TRUE as --upload-only passed in or configured");
			this.uploadOnly = true;
		}
		
		// Configure the localDeleteAfterUpload flag
		if (appConfig.getValueBool("remove_source_files")) {
			log.vdebug("Configuring localDeleteAfterUpload flag to TRUE as --remove-source-files passed in or configured");
			this.localDeleteAfterUpload = true;
		}
		
		// Configure the disableDownloadValidation flag
		if (appConfig.getValueBool("disable_download_validation")) {
			log.vdebug("Configuring disableDownloadValidation flag to TRUE as --disable-download-validation passed in or configured");
			this.disableDownloadValidation = true;
		}
		
		// Configure the disableUploadValidation flag
		if (appConfig.getValueBool("disable_upload_validation")) {
			log.vdebug("Configuring disableUploadValidation flag to TRUE as --disable-upload-validation passed in or configured");
			this.disableUploadValidation = true;
		}
		
		// Do we configure to clean up local files if using --download-only ?
		if ((appConfig.getValueBool("download_only")) && (appConfig.getValueBool("cleanup_local_files"))) {
			// --download-only and --cleanup-local-files were passed in
			log.log("WARNING: Application has been configured to cleanup local files that are not present online.");
			log.log("WARNING: Local data loss MAY occur in this scenario if you are expecting data to remain archived locally.");
			// Set the flag
			this.cleanupLocalFiles = true;
		}
		
		// Do we configure to NOT perform a remote delete if --upload-only & --no-remote-delete configured ?
		if ((appConfig.getValueBool("upload_only")) && (appConfig.getValueBool("no_remote_delete"))) {
			// --upload-only and --no-remote-delete were passed in
			log.log("WARNING: Application has been configured NOT to cleanup remote files that are deleted locally.");
			// Set the flag
			this.noRemoteDelete = true;
		}
		
		// Are we forcing to use /children scan instead of /delta to simulate National Cloud Deployment use of /children?
		if (appConfig.getValueBool("force_children_scan")) {
			log.log("Forcing client to use /children API call rather than /delta API to retrieve objects from the OneDrive API");
			this.nationalCloudDeployment = true;
		}
		
		// Are we forcing the client to bypass any data preservation techniques to NOT rename any local files if there is a conflict?
		// The enabling of this function could lead to data loss
		if (appConfig.getValueBool("bypass_data_preservation")) {
			log.log("WARNING: Application has been configured to bypass local data preservation in the event of file conflict.");
			log.log("WARNING: Local data loss MAY occur in this scenario.");
			this.bypassDataPreservation = true;
		}
		
		// Did the user configure a specific rate limit for the application?
		if (appConfig.getValueLong("rate_limit") > 0) {
			// User configured rate limit
			log.log("User Configured Rate Limit: ", appConfig.getValueLong("rate_limit"));
			
			// If user provided rate limit is < 131072, flag that this is too low, setting to the recommended minimum of 131072
			if (appConfig.getValueLong("rate_limit") < 131072) {
				// user provided limit too low
				log.log("WARNING: User configured rate limit too low for normal application processing and preventing application timeouts. Overriding to recommended minimum of 131072 (128KB/s)");
				appConfig.setValueLong("rate_limit", 131072);
			}
		}
		
		// Did the user downgrade all HTTP operations to force HTTP 1.1
		if (appConfig.getValueBool("force_http_11")) {
			// User is forcing downgrade to curl to use HTTP 1.1 for all operations
			log.vlog("Downgrading all HTTP operations to HTTP/1.1 due to user configuration");
		} else {
			// Use curl defaults
			log.vdebug("Using Curl defaults for HTTP operational protocol version (potentially HTTP/2)");
		}
	}
	
	// Initialise the Sync Engine class
	bool initialise() {

		// create a new instance of the OneDrive API
		oneDriveApiInstance = new OneDriveApi(appConfig);
		if (oneDriveApiInstance.initialise()) {
			try {
				// Get the relevant default account & drive details
				getDefaultDriveDetails();
			} catch (accountDetailsException exception) {
				// details could not be queried
				log.error(exception.msg);
				// Shutdown API instance
				oneDriveApiInstance.shutdown();
				// Free object and memory
				object.destroy(oneDriveApiInstance);
				exit(-1);
			}
			
			try {
				// Get the relevant default account & drive details
				getDefaultRootDetails();
			} catch (accountDetailsException exception) {
				// details could not be queried
				log.error(exception.msg);
				// Shutdown API instance
				oneDriveApiInstance.shutdown();
				// Free object and memory
				object.destroy(oneDriveApiInstance);
				exit(-1);
			}
			
			try {
				// Display details
				displaySyncEngineDetails();
			} catch (accountDetailsException exception) {
				// details could not be queried
				log.error(exception.msg);
				// Shutdown API instance
				oneDriveApiInstance.shutdown();
				// Free object and memory
				object.destroy(oneDriveApiInstance);
				exit(-1);
			}
		} else {
			// API could not be initialised
			log.error("OneDrive API could not be initialised with previously used details");
			// Shutdown API instance
			oneDriveApiInstance.shutdown();
			// Free object and memory
			object.destroy(oneDriveApiInstance);
			exit(-1);
		}
		
		// API was initialised
		log.log("Sync Engine Initialised with new Onedrive API instance");
		
		// Shutdown this API instance, as we will create API instances as required, when required
		oneDriveApiInstance.shutdown();
		// Free object and memory
		object.destroy(oneDriveApiInstance);
		return true;
	}
	
	// Get Default Drive Details for this Account
	void getDefaultDriveDetails() {
		
		// Function variables
		JSONValue defaultOneDriveDriveDetails;
		
		// Get Default Drive Details for this Account
		try {
			log.vdebug("Getting Account Default Drive Details");
			defaultOneDriveDriveDetails = oneDriveApiInstance.getDefaultDriveDetails();
		} catch (OneDriveException exception) {
			log.vdebug("defaultOneDriveDriveDetails = oneDriveApiInstance.getDefaultDriveDetails() generated a OneDriveException");
			
			string thisFunctionName = getFunctionName!({});
			
			if ((exception.httpStatusCode == 400) || (exception.httpStatusCode == 401)) {
				// Handle the 400 | 401 error
				handleClientUnauthorised(exception.httpStatusCode, exception.msg);
			}
			
			// HTTP request returned status code 408,429,503,504
			if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 429) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
				// Handle the 429
				if (exception.httpStatusCode == 429) {
					// HTTP request returned status code 429 (Too Many Requests). We need to leverage the response Retry-After HTTP header to ensure minimum delay until the throttle is removed.
					handleOneDriveThrottleRequest(oneDriveApiInstance);
					log.vdebug("Retrying original request that generated the OneDrive HTTP 429 Response Code (Too Many Requests) - attempting to retry ", thisFunctionName);
				}
				// re-try the specific changes queries
				if ((exception.httpStatusCode == 408) ||(exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
					// 408 - Request Time Out
					// 503 - Service Unavailable
					// 504 - Gateway Timeout
					// Transient error - try again in 30 seconds
					auto errorArray = splitLines(exception.msg);
					log.log(errorArray[0], " when attempting to query Account Default Drive Details - retrying applicable request in 30 seconds");
					log.vdebug("defaultOneDriveDriveDetails = oneDriveApiInstance.getDefaultDriveDetails() previously threw an error - retrying");
					// The server, while acting as a proxy, did not receive a timely response from the upstream server it needed to access in attempting to complete the request. 
					log.vdebug("Thread sleeping for 30 seconds as the server did not receive a timely response from the upstream server it needed to access in attempting to complete the request");
					Thread.sleep(dur!"seconds"(30));
				}
				// re-try original request - retried for 429 and 504 - but loop back calling this function 
				log.vdebug("Retrying Function: getDefaultDriveDetails()");
				getDefaultDriveDetails();
			} else {
				// Default operation if not 408,429,503,504 errors
				// display what the error is
				displayOneDriveErrorMessage(exception.msg, getFunctionName!({}));
			}
		}
		
		// If the JSON response is a correct JSON object, and has an 'id' we can set these details
		if ((defaultOneDriveDriveDetails.type() == JSONType.object) && (hasId(defaultOneDriveDriveDetails))) {
			log.vdebug("OneDrive Account Default Drive Details:      ", defaultOneDriveDriveDetails);
			appConfig.accountType = defaultOneDriveDriveDetails["driveType"].str;
			appConfig.defaultDriveId = defaultOneDriveDriveDetails["id"].str;
			
			// Get the initial remaining size from OneDrive API response JSON
			// This will be updated as we upload data to OneDrive
			if (hasQuota(defaultOneDriveDriveDetails)) {
				if ("remaining" in defaultOneDriveDriveDetails["quota"]){
					// use the value provided
					appConfig.remainingFreeSpace = defaultOneDriveDriveDetails["quota"]["remaining"].integer;
				}
			}
			
			// In some cases OneDrive Business configurations 'restrict' quota details thus is empty / blank / negative value / zero
			if (appConfig.remainingFreeSpace <= 0) {
				// free space is <= 0  .. why ?
				if ("remaining" in defaultOneDriveDriveDetails["quota"]) {
					if (appConfig.accountType == "personal") {
						// zero space available
						log.error("ERROR: OneDrive account currently has zero space available. Please free up some space online.");
						appConfig.quotaAvailable = false;
					} else {
						// zero space available is being reported, maybe being restricted?
						log.error("WARNING: OneDrive quota information is being restricted or providing a zero value. Please fix by speaking to your OneDrive / Office 365 Administrator.");
						appConfig.quotaRestricted = true;
					}
				} else {
					// json response was missing a 'remaining' value
					if (appConfig.accountType == "personal") {
						log.error("ERROR: OneDrive quota information is missing. Potentially your OneDrive account currently has zero space available. Please free up some space online.");
						appConfig.quotaAvailable = false;
					} else {
						// quota details not available
						log.error("ERROR: OneDrive quota information is being restricted. Please fix by speaking to your OneDrive / Office 365 Administrator.");
						appConfig.quotaRestricted = true;
					}
				}
			}
			// What did we set based on the data from the JSON
			log.vdebug("appConfig.accountType        = ", appConfig.accountType);
			log.vdebug("appConfig.defaultDriveId     = ", appConfig.defaultDriveId);
			log.vdebug("appConfig.remainingFreeSpace = ", appConfig.remainingFreeSpace);
			log.vdebug("appConfig.quotaAvailable     = ", appConfig.quotaAvailable);
			log.vdebug("appConfig.quotaRestricted    = ", appConfig.quotaRestricted);
			
			// Make sure that appConfig.defaultDriveId is in our driveIDs array to use when checking if item is in database
			// Keep the driveIDsArray with unique entries only
			if (!canFind(driveIDsArray, appConfig.defaultDriveId)) {
				// Add this drive id to the array to search with
				driveIDsArray ~= appConfig.defaultDriveId;
			}
		} else {
			// Handle the invalid JSON response
			throw new accountDetailsException();
		}
	}
	
	// Get Default Root Details for this Account
	void getDefaultRootDetails() {
		
		// Function variables
		JSONValue defaultOneDriveRootDetails;
		
		// Get Default Root Details for this Account
		try {
			log.vdebug("Getting Account Default Root Details");
			defaultOneDriveRootDetails = oneDriveApiInstance.getDefaultRootDetails();
		} catch (OneDriveException exception) {
			log.vdebug("defaultOneDriveRootDetails = oneDriveApiInstance.getDefaultRootDetails() generated a OneDriveException");

			string thisFunctionName = getFunctionName!({});

			if ((exception.httpStatusCode == 400) || (exception.httpStatusCode == 401)) {
				// Handle the 400 | 401 error
				handleClientUnauthorised(exception.httpStatusCode, exception.msg);
			}
			
			// HTTP request returned status code 408,429,503,504
			if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 429) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
				// Handle the 429
				if (exception.httpStatusCode == 429) {
					// HTTP request returned status code 429 (Too Many Requests). We need to leverage the response Retry-After HTTP header to ensure minimum delay until the throttle is removed.
					handleOneDriveThrottleRequest(oneDriveApiInstance);
					log.vdebug("Retrying original request that generated the OneDrive HTTP 429 Response Code (Too Many Requests) - attempting to retry ", thisFunctionName);
				}
				// re-try the specific changes queries
				if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
					// 503 - Service Unavailable
					// 504 - Gateway Timeout
					// Transient error - try again in 30 seconds
					auto errorArray = splitLines(exception.msg);
					log.log(errorArray[0], " when attempting to query Account Default Root Details - retrying applicable request in 30 seconds");
					log.vdebug("defaultOneDriveRootDetails = oneDriveApiInstance.getDefaultRootDetails() previously threw an error - retrying");
					// The server, while acting as a proxy, did not receive a timely response from the upstream server it needed to access in attempting to complete the request. 
					log.vdebug("Thread sleeping for 30 seconds as the server did not receive a timely response from the upstream server it needed to access in attempting to complete the request");
					Thread.sleep(dur!"seconds"(30));
				}
				// re-try original request - retried for 429, 503, 504 - but loop back calling this function 
				log.vdebug("Retrying Function: getDefaultRootDetails()");
				getDefaultRootDetails();
			} else {
				// Default operation if not 408,429,503,504 errors
				// display what the error is
				displayOneDriveErrorMessage(exception.msg, getFunctionName!({}));
			}
		}
		
		// If the JSON response is a correct JSON object, and has an 'id' we can set these details
		if ((defaultOneDriveRootDetails.type() == JSONType.object) && (hasId(defaultOneDriveRootDetails))) {
			log.vdebug("OneDrive Account Default Root Details:       ", defaultOneDriveRootDetails);
			appConfig.defaultRootId = defaultOneDriveRootDetails["id"].str;
			log.vdebug("appConfig.defaultRootId      = ", appConfig.defaultRootId);
			// Save the item to the database, so the account root drive is is always going to be present in the DB
			saveItem(defaultOneDriveRootDetails);
		} else {
			// Handle the invalid JSON response
			throw new accountDetailsException();
		}
	}
	
	// Reset syncFailures to false
	void resetSyncFailures() {
		// Reset syncFailures to false if these are both empty
		if (syncFailures) {
			if ((fileDownloadFailures.empty) && (fileUploadFailures.empty)) {
				log.log("Resetting syncFailures = false");
				syncFailures = false;
			} else {
				log.log("File activity array's not empty - not resetting syncFailures");
			}
		}
	}
	
	// Perform a sync of the OneDrive Account
	// - Query /delta
	//		- If singleDirectoryScope or nationalCloudDeployment is used we need to generate a /delta like response
	// - Process changes (add, changes, moves, deletes)
	// - Process any items to add (download data to local)
	// - Detail any files that we failed to download
	// - Process any deletes (remove local data)
	void syncOneDriveAccountToLocalDisk() {
	
		// performFullScanTrueUp value
		log.vdebug("Perform a Full Scan True-Up: ", appConfig.fullScanTrueUpRequired);
		// Fetch the API response of /delta to track changes on OneDrive
		fetchOneDriveDeltaAPIResponse(null, null, null);
		// Process any download activities or cleanup actions
		processDownloadActivities();
		
		// If singleDirectoryScope is false, we are not targeting a single directory
		// but if true, the target 'could' be a shared folder - so dont try and scan it again
		if (!singleDirectoryScope) {
			// OneDrive Shared Folder Handling
			if (appConfig.accountType == "personal") {
				// Personal Account Type
				// https://github.com/OneDrive/onedrive-api-docs/issues/764
				
				// Get the Remote Items from the Database
				Item[] remoteItems = itemDB.selectRemoteItems();
				foreach (remoteItem; remoteItems) {
					// Check if this path is specifically excluded by 'skip_dir', but only if 'skip_dir' is not empty
					if (appConfig.getValueString("skip_dir") != "") {
						// The path that needs to be checked needs to include the '/'
						// This due to if the user has specified in skip_dir an exclusive path: '/path' - that is what must be matched
						if (selectiveSync.isDirNameExcluded(remoteItem.name)) {
							// This directory name is excluded
							log.vlog("Skipping item - excluded by skip_dir config: ", remoteItem.name);
							continue;
						}
					}
					
					// Directory name is not excluded or skip_dir is not populated
					if (!appConfig.surpressLoggingOutput) {
						log.log("Syncing this OneDrive Personal Shared Folder: ", remoteItem.name);
					}
					// Check this OneDrive Personal Shared Folder for changes
					fetchOneDriveDeltaAPIResponse(remoteItem.remoteDriveId, remoteItem.remoteId, remoteItem.name);
					// Process any download activities or cleanup actions for this OneDrive Personal Shared Folder
					processDownloadActivities();
				}
			} else {
				// Is this a Business Account with Sync Business Shared Items enabled?
				if ((appConfig.accountType == "business") && ( appConfig.getValueBool("sync_business_shared_items"))) {
				
					// Business Account Shared Items Handling
					// - OneDrive Business Shared Folder
					// - OneDrive Business Shared Files ??
					// - SharePoint Links
				
					// Get the Remote Items from the Database
					Item[] remoteItems = itemDB.selectRemoteItems();
					
					foreach (remoteItem; remoteItems) {
						// Check if this path is specifically excluded by 'skip_dir', but only if 'skip_dir' is not empty
						if (appConfig.getValueString("skip_dir") != "") {
							// The path that needs to be checked needs to include the '/'
							// This due to if the user has specified in skip_dir an exclusive path: '/path' - that is what must be matched
							if (selectiveSync.isDirNameExcluded(remoteItem.name)) {
								// This directory name is excluded
								log.vlog("Skipping item - excluded by skip_dir config: ", remoteItem.name);
								continue;
							}
						}
						
						// Directory name is not excluded or skip_dir is not populated
						if (!appConfig.surpressLoggingOutput) {
							log.log("Syncing this OneDrive Business Shared Folder: ", remoteItem.name);
						}
						
						log.vdebug("Fetching /delta API response for:");
						log.vdebug("    remoteItem.remoteDriveId: ", remoteItem.remoteDriveId);
						log.vdebug("    remoteItem.remoteId:      ", remoteItem.remoteId);
						
						// Check this OneDrive Personal Shared Folder for changes
						fetchOneDriveDeltaAPIResponse(remoteItem.remoteDriveId, remoteItem.remoteId, remoteItem.name);
						
						// Process any download activities or cleanup actions for this OneDrive Personal Shared Folder
						processDownloadActivities();
					}
				}
			}
		}
	}
	
	// Configure singleDirectoryScope = true if this function is called
	// By default, singleDirectoryScope = false
	void setSingleDirectoryScope(string normalisedSingleDirectoryPath) {
		
		// Function variables
		Item searchItem;
		JSONValue onlinePathData;
		
		// Set the main flag
		singleDirectoryScope = true;
		
		// What are we doing?
		log.log("The OneDrive Client was asked to search for this directory online and create it if it's not located: ", normalisedSingleDirectoryPath);
		
		// Query the OneDrive API for the specified path online
		// In a --single-directory scenario, we need to travervse the entire path that we are wanting to sync
		// and then check the path element does it exist online, if it does, is it a POSIX match, or if it does not, create the path
		// Once we have searched online, we have the right drive id and item id so that we can downgrade the sync status, then build up 
		// any object items from that location
		// This is because, in a --single-directory scenario, any folder in the entire path tree could be a 'case-insensitive match'
		
		try {
			onlinePathData = queryOneDriveForSpecificPathAndCreateIfMissing(normalisedSingleDirectoryPath, true);
		} catch (posixException e) {
			displayPosixErrorMessage(e.msg);
			log.error("ERROR: Requested directory to search for and potentially create has a 'case-insensitive match' to an existing directory on OneDrive online.");
		}
		
		// Was a valid JSON response provided?
		if (onlinePathData.type() == JSONType.object) {
			// Valid JSON item was returned
			searchItem = makeItem(onlinePathData);
			log.vdebug("searchItem: ", searchItem);
			
			// Is this item a potential Shared Folder?
			// Is this JSON a remote object
			if (isItemRemote(onlinePathData)) {
				// The path we are seeking is remote to our account drive id
				searchItem.driveId = onlinePathData["remoteItem"]["parentReference"]["driveId"].str;
				searchItem.id = onlinePathData["remoteItem"]["id"].str;
			} 
			
			// Set these items so that these can be used as required
			singleDirectoryScopeDriveId = searchItem.driveId;
			singleDirectoryScopeItemId = searchItem.id;
		} else {
			log.error("\nThe requested --single-directory path to sync has generated an error. Please correct this error and try again.\n");
			exit(EXIT_FAILURE);
		}
	}
	
	// Query OneDrive API for /delta changes and iterate through items online
	void fetchOneDriveDeltaAPIResponse(string driveIdToQuery = null, string itemIdToQuery = null, string sharedFolderName = null) {
				
		string deltaLink = null;
		string currentDeltaLink = null;
		string deltaLinkAvailable;
		JSONValue deltaChanges;
		ulong responseBundleCount;
		ulong jsonItemsReceived = 0;
		
		// Reset jsonItemsToProcess & processedCount
		jsonItemsToProcess = [];
		processedCount = 0;
		
		// Was a driveId provided as an input
		//if (driveIdToQuery == "") {
		if (strip(driveIdToQuery).empty) {
			// No provided driveId to query, use the account default
			log.vdebug("driveIdToQuery was empty, setting to appConfig.defaultDriveId");
			driveIdToQuery = appConfig.defaultDriveId;
			log.vdebug("driveIdToQuery: ", driveIdToQuery);
		}
		
		// Was an itemId provided as an input
		//if (itemIdToQuery == "") {
		if (strip(itemIdToQuery).empty) {
			// No provided itemId to query, use the account default
			log.vdebug("itemIdToQuery was empty, setting to appConfig.defaultRootId");
			itemIdToQuery = appConfig.defaultRootId;
			log.vdebug("itemIdToQuery: ", itemIdToQuery);
		}
		
		// What OneDrive API query do we use?
		// - Are we running against a National Cloud Deployments that does not support /delta ?
		//   National Cloud Deployments do not support /delta as a query
		//   https://docs.microsoft.com/en-us/graph/deployments#supported-features
		//
		// - Are we performing a --single-directory sync, which will exclude many items online, focusing in on a specific online directory
		// 
		// - Are we performing a --download-only --cleanup-local-files action?
		//   - If we are, and we use a normal /delta query, we get all the local 'deleted' objects as well.
		//   - If the user deletes a folder online, then replaces it online, we download the deletion events and process the new 'upload' via the web iterface .. 
		//     the net effect of this, is that the valid local files we want to keep, are actually deleted ...... not desirable
		if ((singleDirectoryScope) || (nationalCloudDeployment) || (cleanupLocalFiles)) {
			// Generate a simulated /delta response so that we correctly capture the current online state, less any 'online' delete and replace activity
			generateSimulatedDeltaResponse = true;
		}
		
		// What /delta query do we use?
		if (!generateSimulatedDeltaResponse) {
			// This should be the majority default pathway application use
			// Get the current delta link from the database for this DriveID and RootID
			deltaLinkAvailable = itemDB.getDeltaLink(driveIdToQuery, itemIdToQuery);
			if (!deltaLinkAvailable.empty) {
				log.vdebug("Using database stored deltaLink");
				currentDeltaLink = deltaLinkAvailable;
			}
			
			// Do we need to perform a Full Scan True Up? Is 'appConfig.fullScanTrueUpRequired' set to 'true'?
			if (appConfig.fullScanTrueUpRequired) {
				log.log("Performing a full scan of online data to ensure consistent local state");
				log.vdebug("Setting currentDeltaLink = null");
				currentDeltaLink = null;
			}
			
			// Dynamic output for non-verbose and verbose run so that the user knows something is being retreived from the OneDrive API
			if (log.verbose <= 1) {
				if (!appConfig.surpressLoggingOutput) {
					log.fileOnly("Fetching items from the OneDrive API for Drive ID: ", driveIdToQuery);
					// Use the dots to show the application is 'doing something'
					write("Fetching items from the OneDrive API for Drive ID: ", driveIdToQuery, " .");
				}
			} else {
				log.vdebug("Fetching /delta response from the OneDrive API for Drive ID: ", driveIdToQuery);
			}
							
			// Create a new API Instance for querying /delta and initialise it
			// Reuse the socket to speed up
			bool keepAlive = true;
			OneDriveApi getDeltaQueryOneDriveApiInstance;
			getDeltaQueryOneDriveApiInstance = new OneDriveApi(appConfig);
			getDeltaQueryOneDriveApiInstance.initialise(keepAlive);
			
			for (;;) {
				responseBundleCount++;
				// Get the /delta changes via the OneDrive API
				// getDeltaChangesByItemId has the re-try logic for transient errors
				deltaChanges = getDeltaChangesByItemId(driveIdToQuery, itemIdToQuery, currentDeltaLink, getDeltaQueryOneDriveApiInstance);
				
				// If the initial deltaChanges response is an invalid JSON object, keep trying ..
				if (deltaChanges.type() != JSONType.object) {
					while (deltaChanges.type() != JSONType.object) {
						// Handle the invalid JSON response adn retry
						log.vdebug("ERROR: Query of the OneDrive API via deltaChanges = getDeltaChangesByItemId() returned an invalid JSON response");
						deltaChanges = getDeltaChangesByItemId(driveIdToQuery, itemIdToQuery, currentDeltaLink, getDeltaQueryOneDriveApiInstance);
					}
				}
				
				ulong nrChanges = count(deltaChanges["value"].array);
				int changeCount = 0;
				
				if (log.verbose <= 1) {
					// Dynamic output for a non-verbose run so that the user knows something is happening
					if (!appConfig.surpressLoggingOutput) {
						write(".");
					}
				} else {
					log.vdebug("API Response Bundle: ", responseBundleCount, " - Quantity of 'changes|items' in this bundle to process: ", nrChanges);
				}
				
				jsonItemsReceived = jsonItemsReceived + nrChanges;
				
				// We have a valid deltaChanges JSON array. This means we have at least 200+ JSON items to process.
				// The API response however cannot be run in parallel as the OneDrive API sends the JSON items in the order in which they must be processed
				foreach (onedriveJSONItem; deltaChanges["value"].array) {
					// increment change count for this item
					changeCount++;
					// Process the OneDrive object item JSON
					processDeltaJSONItem(onedriveJSONItem, nrChanges, changeCount, responseBundleCount, singleDirectoryScope);
				}
				
				// The response may contain either @odata.deltaLink or @odata.nextLink
				if ("@odata.deltaLink" in deltaChanges) {
					// Log action
					log.vdebug("Setting next currentDeltaLink to (@odata.deltaLink): ", deltaChanges["@odata.deltaLink"].str);
					// Update currentDeltaLink
					currentDeltaLink = deltaChanges["@odata.deltaLink"].str;
					// Store this for later use post processing jsonItemsToProcess items
					latestDeltaLink = deltaChanges["@odata.deltaLink"].str;
				}
				
				// Update deltaLink to next changeSet bundle
				if ("@odata.nextLink" in deltaChanges) {	
					// Log action
					log.vdebug("Setting next currentDeltaLink & deltaLinkAvailable to (@odata.nextLink): ", deltaChanges["@odata.nextLink"].str);
					// Update currentDeltaLink
					currentDeltaLink = deltaChanges["@odata.nextLink"].str;
					// Update deltaLinkAvailable to next changeSet bundle to quantify how many changes we have to process
					deltaLinkAvailable = deltaChanges["@odata.nextLink"].str;
					// Store this for later use post processing jsonItemsToProcess items
					latestDeltaLink = deltaChanges["@odata.nextLink"].str;
				}
				else break;
			}
			
			// To finish off the JSON processing items, this is needed to reflect this in the log
			log.vdebug("------------------------------------------------------------------");
			
			// Shutdown the API
			getDeltaQueryOneDriveApiInstance.shutdown();
			// Free object and memory
			object.destroy(getDeltaQueryOneDriveApiInstance);
			
			// Log that we have finished querying the /delta API
			if (log.verbose <= 1) {
				if (!appConfig.surpressLoggingOutput) {
					write("\n");
				}
			} else {
				log.vdebug("Finished processing /delta JSON response from the OneDrive API");
			}
			
			// If this was set, now unset it, as this will have been completed, so that for a true up, we dont do a double full scan
			if (appConfig.fullScanTrueUpRequired) {
				log.vdebug("Unsetting fullScanTrueUpRequired as this has been performed");
				appConfig.fullScanTrueUpRequired = false;
			}
		} else {
			// Why are are generating a /delta response
			log.vdebug("Why are we generating a /delta response:");
			log.vdebug(" singleDirectoryScope:    ", singleDirectoryScope);
			log.vdebug(" nationalCloudDeployment: ", nationalCloudDeployment);
			log.vdebug(" cleanupLocalFiles:       ", cleanupLocalFiles);
			
			// What 'path' are we going to start generating the response for
			string pathToQuery;
			
			// If --single-directory has been called, use the value that has been set
			if (singleDirectoryScope) {
				pathToQuery = appConfig.getValueString("single_directory");
			}
			
			// We could also be syncing a Shared Folder of some description
			if (!sharedFolderName.empty) {
				pathToQuery = sharedFolderName;
			}
			
			// Generate the simulated /delta response
			//
			// The generated /delta response however contains zero deleted JSON items, so the only way that we can track this, is if the object was in sync
			// we have the object in the database, thus, what we need to do is for every DB object in the tree of items, flag 'syncStatus' as 'N', then when we process 
			// the returned JSON items from the API, we flag the item as back in sync, then we can cleanup any out-of-sync items
			//
			// The flagging of the local database items to 'N' is handled within the generateDeltaResponse() function
			//
			// When these JSON items are then processed, if the item exists online, and is in the DB, and that the values match, the DB item is flipped back to 'Y' 
			// This then allows the application to look for any remaining 'N' values, and delete these as no longer needed locally
			deltaChanges = generateDeltaResponse(pathToQuery);
			
			ulong nrChanges = count(deltaChanges["value"].array);
			int changeCount = 0;
			log.vdebug("API Response Bundle: ", responseBundleCount, " - Quantity of 'changes|items' in this bundle to process: ", nrChanges);
			jsonItemsReceived = jsonItemsReceived + nrChanges;
			
			// The API response however cannot be run in parallel as the OneDrive API sends the JSON items in the order in which they must be processed
			foreach (onedriveJSONItem; deltaChanges["value"].array) {
				// increment change count for this item
				changeCount++;
				// Process the OneDrive object item JSON
				processDeltaJSONItem(onedriveJSONItem, nrChanges, changeCount, responseBundleCount, singleDirectoryScope);	
			}
			
			// To finish off the JSON processing items, this is needed to reflect this in the log
			log.vdebug("------------------------------------------------------------------");
			
			// Log that we have finished generating our self generated /delta response
			if (!appConfig.surpressLoggingOutput) {
				log.log("Finished processing self generated /delta JSON response from the OneDrive API");
			}
		}
		
		// Cleanup deltaChanges as this is no longer needed
		object.destroy(deltaChanges);
		
		// We have JSON items received from the OneDrive API
		log.vdebug("Number of JSON Objects received from OneDrive API:                 ", jsonItemsReceived);
		log.vdebug("Number of JSON Objects already processed (root and deleted items): ", (jsonItemsReceived - jsonItemsToProcess.length));
		
		// We should have now at least processed all the JSON items as returned by the /delta call
		// Additionally, we should have a new array, that now contains all the JSON items we need to process that are non 'root' or deleted items
		log.vdebug("Number of JSON items to process is: ", jsonItemsToProcess.length);
		
		// Are there items to process?
		if (jsonItemsToProcess.length > 0) {
			// Lets deal with the JSON items in a batch process
			ulong batchSize = 500;
			ulong batchCount = (jsonItemsToProcess.length + batchSize - 1) / batchSize;
			ulong batchesProcessed = 0;
			
			// Dynamic output for a non-verbose run so that the user knows something is happening
			if (!appConfig.surpressLoggingOutput) {
				write("Processing ", jsonItemsToProcess.length, " applicable changes and items received from Microsoft OneDrive ");
				log.fileOnly("Processing ", jsonItemsToProcess.length, " applicable changes and items received from Microsoft OneDrive");
				if (log.verbose != 0) {
					// close out the write() processing line above
					writeln();
				}
			}
			
			// For each batch, process the JSON items that need to be now processed.
			// 'root' and deleted objects have already been handled
			foreach (batchOfJSONItems; jsonItemsToProcess.chunks(batchSize)) {
				// Chunk the total items to process into 500 lot items
				batchesProcessed++;
				
				if (log.verbose == 0) {
					// Dynamic output for a non-verbose run so that the user knows something is happening
					if (!appConfig.surpressLoggingOutput) {
						write(".");
					}
				} else {
					log.vlog("Processing OneDrive JSON item batch [", batchesProcessed,"/", batchCount, "] to ensure consistent local state");
				}	
					
				// Process the batch
				processJSONItemsInBatch(batchOfJSONItems, batchesProcessed, batchCount);
				
				// To finish off the JSON processing items, this is needed to reflect this in the log
				log.vdebug("------------------------------------------------------------------");
			}
			
			if (log.verbose == 0) {
				// close off '.' output
				if (!appConfig.surpressLoggingOutput) {
					writeln();
				}
			}
			
			// Free up memory and items processed as it is pointless now having this data around
			jsonItemsToProcess = [];
			
			// Debug output - what was processed
			log.vdebug("Number of JSON items to process is: ", jsonItemsToProcess.length);
			log.vdebug("Number of JSON items processed was: ", processedCount);	
		} else {
			if (!appConfig.surpressLoggingOutput) {
				log.log("No additional changes or items that can be applied were discovered while processing the data received from Microsoft OneDrive");
			}
		}
		
		// Update the deltaLink in the database so that we can reuse this now that jsonItemsToProcess has been processed
		if (!latestDeltaLink.empty) {
			log.vdebug("Updating completed deltaLink in DB to: ", latestDeltaLink);
			itemDB.setDeltaLink(driveIdToQuery, itemIdToQuery, latestDeltaLink);
		}
		
		// Keep the driveIDsArray with unique entries only
		if (!canFind(driveIDsArray, driveIdToQuery)) {
			// Add this driveId to the array of driveId's we know about
			driveIDsArray ~= driveIdToQuery;
		}		
	}
	
	// Process the /delta API JSON response items
	void processDeltaJSONItem(JSONValue onedriveJSONItem, ulong nrChanges, int changeCount, ulong responseBundleCount, bool singleDirectoryScope) {
		
		// Variables for this foreach loop
		string thisItemId;
		bool itemIsRoot = false;
		bool handleItemAsRootObject = false;
		bool itemIsDeletedOnline = false;
		bool itemHasParentReferenceId = false;
		bool itemHasParentReferencePath = false;
		bool itemIdMatchesDefaultRootId = false;
		bool itemNameExplicitMatchRoot = false;
		string objectParentDriveId;
		
		log.vdebug("------------------------------------------------------------------");
		log.vdebug("Processing OneDrive Item ", changeCount, " of ", nrChanges, " from API Response Bundle ", responseBundleCount);
		log.vdebug("Raw JSON OneDrive Item: ", onedriveJSONItem);
		// What is this item's id
		thisItemId = onedriveJSONItem["id"].str;
		// Is this a deleted item - only calculate this once
		itemIsDeletedOnline = isItemDeleted(onedriveJSONItem);
		
		if(!itemIsDeletedOnline){
			// This is not a deleted item
			log.vdebug("This item is not a OneDrive deletion change");
			// Only calculate this once
			itemIsRoot = isItemRoot(onedriveJSONItem);
			itemHasParentReferenceId = hasParentReferenceId(onedriveJSONItem);
			itemIdMatchesDefaultRootId = (thisItemId == appConfig.defaultRootId);
			itemNameExplicitMatchRoot = (onedriveJSONItem["name"].str == "root");
			objectParentDriveId = onedriveJSONItem["parentReference"]["driveId"].str;
			
			// Shared Folder Items
			// !hasParentReferenceId(id)
			// !hasParentReferenceId(path)
			
			// Test is this is the OneDrive Users Root?
			// Debug output of change evaluation items
			log.vdebug("defaultRootId                                        = ", appConfig.defaultRootId);
			log.vdebug("'search id'                                          = ", thisItemId);
			log.vdebug("id == defaultRootId                                  = ", itemIdMatchesDefaultRootId);
			log.vdebug("isItemRoot(onedriveJSONItem)                         = ", itemIsRoot);
			log.vdebug("onedriveJSONItem['name'].str == 'root'               = ", itemNameExplicitMatchRoot);
			log.vdebug("itemHasParentReferenceId                             = ", itemHasParentReferenceId);
			
			if ( (itemIdMatchesDefaultRootId || singleDirectoryScope) && itemIsRoot && itemNameExplicitMatchRoot) {
				// This IS a OneDrive Root item or should be classified as such in the case of 'singleDirectoryScope'
				log.vdebug("JSON item will flagged as a 'root' item");
				handleItemAsRootObject = true;
			}
		}
		
		// How do we handle this JSON item from the OneDrive API?
		// Is this a confirmed 'root' item, has no Parent ID, or is a Deleted Item
		if (handleItemAsRootObject || !itemHasParentReferenceId || itemIsDeletedOnline){
			// Is a root item, has no id in parentReference or is a OneDrive deleted item
			log.vdebug("objectParentDriveId                                  = ", objectParentDriveId);
			log.vdebug("handleItemAsRootObject                               = ", handleItemAsRootObject);
			log.vdebug("itemHasParentReferenceId                             = ", itemHasParentReferenceId);
			log.vdebug("itemIsDeletedOnline                                  = ", itemIsDeletedOnline);
			log.vdebug("Handling change immediately as 'root item', or has no parent reference id or is a deleted item");
			// OK ... do something with this JSON post here ....
			processRootAndDeletedJSONItems(onedriveJSONItem, objectParentDriveId, handleItemAsRootObject, itemIsDeletedOnline, itemHasParentReferenceId);
		} else {
			// Do we need to update this RAW JSON from OneDrive?
			if ( (objectParentDriveId != appConfig.defaultDriveId) && (appConfig.accountType == "business") && (appConfig.getValueBool("sync_business_shared_items")) ) {
				// Potentially need to update this JSON data
				log.vdebug("Potentially need to update this source JSON .... need to check the database");
				
				// Check the DB for 'remote' objects, searching 'remoteDriveId' and 'remoteId' items for this remoteItem.driveId and remoteItem.id
				Item remoteDBItem;
				itemDB.selectByRemoteId(objectParentDriveId, thisItemId, remoteDBItem);
				
				// Is the data that was returned from the database what we are looking for?
				if ((remoteDBItem.remoteDriveId == objectParentDriveId) && (remoteDBItem.remoteId == thisItemId)) {
					// Yes, this is the record we are looking for
					log.vdebug("DB Item response for remoteDBItem: ", remoteDBItem);
				
					// Must compare remoteDBItem.name with remoteItem.name
					if (remoteDBItem.name != onedriveJSONItem["name"].str) {
						// Update JSON Item
						string actualOnlineName = onedriveJSONItem["name"].str;
						log.vdebug("Updating source JSON 'name' to that which is the actual local directory");
						log.vdebug("onedriveJSONItem['name'] was:         ", onedriveJSONItem["name"].str);
						log.vdebug("Updating onedriveJSONItem['name'] to: ", remoteDBItem.name);
						onedriveJSONItem["name"] = remoteDBItem.name;
						log.vdebug("onedriveJSONItem['name'] now:         ", onedriveJSONItem["name"].str);
						// Add the original name to the JSON 
						onedriveJSONItem["actualOnlineName"] = actualOnlineName;
					}
				}
			}
		
			// If we are not self-generating a /delta response, check this initial /delta JSON bundle item against the basic checks 
			// of applicability against 'skip_file', 'skip_dir' and 'sync_list'
			// We only do this if we did not generate a /delta response, as generateDeltaResponse() performs the checkJSONAgainstClientSideFiltering()
			// against elements as it is building the /delta compatible response
			// If we blindly just 'check again' all JSON responses then there is potentially double JSON processing going on if we used generateDeltaResponse()
			bool discardDeltaJSONItem = false;
			if (!generateSimulatedDeltaResponse) {
				// Check applicability against 'skip_file', 'skip_dir' and 'sync_list'
				discardDeltaJSONItem = checkJSONAgainstClientSideFiltering(onedriveJSONItem);
			}
			
			// Add this JSON item for further processing if this is not being discarded
			if (!discardDeltaJSONItem) {
				log.vdebug("Adding this Raw JSON OneDrive Item to jsonItemsToProcess array for further processing");
				jsonItemsToProcess ~= onedriveJSONItem;
			}
		}
	}
	
	// Process 'root' and 'deleted' OneDrive JSON items
	void processRootAndDeletedJSONItems(JSONValue onedriveJSONItem, string driveId, bool handleItemAsRootObject, bool itemIsDeletedOnline, bool itemHasParentReferenceId) {
		
		// Use the JSON elements rather can computing a DB struct via makeItem()
		string thisItemId = onedriveJSONItem["id"].str;
		string thisItemDriveId = onedriveJSONItem["parentReference"]["driveId"].str;
			
		// Check if the item has been seen before
		Item existingDatabaseItem;
		bool existingDBEntry = itemDB.selectById(thisItemDriveId, thisItemId, existingDatabaseItem);
		
		// Is the item deleted online?
		if(!itemIsDeletedOnline) {
			
			// Is the item a confirmed root object?
			
			// The JSON item should be considered a 'root' item if:
			// 1. Contains a ["root"] element
			// 2. Has no ["parentReference"]["id"] ... #323 & #324 highlighted that this is false as some 'root' shared objects now can have an 'id' element .. OneDrive API change
			// 2. Has no ["parentReference"]["path"]
			// 3. Was detected by an input flag as to be handled as a root item regardless of actual status
			
			if ((handleItemAsRootObject) || (!itemHasParentReferenceId)) {
				log.vdebug("Handing JSON object as OneDrive 'root' object");
				if (!existingDBEntry) {
					// we have not seen this item before
					saveItem(onedriveJSONItem);
				}
			}
		} else {
			// Change is to delete an item
			log.vdebug("Handing a OneDrive Deleted Item");
			if (existingDBEntry) {
				// Flag to delete
				log.vdebug("Flagging to delete item locally: ", onedriveJSONItem);
				idsToDelete ~= [thisItemDriveId, thisItemId];
			} else {
				// Flag to ignore
				log.vdebug("Flagging item to skip: ", onedriveJSONItem);
				skippedItems.insert(thisItemId);
			}
		}
	}
	
	// Process each of the elements contained in jsonItemsToProcess[]
	void processJSONItemsInBatch(JSONValue[] array, ulong batchGroup, ulong batchCount) {
	
		ulong batchElementCount = array.length;

		foreach (i, onedriveJSONItem; array.enumerate) {
			// Use the JSON elements rather can computing a DB struct via makeItem()
			ulong elementCount = i +1;
			
			// To show this is the processing for this particular item, start off with this breaker line
			log.vdebug("------------------------------------------------------------------");
			log.vdebug("Processing OneDrive JSON item ", elementCount, " of ", batchElementCount, " as part of JSON Item Batch ", batchGroup, " of ", batchCount);
			log.vdebug("Raw JSON OneDrive Item: ", onedriveJSONItem);
			
			string thisItemId = onedriveJSONItem["id"].str;
			string thisItemDriveId = onedriveJSONItem["parentReference"]["driveId"].str;
			string thisItemParentId = onedriveJSONItem["parentReference"]["id"].str;
			string thisItemName = onedriveJSONItem["name"].str;
			
			// Create an empty item struct for an existing DB item
			Item existingDatabaseItem;
			
			// Do we NOT want this item?
			bool unwanted = false; // meaning by default we will WANT this item
			// Is this parent is in the database
			bool parentInDatabase = false;
			// What is the path of the new item
			string newItemPath;
			
			// Configure the remoteItem - so if it is used, it can be utilised later
			Item remoteItem;
			
			// Check the database for an existing entry for this JSON item
			bool existingDBEntry = itemDB.selectById(thisItemDriveId, thisItemId, existingDatabaseItem);
			
			// Calculate if the Parent Item is in the database so that it can be re-used
			parentInDatabase = itemDB.idInLocalDatabase(thisItemDriveId, thisItemParentId);
			
			// Calculate the path of this JSON item, but we can only do this if the parent is in the database
			if (parentInDatabase) {
				// Calculate this items path
				newItemPath = computeItemPath(thisItemDriveId, thisItemParentId) ~ "/" ~ thisItemName;
				log.vdebug("New Item calculated full path is: ", newItemPath);
			} else {
				// Parent not in the database
				// Is the parent a 'folder' from another user? ie - is this a 'shared folder' that has been shared with us?
				log.vdebug("Parent ID is not in DB .. ");
				// Why?
				if (thisItemDriveId == appConfig.defaultDriveId) {
					// Flagging as unwanted
					log.vdebug("Flagging as unwanted: thisItemDriveId (", thisItemDriveId,"), thisItemParentId (", thisItemParentId,") not in local database");
					if (thisItemParentId in skippedItems) {
						log.vdebug("Reason: thisItemParentId listed within skippedItems");
					}
					unwanted = true;
				} else {
					// Edge case as the parent (from another users OneDrive account) will never be in the database - potentially a shared object?
					log.vdebug("Potential Shared Object Item: ", onedriveJSONItem);
					// Format the OneDrive change into a consumable object for the database
					remoteItem = makeItem(onedriveJSONItem);
					log.vdebug("The reported parentId is not in the database. This potentially is a shared folder as 'remoteItem.driveId' != 'appConfig.defaultDriveId'. Relevant Details: remoteItem.driveId (", remoteItem.driveId,"), remoteItem.parentId (", remoteItem.parentId,")");
					
					if (appConfig.accountType == "personal") {
						// Personal Account Handling
						// Ensure that this item has no parent
						log.vdebug("Setting remoteItem.parentId to be null");
						remoteItem.parentId = null;
						// Add this record to the local database
						log.vdebug("Update/Insert local database with remoteItem details with remoteItem.parentId as null: ", remoteItem);
						itemDB.upsert(remoteItem);
					} else {
						// Business or SharePoint Account Handling
						log.vdebug("Handling a Business or SharePoint Shared Item JSON object");
						
						if (appConfig.accountType == "business") {
							// Create a DB Tie Record for this parent object
							Item parentItem;
							parentItem.driveId = onedriveJSONItem["parentReference"]["driveId"].str;
							parentItem.id = onedriveJSONItem["parentReference"]["id"].str;
							parentItem.name = "root";
							parentItem.type = ItemType.dir;
							parentItem.mtime = remoteItem.mtime;
							parentItem.parentId = null;
							
							// Add this parent record to the local database
							log.vdebug("Insert local database with remoteItem parent details: ", parentItem);
							itemDB.upsert(parentItem);
							
							// Ensure that this item has no parent
							log.vdebug("Setting remoteItem.parentId to be null");
							remoteItem.parentId = null;
							
							// Check the DB for 'remote' objects, searching 'remoteDriveId' and 'remoteId' items for this remoteItem.driveId and remoteItem.id
							Item remoteDBItem;
							itemDB.selectByRemoteId(remoteItem.driveId, remoteItem.id, remoteDBItem);
							
							// Must compare remoteDBItem.name with remoteItem.name
							if ((!remoteDBItem.name.empty) && (remoteDBItem.name != remoteItem.name)) {
								// Update DB Item
								log.vdebug("The shared item stored in OneDrive, has a different name to the actual name on the remote drive");
								log.vdebug("Updating remoteItem.name JSON data with the actual name being used on account drive and local folder");
								log.vdebug("remoteItem.name was:              ", remoteItem.name);
								log.vdebug("Updating remoteItem.name to:      ", remoteDBItem.name);
								remoteItem.name = remoteDBItem.name;
								log.vdebug("Setting remoteItem.remoteName to: ", onedriveJSONItem["name"].str);
								
								// Update JSON Item
								remoteItem.remoteName = onedriveJSONItem["name"].str;
								log.vdebug("Updating source JSON 'name' to that which is the actual local directory");
								log.vdebug("onedriveJSONItem['name'] was:         ", onedriveJSONItem["name"].str);
								log.vdebug("Updating onedriveJSONItem['name'] to: ", remoteDBItem.name);
								onedriveJSONItem["name"] = remoteDBItem.name;
								log.vdebug("onedriveJSONItem['name'] now:         ", onedriveJSONItem["name"].str);
								
								// Update newItemPath value
								newItemPath = computeItemPath(thisItemDriveId, thisItemParentId) ~ "/" ~ remoteDBItem.name;
								log.vdebug("New Item updated calculated full path is: ", newItemPath);
							}
								
							// Add this record to the local database
							log.vdebug("Update/Insert local database with remoteItem details: ", remoteItem);
							itemDB.upsert(remoteItem);
						}
					}
				}
			}
			
			// Check the skippedItems array for the parent id of this JSONItem if this is something we need to skip
			if (!unwanted) {
				if (thisItemParentId in skippedItems) {
					// Flag this JSON item as unwanted
					log.vdebug("Flagging as unwanted: find(thisItemParentId).length != 0");
					unwanted = true;
					
					// Is this item id in the database?
					if (existingDBEntry) {
						// item exists in database, most likely moved out of scope for current client configuration
						log.vdebug("This item was previously synced / seen by the client");
						if (("name" in onedriveJSONItem["parentReference"]) != null) {
							
							// How is this out of scope?
							// is sync_list configured
							if (syncListConfigured) {
								// sync_list configured and in use
								if (selectiveSync.isPathExcludedViaSyncList(onedriveJSONItem["parentReference"]["name"].str)) {
									// Previously synced item is now out of scope as it has been moved out of what is included in sync_list
									log.vdebug("This previously synced item is now excluded from being synced due to sync_list exclusion");
								}
							}
							// flag to delete local file as it now is no longer in sync with OneDrive
							log.vdebug("Flagging to delete item locally: ", onedriveJSONItem);
							idsToDelete ~= [thisItemDriveId, thisItemId];
						}
					}	
				}
			}
			
			// Check the item type - if it not an item type that we support, we cant process the JSON item
			if (!unwanted) {
				if (isItemFile(onedriveJSONItem)) {
					log.vdebug("The item we are syncing is a file");
				} else if (isItemFolder(onedriveJSONItem)) {
					log.vdebug("The item we are syncing is a folder");
				} else if (isItemRemote(onedriveJSONItem)) {
					log.vdebug("The item we are syncing is a remote item");
				} else {
					// Why was this unwanted?
					if (newItemPath.empty) {
						// Compute this item path & need the full path for this file
						newItemPath = computeItemPath(thisItemDriveId, thisItemParentId) ~ "/" ~ thisItemName;
						log.vdebug("New Item calculated full path is: ", newItemPath);
					}
					// Microsoft OneNote container objects present as neither folder or file but has file size
					if ((!isItemFile(onedriveJSONItem)) && (!isItemFolder(onedriveJSONItem)) && (hasFileSize(onedriveJSONItem))) {
						// Log that this was skipped as this was a Microsoft OneNote item and unsupported
						log.vlog("The Microsoft OneNote Notebook '", newItemPath, "' is not supported by this client");
					} else {
						// Log that this item was skipped as unsupported 
						log.vlog("The OneDrive item '", newItemPath, "' is not supported by this client");
					}
					unwanted = true;
					log.vdebug("Flagging as unwanted: item type is not supported");
				}
			}
			
			// Check if this is excluded by config option: skip_dir
			if (!unwanted) {
				// Only check path if config is != ""
				if (!appConfig.getValueString("skip_dir").empty) {
					// Is the item a folder?
					if (isItemFolder(onedriveJSONItem)) {
						// work out the 'snippet' path where this folder would be created
						string simplePathToCheck = "";
						string complexPathToCheck = "";
						string matchDisplay = "";
						
						if (hasParentReference(onedriveJSONItem)) {
							// we need to workout the FULL path for this item
							// simple path
							if (("name" in onedriveJSONItem["parentReference"]) != null) {
								simplePathToCheck = onedriveJSONItem["parentReference"]["name"].str ~ "/" ~ onedriveJSONItem["name"].str;
							} else {
								simplePathToCheck = onedriveJSONItem["name"].str;
							}
							log.vdebug("skip_dir path to check (simple):  ", simplePathToCheck);
							
							// complex path
							if (parentInDatabase) {
								// build up complexPathToCheck
								complexPathToCheck = buildNormalizedPath(newItemPath);
							} else {
								log.vdebug("Parent details not in database - unable to compute complex path to check");
							}
							if (!complexPathToCheck.empty) {
								log.vdebug("skip_dir path to check (complex): ", complexPathToCheck);
							}
						} else {
							simplePathToCheck = onedriveJSONItem["name"].str;
						}
						
						// If 'simplePathToCheck' or 'complexPathToCheck'  is of the following format:  root:/folder
						// then isDirNameExcluded matching will not work
						// Clean up 'root:' if present
						if (startsWith(simplePathToCheck, "root:")){
							log.vdebug("Updating simplePathToCheck to remove 'root:'");
							simplePathToCheck = strip(simplePathToCheck, "root:");
						}
						if (startsWith(complexPathToCheck, "root:")){
							log.vdebug("Updating complexPathToCheck to remove 'root:'");
							complexPathToCheck = strip(complexPathToCheck, "root:");
						}
						
						// OK .. what checks are we doing?
						if ((!simplePathToCheck.empty) && (complexPathToCheck.empty)) {
							// just a simple check
							log.vdebug("Performing a simple check only");
							unwanted = selectiveSync.isDirNameExcluded(simplePathToCheck);
						} else {
							// simple and complex
							log.vdebug("Performing a simple then complex path match if required");
							// simple first
							log.vdebug("Performing a simple check first");
							unwanted = selectiveSync.isDirNameExcluded(simplePathToCheck);
							matchDisplay = simplePathToCheck;
							if (!unwanted) {
								log.vdebug("Simple match was false, attempting complex match");
								// simple didnt match, perform a complex check
								unwanted = selectiveSync.isDirNameExcluded(complexPathToCheck);
								matchDisplay = complexPathToCheck;
							}
						}
						// result
						log.vdebug("skip_dir exclude result (directory based): ", unwanted);
						if (unwanted) {
							// This path should be skipped
							log.vlog("Skipping item - excluded by skip_dir config: ", matchDisplay);
						}
					}
					// Is the item a file?
					// We need to check to see if this files path is excluded as well
					if (isItemFile(onedriveJSONItem)) {
					
						string pathToCheck;
						// does the newItemPath start with '/'?
						if (!startsWith(newItemPath, "/")){
							// path does not start with '/', but we need to check skip_dir entries with and without '/'
							// so always make sure we are checking a path with '/'
							pathToCheck = '/' ~ dirName(newItemPath);
						} else {
							pathToCheck = dirName(newItemPath);
						}
						
						// perform the check
						unwanted = selectiveSync.isDirNameExcluded(pathToCheck);
						// result
						log.vdebug("skip_dir exclude result (file based): ", unwanted);
						if (unwanted) {
							// this files path should be skipped
							log.vlog("Skipping item - file path is excluded by skip_dir config: ", newItemPath);	
						}
					}
				}
			}
			
			// Check if this is excluded by config option: skip_file
			if (!unwanted) {
				// Is the JSON item a file?
				if (isItemFile(onedriveJSONItem)) {
					// skip_file can contain 4 types of entries:
					// - wildcard - *.txt
					// - text + wildcard - name*.txt
					// - full path + combination of any above two - /path/name*.txt
					// - full path to file - /path/to/file.txt
					
					// is the parent id in the database?
					if (parentInDatabase) {
						// Compute this item path & need the full path for this file
						if (newItemPath.empty) {
							newItemPath = computeItemPath(thisItemDriveId, thisItemParentId) ~ "/" ~ thisItemName;
							log.vdebug("New Item calculated full path is: ", newItemPath);
						}
						
						// The path that needs to be checked needs to include the '/'
						// This due to if the user has specified in skip_file an exclusive path: '/path/file' - that is what must be matched
						// However, as 'path' used throughout, use a temp variable with this modification so that we use the temp variable for exclusion checks
						string exclusionTestPath = "";
						if (!startsWith(newItemPath, "/")){
							// Add '/' to the path
							exclusionTestPath = '/' ~ newItemPath;
						}
						
						log.vdebug("skip_file item to check: ", exclusionTestPath);
						unwanted = selectiveSync.isFileNameExcluded(exclusionTestPath);
						log.vdebug("Result: ", unwanted);
						if (unwanted) log.vlog("Skipping item - excluded by skip_file config: ", thisItemName);
					} else {
						// parent id is not in the database
						unwanted = true;
						log.vlog("Skipping file - parent path not present in local database");
					}
				}
			}
			
			// Check if this is included or excluded by use of sync_list
			if (!unwanted) {
				// No need to try and process something against a sync_list if it has been configured
				if (syncListConfigured) {
					// Compute the item path if empty - as to check sync_list we need an actual path to check
					if (newItemPath.empty) {
						// Calculate this items path
						newItemPath = computeItemPath(thisItemDriveId, thisItemParentId) ~ "/" ~ thisItemName;
						log.vdebug("New Item calculated full path is: ", newItemPath);
					}
					
					// What path are we checking?
					log.vdebug("sync_list item to check: ", newItemPath);
					
					// Unfortunatly there is no avoiding this call to check if the path is excluded|included via sync_list
					if (selectiveSync.isPathExcludedViaSyncList(newItemPath)) {
						// selective sync advised to skip, however is this a file and are we configured to upload / download files in the root?
						if ((isItemFile(onedriveJSONItem)) && (appConfig.getValueBool("sync_root_files")) && (rootName(newItemPath) == "") ) {
							// This is a file
							// We are configured to sync all files in the root
							// This is a file in the logical root
							unwanted = false;
						} else {
							// path is unwanted
							unwanted = true;
							log.vlog("Skipping item - excluded by sync_list config: ", newItemPath);
							// flagging to skip this item now, but does this exist in the DB thus needs to be removed / deleted?
							if (existingDBEntry) {
								// flag to delete
								log.vlog("Flagging item for local delete as item exists in database: ", newItemPath);
								idsToDelete ~= [thisItemDriveId, thisItemId];
							}
						}
					}
				}
			}
			
			// Check if the user has configured to skip downloading .files or .folders: skip_dotfiles
			if (!unwanted) {
				if (appConfig.getValueBool("skip_dotfiles")) {
					if (isDotFile(newItemPath)) {
						log.vlog("Skipping item - .file or .folder: ", newItemPath);
						unwanted = true;
					}
				}
			}
			
			// Check if this should be skipped due to a --check-for-nosync directive (.nosync)?
			if (!unwanted) {
				if (appConfig.getValueBool("check_nosync")) {
					// need the parent path for this object
					string parentPath = dirName(newItemPath);
					// Check for the presence of a .nosync in the parent path
					if (exists(parentPath ~ "/.nosync")) {
						log.vlog("Skipping downloading item - .nosync found in parent folder & --check-for-nosync is enabled: ", newItemPath);
						unwanted = true;
					}
				}
			}
			
			// Check if this is excluded by a user set maximum filesize to download
			if (!unwanted) {
				if (isItemFile(onedriveJSONItem)) {
					if (fileSizeLimit != 0) {
						if (onedriveJSONItem["size"].integer >= fileSizeLimit) {
							log.vlog("Skipping item - excluded by skip_size config: ", thisItemName, " (", onedriveJSONItem["size"].integer/2^^20, " MB)");
						}
					}
				}
			}
			
			// At this point all the applicable checks on this JSON object from OneDrive are complete:
			// - skip_file
			// - skip_dir
			// - sync_list
			// - skip_dotfiles
			// - check_nosync
			// - skip_size
			// - We know if this item exists in the DB or not in the DB
			
			// We know if this JSON item is unwanted or not
			if (unwanted) {
				// This JSON item is NOT wanted - it is excluded
				log.vdebug("Skipping OneDrive change as this is determined to be unwanted");
				// Add to the skippedItems array, but only if it is a directory ... pointless adding 'files' here, as it is the 'id' we check as the parent path which can only be a directory
				if (!isItemFile(onedriveJSONItem)) {
					skippedItems.insert(thisItemId);
				}
			} else {
				// This JSON item is wanted - we need to process this JSON item further
				// Take the JSON item and create a consumable object for eventual database insertion
				Item newDatabaseItem = makeItem(onedriveJSONItem);
				
				if (existingDBEntry) {
					// The details of this JSON item are already in the DB
					// Is the item in the DB the same as the JSON data provided - or is the JSON data advising this is an updated file?
					log.vdebug("OneDrive change is an update to an existing local item");
					// Compute the existing item path
					// NOTE:
					//		string existingItemPath = computeItemPath(existingDatabaseItem.driveId, existingDatabaseItem.id);
					//
					// This will calculate the path as follows:
					//
					//		existingItemPath:     Document.txt
					//
					// Whereas above we use the following
					//
					//		newItemPath = computeItemPath(newDatabaseItem.driveId, newDatabaseItem.parentId) ~ "/" ~ newDatabaseItem.name;
					//
					// Which generates the following path:
					//
					//  	changedItemPath:      ./Document.txt
					// 
					// Need to be consistent here with how 'newItemPath' was calculated
					string existingItemPath = computeItemPath(existingDatabaseItem.driveId, existingDatabaseItem.parentId) ~ "/" ~ existingDatabaseItem.name;
					// Attempt to apply this changed item
					applyPotentiallyChangedItem(existingDatabaseItem, existingItemPath, newDatabaseItem, newItemPath, onedriveJSONItem);
				} else {
					// Action this JSON item as a new item as we have no DB record of it
					// The actual item may actually exist locally already, meaning that just the database is out-of-date or missing the data due to --resync
					// But we also cannot compute the newItemPath as the parental objects may not exist as well
					log.vdebug("OneDrive change is potentially a new local item");
					
					// Attempt to apply this potentially new item
					applyPotentiallyNewLocalItem(newDatabaseItem, onedriveJSONItem, newItemPath);
				}
			}
			
			// Tracking as to if this item was processed
			processedCount++;
		}
	}
	
	// Perform the download of any required objects in parallel
	void processDownloadActivities() {
			
		// Are there any items to delete locally? Cleanup space locally first
		if (!idsToDelete.empty) {
			// There are elements that potentially need to be deleted locally
			log.vlog("Items to potentially delete locally: ", idsToDelete.length);
			if (appConfig.getValueBool("download_only")) {
				// Download only has been configured
				if (cleanupLocalFiles) {
					// Process online deleted items
					log.vlog("Processing local deletion activity as --download-only & --cleanup-local-files configured");
					processDeleteItems();
				} else {
					// Not cleaning up local files
					log.vlog("Skipping local deletion activity as --download-only has been used");
				}
			} else {
				// Not using --download-only process normally
				processDeleteItems();
			}
			// Cleanup array memory
			idsToDelete = [];
		}
		
		// Are there any items to download post fetching and processing the /delta data?
		if (!fileJSONItemsToDownload.empty) {
			// There are elements to download
			log.vlog("Number of items to download from OneDrive: ", fileJSONItemsToDownload.length);
			downloadOneDriveItems();
			// Cleanup array memory
			fileJSONItemsToDownload = [];
		}
		
		// Are there any skipped items still?
		if (!skippedItems.empty) {
			// Cleanup array memory
			skippedItems.clear();
		}
	}
	
	// If the JSON item is not in the database, it is potentially a new item that we need to action
	void applyPotentiallyNewLocalItem(Item newDatabaseItem, JSONValue onedriveJSONItem, string newItemPath) {
			
		// The JSON and Database items being passed in here have passed the following checks:
		// - skip_file
		// - skip_dir
		// - sync_list
		// - skip_dotfiles
		// - check_nosync
		// - skip_size
		// - Is not currently cached in the local database
		// As such, we should not be doing any other checks here to determine if the JSON item is wanted .. it is
		
		if (exists(newItemPath)) {
			// Issue #2209 fix - test if path is a bad symbolic link
			if (isSymlink(newItemPath)) {
				log.vdebug("Path on local disk is a symbolic link ........");
				if (!exists(readLink(newItemPath))) {
					// reading the symbolic link failed	
					log.vdebug("Reading the symbolic link target failed ........ ");
					log.logAndNotify("Skipping item - invalid symbolic link: ", newItemPath);
					return;
				}
			}
			
			// Path exists locally, is not a bad symbolic link
			// Test if this item is actually in-sync
			// What is the source of this item data?
			string itemSource = "remote";
			if (isItemSynced(newDatabaseItem, newItemPath, itemSource)) {
				// Item details from OneDrive and local item details in database are in-sync
				log.vdebug("The item to sync is already present on the local filesystem and is in-sync with what is reported online");
				log.vdebug("Update/Insert local database with item details");
				log.vdebug("item details to update/insert: ", newDatabaseItem);
				itemDB.upsert(newDatabaseItem);
				return;
			} else {
				// Item details from OneDrive and local item details in database are NOT in-sync
				log.vdebug("The item to sync exists locally but is NOT in the local database - otherwise this would be handled as changed item");
				
				// Which object is newer? The local file or the remote file?
				SysTime localModifiedTime = timeLastModified(newItemPath).toUTC();
				SysTime itemModifiedTime = newDatabaseItem.mtime;
				// Reduce time resolution to seconds before comparing
				localModifiedTime.fracSecs = Duration.zero;
				itemModifiedTime.fracSecs = Duration.zero;
				
				// Is the local modified time greater than that from OneDrive?
				if (localModifiedTime > itemModifiedTime) {
					// Local file is newer than item on OneDrive based on file modified time
					// Is this item id in the database?
					if (itemDB.idInLocalDatabase(newDatabaseItem.driveId, newDatabaseItem.id)) {
						// item id is in the database
						// no local rename
						// no download needed
						log.vlog("Local item modified time is newer based on UTC time conversion - keeping local item as this exists in the local database");
						log.vdebug("Skipping OneDrive change as this is determined to be unwanted due to local item modified time being newer than OneDrive item and present in the sqlite database");
					} else {
						// item id is not in the database .. maybe a --resync ?
						// file exists locally but is not in the sqlite database - maybe a failed download?
						log.vlog("Local item does not exist in local database - replacing with file from OneDrive - failed download?");
						
						// In a --resync scenario or if items.sqlite3 was deleted before startup we have zero way of knowing IF the local file is meant to be the right file
						// To this pint we have passed the following checks:
						// 1. Any client side filtering checks - this determined this is a file that is wanted
						// 2. A file with the exact name exists locally
						// 3. The local modified time > remote modified time
						// 4. The id of the item from OneDrive is not in the database
						
						// Has the user configured to IGNORE local data protection rules?
						if (bypassDataPreservation) {
							// The user has configured to ignore data safety checks and overwrite local data rather than preserve & rename
							log.vlog("WARNING: Local Data Protection has been disabled. You may experience data loss on this file: ", newItemPath);
						} else {
							// local data protection is configured, rename the local file, passing in if we are performing a --dry-run or not
							safeBackup(newItemPath, dryRun);
						}
					}
				} else {
					// Remote file is newer than the existing local item
					log.vlog("Remote item modified time is newer based on UTC time conversion"); // correct message, remote item is newer
					log.vdebug("localModifiedTime (local file):   ", localModifiedTime);
					log.vdebug("itemModifiedTime (OneDrive item): ", itemModifiedTime);
					
					// Has the user configured to IGNORE local data protection rules?
					if (bypassDataPreservation) {
						// The user has configured to ignore data safety checks and overwrite local data rather than preserve & rename
						log.vlog("WARNING: Local Data Protection has been disabled. You may experience data loss on this file: ", newItemPath);
					} else {
						// local data protection is configured, rename the local file, passing in if we are performing a --dry-run or not
						safeBackup(newItemPath, dryRun);							
					}
				}
			}
		} 
			
		// Path does not exist locally (should not exist locally if renamed file) - this will be a new file download or new folder creation
		// How to handle this Potentially New Local Item JSON ?
		final switch (newDatabaseItem.type) {
			case ItemType.file:
				// Add to the items to download array for processing
				fileJSONItemsToDownload ~= onedriveJSONItem;
				break;
			case ItemType.dir:
			case ItemType.remote:
				log.log("Creating local directory: ", newItemPath);
				if (!dryRun) {
					try {
						// Create the new directory
						log.vdebug("Requested path does not exist, creating directory structure: ", newItemPath);
						mkdirRecurse(newItemPath);
						// Configure the applicable permissions for the folder
						log.vdebug("Setting directory permissions for: ", newItemPath);
						newItemPath.setAttributes(appConfig.returnRequiredDirectoryPermisions());
						// Update the time of the folder to match the last modified time as is provided by OneDrive
						// If there are any files then downloaded into this folder, the last modified time will get 
						// updated by the local Operating System with the latest timestamp - as this is normal operation
						// as the directory has been modified
						log.vdebug("Setting directory lastModifiedDateTime for: ", newItemPath , " to ", newDatabaseItem.mtime);
						log.vdebug("Calling setTimes() for this file: ", newItemPath);
						setTimes(newItemPath, newDatabaseItem.mtime, newDatabaseItem.mtime);
						// Save the item to the database
						saveItem(onedriveJSONItem);
					} catch (FileException e) {
						// display the error message
						displayFileSystemErrorMessage(e.msg, getFunctionName!({}));
					}
				} else {
					// we dont create the directory, but we need to track that we 'faked it'
					idsFaked ~= [newDatabaseItem.driveId, newDatabaseItem.id];
					// Save the item to the dry-run database
					saveItem(onedriveJSONItem);
				}
				break;
			case ItemType.unknown:
				// Unknown type - we dont action or sync these items
				break;
		}
	}
	
	// If the JSON item IS in the database, this will be an update to an existing in-sync item
	void applyPotentiallyChangedItem(Item existingDatabaseItem, string existingItemPath, Item changedOneDriveItem, string changedItemPath, JSONValue onedriveJSONItem) {
				
		// If we are moving the item, we do not need to download it again
		bool itemWasMoved = false;
		
		// Do we need to actually update the database with the details that were provided by the OneDrive API?
		// Calculate these time items from the provided items
		SysTime existingItemModifiedTime = existingDatabaseItem.mtime;
		existingItemModifiedTime.fracSecs = Duration.zero;
		SysTime changedOneDriveItemModifiedTime = changedOneDriveItem.mtime;
		changedOneDriveItemModifiedTime.fracSecs = Duration.zero;
		
		if (existingDatabaseItem.eTag != changedOneDriveItem.eTag) {
			// The eTag has changed to what we previously cached
			if (existingItemPath != changedItemPath) {
				// Log that we are changing / moving an item to a new name
				log.log("Moving ", existingItemPath, " to ", changedItemPath);
				// Is the destination path empty .. or does something exist at that location?
				if (exists(changedItemPath)) {
					// Destination we are moving to exists ... 
					Item changedLocalItem;
					// Query DB for this changed item in specified path that exists and see if it is in-sync
					if (itemDB.selectByPath(changedItemPath, changedOneDriveItem.driveId, changedLocalItem)) {
						// The 'changedItemPath' is in the database
						string itemSource = "database";
						if (isItemSynced(changedLocalItem, changedItemPath, itemSource)) {
							// The destination item is in-sync
							log.vlog("Destination is in sync and will be overwritten");
						} else {
							// The destination item is different
							log.vlog("The destination is occupied with a different item, renaming the conflicting file...");
							// Backup this item, passing in if we are performing a --dry-run or not
							safeBackup(changedItemPath, dryRun);
						}
					} else {
						// The to be overwritten item is not already in the itemdb, so it should saved to avoid data loss
						log.vlog("The destination is occupied by an existing un-synced file, renaming the conflicting file...");
						// Backup this item, passing in if we are performing a --dry-run or not
						safeBackup(changedItemPath, dryRun);
					}
				}
				
				// Try and rename path, catch any exception generated
				try {
					// Rename this item, passing in if we are performing a --dry-run or not
					safeBackup(changedItemPath, dryRun);
					
					// If the item is a file, make sure that the local timestamp now is the same as the timestamp online
					// Otherwise when we do the DB check, the move on the file system, the file technically has a newer timestamp
					// which is 'correct' .. but we need to report locally the online timestamp here as the move was made online
					if (changedOneDriveItem.type == ItemType.file) {
						setTimes(changedItemPath, changedOneDriveItem.mtime, changedOneDriveItem.mtime);
					}
					
					// Flag that the item was moved | renamed
					itemWasMoved = true;
										
					// If we are in a --dry-run situation, the actual rename did not occur - but we need to track like it did
					if (dryRun) {
						// Track this as a faked id item
						idsFaked ~= [changedOneDriveItem.driveId, changedOneDriveItem.id];
						// We also need to track that we did not rename this path
						pathsRenamed ~= [existingItemPath];
					}
				} catch (FileException e) {
					// display the error message
					displayFileSystemErrorMessage(e.msg, getFunctionName!({}));
				}
			}
			
			// What sort of changed item is this?
			// Is it a file, and we did not move it ..
			if ((changedOneDriveItem.type == ItemType.file) && (!itemWasMoved)) {
				// The eTag is notorious for being 'changed' online by some backend Microsoft process
				if (existingDatabaseItem.quickXorHash != changedOneDriveItem.quickXorHash) {
					// Add to the items to download array for processing - the file hash we previously recorded is not the same as online
					fileJSONItemsToDownload ~= onedriveJSONItem;
				} else {
					// If the timestamp is different, or we are running a client operational mode that does not support /delta queries - we have to update the DB with the details from OneDrive
					// Unfortunatly because of the consequence of Nataional Cloud Deployments not supporting /delta queries, the application uses the local database to flag what is out-of-date / track changes
					// This means that the constant disk writing to the database fix implemented with https://github.com/abraunegg/onedrive/pull/2004 cannot be utilised when using these operational modes
					// as all records are touched / updated when performing the OneDrive sync operations. The impacted operational modes are:
					// - National Cloud Deployments do not support /delta as a query
					// - When using --single-directory
					// - When using --download-only --cleanup-local-files
				
					// Is the last modified timestamp in the DB the same as the API data or are we running an operational mode where we simulated the /delta response?
					if ((existingItemModifiedTime != changedOneDriveItemModifiedTime) || (generateSimulatedDeltaResponse)) {
					// Save this item in the database
						// Add to the local database
						log.vdebug("Adding changed OneDrive Item to database: ", changedOneDriveItem);
						itemDB.upsert(changedOneDriveItem);
					}
				}
			} else {
				// Save this item in the database
				saveItem(onedriveJSONItem);
				
				// If the 'Add shortcut to My files' link was the item that was actually renamed .. we have to update our DB records
				if (changedOneDriveItem.type == ItemType.remote) {
					// Select remote item data from the database
					Item existingRemoteDbItem;
					itemDB.selectById(changedOneDriveItem.remoteDriveId, changedOneDriveItem.remoteId, existingRemoteDbItem);
					// Update the 'name' in existingRemoteDbItem and save it back to the database
					// This is the local name stored on disk that was just 'moved'
					existingRemoteDbItem.name = changedOneDriveItem.name;
					itemDB.upsert(existingRemoteDbItem);
				}
			}
		} else {
			// The existingDatabaseItem.eTag == changedOneDriveItem.eTag .. nothing has changed eTag wise
			
			// If the timestamp is different, or we are running a client operational mode that does not support /delta queries - we have to update the DB with the details from OneDrive
			// Unfortunatly because of the consequence of Nataional Cloud Deployments not supporting /delta queries, the application uses the local database to flag what is out-of-date / track changes
			// This means that the constant disk writing to the database fix implemented with https://github.com/abraunegg/onedrive/pull/2004 cannot be utilised when using these operational modes
			// as all records are touched / updated when performing the OneDrive sync operations. The impacted operational modes are:
			// - National Cloud Deployments do not support /delta as a query
			// - When using --single-directory
			// - When using --download-only --cleanup-local-files
		
			// Is the last modified timestamp in the DB the same as the API data or are we running an operational mode where we simulated the /delta response?
			if ((existingItemModifiedTime != changedOneDriveItemModifiedTime) || (generateSimulatedDeltaResponse)) {
				// Database update needed for this item because our local record is out-of-date
				// Add to the local database
				log.vdebug("Adding changed OneDrive Item to database: ", changedOneDriveItem);
				itemDB.upsert(changedOneDriveItem);
			}
		}
	}
	
	// Download new file items as identified
	void downloadOneDriveItems() {
		// Lets deal with all the JSON items that need to be downloaded in a batch process
		ulong batchSize = appConfig.concurrentThreads;
		ulong batchCount = (fileJSONItemsToDownload.length + batchSize - 1) / batchSize;
		ulong batchesProcessed = 0;
		
		foreach (chunk; fileJSONItemsToDownload.chunks(batchSize)) {
			// send an array containing 'appConfig.concurrentThreads' (16) JSON items to download
			downloadOneDriveItemsInParallel(chunk);
		}
	}
	
	// Download items in parallel
	void downloadOneDriveItemsInParallel(JSONValue[] array) {
		// This function recieved an array of 16 JSON items to download
		foreach (i, onedriveJSONItem; taskPool.parallel(array)) {
			// Take each JSON item and 
			downloadFileItem(onedriveJSONItem);
		}
	}
	
	// Perform the actual download of an object from OneDrive
	void downloadFileItem(JSONValue onedriveJSONItem) {
				
		bool downloadFailed = false;
		string OneDriveFileXORHash;
		string OneDriveFileSHA256Hash;
		ulong jsonFileSize = 0;
		
		// Download item specifics
		string downloadDriveId = onedriveJSONItem["parentReference"]["driveId"].str;
		string downloadParentId = onedriveJSONItem["parentReference"]["id"].str;
		string downloadItemName = onedriveJSONItem["name"].str;
		string downloadItemId = onedriveJSONItem["id"].str;
	
		// Calculate this items path
		string newItemPath = computeItemPath(downloadDriveId, downloadParentId) ~ "/" ~ downloadItemName;
		log.vdebug("New Item calculated full path is: ", newItemPath);
		
		// Is the item reported as Malware ?
		if (isMalware(onedriveJSONItem)){
			// OneDrive reports that this file is malware
			log.error("ERROR: MALWARE DETECTED IN FILE - DOWNLOAD SKIPPED: ", newItemPath);
			downloadFailed = true;
		} else {
			// Grab this file's filesize
			if (hasFileSize(onedriveJSONItem)) {
				// Use the configured filesize as reported by OneDrive
				jsonFileSize = onedriveJSONItem["size"].integer;
			} else {
				// filesize missing
				log.vdebug("WARNING: onedriveJSONItem['size'] is missing");
			}
			
			// Configure the hashes for comparison post download
			if (hasHashes(onedriveJSONItem)) {
				// File details returned hash details
				// QuickXorHash
				if (hasQuickXorHash(onedriveJSONItem)) {
					// Use the provided quickXorHash as reported by OneDrive
					if (onedriveJSONItem["file"]["hashes"]["quickXorHash"].str != "") {
						OneDriveFileXORHash = onedriveJSONItem["file"]["hashes"]["quickXorHash"].str;
					}
				} else {
					// Fallback: Check for SHA256Hash
					if (hasSHA256Hash(onedriveJSONItem)) {
						// Use the provided sha256Hash as reported by OneDrive
						if (onedriveJSONItem["file"]["hashes"]["sha256Hash"].str != "") {
							OneDriveFileSHA256Hash = onedriveJSONItem["file"]["hashes"]["sha256Hash"].str;
						}
					}
				}
			} else {
				// file hash data missing
				log.vdebug("WARNING: onedriveJSONItem['file']['hashes'] is missing - unable to compare file hash after download");
			}
		
			// Is this a --download-only scenario?
			if (appConfig.getValueBool("download_only")) {
				if (exists(newItemPath)) {
					// file exists locally already
					Item databaseItem;
					bool fileFoundInDB = false;
					
					foreach (driveId; driveIDsArray) {
						if (itemDB.selectByPath(newItemPath, driveId, databaseItem)) {
							fileFoundInDB = true;
							break;
						}
					}
					
					// Log the DB details
					log.vdebug("File to download exists locally and this is the DB record: ", databaseItem);
					
					// Does the DB (what we think is in sync) hash match the existing local file hash?
					if (!testFileHash(newItemPath, databaseItem)) {
						// local file is different to what we know to be true
						log.log("The local file to replace (", newItemPath,") has been modified locally since the last download. Renaming it to avoid potential local data loss.");
						
						// Perform the local rename of the existing local file, passing in if we are performing a --dry-run or not
						safeBackup(newItemPath, dryRun);
					}
				}
			}
			
			// Is there enough free space locally to download the file
			// - We can use '.' here as we change the current working directory to the configured 'sync_dir'
			ulong localActualFreeSpace = to!ulong(getAvailableDiskSpace("."));
			// So that we are not responsible in making the disk 100% full if we can download the file, compare the current available space against the reservation set and file size
			// The reservation value is user configurable in the config file, 50MB by default
			ulong freeSpaceReservation = appConfig.getValueLong("space_reservation");
			// debug output
			log.vdebug("Local Disk Space Actual: ", localActualFreeSpace);
			log.vdebug("Free Space Reservation:  ", freeSpaceReservation);
			log.vdebug("File Size to Download:   ", jsonFileSize);
			
			// Calculate if we can actually download file - is there enough free space?
			if ((localActualFreeSpace < freeSpaceReservation) || (jsonFileSize > localActualFreeSpace)) {
				// localActualFreeSpace is less than freeSpaceReservation .. insufficient free space
				// jsonFileSize is greater than localActualFreeSpace .. insufficient free space
				log.log("Downloading file ", newItemPath, " ... failed!");
				log.log("Insufficient local disk space to download file");
				downloadFailed = true;
			} else {
				// If we are in a --dry-run situation - if not, actually perform the download
				if (!dryRun) {
					// Attempt to download the file as there is enough free space locally
					OneDriveApi downloadFileOneDriveApiInstance;
					downloadFileOneDriveApiInstance = new OneDriveApi(appConfig);
					try {	
						downloadFileOneDriveApiInstance.initialise();
						downloadFileOneDriveApiInstance.downloadById(downloadDriveId, downloadItemId, newItemPath, jsonFileSize);
						downloadFileOneDriveApiInstance.shutdown();
						// Free object and memory
						object.destroy(downloadFileOneDriveApiInstance);
					} catch (OneDriveException exception) {
						log.vdebug("downloadFileOneDriveApiInstance.downloadById(downloadDriveId, downloadItemId, newItemPath, jsonFileSize); generated a OneDriveException");
						
						string thisFunctionName = getFunctionName!({});
						// HTTP request returned status code 408,429,503,504
						if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 429) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
							// Handle the 429
							if (exception.httpStatusCode == 429) {
								// HTTP request returned status code 429 (Too Many Requests). We need to leverage the response Retry-After HTTP header to ensure minimum delay until the throttle is removed.
								handleOneDriveThrottleRequest(downloadFileOneDriveApiInstance);
								log.vdebug("Retrying original request that generated the OneDrive HTTP 429 Response Code (Too Many Requests) - attempting to retry ", thisFunctionName);
							}
							// re-try the specific changes queries
							if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
								// 408 - Request Time Out
								// 503 - Service Unavailable
								// 504 - Gateway Timeout
								// Transient error - try again in 30 seconds
								auto errorArray = splitLines(exception.msg);
								log.log(errorArray[0], " when attempting to download an item from OneDrive - retrying applicable request in 30 seconds");
								log.vdebug(thisFunctionName, " previously threw an error - retrying");
								// The server, while acting as a proxy, did not receive a timely response from the upstream server it needed to access in attempting to complete the request. 
								log.vdebug("Thread sleeping for 30 seconds as the server did not receive a timely response from the upstream server it needed to access in attempting to complete the request");
								Thread.sleep(dur!"seconds"(30));
							}
							// re-try original request - retried for 429, 503, 504 - but loop back calling this function 
							log.vdebug("Retrying Function: ", thisFunctionName);
							downloadFileItem(onedriveJSONItem);
						} else {
							// Default operation if not 408,429,503,504 errors
							// display what the error is
							displayOneDriveErrorMessage(exception.msg, getFunctionName!({}));
						}
						
					} catch (FileException e) {
						// There was a file system error
						// display the error message
						displayFileSystemErrorMessage(e.msg, getFunctionName!({}));
						downloadFailed = true;
					} catch (ErrnoException e) {
						// There was a file system error
						// display the error message
						displayFileSystemErrorMessage(e.msg, getFunctionName!({}));
						downloadFailed = true;
					}
				
					// If we get to this point, something was downloaded .. does it match what we expected?
					if (exists(newItemPath)) {
						// When downloading some files from SharePoint, the OneDrive API reports one file size, 
						// but the SharePoint HTTP Server sends a totally different byte count for the same file
						// we have implemented --disable-download-validation to disable these checks
					
						if (!disableDownloadValidation) {
							// A 'file' was downloaded - does what we downloaded = reported jsonFileSize or if there is some sort of funky local disk compression going on
							// Does the file hash OneDrive reports match what we have locally?
							string onlineFileHash;
							string downloadedFileHash;
							ulong downloadFileSize = getSize(newItemPath);
							
							if (!OneDriveFileXORHash.empty) {
								onlineFileHash = OneDriveFileXORHash;
								// Calculate the QuickXOHash for this file
								downloadedFileHash = computeQuickXorHash(newItemPath);
							} else {
								onlineFileHash = OneDriveFileSHA256Hash;
								// Fallback: Calculate the SHA256 Hash for this file
								downloadedFileHash = computeSHA256Hash(newItemPath);
							}
							
							if ((downloadFileSize == jsonFileSize) && (downloadedFileHash == onlineFileHash)) {
								// Downloaded file matches size and hash
								log.vdebug("Downloaded file matches reported size and reported file hash");
								try {
									// get the mtime from the JSON data
									SysTime itemModifiedTime;
									if (isItemRemote(onedriveJSONItem)) {
										// remote file item
										itemModifiedTime = SysTime.fromISOExtString(onedriveJSONItem["remoteItem"]["fileSystemInfo"]["lastModifiedDateTime"].str);
									} else {
										// not a remote item
										itemModifiedTime = SysTime.fromISOExtString(onedriveJSONItem["fileSystemInfo"]["lastModifiedDateTime"].str);
									}
									
									// set the correct time on the downloaded file
									log.vdebug("Calling setTimes() for this file: ", newItemPath);
									setTimes(newItemPath, itemModifiedTime, itemModifiedTime);
								} catch (FileException e) {
									// display the error message
									displayFileSystemErrorMessage(e.msg, getFunctionName!({}));
								}
							} else {
								// Downloaded file does not match size or hash .. which is it?
								bool downloadValueMismatch = false;
								// Size error?
								if (downloadFileSize != jsonFileSize) {
									// downloaded file size does not match
									downloadValueMismatch = true;
									log.vdebug("Actual file size on disk:   ", downloadFileSize);
									log.vdebug("OneDrive API reported size: ", jsonFileSize);
									log.error("ERROR: File download size mis-match. Increase logging verbosity to determine why.");
								}
								// Hash Error
								if (downloadedFileHash != onlineFileHash) {
									// downloaded file hash does not match
									downloadValueMismatch = true;
									log.vdebug("Actual local file hash:     ", downloadedFileHash);
									log.vdebug("OneDrive API reported hash: ", onlineFileHash);
									log.error("ERROR: File download hash mis-match. Increase logging verbosity to determine why.");
								}
								// .heic data loss check
								// - https://github.com/abraunegg/onedrive/issues/2471
								// - https://github.com/OneDrive/onedrive-api-docs/issues/1532
								// - https://github.com/OneDrive/onedrive-api-docs/issues/1723
								if (downloadValueMismatch && (toLower(extension(newItemPath)) == ".heic")) {
									// Need to display a message to the user that they have experienced data loss
									log.error("DATA-LOSS: File downloaded has experienced data loss due to a Microsoft OneDrive API bug. DO NOT DELETE THIS FILE ONLINE.");
									log.vlog("           Please read https://github.com/OneDrive/onedrive-api-docs/issues/1723 for more details.");
								}
								
								// Add some workaround messaging for SharePoint
								if (appConfig.accountType == "documentLibrary"){
									// It has been seen where SharePoint / OneDrive API reports one size via the JSON 
									// but the content length and file size written to disk is totally different - example:
									// From JSON:         "size": 17133
									// From HTTPS Server: < Content-Length: 19340
									// with no logical reason for the difference, except for a 302 redirect before file download
									log.error("INFO: It is most likely that a SharePoint OneDrive API issue is the root cause. Add --disable-download-validation to work around this issue but downloaded data integrity cannot be guaranteed.");
								} else {
									// other account types
									log.error("INFO: Potentially add --disable-download-validation to work around this issue but downloaded data integrity cannot be guaranteed.");
								}
								// We do not want this local file to remain on the local file system as it failed the integrity checks
								log.log("Removing file ", newItemPath, " due to failed integrity checks");
								if (!dryRun) {
									safeRemove(newItemPath);
								}
								downloadFailed = true;
							}
						} else {
							// Download validation checks were disabled
							log.vdebug("Downloaded file validation disabled due to --disable-download-validation");
							log.vlog("WARNING: Skipping download integrity check for: ", newItemPath);
						}	 // end of (!disableDownloadValidation)
					} else {
						log.error("ERROR: File failed to download. Increase logging verbosity to determine why.");
						downloadFailed = true;
					}
				}
			}
			
			// File should have been downloaded
			if (!downloadFailed) {
				// Download did not fail
				log.log("Downloading file ", newItemPath, " ... done");
				// Save this item into the database
				saveItem(onedriveJSONItem);
				
				// If we are in a --dry-run situation - if we are, we need to track that we faked the download
				if (dryRun) {
					// track that we 'faked it'
					idsFaked ~= [downloadDriveId, downloadItemId];
				}
			} else {
				// Output download failed
				log.log("Downloading file ", newItemPath, " ... failed!");
				// Add the path to a list of items that failed to download
				fileDownloadFailures ~= newItemPath;
			}
		}
	}
	
	// Test if the given item is in-sync. Returns true if the given item corresponds to the local one
	bool isItemSynced(Item item, string path, string itemSource) {
		
		if (!exists(path)) return false;
		final switch (item.type) {
		case ItemType.file:
			if (isFile(path)) {
				// can we actually read the local file?
				if (readLocalFile(path)){
					// local file is readable
					SysTime localModifiedTime = timeLastModified(path).toUTC();
					SysTime itemModifiedTime = item.mtime;
					// Reduce time resolution to seconds before comparing
					localModifiedTime.fracSecs = Duration.zero;
					itemModifiedTime.fracSecs = Duration.zero;
					if (localModifiedTime == itemModifiedTime) {
						return true;
					} else {
						log.vlog("Local item time discrepancy detected: ", path);
						log.vlog("This local item has a different modified time ", localModifiedTime, " when compared to ", itemSource, " modified time ", itemModifiedTime);
						// The file has been modified ... is the hash the same?
						// Test the file hash as the date / time stamp is different
						// Generating a hash is computationally expensive - we only generate the hash if timestamp was different
						if (testFileHash(path, item)) {
							// The hash is the same .. so we need to fix-up the timestamp depending on where it is wrong
							log.vlog("Local item has the same hash value as the item online - correcting timestamp");
							// Test if the local timestamp is newer
							if (localModifiedTime > itemModifiedTime) {
								// The source of the out-of-date timestamp was OneDrive and this needs to be corrected to avoid always generating a hash test if timestamp is different
								log.vlog("The source of the incorrect timestamp was OneDrive online - correcting timestamp online");
								if (!dryRun) {
									// Attempt to update the online date time stamp
									uploadLastModifiedTime(item.driveId, item.id, localModifiedTime.toUTC(), item.eTag);
								}
							} else {
								// The source of the out-of-date timestamp was the local file and this needs to be corrected to avoid always generating a hash test if timestamp is different
								log.vlog("The source of the incorrect timestamp was the local file - correcting timestamp locally");
								if (!dryRun) {
									log.vdebug("Calling setTimes() for this file: ", path);
									setTimes(path, item.mtime, item.mtime);
								}
							}
							return true;
						} else {
							// The hash is different so the content of the file has to be different as to what is stored online
							log.vlog("The local item has a different hash when compared to ", itemSource, " item hash");
							return false;
						}
					}
				} else {
					// Unable to read local file
					log.log("Unable to determine the sync state of this file as it cannot be read (file permissions or file corruption): ", path);
					return false;
				}
			} else {
				log.vlog("The local item is a directory but should be a file");
			}
			break;
		case ItemType.dir:
		case ItemType.remote:
			if (isDir(path)) {
				return true;
			} else {
				log.vlog("The local item is a file but should be a directory");
			}
			break;
		case ItemType.unknown:
			// Unknown type - return true but we dont action or sync these items 
			return true;
		}
		return false;
	}
	
	// Get the /delta data using the provided details
	JSONValue getDeltaChangesByItemId(string selectedDriveId, string selectedItemId, string providedDeltaLink, OneDriveApi getDeltaQueryOneDriveApiInstance) {
		
		// Function variables
		JSONValue deltaChangesBundle;
		
		// Get the /delta data for this account | driveId | deltaLink combination
		log.vdebug("------------------------------------------------------------------");
		log.vdebug("selectedDriveId:   ", selectedDriveId);
		log.vdebug("selectedItemId:    ", selectedItemId);
		log.vdebug("providedDeltaLink: ", providedDeltaLink);
		log.vdebug("------------------------------------------------------------------");
		
		try {
			deltaChangesBundle = getDeltaQueryOneDriveApiInstance.viewChangesByItemId(selectedDriveId, selectedItemId, providedDeltaLink);
		} catch (OneDriveException exception) {
			// caught an exception
			log.vdebug("getDeltaQueryOneDriveApiInstance.viewChangesByItemId(selectedDriveId, selectedItemId, providedDeltaLink) generated a OneDriveException");
			
			auto errorArray = splitLines(exception.msg);
			string thisFunctionName = getFunctionName!({});
			// HTTP request returned status code 408,429,503,504
			if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 429) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
				// Handle the 429
				if (exception.httpStatusCode == 429) {
					// HTTP request returned status code 429 (Too Many Requests). We need to leverage the response Retry-After HTTP header to ensure minimum delay until the throttle is removed.
					handleOneDriveThrottleRequest(getDeltaQueryOneDriveApiInstance);
					log.vdebug("Retrying original request that generated the OneDrive HTTP 429 Response Code (Too Many Requests) - attempting to retry ", thisFunctionName);
				}
				// re-try the specific changes queries
				if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
					// 408 - Request Time Out
					// 503 - Service Unavailable
					// 504 - Gateway Timeout
					// Transient error - try again in 30 seconds
					log.log(errorArray[0], " when attempting to query OneDrive API for Delta Changes - retrying applicable request in 30 seconds");
					log.vdebug(thisFunctionName, " previously threw an error - retrying");
					// The server, while acting as a proxy, did not receive a timely response from the upstream server it needed to access in attempting to complete the request. 
					log.vdebug("Thread sleeping for 30 seconds as the server did not receive a timely response from the upstream server it needed to access in attempting to complete the request");
					Thread.sleep(dur!"seconds"(30));
				}
				// dont retry request, loop back to calling function
				log.vdebug("Looping back after failure");
				deltaChangesBundle = null;
			} else {
				// Default operation if not 408,429,503,504 errors
				if (exception.httpStatusCode == 410) {
					log.log("\nWARNING: The OneDrive API responded with an error that indicates the locally stored deltaLink value is invalid");
					// Essentially the 'providedDeltaLink' that we have stored is no longer available ... re-try without the stored deltaLink
					log.log("WARNING: Retrying OneDrive API call without using the locally stored deltaLink value");
					// Configure an empty deltaLink
					log.vdebug("Delta link expired for 'getDeltaQueryOneDriveApiInstance.viewChangesByItemId(selectedDriveId, selectedItemId, providedDeltaLink)', setting 'deltaLink = null'");
					string emptyDeltaLink = "";
					// retry with empty deltaLink
					deltaChangesBundle = getDeltaQueryOneDriveApiInstance.viewChangesByItemId(selectedDriveId, selectedItemId, emptyDeltaLink);
				} else {
					// display what the error is
					log.log("CODING TO DO: Hitting this failure error output");
					displayOneDriveErrorMessage(exception.msg, thisFunctionName);
					deltaChangesBundle = null;
				}
			}
		}
		
		return deltaChangesBundle;
	}
	
	// Common code to handle a 408 or 429 response from the OneDrive API
	void handleOneDriveThrottleRequest(OneDriveApi activeOneDriveApiInstance) {
		
		// If OneDrive sends a status code 429 then this function will be used to process the Retry-After response header which contains the value by which we need to wait
		log.vdebug("Handling a OneDrive HTTP 429 Response Code (Too Many Requests)");
		// Read in the Retry-After HTTP header as set and delay as per this value before retrying the request
		auto retryAfterValue = activeOneDriveApiInstance.getRetryAfterValue();
		log.vdebug("Using Retry-After Value = ", retryAfterValue);
		
		// HTTP request returned status code 429 (Too Many Requests)
		// https://github.com/abraunegg/onedrive/issues/133
		// https://github.com/abraunegg/onedrive/issues/815
		
		ulong delayBeforeRetry = 0;
		if (retryAfterValue != 0) {
			// Use the HTTP Response Header Value
			delayBeforeRetry = retryAfterValue;
		} else {
			// Use a 120 second delay as a default given header value was zero
			// This value is based on log files and data when determining correct process for 429 response handling
			delayBeforeRetry = 120;
			// Update that we are over-riding the provided value with a default
			log.vdebug("HTTP Response Header retry-after value was 0 - Using a preconfigured default of: ", delayBeforeRetry);
		}
		
		// Sleep thread as per request
		log.log("Thread sleeping due to 'HTTP request returned status code 429' - The request has been throttled");
		log.log("Sleeping for ", delayBeforeRetry, " seconds");
		Thread.sleep(dur!"seconds"(delayBeforeRetry));
		
		// Reset retry-after value to zero as we have used this value now and it may be changed in the future to a different value
		activeOneDriveApiInstance.resetRetryAfterValue();
	}
	
	// If the JSON response is not correct JSON object, exit
	void invalidJSONResponseFromOneDriveAPI() {
		log.error("ERROR: Query of the OneDrive API returned an invalid JSON response");
		// Must exit
		exit(-1);
	}
	
	// Handle an unhandled API error
	void defaultUnhandledHTTPErrorCode(OneDriveException exception) {
		
		// display error
		displayOneDriveErrorMessage(exception.msg, getFunctionName!({}));
		// Must exit here
		exit(-1);
	}
	
	// Display the pertinant details of the sync engine
	void displaySyncEngineDetails() {
		
		// Display accountType, defaultDriveId, defaultRootId & remainingFreeSpace for verbose logging purposes
		//log.vlog("Application version:  ", strip(import("version")));
		
		string tempVersion = "v2.5.0-alpha-3" ~ " GitHub version: " ~ strip(import("version"));
		log.vlog("Application version:  ", tempVersion);
		
		log.vlog("Account Type:         ", appConfig.accountType);
		log.vlog("Default Drive ID:     ", appConfig.defaultDriveId);
		log.vlog("Default Root ID:      ", appConfig.defaultRootId);
		
		// What do we display here for space remaining
		if (appConfig.remainingFreeSpace > 0) {
			// Display the actual value
			log.vlog("Remaining Free Space: ", byteToGibiByte(appConfig.remainingFreeSpace) , " GB (", appConfig.remainingFreeSpace, " bytes)");
		} else {
			// zero or non-zero value or restricted
			if (!appConfig.quotaRestricted){
				log.vlog("Remaining Free Space:       0 KB");
			} else {
				log.vlog("Remaining Free Space:       Not Available");
			}
		}
	}
	
	// Query itemdb.computePath() and catch potential assert when DB consistency issue occurs
	string computeItemPath(string thisDriveId, string thisItemId) {
		
		// static declare this for this function
		static import core.exception;
		string calculatedPath;
		log.vdebug("Attempting to calculate local filesystem path for ", thisDriveId, " and ", thisItemId);
		try {
			calculatedPath = itemDB.computePath(thisDriveId, thisItemId);
		} catch (core.exception.AssertError) {
			// broken tree in the database, we cant compute the path for this item id, exit
			log.error("ERROR: A database consistency issue has been caught. A --resync is needed to rebuild the database.");
			// Must exit here to preserve data
			exit(-1);
		}
		
		// return calculated path as string
		return calculatedPath;
	}
	
	// Try and compute the file hash for the given item
	bool testFileHash(string path, Item item) {
		
		// Generate QuickXORHash first before attempting to generate any other type of hash
		if (item.quickXorHash) {
			if (item.quickXorHash == computeQuickXorHash(path)) return true;
		} else if (item.sha256Hash) {
			if (item.sha256Hash == computeSHA256Hash(path)) return true;
		}
		return false;
	}
	
	// Process items that need to be removed
	void processDeleteItems() {
		
		foreach_reverse (i; idsToDelete) {
			Item item;
			string path;
			if (!itemDB.selectById(i[0], i[1], item)) continue; // check if the item is in the db
			// Compute this item path
			path = computeItemPath(i[0], i[1]);
			
			// Log the action if the path exists .. it may of already been removed and this is a legacy array item
			if (exists(path)) {
				if (item.type == ItemType.file) {
					log.log("Trying to delete file ", path);
				} else {
					log.log("Trying to delete directory ", path);
				}
			}
			
			// Process the database entry removal. In a --dry-run scenario, this is being done against a DB copy
			itemDB.deleteById(item.driveId, item.id);
			if (item.remoteDriveId != null) {
				// delete the linked remote folder
				itemDB.deleteById(item.remoteDriveId, item.remoteId);
			}
			
			// Add to pathFakeDeletedArray
			// We dont want to try and upload this item again, so we need to track this object
			if (dryRun) {
				// We need to add './' here so that it can be correctly searched to ensure it is not uploaded
				string pathToAdd = "./" ~ path;
				pathFakeDeletedArray ~= pathToAdd;
			}
				
			bool needsRemoval = false;
			if (exists(path)) {
				// path exists on the local system	
				// make sure that the path refers to the correct item
				Item pathItem;
				if (itemDB.selectByPath(path, item.driveId, pathItem)) {
					if (pathItem.id == item.id) {
						needsRemoval = true;
					} else {
						log.log("Skipped due to id difference!");
					}
				} else {
					// item has disappeared completely
					needsRemoval = true;
				}
			}
			if (needsRemoval) {
				// Log the action
				if (item.type == ItemType.file) {
					log.log("Deleting file ", path);
				} else {
					log.log("Deleting directory ", path);
				}
				
				// Perform the action
				if (!dryRun) {
					if (isFile(path)) {
						remove(path);
					} else {
						try {
							// Remove any children of this path if they still exist
							// Resolve 'Directory not empty' error when deleting local files
							foreach (DirEntry child; dirEntries(path, SpanMode.depth, false)) {
								attrIsDir(child.linkAttributes) ? rmdir(child.name) : remove(child.name);
							}
							// Remove the path now that it is empty of children
							rmdirRecurse(path);
						} catch (FileException e) {
							// display the error message
							displayFileSystemErrorMessage(e.msg, getFunctionName!({}));
						}
					}
				}
			}
		}
		
		if (!dryRun) {
			// Cleanup array memory
			idsToDelete = [];
		}
	}
	
	// Update the timestamp of an object online
	void uploadLastModifiedTime(string driveId, string id, SysTime mtime, string eTag) {
		
		string itemModifiedTime;
		itemModifiedTime = mtime.toISOExtString();
		JSONValue data = [
			"fileSystemInfo": JSONValue([
				"lastModifiedDateTime": itemModifiedTime
			])
		];
		
		// What eTag value do we use?
		string eTagValue;
		if (appConfig.accountType == "personal") {
			eTagValue = null;
		} else {
			eTagValue = eTag;
		}
		
		JSONValue response;
		// Create a new OneDrive API instance
		OneDriveApi uploadLastModifiedTimeApiInstance;
		uploadLastModifiedTimeApiInstance = new OneDriveApi(appConfig);
		uploadLastModifiedTimeApiInstance.initialise();
		
		// Try and update the online last modified time
		try {
			// Use this instance
			response = uploadLastModifiedTimeApiInstance.updateById(driveId, id, data, eTagValue);
			// Shut the instance down
			uploadLastModifiedTimeApiInstance.shutdown();
			// Free object and memory
			object.destroy(uploadLastModifiedTimeApiInstance);
			// Is the response a valid JSON object - validation checking done in saveItem
			saveItem(response);
		} catch (OneDriveException exception) {
			
			string thisFunctionName = getFunctionName!({});
			// HTTP request returned status code 408,429,503,504
			if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 429) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
				// Handle the 429
				if (exception.httpStatusCode == 429) {
					// HTTP request returned status code 429 (Too Many Requests). We need to leverage the response Retry-After HTTP header to ensure minimum delay until the throttle is removed.
					handleOneDriveThrottleRequest(uploadLastModifiedTimeApiInstance);
					log.vdebug("Retrying original request that generated the OneDrive HTTP 429 Response Code (Too Many Requests) - attempting to retry ", thisFunctionName);
				}
				// re-try the specific changes queries
				if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
					// 408 - Request Time Out
					// 503 - Service Unavailable
					// 504 - Gateway Timeout
					// Transient error - try again in 30 seconds
					auto errorArray = splitLines(exception.msg);
					log.log(errorArray[0], " when attempting to update the timestamp on an item on OneDrive - retrying applicable request in 30 seconds");
					log.vdebug(thisFunctionName, " previously threw an error - retrying");
					// The server, while acting as a proxy, did not receive a timely response from the upstream server it needed to access in attempting to complete the request. 
					log.vdebug("Thread sleeping for 30 seconds as the server did not receive a timely response from the upstream server it needed to access in attempting to complete the request");
					Thread.sleep(dur!"seconds"(30));
				}
				// re-try original request - retried for 429, 503, 504 - but loop back calling this function 
				log.vdebug("Retrying Function: ", thisFunctionName);
				uploadLastModifiedTime(driveId, id, mtime, eTag);
				return;
			} else {
				// Default operation if not 408,429,503,504 errors
				if (exception.httpStatusCode == 409) {
					// ETag does not match current item's value - use a null eTag
					log.vdebug("Retrying Function: ", thisFunctionName);
					uploadLastModifiedTime(driveId, id, mtime, null);
				} else {
					// display what the error is
					displayOneDriveErrorMessage(exception.msg, getFunctionName!({}));
				}
			}
		}
	}
	
	// Perform a database integrity check - checking all the items that are in-sync at the moment, validating what we know should be on disk, to what is actually on disk
	void performDatabaseConsistencyAndIntegrityCheck() {
		
		// Log what we are doing
		if (!appConfig.surpressLoggingOutput) {
			log.log("Performing a database consistency and integrity check on locally stored data ... ");
		}
		
		// What driveIDsArray do we use? If we are doing a --single-directory we need to use just the drive id associated with that operation
		string[] consistencyCheckDriveIdsArray;
		if (singleDirectoryScope) {
			consistencyCheckDriveIdsArray ~= singleDirectoryScopeDriveId;
		} else {
			consistencyCheckDriveIdsArray = driveIDsArray;
		}
		
		// Create a new DB blank item
		Item item;
		// Use the array we populate, rather than selecting all distinct driveId's from the database
		foreach (driveId; consistencyCheckDriveIdsArray) {
			// Make the logging more accurate - we cant update driveId as this then breaks the below queries
			log.vlog("Processing DB entries for this Drive ID: ", driveId);
			
			// What OneDrive API query do we use?
			// - Are we running against a National Cloud Deployments that does not support /delta ?
			//   National Cloud Deployments do not support /delta as a query
			//   https://docs.microsoft.com/en-us/graph/deployments#supported-features
			//
			// - Are we performing a --single-directory sync, which will exclude many items online, focusing in on a specific online directory
			// 
			// - Are we performing a --download-only --cleanup-local-files action?
			//
			// If we did, we self generated a /delta response, thus need to now process elements that are still flagged as out-of-sync
			if ((singleDirectoryScope) || (nationalCloudDeployment) || (cleanupLocalFiles)) {
				// Any entry in the DB than is flagged as out-of-sync needs to be cleaned up locally first before we scan the entire DB
				// Normally, this is done at the end of processing all /delta queries, however when using --single-directory or a National Cloud Deployments is configured
				// We cant use /delta to query the OneDrive API as National Cloud Deployments dont support /delta
				// https://docs.microsoft.com/en-us/graph/deployments#supported-features
				// We dont use /delta for --single-directory as, in order to sync a single path with /delta, we need to query the entire OneDrive API JSON data to then filter out
				// objects that we dont want, thus, it is easier to use the same method as National Cloud Deployments, but query just the objects we are after
			
				// For each unique OneDrive driveID we know about
				Item[] outOfSyncItems = itemDB.selectOutOfSyncItems(driveId);
				foreach (outOfSyncItem; outOfSyncItems) {
					if (!dryRun) {
						// clean up idsToDelete
						idsToDelete.length = 0;
						assumeSafeAppend(idsToDelete);
						// flag to delete local file as it now is no longer in sync with OneDrive
						log.vdebug("Flagging to delete local item as it now is no longer in sync with OneDrive");
						log.vdebug("outOfSyncItem: ", outOfSyncItem);
						idsToDelete ~= [outOfSyncItem.driveId, outOfSyncItem.id];	
						// delete items in idsToDelete
						if (idsToDelete.length > 0) processDeleteItems();
					}
				}
						
				// Fetch database items associated with this path
				Item[] driveItems;
				if (singleDirectoryScope) {
					// Use the --single-directory items we previously configured
					// - query database for children objects using those items
					driveItems = getChildren(singleDirectoryScopeDriveId, singleDirectoryScopeItemId);
				} else {
					// Check everything associated with each driveId we know about
					log.vdebug("Selecting DB items via itemDB.selectByDriveId(driveId)");
					// Query database
					driveItems = itemDB.selectByDriveId(driveId);
				}
				
				log.vdebug("Database items to process for this driveId: ", driveItems.count);
				// Process each database database item associated with the driveId
				foreach(dbItem; driveItems) {
					// Does it still exist on disk in the location the DB thinks it is
					checkDatabaseItemForConsistency(dbItem);
				}
			} else {
				// Check everything associated with each driveId we know about
				log.vdebug("Selecting DB items via itemDB.selectByDriveId(driveId)");
				// Query database
				auto driveItems = itemDB.selectByDriveId(driveId);
				log.vdebug("Database items to process for this driveId: ", driveItems.count);
				// Process each database database item associated with the driveId
				foreach(dbItem; driveItems) {
					// Does it still exist on disk in the location the DB thinks it is
					checkDatabaseItemForConsistency(dbItem);
				}
			}
		}
		
		// Are we doing a --download-only sync?
		if (!appConfig.getValueBool("download_only")) {
			// Do we have any known items, where the content has changed locally, that needs to be uploaded?
			if (!databaseItemsWhereContentHasChanged.empty) {
				// There are changed local files that were in the DB to upload
				log.log("Changed local items to upload to OneDrive: ", databaseItemsWhereContentHasChanged.length);
				processChangedLocalItemsToUpload();
				// Cleanup array memory
				databaseItemsWhereContentHasChanged = [];
			}
		}
	}
	
	// Check this Database Item for its consistency on disk
	void checkDatabaseItemForConsistency(Item dbItem) {
			
		// What is the local path item
		string localFilePath;
		// Do we want to onward process this item?
		bool unwanted = false;
		
		// Compute this dbItem path early as we we use this path often
		localFilePath = buildNormalizedPath(computeItemPath(dbItem.driveId, dbItem.id));
		
		// To improve logging output for this function, what is the 'logical path'?
		string logOutputPath;
		if (localFilePath == ".") {
			// get the configured sync_dir
			logOutputPath = buildNormalizedPath(appConfig.getValueString("sync_dir"));
		} else {
			// use what was computed
			logOutputPath = localFilePath;
		}
		
		// Log what we are doing
		log.vlog("Processing ", logOutputPath);
		
		// Determine which action to take
		final switch (dbItem.type) {
		case ItemType.file:
			// Logging output
			checkFileDatabaseItemForConsistency(dbItem, localFilePath);
			break;
		case ItemType.dir:
			// Logging output
			checkDirectoryDatabaseItemForConsistency(dbItem, localFilePath);
			break;
		case ItemType.remote:
			// checkRemoteDirectoryDatabaseItemForConsistency(dbItem, localFilePath);
			break;
		case ItemType.unknown:
			// Unknown type - we dont action these items
			break;
		}
	}
	
	// Perform the database consistency check on this file item
	void checkFileDatabaseItemForConsistency(Item dbItem, string localFilePath) {
		
		// What is the source of this item data?
		string itemSource = "database";
		
		// Does this item|file still exist on disk?
		if (exists(localFilePath)) {
			// Path exists locally, is this path a file?
			if (isFile(localFilePath)) {
				// Can we actually read the local file?
				if (readLocalFile(localFilePath)){
					// File is readable
					SysTime localModifiedTime = timeLastModified(localFilePath).toUTC();
					SysTime itemModifiedTime = dbItem.mtime;
					// Reduce time resolution to seconds before comparing
					itemModifiedTime.fracSecs = Duration.zero;
					localModifiedTime.fracSecs = Duration.zero;
					
					if (localModifiedTime != itemModifiedTime) {
						// The modified dates are different
						log.vdebug("The local item has a different modified time ", localModifiedTime, " when compared to ", itemSource, " modified time ", itemModifiedTime);
						// Test the file hash
						if (!testFileHash(localFilePath, dbItem)) {
							// Is the local file 'newer' or 'older' (ie was an old file 'restored locally' by a different backup / replacement process?)
							if (localModifiedTime >= itemModifiedTime) {
								// Local file is newer
								if (!appConfig.getValueBool("download_only")) {
									log.vlog("The file content has changed locally and has a newer timestamp, thus needs to be uploaded to OneDrive");
									// Add to an array of files we need to upload as this file has changed locally in-between doing the /delta check and performing this check
									databaseItemsWhereContentHasChanged ~= [dbItem.driveId, dbItem.id, localFilePath];
								} else {
									log.vlog("The file content has changed locally and has a newer timestamp. The file will remain different to online file due to --download-only being used");
								}
							} else {
								// Local file is older - data recovery process? something else?
								if (!appConfig.getValueBool("download_only")) {
									log.vlog("The file content has changed locally and file now has a older timestamp. Uploading this file to OneDrive may potentially cause data-loss online");
									// Add to an array of files we need to upload as this file has changed locally in-between doing the /delta check and performing this check
									databaseItemsWhereContentHasChanged ~= [dbItem.driveId, dbItem.id, localFilePath];
								} else {
									log.vlog("The file content has changed locally and file now has a older timestamp. The file will remain different to online file due to --download-only being used");
								}
							}
						} else {
							// The file contents have not changed, but the modified timestamp has
							log.vlog("The last modified timestamp has changed however the file content has not changed");
							log.vlog("The local item has the same hash value as the item online - correcting timestamp online");
							if (!dryRun) {
								// Attempt to update the online date time stamp
								uploadLastModifiedTime(dbItem.driveId, dbItem.id, localModifiedTime.toUTC(), dbItem.eTag);
							}
						}
					} else {
						// The file has not changed
						log.vlog("The file has not changed");
					}
				} else {
					//The file is not readable - skipped
					log.log("Skipping processing this file as it cannot be read (file permissions or file corruption): ", localFilePath);
				}
			} else {
				// The item was a file but now is a directory
				log.vlog("The item was a file but now is a directory");
			}
		} else {
			// File does not exist locally, but is in our database as a dbItem containing all the data was passed into this function
			// If we are in a --dry-run situation - this file may never have existed as we never downloaded it
			if (!dryRun) {
				// Not --dry-run situation
				log.vlog("The file has been deleted locally");
				// Upload to OneDrive the instruction to delete this item. This will handle the 'noRemoteDelete' flag if set
				uploadDeletedItem(dbItem, localFilePath);
			} else {
				// We are in a --dry-run situation, file appears to have been deleted locally - this file may never have existed locally as we never downloaded it due to --dry-run
				// Did we 'fake create it' as part of --dry-run ?
				bool idsFakedMatch = false;
				foreach (i; idsFaked) {
					if (i[1] == dbItem.id) {
						log.vdebug("Matched faked file which is 'supposed' to exist but not created due to --dry-run use");
						log.vlog("The file has not changed");
						idsFakedMatch = true;
					}
				}
				if (!idsFakedMatch) {
					// dbItem.id did not match a 'faked' download new file creation - so this in-sync object was actually deleted locally, but we are in a --dry-run situation
					log.vlog("The file has been deleted locally");
					// Upload to OneDrive the instruction to delete this item. This will handle the 'noRemoteDelete' flag if set
					uploadDeletedItem(dbItem, localFilePath);
				}
			}
		}
	}
	
	// Perform the database consistency check on this directory item
	void checkDirectoryDatabaseItemForConsistency(Item dbItem, string localFilePath) {
			
		// What is the source of this item data?
		string itemSource = "database";
		
		// Does this item|directory still exist on disk?
		if (exists(localFilePath)) {
			// Fix https://github.com/abraunegg/onedrive/issues/1915
			try {
				if (!isDir(localFilePath)) {
					log.vlog("The item was a directory but now it is a file");
					uploadDeletedItem(dbItem, localFilePath);
					uploadNewFile(localFilePath);
				} else {
					// Directory still exists locally
					log.vlog("The directory has not changed");
					// When we are using --single-directory, we use a the getChildren() call to get all children of a path, meaning all children are already traversed
					// Thus, if we traverse the path of this directory .. we end up with double processing & log output .. which is not ideal
					if (!singleDirectoryScope) {
						// loop through the children
						foreach (Item child; itemDB.selectChildren(dbItem.driveId, dbItem.id)) {
							checkDatabaseItemForConsistency(child);
						}
					}
				}
			} catch (FileException e) {
				// display the error message
				displayFileSystemErrorMessage(e.msg, getFunctionName!({}));
			}
		} else {
			// Directory does not exist locally, but it is in our database as a dbItem containing all the data was passed into this function
			// If we are in a --dry-run situation - this directory may never have existed as we never created it
			if (!dryRun) {
				// Not --dry-run situation
				if (!appConfig.getValueBool("monitor")) {
					// Not in --monitor mode
					log.vlog("The directory has been deleted locally");
				} else {
					// Appropriate message as we are in --monitor mode
					log.vlog("The directory appears to have been deleted locally .. but we are running in --monitor mode. This may have been 'moved' on the local filesystem rather than being 'deleted'");
					log.vdebug("Most likely cause - 'inotify' event was missing for whatever action was taken locally or action taken when application was stopped");
				}
				// A moved directory will be uploaded as 'new', delete the old directory and database reference
				// Upload to OneDrive the instruction to delete this item. This will handle the 'noRemoteDelete' flag if set
				uploadDeletedItem(dbItem, localFilePath);
			} else {
				// We are in a --dry-run situation, directory appears to have been deleted locally - this directory may never have existed locally as we never created it due to --dry-run
				// Did we 'fake create it' as part of --dry-run ?
				bool idsFakedMatch = false;
				foreach (i; idsFaked) {
					if (i[1] == dbItem.id) {
						log.vdebug("Matched faked dir which is 'supposed' to exist but not created due to --dry-run use");
						log.vlog("The directory has not changed");
						idsFakedMatch = true;
					}
				}
				if (!idsFakedMatch) {
					// dbItem.id did not match a 'faked' download new directory creation - so this in-sync object was actually deleted locally, but we are in a --dry-run situation
					log.vlog("The directory has been deleted locally");
					// Upload to OneDrive the instruction to delete this item. This will handle the 'noRemoteDelete' flag if set
					uploadDeletedItem(dbItem, localFilePath);
				} else {
					// When we are using --single-directory, we use a the getChildren() call to get all children of a path, meaning all children are already traversed
					// Thus, if we traverse the path of this directory .. we end up with double processing & log output .. which is not ideal
					if (!singleDirectoryScope) {
						// loop through the children
						foreach (Item child; itemDB.selectChildren(dbItem.driveId, dbItem.id)) {
							checkDatabaseItemForConsistency(child);
						}
					}
				}
			}
		}
	}
	
	// Does this local path (directory or file) conform with the Microsoft Naming Restrictions?
	bool checkPathAgainstMicrosoftNamingRestrictions(string localFilePath) {
			
		// Check if the given path violates certain Microsoft restrictions and limitations
		// Return a true|false response
		bool invalidPath = false;
		
		// Check against Microsoft OneDrive restriction and limitations about Windows naming files
		if (!invalidPath) {
			if (!isValidName(localFilePath)) {
				log.logAndNotify("Skipping item - invalid name (Microsoft Naming Convention): ", localFilePath);
				invalidPath = true;
			}
		}
		
		// Check for bad whitespace items
		if (!invalidPath) {
			if (!containsBadWhiteSpace(localFilePath)) {
				log.logAndNotify("Skipping item - invalid name (Contains an invalid whitespace item): ", localFilePath);
				invalidPath = true;
			}
		}
		
		// Check for HTML ASCII Codes as part of file name
		if (!invalidPath) {
			if (!containsASCIIHTMLCodes(localFilePath)) {
				log.logAndNotify("Skipping item - invalid name (Contains HTML ASCII Code): ", localFilePath);
				invalidPath = true;
			}
		}
		// Return if this is a valid path
		return invalidPath;
	}
	
	// Does this local path (directory or file) get excluded from any operation based on any client side filtering rules?
	bool checkPathAgainstClientSideFiltering(string localFilePath) {
		
		// Check the path against client side filtering rules
		// - check_nosync
		// - skip_dotfiles
		// - skip_symlinks
		// - skip_file
		// - skip_dir
		// - sync_list
		// - skip_size
		// Return a true|false response
		
		bool clientSideRuleExcludesPath = false;
		
		// does the path exist?
		if (!exists(localFilePath)) {
			// path does not exist - we cant review any client side rules on something that does not exist locally
			return clientSideRuleExcludesPath;
		}
	
		// - check_nosync
		if (!clientSideRuleExcludesPath) {
			// Do we need to check for .nosync? Only if --check-for-nosync was passed in
			if (appConfig.getValueBool("check_nosync")) {
				if (exists(localFilePath ~ "/.nosync")) {
					log.vlog("Skipping item - .nosync found & --check-for-nosync enabled: ", localFilePath);
					clientSideRuleExcludesPath = true;
				}
			}
		}
		
		// - skip_dotfiles
		if (!clientSideRuleExcludesPath) {
			// Do we need to check skip dot files if configured
			if (appConfig.getValueBool("skip_dotfiles")) {
				if (isDotFile(localFilePath)) {
					log.vlog("Skipping item - .file or .folder: ", localFilePath);
					clientSideRuleExcludesPath = true;
				}
			}
		}
		
		// - skip_symlinks
		if (!clientSideRuleExcludesPath) {
			// Is the path a symbolic link
			if (isSymlink(localFilePath)) {
				// if config says so we skip all symlinked items
				if (appConfig.getValueBool("skip_symlinks")) {
					log.vlog("Skipping item - skip symbolic links configured: ", localFilePath);
					clientSideRuleExcludesPath = true;

				}
				// skip unexisting symbolic links
				else if (!exists(readLink(localFilePath))) {
					// reading the symbolic link failed - is the link a relative symbolic link
					//   drwxrwxr-x. 2 alex alex 46 May 30 09:16 .
					//   drwxrwxr-x. 3 alex alex 35 May 30 09:14 ..
					//   lrwxrwxrwx. 1 alex alex 61 May 30 09:16 absolute.txt -> /home/alex/OneDrivePersonal/link_tests/intercambio/prueba.txt
					//   lrwxrwxrwx. 1 alex alex 13 May 30 09:16 relative.txt -> ../prueba.txt
					//
					// absolute links will be able to be read, but 'relative' links will fail, because they cannot be read based on the current working directory 'sync_dir'
					string currentSyncDir = getcwd();
					string fullLinkPath = buildNormalizedPath(absolutePath(localFilePath));
					string fileName = baseName(fullLinkPath);
					string parentLinkPath = dirName(fullLinkPath);
					// test if this is a 'relative' symbolic link
					chdir(parentLinkPath);
					auto relativeLink = readLink(fileName);
					auto relativeLinkTest = exists(readLink(fileName));
					// reset back to our 'sync_dir'
					chdir(currentSyncDir);
					// results
					if (relativeLinkTest) {
						log.vdebug("Not skipping item - symbolic link is a 'relative link' to target ('", relativeLink, "') which can be supported: ", localFilePath);
					} else {
						log.logAndNotify("Skipping item - invalid symbolic link: ", localFilePath);
						clientSideRuleExcludesPath = true;
					}
				}
			}
		}
		
		// Is this item excluded by user configuration of skip_dir or skip_file?
		if (!clientSideRuleExcludesPath) {
			if (localFilePath != ".") {
				// skip_dir handling
				if (isDir(localFilePath)) {
					log.vdebug("Checking local path: ", localFilePath);
					// Only check path if config is != ""
					if (appConfig.getValueString("skip_dir") != "") {
						// The path that needs to be checked needs to include the '/'
						// This due to if the user has specified in skip_dir an exclusive path: '/path' - that is what must be matched
						if (selectiveSync.isDirNameExcluded(localFilePath.strip('.'))) {
							log.vlog("Skipping item - excluded by skip_dir config: ", localFilePath);
							clientSideRuleExcludesPath = true;
						}
					}
				}
				
				// skip_file handling
				if (isFile(localFilePath)) {
					log.vdebug("Checking file: ", localFilePath);
					// The path that needs to be checked needs to include the '/'
					// This due to if the user has specified in skip_file an exclusive path: '/path/file' - that is what must be matched
					if (selectiveSync.isFileNameExcluded(localFilePath.strip('.'))) {
						log.vlog("Skipping item - excluded by skip_file config: ", localFilePath);
						clientSideRuleExcludesPath = true;
					}
				}
			}
		}
	
		// Is this item excluded by user configuration of sync_list?
		if (!clientSideRuleExcludesPath) {
			if (localFilePath != ".") {
				if (syncListConfigured) {
					// sync_list configured and in use
					if (selectiveSync.isPathExcludedViaSyncList(localFilePath)) {
						if ((isFile(localFilePath)) && (appConfig.getValueBool("sync_root_files")) && (rootName(localFilePath.strip('.').strip('/')) == "")) {
							log.vdebug("Not skipping path due to sync_root_files inclusion: ", localFilePath);
						} else {
							if (exists(appConfig.syncListFilePath)){
								// skipped most likely due to inclusion in sync_list
								log.vlog("Skipping item - excluded by sync_list config: ", localFilePath);
								clientSideRuleExcludesPath = true;
							} else {
								// skipped for some other reason
								log.vlog("Skipping item - path excluded by user config: ", localFilePath);
								clientSideRuleExcludesPath = true;
							}
						}
					}
				}
			}
		}
		
		// Check if this is excluded by a user set maximum filesize to upload
		if (!clientSideRuleExcludesPath) {
			if (isFile(localFilePath)) {
				if (fileSizeLimit != 0) {
					// Get the file size
					ulong thisFileSize = getSize(localFilePath);
					if (thisFileSize >= fileSizeLimit) {
						log.vlog("Skipping item - excluded by skip_size config: ", localFilePath, " (", thisFileSize/2^^20," MB)");
					}
				}
			}
		}
		
		return clientSideRuleExcludesPath;
	}
	
	// Does this JSON item (as received from OneDrive API) get excluded from any operation based on any client side filtering rules?
	// This function is only used when we are fetching objects from the OneDrive API using a /children query to help speed up what object we query
	bool checkJSONAgainstClientSideFiltering(JSONValue onedriveJSONItem) {
			
		bool clientSideRuleExcludesPath = false;
		
		// Check the path against client side filtering rules
		// - check_nosync (MISSING)
		// - skip_dotfiles (MISSING)
		// - skip_symlinks (MISSING)
		// - skip_file
		// - skip_dir 
		// - sync_list
		// - skip_size (MISSING)
		// Return a true|false response
		
		// Use the JSON elements rather can computing a DB struct via makeItem()
		string thisItemId = onedriveJSONItem["id"].str;
		string thisItemDriveId = onedriveJSONItem["parentReference"]["driveId"].str;
		string thisItemParentId = onedriveJSONItem["parentReference"]["id"].str;
		string thisItemName = onedriveJSONItem["name"].str;
		
		// Is this parent is in the database
		bool parentInDatabase = false;
		
		// Calculate if the Parent Item is in the database so that it can be re-used
		parentInDatabase = itemDB.idInLocalDatabase(thisItemDriveId, thisItemParentId);
		
		// Check if this is excluded by config option: skip_dir 
		if (!clientSideRuleExcludesPath) {
			// Is the item a folder?
			if (isItemFolder(onedriveJSONItem)) {
				// Only check path if config is != ""
				if (!appConfig.getValueString("skip_dir").empty) {
					// work out the 'snippet' path where this folder would be created
					string simplePathToCheck = "";
					string complexPathToCheck = "";
					string matchDisplay = "";
					
					if (hasParentReference(onedriveJSONItem)) {
						// we need to workout the FULL path for this item
						// simple path
						if (("name" in onedriveJSONItem["parentReference"]) != null) {
							simplePathToCheck = onedriveJSONItem["parentReference"]["name"].str ~ "/" ~ onedriveJSONItem["name"].str;
						} else {
							simplePathToCheck = onedriveJSONItem["name"].str;
						}
						log.vdebug("skip_dir path to check (simple):  ", simplePathToCheck);
						
						// complex path
						if (parentInDatabase) {
							// build up complexPathToCheck
							//complexPathToCheck = buildNormalizedPath(newItemPath);
							complexPathToCheck = computeItemPath(thisItemDriveId, thisItemParentId) ~ "/" ~ thisItemName;
						} else {
							log.vdebug("Parent details not in database - unable to compute complex path to check");
						}
						if (!complexPathToCheck.empty) {
							log.vdebug("skip_dir path to check (complex): ", complexPathToCheck);
						}
					} else {
						simplePathToCheck = onedriveJSONItem["name"].str;
					}
					
					// If 'simplePathToCheck' or 'complexPathToCheck'  is of the following format:  root:/folder
					// then isDirNameExcluded matching will not work
					// Clean up 'root:' if present
					if (startsWith(simplePathToCheck, "root:")){
						log.vdebug("Updating simplePathToCheck to remove 'root:'");
						simplePathToCheck = strip(simplePathToCheck, "root:");
					}
					if (startsWith(complexPathToCheck, "root:")){
						log.vdebug("Updating complexPathToCheck to remove 'root:'");
						complexPathToCheck = strip(complexPathToCheck, "root:");
					}
					
					// OK .. what checks are we doing?
					if ((!simplePathToCheck.empty) && (complexPathToCheck.empty)) {
						// just a simple check
						log.vdebug("Performing a simple check only");
						clientSideRuleExcludesPath = selectiveSync.isDirNameExcluded(simplePathToCheck);
					} else {
						// simple and complex
						log.vdebug("Performing a simple then complex path match if required");
						// simple first
						log.vdebug("Performing a simple check first");
						clientSideRuleExcludesPath = selectiveSync.isDirNameExcluded(simplePathToCheck);
						matchDisplay = simplePathToCheck;
						if (!clientSideRuleExcludesPath) {
							log.vdebug("Simple match was false, attempting complex match");
							// simple didnt match, perform a complex check
							clientSideRuleExcludesPath = selectiveSync.isDirNameExcluded(complexPathToCheck);
							matchDisplay = complexPathToCheck;
						}
					}
					// result
					log.vdebug("skip_dir exclude result (directory based): ", clientSideRuleExcludesPath);
					if (clientSideRuleExcludesPath) {
						// This path should be skipped
						log.vlog("Skipping item - excluded by skip_dir config: ", matchDisplay);
					}
				}
			}
		}
		
		// Check if this is excluded by config option: skip_file
		if (!clientSideRuleExcludesPath) {
			// is the item a file ?
			if (isFileItem(onedriveJSONItem)) {
				// JSON item is a file
				
				// skip_file can contain 4 types of entries:
				// - wildcard - *.txt
				// - text + wildcard - name*.txt
				// - full path + combination of any above two - /path/name*.txt
				// - full path to file - /path/to/file.txt
				
				string exclusionTestPath = "";
				
				// is the parent id in the database?
				if (parentInDatabase) {
					// parent id is in the database, so we can try and calculate the full file path
					string jsonItemPath = "";
					
					// Compute this item path & need the full path for this file
					jsonItemPath = computeItemPath(thisItemDriveId, thisItemParentId) ~ "/" ~ thisItemName;
					// Log the calculation
					log.vdebug("New Item calculated full path is: ", jsonItemPath);
					
					// The path that needs to be checked needs to include the '/'
					// This due to if the user has specified in skip_file an exclusive path: '/path/file' - that is what must be matched
					// However, as 'path' used throughout, use a temp variable with this modification so that we use the temp variable for exclusion checks
					if (!startsWith(jsonItemPath, "/")){
						// Add '/' to the path
						exclusionTestPath = '/' ~ jsonItemPath;
					}
					
					// what are we checking
					log.vdebug("skip_file item to check (full calculated path): ", exclusionTestPath);
				} else {
					// parent not in database, we can only check using this JSON item's name
					if (!startsWith(thisItemName, "/")){
						// Add '/' to the path
						exclusionTestPath = '/' ~ thisItemName;
					}
					
					// what are we checking
					log.vdebug("skip_file item to check (file name only - parent path not in database): ", exclusionTestPath);
					clientSideRuleExcludesPath = selectiveSync.isFileNameExcluded(exclusionTestPath);
				}
				
				// Perform the 'skip_file' evaluation
				clientSideRuleExcludesPath = selectiveSync.isFileNameExcluded(exclusionTestPath);
				log.vdebug("Result: ", clientSideRuleExcludesPath);
				if (clientSideRuleExcludesPath) {
					// This path should be skipped
					log.vlog("Skipping item - excluded by skip_file config: ", exclusionTestPath);
				}
			}
		}
			
		// Check if this is included or excluded by use of sync_list
		if (!clientSideRuleExcludesPath) {
			// No need to try and process something against a sync_list if it has been configured
			if (syncListConfigured) {
				// Compute the item path if empty - as to check sync_list we need an actual path to check
				
				// What is the path of the new item
				string newItemPath;
				
				// Is the parent in the database? If not, we cannot compute the the full path based on the database entries
				// In a --resync scenario - the database is empty
				if (parentInDatabase) {
					// Calculate this items path based on database entries
					newItemPath = computeItemPath(thisItemDriveId, thisItemParentId) ~ "/" ~ thisItemName;
				} else {
					// parent not in the database
					if (("path" in onedriveJSONItem["parentReference"]) != null) {
						// If there is a parent reference path, try and use it
						string selfBuiltPath = onedriveJSONItem["parentReference"]["path"].str ~ "/" ~ onedriveJSONItem["name"].str;
						
						// Check for ':' and split if present
						auto splitIndex = selfBuiltPath.indexOf(":");
						if (splitIndex != -1) {
							// Keep only the part after ':'
							selfBuiltPath = selfBuiltPath[splitIndex + 1 .. $];
						}
						
						// Check for HTML entities (e.g., '%20' for space) in source JSON
						if (selfBuiltPath.canFind("%")) {
							log.error("CAUTION:    Microsoft OneDrive API sent a JSON element containing HTML entities. This will cause issues performing pattern matching and potentially cause this path not to sync.");
							log.error("WORKAROUND: A possible workaround is to rename this item online: " ~ selfBuiltPath);
							log.error("See: https://github.com/OneDrive/onedrive-api-docs/issues/1765 for further details");
						}
						
						// Set newItemPath to the self built path
						newItemPath = selfBuiltPath;
					} else {
						// no parent reference path available
						newItemPath = thisItemName;
					}
				}
				
				// Update newItemPath
				if(newItemPath[0] == '/') {
					newItemPath = newItemPath[1..$];
				}
				
				// What path are we checking?
				log.vdebug("sync_list item to check: ", newItemPath);
				
				// Unfortunatly there is no avoiding this call to check if the path is excluded|included via sync_list
				if (selectiveSync.isPathExcludedViaSyncList(newItemPath)) {
					// selective sync advised to skip, however is this a file and are we configured to upload / download files in the root?
					if ((isItemFile(onedriveJSONItem)) && (appConfig.getValueBool("sync_root_files")) && (rootName(newItemPath) == "") ) {
						// This is a file
						// We are configured to sync all files in the root
						// This is a file in the logical root
						clientSideRuleExcludesPath = false;
					} else {
						// path is unwanted
						clientSideRuleExcludesPath = true;
						log.vlog("Skipping item - excluded by sync_list config: ", newItemPath);
					}
				}
			}
		}
		
		// return if path is excluded
		return clientSideRuleExcludesPath;
	}
	
	// Process the list of local changes to upload to OneDrive
	void processChangedLocalItemsToUpload() {
		
		// Each element in this array 'databaseItemsWhereContentHasChanged' is an Database Item ID that has been modified locally
		ulong batchSize = appConfig.concurrentThreads;
		ulong batchCount = (databaseItemsWhereContentHasChanged.length + batchSize - 1) / batchSize;
		ulong batchesProcessed = 0;
		
		// For each batch of files to upload, upload the changed data to OneDrive
		foreach (chunk; databaseItemsWhereContentHasChanged.chunks(batchSize)) {
			uploadChangedLocalFileToOneDrive(chunk);
		}
	}
	
	// Upload changed local files to OneDrive in parallel
	void uploadChangedLocalFileToOneDrive(string[3][] array) {
			
		foreach (i, localItemDetails; taskPool.parallel(array)) {
		
			log.vdebug("Thread ", i, " Starting: ", Clock.currTime());
		
			// These are the details of the item we need to upload
			string changedItemParentId = localItemDetails[0];
			string changedItemId = localItemDetails[1];
			string localFilePath = localItemDetails[2];
			
			// How much space is remaining on OneDrive
			ulong remainingFreeSpace;
			// Did the upload fail?
			bool uploadFailed = false;
			// Did we skip due to exceeding maximum allowed size?
			bool skippedMaxSize = false;
			// Did we skip to an exception error?
			bool skippedExceptionError = false;
			
			// Unfortunatly, we cant store an array of Item's ... so we have to re-query the DB again - unavoidable extra processing here
			// This is because the Item[] has no other functions to allow is to parallel process those elements, so we have to use a string array as input to this function
			Item dbItem;
			itemDB.selectById(changedItemParentId, changedItemId, dbItem);
		
			// Query the available space online
			// This will update appConfig.quotaAvailable & appConfig.quotaRestricted values
			remainingFreeSpace = getRemainingFreeSpace(dbItem.driveId);
			
			// Get the file size
			ulong thisFileSizeLocal = getSize(localFilePath);
			ulong thisFileSizeFromDB = to!ulong(dbItem.size);
			
			// remainingFreeSpace online includes the current file online
			// we need to remove the online file (add back the existing file size) then take away the new local file size to get a new approximate value
			ulong calculatedSpaceOnlinePostUpload = (remainingFreeSpace + thisFileSizeFromDB) - thisFileSizeLocal;
			
			// Based on what we know, for this thread - can we safely upload this modified local file?
			log.vdebug("This Thread Current Free Space Online:                ", remainingFreeSpace);
			log.vdebug("This Thread Calculated Free Space Online Post Upload: ", calculatedSpaceOnlinePostUpload);
		
			JSONValue uploadResponse;
			
			bool spaceAvailableOnline = false;
			// If 'personal' accounts, if driveId == defaultDriveId, then we will have data - appConfig.quotaAvailable will be updated
			// If 'personal' accounts, if driveId != defaultDriveId, then we will not have quota data - appConfig.quotaRestricted will be set as true
			// If 'business' accounts, if driveId == defaultDriveId, then we will have data
			// If 'business' accounts, if driveId != defaultDriveId, then we will have data, but it will be a 0 value - appConfig.quotaRestricted will be set as true
			
			// What was the latest getRemainingFreeSpace() value?
			if (appConfig.quotaAvailable) {
				// Our query told us we have free space online .. if we upload this file, will we exceed space online - thus upload will fail during upload?
				if (calculatedSpaceOnlinePostUpload > 0) {
					// Based on this thread action, we beleive that there is space available online to upload - proceed
					spaceAvailableOnline = true;
				}
			}
			// Is quota being restricted?
			if (appConfig.quotaRestricted) {
				// Space available online is being restricted - so we have no way to really know if there is space available online
				spaceAvailableOnline = true;
			}
				
			// Do we have space available or is space available being restricted (so we make the blind assumption that there is space available)
			if (spaceAvailableOnline) {
				// Does this file exceed the maximum file size to upload to OneDrive?
				if (thisFileSizeLocal <= maxUploadFileSize) {
					// Attempt to upload the modified file
					// Error handling is in performModifiedFileUpload(), and the JSON that is responded with - will either be null or a valid JSON object containing the upload result
					uploadResponse = performModifiedFileUpload(dbItem, localFilePath, thisFileSizeLocal);
					
					// Evaluate the returned JSON uploadResponse
					// If there was an error uploading the file, uploadResponse should be empty and invalid
					if (uploadResponse.type() != JSONType.object) {
						uploadFailed = true;
						skippedExceptionError = true;
					}
					
				} else {
					// Skip file - too large
					uploadFailed = true;
					skippedMaxSize = true;
				}
			} else {
				// Cant upload this file - no space available
				uploadFailed = true;
			}
			
			// Did the upload fail?
			if (uploadFailed) {
				// Upload failed .. why?
				// No space available online
				if (!spaceAvailableOnline) {
					log.logAndNotify("Skipping uploading modified file ", localFilePath, " due to insufficient free space available on OneDrive");
				}
				// File exceeds max allowed size
				if (skippedMaxSize) {
					log.logAndNotify("Skipping uploading this modified file as it exceeds the maximum size allowed by OneDrive: ", localFilePath);
				}
				// Generic message
				if (skippedExceptionError) {
					// normal failure message if API or exception error generated
					log.logAndNotify("Uploading modified file ", localFilePath, " ... failed!");
				}
			} else {
				// Upload was successful
				log.logAndNotify("Uploading modified file ", localFilePath, " ... done.");
				
				// Save JSON item in database
				saveItem(uploadResponse);
				
				if (!dryRun) {
					// Check the integrity of the uploaded modified file
					performUploadIntegrityValidationChecks(uploadResponse, localFilePath, thisFileSizeLocal);
					
					// Update the date / time of the file online to match the local item
					// Get the local file last modified time
					SysTime localModifiedTime = timeLastModified(localFilePath).toUTC();
					localModifiedTime.fracSecs = Duration.zero;
					// Get the latest eTag, and use that
					string etagFromUploadResponse = uploadResponse["eTag"].str;
					// Attempt to update the online date time stamp based on our local data
					uploadLastModifiedTime(dbItem.driveId, dbItem.id, localModifiedTime, etagFromUploadResponse);
				}
			}
			
			log.vdebug("Thread ", i, " Finished: ", Clock.currTime());
		
		} // end of 'foreach (i, localItemDetails; array.enumerate)'
	}
	
	// Perform the upload of a locally modified file to OneDrive
	JSONValue performModifiedFileUpload(Item dbItem, string localFilePath, ulong thisFileSizeLocal) {
			
		JSONValue uploadResponse;
		OneDriveApi uploadFileOneDriveApiInstance;
		uploadFileOneDriveApiInstance = new OneDriveApi(appConfig);
		uploadFileOneDriveApiInstance.initialise();
		
		// Is this a dry-run scenario?
		if (!dryRun) {
			// Do we use simpleUpload or create an upload session?
			bool useSimpleUpload = false;
			
			//if ((appConfig.accountType == "personal") && (thisFileSizeLocal <= sessionThresholdFileSize)) {
			
			if (thisFileSizeLocal <= sessionThresholdFileSize) {
				useSimpleUpload = true;
			}
		
			// We can only upload zero size files via simpleFileUpload regardless of account type
			// Reference: https://github.com/OneDrive/onedrive-api-docs/issues/53
			// Additionally, all files where file size is < 4MB should be uploaded by simpleUploadReplace - everything else should use a session to upload the modified file
		
			if ((thisFileSizeLocal == 0) || (useSimpleUpload)) {
				// Must use Simple Upload to replace the file online
				try {
					uploadResponse = uploadFileOneDriveApiInstance.simpleUploadReplace(localFilePath, dbItem.driveId, dbItem.id);
				} catch (OneDriveException exception) {
				
					string thisFunctionName = getFunctionName!({});
					// HTTP request returned status code 408,429,503,504
					if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 429) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
						// Handle the 429
						if (exception.httpStatusCode == 429) {
							// HTTP request returned status code 429 (Too Many Requests). We need to leverage the response Retry-After HTTP header to ensure minimum delay until the throttle is removed.
							handleOneDriveThrottleRequest(uploadFileOneDriveApiInstance);
							log.vdebug("Retrying original request that generated the OneDrive HTTP 429 Response Code (Too Many Requests) - attempting to retry ", thisFunctionName);
						}
						// re-try the specific changes queries
						if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
							// 408 - Request Time Out
							// 503 - Service Unavailable
							// 504 - Gateway Timeout
							// Transient error - try again in 30 seconds
							auto errorArray = splitLines(exception.msg);
							log.log(errorArray[0], " when attempting to upload a modified file to OneDrive - retrying applicable request in 30 seconds");
							log.vdebug(thisFunctionName, " previously threw an error - retrying");
							// The server, while acting as a proxy, did not receive a timely response from the upstream server it needed to access in attempting to complete the request. 
							log.vdebug("Thread sleeping for 30 seconds as the server did not receive a timely response from the upstream server it needed to access in attempting to complete the request");
							Thread.sleep(dur!"seconds"(30));
						}
						// re-try original request - retried for 429, 503, 504 - but loop back calling this function 
						log.vdebug("Retrying Function: ", thisFunctionName);
						performModifiedFileUpload(dbItem, localFilePath, thisFileSizeLocal);	
					} else {
						// Default operation if not 408,429,503,504 errors
						// display what the error is
						displayOneDriveErrorMessage(exception.msg, getFunctionName!({}));
					}
				
				} catch (FileException e) {
					// filesystem error
					displayFileSystemErrorMessage(e.msg, getFunctionName!({}));
				}
			} else {
				// Configure JSONValue variables we use for a session upload
				JSONValue currentOnlineData;
				JSONValue uploadSessionData;
				string currentETag;
				
				// As this is a unique thread, the sessionFilePath for where we save the data needs to be unique
				// The best way to do this is generate a 10 digit alphanumeric string, and use this as the file extention
				string threadUploadSessionFilePath = appConfig.uploadSessionFilePath ~ "." ~ generateAlphanumericString();
				
				// Get the absolute latest object details from online
				try {
					currentOnlineData = uploadFileOneDriveApiInstance.getPathDetailsByDriveId(dbItem.driveId, localFilePath);
				} catch (OneDriveException exception) {
				
					string thisFunctionName = getFunctionName!({});
					// HTTP request returned status code 408,429,503,504
					if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 429) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
						// Handle the 429
						if (exception.httpStatusCode == 429) {
							// HTTP request returned status code 429 (Too Many Requests). We need to leverage the response Retry-After HTTP header to ensure minimum delay until the throttle is removed.
							handleOneDriveThrottleRequest(uploadFileOneDriveApiInstance);
							log.vdebug("Retrying original request that generated the OneDrive HTTP 429 Response Code (Too Many Requests) - attempting to retry ", thisFunctionName);
						}
						// re-try the specific changes queries
						if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
							// 408 - Request Time Out
							// 503 - Service Unavailable
							// 504 - Gateway Timeout
							// Transient error - try again in 30 seconds
							auto errorArray = splitLines(exception.msg);
							log.log(errorArray[0], " when attempting to obtain latest file details from OneDrive - retrying applicable request in 30 seconds");
							log.vdebug(thisFunctionName, " previously threw an error - retrying");
							// The server, while acting as a proxy, did not receive a timely response from the upstream server it needed to access in attempting to complete the request. 
							log.vdebug("Thread sleeping for 30 seconds as the server did not receive a timely response from the upstream server it needed to access in attempting to complete the request");
							Thread.sleep(dur!"seconds"(30));
						}
						// re-try original request - retried for 429, 503, 504 - but loop back calling this function 
						log.vdebug("Retrying Function: ", thisFunctionName);
						performModifiedFileUpload(dbItem, localFilePath, thisFileSizeLocal);
					} else {
						// Default operation if not 408,429,503,504 errors
						// display what the error is
						displayOneDriveErrorMessage(exception.msg, getFunctionName!({}));
					}
					
				}
				
				// Was a valid JSON response provided?
				if (currentOnlineData.type() == JSONType.object) {
					// Does the response contain an eTag?
					if (hasETag(currentOnlineData)) {
						// Use the value returned from online
						currentETag = currentOnlineData["eTag"].str;
					} else {
						// Use the database value
						currentETag = dbItem.eTag;
					}
				} else {
					// no valid JSON response
					currentETag = dbItem.eTag;
				}
				
				// Create the Upload Session
				try {
					uploadSessionData = createSessionFileUpload(uploadFileOneDriveApiInstance, localFilePath, dbItem.driveId, dbItem.parentId, baseName(localFilePath), currentETag, threadUploadSessionFilePath);
				} catch (OneDriveException exception) {
					
					string thisFunctionName = getFunctionName!({});
					// HTTP request returned status code 408,429,503,504
					if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 429) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
						// Handle the 429
						if (exception.httpStatusCode == 429) {
							// HTTP request returned status code 429 (Too Many Requests). We need to leverage the response Retry-After HTTP header to ensure minimum delay until the throttle is removed.
							handleOneDriveThrottleRequest(uploadFileOneDriveApiInstance);
							log.vdebug("Retrying original request that generated the OneDrive HTTP 429 Response Code (Too Many Requests) - attempting to retry ", thisFunctionName);
						}
						// re-try the specific changes queries
						if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
							// 408 - Request Time Out
							// 503 - Service Unavailable
							// 504 - Gateway Timeout
							// Transient error - try again in 30 seconds
							auto errorArray = splitLines(exception.msg);
							log.log(errorArray[0], " when attempting to create an upload session on OneDrive - retrying applicable request in 30 seconds");
							log.vdebug(thisFunctionName, " previously threw an error - retrying");
							// The server, while acting as a proxy, did not receive a timely response from the upstream server it needed to access in attempting to complete the request. 
							log.vdebug("Thread sleeping for 30 seconds as the server did not receive a timely response from the upstream server it needed to access in attempting to complete the request");
							Thread.sleep(dur!"seconds"(30));
						}
						// re-try original request - retried for 429, 503, 504 - but loop back calling this function 
						log.vdebug("Retrying Function: ", thisFunctionName);
						performModifiedFileUpload(dbItem, localFilePath, thisFileSizeLocal);	
					} else {
						// Default operation if not 408,429,503,504 errors
						// display what the error is
						displayOneDriveErrorMessage(exception.msg, getFunctionName!({}));
					}
					
				} catch (FileException e) {
					writeln("DEBUG TO REMOVE: Modified file upload FileException Handling (Create the Upload Session)");
					displayFileSystemErrorMessage(e.msg, getFunctionName!({}));
				}
				
				// Perform the Upload using the session
				try {
					uploadResponse = performSessionFileUpload(uploadFileOneDriveApiInstance, thisFileSizeLocal, uploadSessionData, threadUploadSessionFilePath);
				} catch (OneDriveException exception) {
					
					string thisFunctionName = getFunctionName!({});
					// HTTP request returned status code 408,429,503,504
					if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 429) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
						// Handle the 429
						if (exception.httpStatusCode == 429) {
							// HTTP request returned status code 429 (Too Many Requests). We need to leverage the response Retry-After HTTP header to ensure minimum delay until the throttle is removed.
							handleOneDriveThrottleRequest(uploadFileOneDriveApiInstance);
							log.vdebug("Retrying original request that generated the OneDrive HTTP 429 Response Code (Too Many Requests) - attempting to retry ", thisFunctionName);
						}
						// re-try the specific changes queries
						if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
							// 408 - Request Time Out
							// 503 - Service Unavailable
							// 504 - Gateway Timeout
							// Transient error - try again in 30 seconds
							auto errorArray = splitLines(exception.msg);
							log.log(errorArray[0], " when attempting to upload a file via a session to OneDrive - retrying applicable request in 30 seconds");
							log.vdebug(thisFunctionName, " previously threw an error - retrying");
							// The server, while acting as a proxy, did not receive a timely response from the upstream server it needed to access in attempting to complete the request. 
							log.vdebug("Thread sleeping for 30 seconds as the server did not receive a timely response from the upstream server it needed to access in attempting to complete the request");
							Thread.sleep(dur!"seconds"(30));
						}
						// re-try original request - retried for 429, 503, 504 - but loop back calling this function 
						log.vdebug("Retrying Function: ", thisFunctionName);
						performModifiedFileUpload(dbItem, localFilePath, thisFileSizeLocal);
					} else {
						// Default operation if not 408,429,503,504 errors
						// display what the error is
						displayOneDriveErrorMessage(exception.msg, getFunctionName!({}));
					}
					
				} catch (FileException e) {
					writeln("DEBUG TO REMOVE: Modified file upload FileException Handling (Perform the Upload using the session)");
					displayFileSystemErrorMessage(e.msg, getFunctionName!({}));
				}
			}
		
		} else {
			// We are in a --dry-run scenario
			uploadResponse = createFakeResponse(localFilePath);
		}
		
		// Debug Log the modified upload response
		log.vdebug("Modified File Upload Response: ", uploadResponse);
		
		// Shutdown the API instance
		uploadFileOneDriveApiInstance.shutdown();
		// Free object and memory
		object.destroy(uploadFileOneDriveApiInstance);
		// Return JSON
		return uploadResponse;
	}
		
	// Query the OneDrive API using the provided driveId to get the latest quota details
	ulong getRemainingFreeSpace(string driveId) {
				
		// Get the quota details for this driveId, as this could have changed since we started the application - the user could have added / deleted data online, or purchased additional storage
		// Quota details are ONLY available for the main default driveId, as the OneDrive API does not provide quota details for shared folders
		
		JSONValue currentDriveQuota;
		ulong remainingQuota;
		
		try {
			// Create a new OneDrive API instance
			OneDriveApi getCurrentDriveQuotaApiInstance;
			getCurrentDriveQuotaApiInstance = new OneDriveApi(appConfig);
			getCurrentDriveQuotaApiInstance.initialise();
			log.vdebug("Seeking available quota for this drive id: ", driveId);
			currentDriveQuota = getCurrentDriveQuotaApiInstance.getDriveQuota(driveId);
			// Shut this API instance down
			getCurrentDriveQuotaApiInstance.shutdown();
			// Free object and memory
			object.destroy(getCurrentDriveQuotaApiInstance);
		} catch (OneDriveException e) {
			log.vdebug("currentDriveQuota = onedrive.getDriveQuota(driveId) generated a OneDriveException");
		}
		
		// validate that currentDriveQuota is a JSON value
		if (currentDriveQuota.type() == JSONType.object) {
			// Response from API contains valid data
			// If 'personal' accounts, if driveId == defaultDriveId, then we will have data
			// If 'personal' accounts, if driveId != defaultDriveId, then we will not have quota data
			// If 'business' accounts, if driveId == defaultDriveId, then we will have data
			// If 'business' accounts, if driveId != defaultDriveId, then we will have data, but it will be a 0 value
			
			if ("quota" in currentDriveQuota){
				if (driveId == appConfig.defaultDriveId) {
					// We potentially have updated quota remaining details available
					// However in some cases OneDrive Business configurations 'restrict' quota details thus is empty / blank / negative value / zero
					if ("remaining" in currentDriveQuota["quota"]){
						// We have valid quota remaining details returned for the provided drive id
						remainingQuota = currentDriveQuota["quota"]["remaining"].integer;
						
						if (remainingQuota <= 0) {
							if (appConfig.accountType == "personal"){
								// zero space available
								log.error("ERROR: OneDrive account currently has zero space available. Please free up some space online or purchase additional space.");
								remainingQuota = 0;
								appConfig.quotaAvailable = false;
							} else {
								// zero space available is being reported, maybe being restricted?
								log.error("WARNING: OneDrive quota information is being restricted or providing a zero value. Please fix by speaking to your OneDrive / Office 365 Administrator.");
								remainingQuota = 0;
								appConfig.quotaRestricted = true;
							}
						}
					}
				} else {
					// quota details returned, but for a drive id that is not ours
					if ("remaining" in currentDriveQuota["quota"]){
						// remaining is in the quota JSON response					
						if (currentDriveQuota["quota"]["remaining"].integer <= 0) {
							// value returned is 0 or less than 0
							log.vlog("OneDrive quota information is set at zero, as this is not our drive id, ignoring");
							remainingQuota = 0;
							appConfig.quotaRestricted = true;
						}
					}
				}
			} else {
				// No quota details returned
				if (driveId == appConfig.defaultDriveId) {
					// no quota details returned for current drive id
					log.error("ERROR: OneDrive quota information is missing. Potentially your OneDrive account currently has zero space available. Please free up some space online or purchase additional space.");
					remainingQuota = 0;
					appConfig.quotaRestricted = true;
				} else {
					// quota details not available
					log.vdebug("WARNING: OneDrive quota information is being restricted as this is not our drive id.");
					remainingQuota = 0;
					appConfig.quotaRestricted = true;
				}
			}
		}
		
		// what was the determined available quota?
		log.vdebug("Available quota: ", remainingQuota);
		return remainingQuota;
	}
	
	// Perform a filesystem walk to uncover new data to upload to OneDrive
	void scanLocalFilesystemPathForNewData(string path) {
		
		// To improve logging output for this function, what is the 'logical path' we are scanning for file & folder differences?
		string logPath;
		if (path == ".") {
			// get the configured sync_dir
			logPath = buildNormalizedPath(appConfig.getValueString("sync_dir"));
		} else {
			// use what was passed in
			if (!appConfig.getValueBool("monitor")) {
				logPath = buildNormalizedPath(appConfig.getValueString("sync_dir")) ~ "/" ~ path;
			} else {
				logPath = path;
			}
		}
		
		// Log the action that we are performing, however only if this is a directory
		if (isDir(path)) {
			if (!appConfig.surpressLoggingOutput) {
				if (!cleanupLocalFiles) {
					log.log("Scanning the local file system '", logPath, "' for new data to upload ...");
				} else {
					log.log("Scanning the local file system '", logPath, "' for data to cleanup ...");
				}
			}
		}
		
		auto startTime = Clock.currTime();
		log.vdebug("Starting Filesystem Walk:     ", startTime);
	
		// Perform the filesystem walk of this path, building an array of new items to upload
		scanPathForNewData(path);
		
		// To finish off the processing items, this is needed to reflect this in the log
		log.vdebug("------------------------------------------------------------------");
		
		auto finishTime = Clock.currTime();
		log.vdebug("Finished Filesystem Walk:     ", finishTime);
		
		auto elapsedTime = finishTime - startTime;
		log.vdebug("Elapsed Time Filesystem Walk: ", elapsedTime);
		
		// Upload new data that has been identified
		// Are there any items to download post fetching the /delta data?
		if (!newLocalFilesToUploadToOneDrive.empty) {
			// There are elements to upload
			log.vlog("New items to upload to OneDrive: ", newLocalFilesToUploadToOneDrive.length);
			
			// How much data do we need to upload? This is important, as, we need to know how much data to determine if all the files can be uploaded
			foreach (uploadFilePath; newLocalFilesToUploadToOneDrive) {
				// validate that the path actually exists so that it can be counted
				if (exists(uploadFilePath)) {
					totalDataToUpload = totalDataToUpload + getSize(uploadFilePath);
				}
			}
			
			// How many bytes to upload
			if (totalDataToUpload < 1024) {
				// Display as Bytes to upload
				log.vlog("Total New Data to Upload:        ", totalDataToUpload, " Bytes");
			} else {
				if ((totalDataToUpload > 1024) && (totalDataToUpload < 1048576)) {
					// Display as KB to upload
					log.vlog("Total New Data to Upload:        ", (totalDataToUpload / 1024), " KB");
				} else {
					// Display as MB to upload
					log.vlog("Total New Data to Upload:        ", (totalDataToUpload / 1024 / 1024), " MB");
				}
			}
			
			// How much space is available (Account Drive ID)
			// The file, could be uploaded to a shared folder, which, we are not tracking how much free space is available there ... 
			log.vdebug("Current Available Space Online (Account Drive ID): ", (appConfig.remainingFreeSpace / 1024 / 1024), " MB");
			
			// Perform the upload
			uploadNewLocalFileItems();
			
			// Cleanup array memory
			newLocalFilesToUploadToOneDrive = [];
		}
	}
	
	// Scan this path for new data
	void scanPathForNewData(string path) {
			
		ulong maxPathLength;
		ulong pathWalkLength;
		
		// Add this logging break to assist with what was checked for each path
		if (path != ".") {
			log.vdebug("------------------------------------------------------------------");
		}
		
		// https://support.microsoft.com/en-us/help/3125202/restrictions-and-limitations-when-you-sync-files-and-folders
		// If the path is greater than allowed characters, then one drive will return a '400 - Bad Request'
		// Need to ensure that the URI is encoded before the check is made:
		// - 400 Character Limit for OneDrive Business / Office 365
		// - 430 Character Limit for OneDrive Personal
		
		// Configure maxPathLength based on account type
		if (appConfig.accountType == "personal") {
			// Personal Account
			maxPathLength = 430;
		} else {
			// Business Account / Office365 / SharePoint
			maxPathLength = 400;
		}
		
		// A short lived item that has already disappeared will cause an error - is the path still valid?
		if (!exists(path)) {
			log.log("Skipping item - path has disappeared: ", path);
			return;
		}
		
		// Calculate the path length by walking the path and catch any UTF-8 sequence errors at the same time
		// https://github.com/skilion/onedrive/issues/57
		// https://github.com/abraunegg/onedrive/issues/487
		// https://github.com/abraunegg/onedrive/issues/1192
		try {
			pathWalkLength = path.byGrapheme.walkLength;
		} catch (std.utf.UTFException e) {
			// Path contains characters which generate a UTF exception
			log.logAndNotify("Skipping item - invalid UTF sequence: ", path);
			log.vdebug("  Error Reason:", e.msg);
			return;
		}
		
		// Is the path length is less than maxPathLength
		if (pathWalkLength < maxPathLength) {
			// Is this path unwanted
			bool unwanted = false;
			
			// First check of this item - if we are in a --dry-run scenario, we may have 'fake deleted' this path
			// thus, the entries are not in the dry-run DB copy, thus, at this point the client thinks that this is an item to upload
			// Check this 'path' for an entry in pathFakeDeletedArray - if it is there, this is unwanted
			if (dryRun) {
				// Is this path in the array of fake deleted items? If yes, return early, nothing else to do, save processing
				if (canFind(pathFakeDeletedArray, path)) return;
			}
			
			// This not a Client Side Filtering check, nor a Microsoft Check, but is a sanity check that the path provided is UTF encoded correctly
			// Check the std.encoding of the path against: Unicode 5.0, ASCII, ISO-8859-1, ISO-8859-2, WINDOWS-1250, WINDOWS-1251, WINDOWS-1252
			if (!unwanted) {
				if(!isValid(path)) {
					// Path is not valid according to https://dlang.org/phobos/std_encoding.html
					log.logAndNotify("Skipping item - invalid character encoding sequence: ", path);
					unwanted = true;
				}
			}
			
			// Check this path against the Client Side Filtering Rules
			// - check_nosync
			// - skip_dotfiles
			// - skip_symlinks
			// - skip_file
			// - skip_dir
			// - sync_list
			// - skip_size
			if (!unwanted) {
				unwanted = checkPathAgainstClientSideFiltering(path);
			}
			
			// Check this path against the Microsoft Naming Conventions & Restristions
			// - Microsoft OneDrive restriction and limitations about Windows naming files
			// - Bad whitespace items
			// - HTML ASCII Codes as part of file name
			if (!unwanted) {
				unwanted = checkPathAgainstMicrosoftNamingRestrictions(path);
			}
			
			if (!unwanted) {
				// At this point, this path, we want to scan for new data as it is not excluded
				if (isDir(path)) {
					// Check if this path in the database
					bool directoryFoundInDB = pathFoundInDatabase(path);
					
					// Was the path found in the database?
					if (!directoryFoundInDB) {
						// Path not found in database when searching all drive id's
						if (!cleanupLocalFiles) {
							// --download-only --cleanup-local-files not used
							// Create this directory on OneDrive so that we can upload files to it
							createDirectoryOnline(path);
						} else {
							// we need to clean up this directory
							log.log("Removing local directory as --download-only & --cleanup-local-files configured");
							// Remove any children of this path if they still exist
							// Resolve 'Directory not empty' error when deleting local files
							try {
								foreach (DirEntry child; dirEntries(path, SpanMode.depth, false)) {
									// what sort of child is this?
									if (isDir(child.name)) {
										log.log("Removing local directory: ", child.name);
									} else {
										log.log("Removing local file: ", child.name);
									}
									
									// are we in a --dry-run scenario?
									if (!dryRun) {
										// No --dry-run ... process local delete
										if (exists(child)) {
											try {
												attrIsDir(child.linkAttributes) ? rmdir(child.name) : remove(child.name);
											} catch (FileException e) {
												// display the error message
												displayFileSystemErrorMessage(e.msg, getFunctionName!({}));
											}
										}
									}
								}
								// Remove the path now that it is empty of children
								log.log("Removing local directory: ", path);
								// are we in a --dry-run scenario?
								if (!dryRun) {
									// No --dry-run ... process local delete
									try {
										rmdirRecurse(path);
									} catch (FileException e) {
										// display the error message
										displayFileSystemErrorMessage(e.msg, getFunctionName!({}));
									}
								}
							} catch (FileException e) {
								// display the error message
								displayFileSystemErrorMessage(e.msg, getFunctionName!({}));
								return;
							}
						}
					}
				
					// flag for if we are going traverse this path
					bool skipFolderTraverse = false;
					
					// Before we traverse this 'path', we need to make a last check to see if this was just excluded
					if (appConfig.accountType == "business") {
						// search businessSharedFoldersOnlineToSkip for this path
						if (canFind(businessSharedFoldersOnlineToSkip, path)) {
							// This path was skipped - why?
							log.logAndNotify("Skipping item '", path, "' due to this path matching an existing online Business Shared Folder name");
							skipFolderTraverse = true;
						}
					}
					
					// Do we traverse this path?
					if (!skipFolderTraverse) {
						// Try and access this directory and any path below
						try {
							auto entries = dirEntries(path, SpanMode.shallow, false);
							foreach (DirEntry entry; entries) {
								string thisPath = entry.name;
								scanPathForNewData(thisPath);
							}
						} catch (FileException e) {
							// display the error message
							displayFileSystemErrorMessage(e.msg, getFunctionName!({}));
							return;
						}
					}
				} else {
					// https://github.com/abraunegg/onedrive/issues/984
					// path is not a directory, is it a valid file?
					// pipes - whilst technically valid files, are not valid for this client
					//  prw-rw-r--.  1 user user    0 Jul  7 05:55 my_pipe
					if (isFile(path)) {
						// Path is a valid file, not a pipe
						bool fileFoundInDB = pathFoundInDatabase(path);
						// Was the file found in the database?
						if (!fileFoundInDB) {
							// File not found in database when searching all drive id's
							// Do we upload the file or clean up the file?
							if (!cleanupLocalFiles) {
								// --download-only --cleanup-local-files not used
								// Add this path as a file we need to upload
								log.vdebug("OneDrive Client flagging to upload this file to OneDrive: ", path);
								newLocalFilesToUploadToOneDrive ~= path;
							} else {
								// we need to clean up this file
								log.log("Removing local file as --download-only & --cleanup-local-files configured");
								// are we in a --dry-run scenario?
								log.log("Removing local file: ", path);
								if (!dryRun) {
									// No --dry-run ... process local file delete
									safeRemove(path);
								}
							}
						}
					} else {
						// path is not a valid file
						log.logAndNotify("Skipping item - item is not a valid file: ", path);
					}
				}
			}
		} else {
			// This path was skipped - why?
			log.logAndNotify("Skipping item '", path, "' due to the full path exceeding ", maxPathLength, " characters (Microsoft OneDrive limitation)");
		}
	}
	
	// Handle a single file inotify trigger when using --monitor
	void handleLocalFileTrigger(string localFilePath) {
		// Is this path a new file or an existing one?
		// Normally we would use pathFoundInDatabase() to calculate, but we need 'databaseItem' as well if the item is in the database
		Item databaseItem;
		bool fileFoundInDB = false;
		string[3][] modifiedItemToUpload; 
		
		foreach (driveId; driveIDsArray) {
			if (itemDB.selectByPath(localFilePath, driveId, databaseItem)) {
				fileFoundInDB = true;
			}
		}
		
		// Was the file found in the database?
		if (!fileFoundInDB) {
			// This is a new file
			scanLocalFilesystemPathForNewData(localFilePath);
		} else {
			// This is a modified file, needs to be handled as such
			modifiedItemToUpload ~= [databaseItem.driveId, databaseItem.id, localFilePath];
			uploadChangedLocalFileToOneDrive(modifiedItemToUpload);
		}
	}
	
	// Query the database to determine if this path is within the existing database
	bool pathFoundInDatabase(string searchPath) {
		
		// Check if this path in the database
		Item databaseItem;
		bool pathFoundInDB = false;
		foreach (driveId; driveIDsArray) {
			if (itemDB.selectByPath(searchPath, driveId, databaseItem)) {
				pathFoundInDB = true;
			}
		}
		return pathFoundInDB;
	}
	
	// Create a new directory online on OneDrive
	// - Test if we can get the parent path details from the database, otherwise we need to search online
	//   for the path flow and create the folder that way
	void createDirectoryOnline(string thisNewPathToCreate) {
		
		log.log("OneDrive Client requested to create this directory online: ", thisNewPathToCreate);
		
		Item parentItem;
		JSONValue onlinePathData;
		
		// Create a new API Instance for this thread and initialise it
		OneDriveApi createDirectoryOnlineOneDriveApiInstance;
		createDirectoryOnlineOneDriveApiInstance = new OneDriveApi(appConfig);
		createDirectoryOnlineOneDriveApiInstance.initialise();
		
		// What parent path to use?
		string parentPath = dirName(thisNewPathToCreate); // will be either . or something else
		
		// Configure the parentItem by if this is the account 'root' use the root details, or search the database for the parent details
		if (parentPath == ".") {
			// Parent path is '.' which is the account root
			// Use client defaults
			parentItem.driveId = appConfig.defaultDriveId; 	// Should give something like 12345abcde1234a1
			parentItem.id = appConfig.defaultRootId;  		// Should give something like 12345ABCDE1234A1!101
		} else {
			// Query the parent path online
			log.vdebug("Attempting to query Local Database for this parent path: ", parentPath);
			
			// Attempt a 2 step process to work out where to create the directory
			// Step 1: Query the DB first
			// Step 2: Query online as last resort
			
			// Step 1: Check if this path in the database
			Item databaseItem;
			bool pathFoundInDB = false;
			foreach (driveId; driveIDsArray) {
				if (itemDB.selectByPath(parentPath, driveId, databaseItem)) {
					pathFoundInDB = true;
					log.vdebug("databaseItem: ", databaseItem);
					log.vdebug("pathFoundInDB: ", pathFoundInDB);
				}
			}
			
			// Step 2: Query for the path online
			if (!pathFoundInDB) {
				// path not found in database
				try {
					log.vdebug("Attempting to query OneDrive Online for this parent path as path not found in local database: ", parentPath);
					onlinePathData = createDirectoryOnlineOneDriveApiInstance.getPathDetails(parentPath);
					// Save item to the database
					saveItem(onlinePathData);
					parentItem = makeItem(onlinePathData);
				} catch (OneDriveException exception) {
					if (exception.httpStatusCode == 404) {
						// Parent does not exist ... need to create parent
						log.vdebug("Parent path does not exist online: ", parentPath);
						createDirectoryOnline(parentPath);
						// no return here as we need to continue, but need to re-query the OneDrive API to get the right parental details now that they exist
						onlinePathData = createDirectoryOnlineOneDriveApiInstance.getPathDetails(parentPath);
						parentItem = makeItem(onlinePathData);
					} else {
						string thisFunctionName = getFunctionName!({});
						// HTTP request returned status code 408,429,503,504
						if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 429) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
							// Handle the 429
							if (exception.httpStatusCode == 429) {
								// HTTP request returned status code 429 (Too Many Requests). We need to leverage the response Retry-After HTTP header to ensure minimum delay until the throttle is removed.
								handleOneDriveThrottleRequest(createDirectoryOnlineOneDriveApiInstance);
								log.vdebug("Retrying original request that generated the OneDrive HTTP 429 Response Code (Too Many Requests) - attempting to retry ", thisFunctionName);
							}
							// re-try the specific changes queries
							if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
								// 408 - Request Time Out
								// 503 - Service Unavailable
								// 504 - Gateway Timeout
								// Transient error - try again in 30 seconds
								auto errorArray = splitLines(exception.msg);
								log.log(errorArray[0], " when attempting to create a remote directory on OneDrive - retrying applicable request in 30 seconds");
								log.vdebug(thisFunctionName, " previously threw an error - retrying");
								// The server, while acting as a proxy, did not receive a timely response from the upstream server it needed to access in attempting to complete the request. 
								log.vdebug("Thread sleeping for 30 seconds as the server did not receive a timely response from the upstream server it needed to access in attempting to complete the request");
								Thread.sleep(dur!"seconds"(30));
							}
							// re-try original request - retried for 429, 503, 504 - but loop back calling this function 
							log.vdebug("Retrying Function: ", thisFunctionName);
							createDirectoryOnline(thisNewPathToCreate);
						} else {
							// Default operation if not 408,429,503,504 errors
							// display what the error is
							displayOneDriveErrorMessage(exception.msg, thisFunctionName);
						}
					}
				}
			} else {
				// parent path found in database ... use those details ...
				parentItem = databaseItem;
			}
		}
		
		// Make sure the full path does not exist online, this should generate a 404 response, to which then the folder will be created online
		try {
			// Try and query the OneDrive API for the path we need to create
			log.vdebug("Attempting to query OneDrive for this path: ", thisNewPathToCreate);
			
			if (parentItem.driveId == appConfig.defaultDriveId) {
				// Use getPathDetailsByDriveId
				onlinePathData = createDirectoryOnlineOneDriveApiInstance.getPathDetailsByDriveId(parentItem.driveId, thisNewPathToCreate);
			} else {
				// If the parentItem.driveId is not our driveId - the path we are looking for will not be at the logical location that getPathDetailsByDriveId 
				// can use - as it will always return a 404 .. even if the path actually exists (which is the whole point of this test)
				// Search the parentItem.driveId for any folder name match that we are going to create, then compare response JSON items with parentItem.id
				// If no match, the folder we want to create does not exist at the location we are seeking to create it at, thus generate a 404
				onlinePathData = createDirectoryOnlineOneDriveApiInstance.searchDriveForPath(parentItem.driveId, baseName(thisNewPathToCreate));
				
				// Process the response from searching the drive
				ulong responseCount = count(onlinePathData["value"].array);
				if (responseCount > 0) {
					// Search 'name' matches were found .. need to match these against parentItem.id
					bool foundDirectoryOnline = false;
					JSONValue foundDirectoryJSONItem;
					// Items were returned .. but is one of these what we are looking for?
					foreach (childJSON; onlinePathData["value"].array) {
						// Is this item not a file?
						if (!isFileItem(childJSON)) {
							Item thisChildItem = makeItem(childJSON);
							// Direct Match Check
							if ((parentItem.id == thisChildItem.parentId) && (baseName(thisNewPathToCreate) == thisChildItem.name)) {
								// High confidence that this child folder is a direct match we are trying to create and it already exists online
								log.vdebug("Path we are searching for exists online: ", baseName(thisNewPathToCreate));
								log.vdebug("childJSON: ", childJSON);
								foundDirectoryOnline = true;
								foundDirectoryJSONItem = childJSON;
								break;
							}
							// Full Lower Case POSIX Match Check
							string childAsLower = toLower(childJSON["name"].str);
							string thisFolderNameAsLower = toLower(baseName(thisNewPathToCreate));
							
							if (childAsLower == thisFolderNameAsLower) {	
								// This is a POSIX 'case in-sensitive match' ..... 
								// Local item name has a 'case-insensitive match' to an existing item on OneDrive
								foundDirectoryOnline = true;
								foundDirectoryJSONItem = childJSON;
								break;
							}
						}
					}
					
					if (foundDirectoryOnline) {
						// Directory we are seeking was found online ... 
						onlinePathData = foundDirectoryJSONItem;
					} else {
						// No 'search item matches found' - raise a 404 so that the exception handling will take over to create the folder
						throw new OneDriveException(404, "Name not found via search");
					}
				} else {
					// No 'search item matches found' - raise a 404 so that the exception handling will take over to create the folder
					throw new OneDriveException(404, "Name not found via search");
				}
			}
		} catch (OneDriveException exception) {
			if (exception.httpStatusCode == 404) {
				// This is a good error - it means that the directory to create 100% does not exist online
				// The directory was not found on the drive id we queried
				log.vlog("The requested directory to create was not found on OneDrive - creating remote directory: ", thisNewPathToCreate);
				
				// Build up the create directory request
				JSONValue createDirectoryOnlineAPIResponse;
				JSONValue newDriveItem = [
						"name": JSONValue(baseName(thisNewPathToCreate)),
						"folder": parseJSON("{}")
				];
				
				// Submit the creation request
				// Fix for https://github.com/skilion/onedrive/issues/356
				if (!dryRun) {
					try {
						// Attempt to create a new folder on the configured parent driveId & parent id
						createDirectoryOnlineAPIResponse = createDirectoryOnlineOneDriveApiInstance.createById(parentItem.driveId, parentItem.id, newDriveItem);
						// Is the response a valid JSON object - validation checking done in saveItem
						saveItem(createDirectoryOnlineAPIResponse);
						// Log that the directory was created
						log.log("Successfully created the remote directory ", thisNewPathToCreate, " on OneDrive");
					} catch (OneDriveException exception) {
						if (exception.httpStatusCode == 409) {
							// OneDrive API returned a 404 (above) to say the directory did not exist
							// but when we attempted to create it, OneDrive responded that it now already exists
							log.vlog("OneDrive reported that ", thisNewPathToCreate, " already exists .. OneDrive API race condition");
							return;
						} else {
							// some other error from OneDrive was returned - display what it is
							log.error("OneDrive generated an error when creating this path: ", thisNewPathToCreate);
							displayOneDriveErrorMessage(exception.msg, getFunctionName!({}));
							return;
						}
					}
				} else {
					// Simulate a successful 'directory create' & save it to the dryRun database copy
					log.log("Successfully created the remote directory ", thisNewPathToCreate, " on OneDrive");
					// The simulated response has to pass 'makeItem' as part of saveItem
					auto fakeResponse = createFakeResponse(thisNewPathToCreate);
					// Save item to the database
					saveItem(fakeResponse);
				}
				
				// Shutdown API instance
				createDirectoryOnlineOneDriveApiInstance.shutdown();
				// Free object and memory
				object.destroy(createDirectoryOnlineOneDriveApiInstance);
				return;
				
			} else {
			
				string thisFunctionName = getFunctionName!({});
				// HTTP request returned status code 408,429,503,504
				if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 429) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
					// Handle the 429
					if (exception.httpStatusCode == 429) {
						// HTTP request returned status code 429 (Too Many Requests). We need to leverage the response Retry-After HTTP header to ensure minimum delay until the throttle is removed.
						handleOneDriveThrottleRequest(createDirectoryOnlineOneDriveApiInstance);
						log.vdebug("Retrying original request that generated the OneDrive HTTP 429 Response Code (Too Many Requests) - attempting to retry ", thisFunctionName);
					}
					// re-try the specific changes queries
					if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
						// 408 - Request Time Out
						// 503 - Service Unavailable
						// 504 - Gateway Timeout
						// Transient error - try again in 30 seconds
						auto errorArray = splitLines(exception.msg);
						log.log(errorArray[0], " when attempting to create a remote directory on OneDrive - retrying applicable request in 30 seconds");
						log.vdebug(thisFunctionName, " previously threw an error - retrying");
						// The server, while acting as a proxy, did not receive a timely response from the upstream server it needed to access in attempting to complete the request. 
						log.vdebug("Thread sleeping for 30 seconds as the server did not receive a timely response from the upstream server it needed to access in attempting to complete the request");
						Thread.sleep(dur!"seconds"(30));
					}
					// re-try original request - retried for 429, 503, 504 - but loop back calling this function 
					log.vdebug("Retrying Function: ", thisFunctionName);
					createDirectoryOnline(thisNewPathToCreate);
				} else {
					// Re-Try
					createDirectoryOnline(thisNewPathToCreate);
				}
			}
		}
		
		// If we get to this point - onlinePathData = createDirectoryOnlineOneDriveApiInstance.getPathDetailsByDriveId(parentItem.driveId, thisNewPathToCreate) generated a 'valid' response ....
		// This means that the folder potentially exists online .. which is odd .. as it should not have existed
		if (onlinePathData.type() == JSONType.object) {
			// A valid object was responded with
			if (onlinePathData["name"].str == baseName(thisNewPathToCreate)) {
				// OneDrive 'name' matches local path name
				if (appConfig.accountType == "business") {
					// We are a business account, this existing online folder, could be a Shared Online Folder and is the 'Add shortcut to My files' item
					log.vdebug("onlinePathData: ", onlinePathData);
					if (isItemRemote(onlinePathData)) {
						// The folder is a remote item ... we do not want to create this ...
						log.vdebug("Remote Existing Online Folder is most likely a OneDrive Shared Business Folder Link added by 'Add shortcut to My files'");
						log.vdebug("We need to skip this path: ", thisNewPathToCreate);
						// Add this path to businessSharedFoldersOnlineToSkip
						businessSharedFoldersOnlineToSkip ~= [thisNewPathToCreate];
						// no save to database, no online create
						return;
					}
				}
				
				log.vlog("The requested directory to create was found on OneDrive - skipping creating the directory: ", thisNewPathToCreate);
				// Is the response a valid JSON object - validation checking done in saveItem
				saveItem(onlinePathData);
				return;
			} else {
				// Normally this would throw an error, however we cant use throw new posixException()
				string msg = format("POSIX 'case-insensitive match' between '%s' (local) and '%s' (online) which violates the Microsoft OneDrive API namespace convention", baseName(thisNewPathToCreate), onlinePathData["name"].str);
				displayPosixErrorMessage(msg);
				log.error("ERROR: Requested directory to create has a 'case-insensitive match' to an existing directory on OneDrive online.");
				log.error("ERROR: To resolve, rename this local directory: ", buildNormalizedPath(absolutePath(thisNewPathToCreate)));
				log.log("Skipping creating this directory online due to 'case-insensitive match': ", thisNewPathToCreate);
				// Add this path to posixViolationPaths
				posixViolationPaths ~= [thisNewPathToCreate];
				return;
			}
		} else {
			// response is not valid JSON, an error was returned from OneDrive
			log.error("ERROR: There was an error performing this operation on OneDrive");
			log.error("ERROR: Increase logging verbosity to assist determining why.");
			log.log("Skipping: ", buildNormalizedPath(absolutePath(thisNewPathToCreate)));
			return;
		}
	}
	
	// Test that the online name actually matches the requested local name
	void performPosixTest(string localNameToCheck, string onlineName) {
			
		// https://docs.microsoft.com/en-us/windows/desktop/FileIO/naming-a-file
		// Do not assume case sensitivity. For example, consider the names OSCAR, Oscar, and oscar to be the same, 
		// even though some file systems (such as a POSIX-compliant file system) may consider them as different. 
		// Note that NTFS supports POSIX semantics for case sensitivity but this is not the default behavior.
		if (localNameToCheck != onlineName) {
			// POSIX Error
			// Local item name has a 'case-insensitive match' to an existing item on OneDrive
			throw new posixException(localNameToCheck, onlineName);
		}
	}
	
	// Upload new file items as identified
	void uploadNewLocalFileItems() {
		
		// Lets deal with the new local items in a batch process
		ulong batchSize = appConfig.concurrentThreads;
		ulong batchCount = (newLocalFilesToUploadToOneDrive.length + batchSize - 1) / batchSize;
		ulong batchesProcessed = 0;
		
		foreach (chunk; newLocalFilesToUploadToOneDrive.chunks(batchSize)) {
			uploadNewLocalFileItemsInParallel(chunk);
		}
	}
	
	// Upload the file batches in parallel
	void uploadNewLocalFileItemsInParallel(string[] array) {
		
		foreach (i, fileToUpload; taskPool.parallel(array)) {
			log.vdebug("Upload Thread ", i, " Starting: ", Clock.currTime());
			uploadNewFile(fileToUpload);
			log.vdebug("Upload Thread ", i, " Finished: ", Clock.currTime());
		}
	}
	
	// Upload a new file to OneDrive
	void uploadNewFile(string fileToUpload) {
			
		// Debug for the moment
		log.vdebug("fileToUpload: ", fileToUpload);
		
		// These are the details of the item we need to upload
		// How much space is remaining on OneDrive
		ulong remainingFreeSpaceOnline;
		// Did the upload fail?
		bool uploadFailed = false;
		// Did we skip due to exceeding maximum allowed size?
		bool skippedMaxSize = false;
		// Did we skip to an exception error?
		bool skippedExceptionError = false;
		// Is the parent path in the item database?
		bool parentPathFoundInDB = false;
		// Get this file size
		ulong thisFileSize;
		// Is there space available online
		bool spaceAvailableOnline = false;
		
		// Check the database for the parent path of fileToUpload
		Item parentItem;
		// What parent path to use?
		string parentPath = dirName(fileToUpload); // will be either . or something else
		if (parentPath == "."){
			// Assume this is a new file in the users configured sync_dir root
			// Use client defaults
			parentItem.id = appConfig.defaultRootId;  		// Should give something like 12345ABCDE1234A1!101
			parentItem.driveId = appConfig.defaultDriveId; 	// Should give something like 12345abcde1234a1
			parentPathFoundInDB = true;
		} else {
			// Query the database using each of the driveId's we are using
			foreach (driveId; driveIDsArray) {
				// Query the database for this parent path using each driveId
				Item dbResponse;
				if(itemDB.selectByPath(parentPath, driveId, dbResponse)){
					// parent path was found in the database
					parentItem = dbResponse;
					parentPathFoundInDB = true;
				}
			}
		}
		
		// If the parent path was found in the DB, to ensure we are uploading the the right location 'parentItem.driveId' must not be empty
		if ((parentPathFoundInDB) && (parentItem.driveId.empty)) {
			// switch to using defaultDriveId
			log.log("parentItem.driveId is empty - using defaultDriveId for upload API calls");
			parentItem.driveId = appConfig.defaultDriveId;
		}
		
		// Can we read the file - as a permissions issue or actual file corruption will cause a failure
		// Resolves: https://github.com/abraunegg/onedrive/issues/113
		if (readLocalFile(fileToUpload)) {
			if (parentPathFoundInDB) {
				// The local file can be read - so we can read it to attemtp to upload it in this thread
				// Get the file size
				thisFileSize = getSize(fileToUpload);
				// Does this file exceed the maximum filesize for OneDrive
				// Resolves: https://github.com/skilion/onedrive/issues/121 , https://github.com/skilion/onedrive/issues/294 , https://github.com/skilion/onedrive/issues/329
				if (thisFileSize <= maxUploadFileSize) {
					// Is there enough free space on OneDrive when we started this thread, to upload the file to OneDrive?
					remainingFreeSpaceOnline = getRemainingFreeSpace(parentItem.driveId);
					log.vdebug("Current Available Space Online (Upload Target Drive ID): ", (remainingFreeSpaceOnline / 1024 / 1024), " MB");
					
					// When we compare the space online to the total we are trying to upload - is there space online?
					ulong calculatedSpaceOnlinePostUpload = remainingFreeSpaceOnline - thisFileSize;
					
					// If 'personal' accounts, if driveId == defaultDriveId, then we will have data - appConfig.quotaAvailable will be updated
					// If 'personal' accounts, if driveId != defaultDriveId, then we will not have quota data - appConfig.quotaRestricted will be set as true
					// If 'business' accounts, if driveId == defaultDriveId, then we will have data
					// If 'business' accounts, if driveId != defaultDriveId, then we will have data, but it will be a 0 value - appConfig.quotaRestricted will be set as true
					
					if (remainingFreeSpaceOnline > totalDataToUpload) {
						// Space available
						spaceAvailableOnline = true;
					} else {
						// we need to look more granular
						// What was the latest getRemainingFreeSpace() value?
						if (appConfig.quotaAvailable) {
							// Our query told us we have free space online .. if we upload this file, will we exceed space online - thus upload will fail during upload?
							if (calculatedSpaceOnlinePostUpload > 0) {
								// Based on this thread action, we beleive that there is space available online to upload - proceed
								spaceAvailableOnline = true;
							}
						}
					}
					
					// Is quota being restricted?
					if (appConfig.quotaRestricted) {
						// If the upload target drive is not our drive id, then it is a shared folder .. we need to print a space warning message
						if (parentItem.driveId != appConfig.defaultDriveId) {
							// Different message depending on account type
							if (appConfig.accountType == "personal") {
								log.vlog("WARNING: Shared Folder OneDrive quota information is being restricted or providing a zero value. Space available online cannot be guaranteed.");
							} else {
								log.vlog("WARNING: Shared Folder OneDrive quota information is being restricted or providing a zero value. Please fix by speaking to your OneDrive / Office 365 Administrator.");
							}
						} else {
							if (appConfig.accountType == "personal") {
								log.vlog("WARNING: OneDrive quota information is being restricted or providing a zero value. Space available online cannot be guaranteed.");
							} else {
								log.vlog("WARNING: OneDrive quota information is being restricted or providing a zero value. Please fix by speaking to your OneDrive / Office 365 Administrator.");
							}
						}
						// Space available online is being restricted - so we have no way to really know if there is space available online
						spaceAvailableOnline = true;
					}
					
					// Do we have space available or is space available being restricted (so we make the blind assumption that there is space available)
					if (spaceAvailableOnline) {
						// We need to check that this new local file does not exist on OneDrive
						
						// Create a new API Instance for this thread and initialise it
						OneDriveApi checkFileOneDriveApiInstance;
						checkFileOneDriveApiInstance = new OneDriveApi(appConfig);
						checkFileOneDriveApiInstance.initialise();
						
						JSONValue fileDetailsFromOneDrive;

						// https://docs.microsoft.com/en-us/windows/desktop/FileIO/naming-a-file
						// Do not assume case sensitivity. For example, consider the names OSCAR, Oscar, and oscar to be the same, 
						// even though some file systems (such as a POSIX-compliant file systems that Linux use) may consider them as different.
						// Note that NTFS supports POSIX semantics for case sensitivity but this is not the default behavior, OneDrive does not use this.
						
						// In order to upload this file - this query HAS to respond as a 404 - Not Found
						
						// Does this 'file' already exist on OneDrive?
						try {
							fileDetailsFromOneDrive = checkFileOneDriveApiInstance.getPathDetailsByDriveId(parentItem.driveId, fileToUpload);
							// Portable Operating System Interface (POSIX) testing of JSON response from OneDrive API
							performPosixTest(baseName(fileToUpload), fileDetailsFromOneDrive["name"].str);
							
							// No 404 or otherwise was triggered, meaning that the file already exists online and passes the POSIX test ...
							log.vdebug("fileDetailsFromOneDrive after exist online check: ", fileDetailsFromOneDrive);
							// Does the data from online match our local file?
							if (performUploadIntegrityValidationChecks(fileDetailsFromOneDrive, fileToUpload, thisFileSize)) {
								// Save item to the database
								saveItem(fileDetailsFromOneDrive);
							}
						} catch (OneDriveException exception) {
							// If we get a 404 .. the file is not online .. this is what we want .. file does not exist online
							if (exception.httpStatusCode == 404) {
								// The file has been checked, client side filtering checked, does not exist online - we need to upload it
								log.vdebug("fileDetailsFromOneDrive = checkFileOneDriveApiInstance.getPathDetailsByDriveId(parentItem.driveId, fileToUpload); generated a 404 - file does not exist online - must upload it");
								uploadFailed = performNewFileUpload(parentItem, fileToUpload, thisFileSize);
							} else {
								
								string thisFunctionName = getFunctionName!({});
								// HTTP request returned status code 408,429,503,504
								if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 429) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
									// Handle the 429
									if (exception.httpStatusCode == 429) {
										// HTTP request returned status code 429 (Too Many Requests). We need to leverage the response Retry-After HTTP header to ensure minimum delay until the throttle is removed.
										handleOneDriveThrottleRequest(checkFileOneDriveApiInstance);
										log.vdebug("Retrying original request that generated the OneDrive HTTP 429 Response Code (Too Many Requests) - attempting to retry ", thisFunctionName);
									}
									// re-try the specific changes queries
									if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
										// 408 - Request Time Out
										// 503 - Service Unavailable
										// 504 - Gateway Timeout
										// Transient error - try again in 30 seconds
										auto errorArray = splitLines(exception.msg);
										log.log(errorArray[0], " when attempting to validate file details on OneDrive - retrying applicable request in 30 seconds");
										log.vdebug(thisFunctionName, " previously threw an error - retrying");
										// The server, while acting as a proxy, did not receive a timely response from the upstream server it needed to access in attempting to complete the request. 
										log.vdebug("Thread sleeping for 30 seconds as the server did not receive a timely response from the upstream server it needed to access in attempting to complete the request");
										Thread.sleep(dur!"seconds"(30));
									}
									// re-try original request - retried for 429, 503, 504 - but loop back calling this function 
									log.vdebug("Retrying Function: ", thisFunctionName);
									uploadNewFile(fileToUpload);
								} else {
									// Default operation if not 408,429,503,504 errors
									// display what the error is
									displayOneDriveErrorMessage(exception.msg, thisFunctionName);
								}
							}
						} catch (posixException e) {
							displayPosixErrorMessage(e.msg);
							uploadFailed = true;
						}
						
						// Operations in this thread are done / complete - either upload was done or it failed
						checkFileOneDriveApiInstance.shutdown();
						// Free object and memory
						object.destroy(checkFileOneDriveApiInstance);
					} else {
						// skip file upload - insufficent space to upload
						log.log("Skipping uploading this new file as it exceeds the available free space on OneDrive: ", fileToUpload);
						uploadFailed = true;
					}
				} else {
					// Skip file upload - too large
					log.log("Skipping uploading this new file as it exceeds the maximum size allowed by OneDrive: ", fileToUpload);
					uploadFailed = true;
				}
			} else {
				// why was the parent path not in the database?
				if (canFind(posixViolationPaths, parentPath)) {
					log.error("ERROR: POSIX 'case-insensitive match' for the parent path which violates the Microsoft OneDrive API namespace convention.");
				} else {
					log.error("ERROR: Parent path is not in the database or online.");
				}
				log.error("ERROR: Unable to upload this file: ", fileToUpload);
				uploadFailed = true;
			}
		} else {
			// Unable to read local file
			log.log("Skipping uploading this file as it cannot be read (file permissions or file corruption): ", fileToUpload);
			uploadFailed = true;
		}
		
		// Upload success or failure?
		if (uploadFailed) {
			// Need to add this to fileUploadFailures to capture at the end
			fileUploadFailures ~= fileToUpload;
		}
	}
	
	// Perform the actual upload to OneDrive
	bool performNewFileUpload(Item parentItem, string fileToUpload, ulong thisFileSize) {
			
		// Assume that by default the upload fails
		bool uploadFailed = true;
		
		// OneDrive API Upload Response
		JSONValue uploadResponse;
		
		// Create the OneDriveAPI Upload Instance
		OneDriveApi uploadFileOneDriveApiInstance;
		uploadFileOneDriveApiInstance = new OneDriveApi(appConfig);
		uploadFileOneDriveApiInstance.initialise();
		
		// Calculate upload speed
		auto uploadStartTime = Clock.currTime();
		
		// Is this a dry-run scenario?
		if (!dryRun) {
			// Not a dry-run situation
			// Do we use simpleUpload or create an upload session?
			bool useSimpleUpload = false;
			if (thisFileSize <= sessionThresholdFileSize) {
				useSimpleUpload = true;
			}
			
			// We can only upload zero size files via simpleFileUpload regardless of account type
			// Reference: https://github.com/OneDrive/onedrive-api-docs/issues/53
			// Additionally, only where file size is < 4MB should be uploaded by simpleUpload - everything else should use a session to upload
			
			if ((thisFileSize == 0) || (useSimpleUpload)) { 
				try {
					// Attempt to upload the zero byte file using simpleUpload for all account types
					uploadResponse = uploadFileOneDriveApiInstance.simpleUpload(fileToUpload, parentItem.driveId, parentItem.id, baseName(fileToUpload));
					uploadFailed = false;
					log.log("Uploading new file ", fileToUpload, " ... done.");
					// Shutdown the API
					uploadFileOneDriveApiInstance.shutdown();
					// Free object and memory
					object.destroy(uploadFileOneDriveApiInstance);
				} catch (OneDriveException exception) {
					// An error was responded with - what was it
					
					string thisFunctionName = getFunctionName!({});
					// HTTP request returned status code 408,429,503,504
					if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 429) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
						// Handle the 429
						if (exception.httpStatusCode == 429) {
							// HTTP request returned status code 429 (Too Many Requests). We need to leverage the response Retry-After HTTP header to ensure minimum delay until the throttle is removed.
							handleOneDriveThrottleRequest(uploadFileOneDriveApiInstance);
							log.vdebug("Retrying original request that generated the OneDrive HTTP 429 Response Code (Too Many Requests) - attempting to retry ", thisFunctionName);
						}
						// re-try the specific changes queries
						if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
							// 408 - Request Time Out
							// 503 - Service Unavailable
							// 504 - Gateway Timeout
							// Transient error - try again in 30 seconds
							auto errorArray = splitLines(exception.msg);
							log.log(errorArray[0], " when attempting to upload a new file to OneDrive - retrying applicable request in 30 seconds");
							log.vdebug(thisFunctionName, " previously threw an error - retrying");
							// The server, while acting as a proxy, did not receive a timely response from the upstream server it needed to access in attempting to complete the request. 
							log.vdebug("Thread sleeping for 30 seconds as the server did not receive a timely response from the upstream server it needed to access in attempting to complete the request");
							Thread.sleep(dur!"seconds"(30));
						}
						// re-try original request - retried for 429, 503, 504 - but loop back calling this function 
						performNewFileUpload(parentItem, fileToUpload, thisFileSize);
						// Return upload status
						return uploadFailed;
					} else {
						// Default operation if not 408,429,503,504 errors
						// display what the error is
						log.log("Uploading new file ", fileToUpload, " ... failed.");
						displayOneDriveErrorMessage(exception.msg, thisFunctionName);
					}
					
				} catch (FileException e) {
					// display the error message
					log.log("Uploading new file ", fileToUpload, " ... failed.");
					displayFileSystemErrorMessage(e.msg, getFunctionName!({}));
				}
			} else {
				// Session Upload for this criteria:
				// - Personal Account and file size > 4MB
				// - All Business | Office365 | SharePoint files > 0 bytes
				JSONValue uploadSessionData;
				// As this is a unique thread, the sessionFilePath for where we save the data needs to be unique
				// The best way to do this is generate a 10 digit alphanumeric string, and use this as the file extention
				string threadUploadSessionFilePath = appConfig.uploadSessionFilePath ~ "." ~ generateAlphanumericString();
				
				// Attempt to upload the > 4MB file using an upload session for all account types
				try {
					// Create the Upload Session
					uploadSessionData = createSessionFileUpload(uploadFileOneDriveApiInstance, fileToUpload, parentItem.driveId, parentItem.id, baseName(fileToUpload), null, threadUploadSessionFilePath);
				} catch (OneDriveException exception) {
					// An error was responded with - what was it
					
					string thisFunctionName = getFunctionName!({});
					// HTTP request returned status code 408,429,503,504
					if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 429) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
						// Handle the 429
						if (exception.httpStatusCode == 429) {
							// HTTP request returned status code 429 (Too Many Requests). We need to leverage the response Retry-After HTTP header to ensure minimum delay until the throttle is removed.
							handleOneDriveThrottleRequest(uploadFileOneDriveApiInstance);
							log.vdebug("Retrying original request that generated the OneDrive HTTP 429 Response Code (Too Many Requests) - attempting to retry ", thisFunctionName);
						}
						// re-try the specific changes queries
						if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
							// 408 - Request Time Out
							// 503 - Service Unavailable
							// 504 - Gateway Timeout
							// Transient error - try again in 30 seconds
							auto errorArray = splitLines(exception.msg);
							log.log(errorArray[0], " when attempting to create an upload session on OneDrive - retrying applicable request in 30 seconds");
							log.vdebug(thisFunctionName, " previously threw an error - retrying");
							// The server, while acting as a proxy, did not receive a timely response from the upstream server it needed to access in attempting to complete the request. 
							log.vdebug("Thread sleeping for 30 seconds as the server did not receive a timely response from the upstream server it needed to access in attempting to complete the request");
							Thread.sleep(dur!"seconds"(30));
						}
						// re-try original request - retried for 429, 503, 504 - but loop back calling this function 
						log.vdebug("Retrying Function: ", thisFunctionName);
						performNewFileUpload(parentItem, fileToUpload, thisFileSize);
					} else {
						// Default operation if not 408,429,503,504 errors
						// display what the error is
						log.log("Uploading new file ", fileToUpload, " ... failed.");
						displayOneDriveErrorMessage(exception.msg, thisFunctionName);
					}
					
				} catch (FileException e) {
					// display the error message
					log.log("Uploading new file ", fileToUpload, " ... failed.");
					displayFileSystemErrorMessage(e.msg, getFunctionName!({}));
				}
				
				// Do we have a valid session URL that we can use ?
				if (uploadSessionData.type() == JSONType.object) {
					// This is a valid JSON object
					bool sessionDataValid = true;
					
					// Validate that we have the following items which we need
					if (!hasUploadURL(uploadSessionData)) {
						sessionDataValid = false;
						log.vdebug("Session data missing 'uploadUrl'");
					}
					
					if (!hasNextExpectedRanges(uploadSessionData)) {
						sessionDataValid = false;
						log.vdebug("Session data missing 'nextExpectedRanges'");
					}
					
					if (!hasLocalPath(uploadSessionData)) {
						sessionDataValid = false;
						log.vdebug("Session data missing 'localPath'");
					}
								
					if (sessionDataValid) {
						// We have a valid Upload Session Data we can use
						
						try {
							// Try and perform the upload session
							uploadResponse = performSessionFileUpload(uploadFileOneDriveApiInstance, thisFileSize, uploadSessionData, threadUploadSessionFilePath);
							
							if (uploadResponse.type() == JSONType.object) {
								uploadFailed = false;
								log.log("Uploading new file ", fileToUpload, " ... done.");
							} else {
								log.log("Uploading new file ", fileToUpload, " ... failed.");
								uploadFailed = true;
							}
						} catch (OneDriveException exception) {
						
							string thisFunctionName = getFunctionName!({});
							// HTTP request returned status code 408,429,503,504
							if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 429) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
								// Handle the 429
								if (exception.httpStatusCode == 429) {
									// HTTP request returned status code 429 (Too Many Requests). We need to leverage the response Retry-After HTTP header to ensure minimum delay until the throttle is removed.
									handleOneDriveThrottleRequest(uploadFileOneDriveApiInstance);
									log.vdebug("Retrying original request that generated the OneDrive HTTP 429 Response Code (Too Many Requests) - attempting to retry ", thisFunctionName);
								}
								// re-try the specific changes queries
								if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
									// 408 - Request Time Out
									// 503 - Service Unavailable
									// 504 - Gateway Timeout
									// Transient error - try again in 30 seconds
									auto errorArray = splitLines(exception.msg);
									log.log(errorArray[0], " when attempting to upload a new file via a session to OneDrive - retrying applicable request in 30 seconds");
									log.vdebug(thisFunctionName, " previously threw an error - retrying");
									// The server, while acting as a proxy, did not receive a timely response from the upstream server it needed to access in attempting to complete the request. 
									log.vdebug("Thread sleeping for 30 seconds as the server did not receive a timely response from the upstream server it needed to access in attempting to complete the request");
									Thread.sleep(dur!"seconds"(30));
								}
								// re-try original request - retried for 429, 503, 504 - but loop back calling this function 
								log.vdebug("Retrying Function: ", thisFunctionName);
								performNewFileUpload(parentItem, fileToUpload, thisFileSize);
							} else {
								// Default operation if not 408,429,503,504 errors
								// display what the error is
								log.log("Uploading new file ", fileToUpload, " ... failed.");
								displayOneDriveErrorMessage(exception.msg, thisFunctionName);
							}
						}
					} else {
						// No Upload URL or nextExpectedRanges or localPath .. not a valid JSON we can use
						log.vlog("Session data is missing required elements to perform a session upload.");
						log.log("Uploading new file ", fileToUpload, " ... failed.");
					}
				} else {
					// Create session Upload URL failed
					log.log("Uploading new file ", fileToUpload, " ... failed.");
				}
			}
		} else {
			// We are in a --dry-run scenario
			uploadResponse = createFakeResponse(fileToUpload);
			uploadFailed = false;
			log.logAndNotify("Uploading new file ", fileToUpload, " ... done.");
		}
		
		// Upload has finished
		auto uploadFinishTime = Clock.currTime();
		// If no upload failure, calculate metrics, perform integrity validation
		if (!uploadFailed) {
			// Upload did not fail ...
			auto uploadDuration = uploadFinishTime - uploadStartTime;
			log.vdebug("File Size: ", thisFileSize, " Bytes");
			log.vdebug("Upload Duration: ", (uploadDuration.total!"msecs"/1e3), " Seconds");
			auto uploadSpeed = (thisFileSize / (uploadDuration.total!"msecs"/1e3)/ 1024 / 1024);
			log.vdebug("Upload Speed: ", uploadSpeed, " Mbps (approx)");
		
			// OK as the upload did not fail, we need to save the response from OneDrive, but it has to be a valid JSON response
			if (uploadResponse.type() == JSONType.object) {
				// check if the path still exists locally before we try to set the file times online - as short lived files, whilst we uploaded it - it may not exist locally aready
				if (exists(fileToUpload)) {
					if (!dryRun) {
						// Check the integrity of the uploaded file, if the local file still exists
						performUploadIntegrityValidationChecks(uploadResponse, fileToUpload, thisFileSize);
						
						// Update the file modified time on OneDrive and save item details to database
						// Update the item's metadata on OneDrive
						SysTime mtime = timeLastModified(fileToUpload).toUTC();
						mtime.fracSecs = Duration.zero;
						string newFileId = uploadResponse["id"].str;
						string newFileETag = uploadResponse["eTag"].str;
						// Attempt to update the online date time stamp based on our local data
						uploadLastModifiedTime(parentItem.driveId, newFileId, mtime, newFileETag);
					}
				} else {
					// will be removed in different event!
					log.log("File disappeared locally after upload: ", fileToUpload);
				}
			} else {
				// Log that an invalid JSON object was returned
				log.vdebug("uploadFileOneDriveApiInstance.simpleUpload or session.upload call returned an invalid JSON Object from the OneDrive API");
			}
		}
		
		// Return upload status
		return uploadFailed;
	}
	
	// Create the OneDrive Upload Session
	JSONValue createSessionFileUpload(OneDriveApi activeOneDriveApiInstance, string fileToUpload, string parentDriveId, string parentId, string filename, string eTag, string threadUploadSessionFilePath) {
		
		// Upload file via a OneDrive API session
		JSONValue uploadSession;
		
		// Calculate modification time
		SysTime localFileLastModifiedTime = timeLastModified(fileToUpload).toUTC();
		localFileLastModifiedTime.fracSecs = Duration.zero;
		
		// Construct the fileSystemInfo JSON component needed to create the Upload Session
		JSONValue fileSystemInfo = [
				"item": JSONValue([
					"@microsoft.graph.conflictBehavior": JSONValue("replace"),
					"fileSystemInfo": JSONValue([
						"lastModifiedDateTime": localFileLastModifiedTime.toISOExtString()
					])
				])
			];
		
		// Try to create the upload session for this file
		uploadSession = activeOneDriveApiInstance.createUploadSession(parentDriveId, parentId, filename, eTag, fileSystemInfo);
		
		if (uploadSession.type() == JSONType.object) {
			// a valid session object was created
			if ("uploadUrl" in uploadSession) {
				// Add the file path we are uploading to this JSON Session Data
				uploadSession["localPath"] = fileToUpload;
				// Save this session
				saveSessionFile(threadUploadSessionFilePath, uploadSession);
			}
		} else {
			// no valid session was created
			log.vlog("Creation of OneDrive API Upload Session failed.");
			// return upload() will return a JSONValue response, create an empty JSONValue response to return
			uploadSession = null;
		}
		// Return the JSON
		return uploadSession;
	}
	
	// Save the session upload data
	void saveSessionFile(string threadUploadSessionFilePath, JSONValue uploadSessionData) {
		
		try {
			std.file.write(threadUploadSessionFilePath, uploadSessionData.toString());
		} catch (FileException e) {
			// display the error message
			displayFileSystemErrorMessage(e.msg, getFunctionName!({}));
		}
	}
	
	// Perform the upload of file via the Upload Session that was created
	JSONValue performSessionFileUpload(OneDriveApi activeOneDriveApiInstance, ulong thisFileSize, JSONValue uploadSessionData, string threadUploadSessionFilePath) {
			
		// Response for upload
		JSONValue uploadResponse;
	
		// Session JSON needs to contain valid elements
		// Get the offset details
		ulong fragmentSize = 10 * 2^^20; // 10 MiB
		ulong fragmentCount = 0;
		ulong fragSize = 0;
		ulong offset = uploadSessionData["nextExpectedRanges"][0].str.splitter('-').front.to!ulong;
		size_t iteration = (roundTo!int(double(thisFileSize)/double(fragmentSize)))+1;
		Progress p = new Progress(iteration);
		p.title = "Uploading";
		
		// Initialise the download bar at 0%
		p.next();
		
		// Start the session upload using the active API instance for this thread
		while (true) {
			fragmentCount++;
			log.vdebugNewLine("Fragment: ", fragmentCount, " of ", iteration);
			p.next();
			log.vdebugNewLine("fragmentSize: ", fragmentSize, "offset: ", offset, " thisFileSize: ", thisFileSize );
			fragSize = fragmentSize < thisFileSize - offset ? fragmentSize : thisFileSize - offset;
			log.vdebugNewLine("Using fragSize: ", fragSize);
			
			// fragSize must not be a negative value
			if (fragSize < 0) {
				// Session upload will fail
				// not a JSON object - fragment upload failed
				log.vlog("File upload session failed - invalid calculation of fragment size");
				if (exists(threadUploadSessionFilePath)) {
					remove(threadUploadSessionFilePath);
				}
				// set uploadResponse to null as error
				uploadResponse = null;
				return uploadResponse;
			}
			
			// If the resume upload fails, we need to check for a return code here
			try {
				uploadResponse = activeOneDriveApiInstance.uploadFragment(
					uploadSessionData["uploadUrl"].str,
					uploadSessionData["localPath"].str,
					offset,
					fragSize,
					thisFileSize
				);
			} catch (OneDriveException exception) {
				// if a 100 uploadResponse is generated, continue
				if (exception.httpStatusCode == 100) {
					continue;
				}
				// There was an error uploadResponse from OneDrive when uploading the file fragment
				
				// Handle transient errors:
				//   408 - Request Time Out
				//   429 - Too Many Requests
				//   503 - Service Unavailable
				//   504 - Gateway Timeout
					
				// HTTP request returned status code 408,429,503,504
				if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 429) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
					// Handle 'HTTP request returned status code 429 (Too Many Requests)' first
					log.vdebug("Fragment upload failed - received throttle request uploadResponse from OneDrive");
					if (exception.httpStatusCode == 429) {
						auto retryAfterValue = activeOneDriveApiInstance.getRetryAfterValue();
						log.vdebug("Using Retry-After Value = ", retryAfterValue);
						// Sleep thread as per request
						log.log("\nThread sleeping due to 'HTTP request returned status code 429' - The request has been throttled");
						log.log("Sleeping for ", retryAfterValue, " seconds");
						Thread.sleep(dur!"seconds"(retryAfterValue));
						log.log("Retrying fragment upload");
					} else {
						// Handle 408, 503 and 504
						auto errorArray = splitLines(exception.msg);
						auto retryAfterValue = 30;
						log.log("\nThread sleeping due to '", errorArray[0], "' - retrying applicable request in 30 seconds");
						log.log("Sleeping for ", retryAfterValue, " seconds");
						Thread.sleep(dur!"seconds"(retryAfterValue));
						log.log("Retrying fragment upload");
					}
				} else {
					// insert a new line as well, so that the below error is inserted on the console in the right location
					log.vlog("\nFragment upload failed - received an exception response from OneDrive API");
					// display what the error is
					displayOneDriveErrorMessage(exception.msg, getFunctionName!({}));
					// retry fragment upload in case error is transient
					log.vlog("Retrying fragment upload");
				}
				
				try {
					uploadResponse = activeOneDriveApiInstance.uploadFragment(
						uploadSessionData["uploadUrl"].str,
						uploadSessionData["localPath"].str,
						offset,
						fragSize,
						thisFileSize
					);
				} catch (OneDriveException e) {
					// OneDrive threw another error on retry
					log.vlog("Retry to upload fragment failed");
					// display what the error is
					displayOneDriveErrorMessage(e.msg, getFunctionName!({}));
					// set uploadResponse to null as the fragment upload was in error twice
					uploadResponse = null;
				} catch (std.exception.ErrnoException e) {
					// There was a file system error - display the error message
					displayFileSystemErrorMessage(e.msg, getFunctionName!({}));
					return uploadResponse;
				}
			}
			
			// was the fragment uploaded without issue?
			if (uploadResponse.type() == JSONType.object){
				offset += fragmentSize;
				if (offset >= thisFileSize) break;
				// update the uploadSessionData details
				uploadSessionData["expirationDateTime"] = uploadResponse["expirationDateTime"];
				uploadSessionData["nextExpectedRanges"] = uploadResponse["nextExpectedRanges"];
				saveSessionFile(threadUploadSessionFilePath, uploadSessionData);
			} else {
				// not a JSON object - fragment upload failed
				log.vlog("File upload session failed - invalid response from OneDrive API");
				if (exists(threadUploadSessionFilePath)) {
					remove(threadUploadSessionFilePath);
				}
				// set uploadResponse to null as error
				uploadResponse = null;
				return uploadResponse;
			}
		}
		
		// upload complete
		p.next();
		writeln();
		if (exists(threadUploadSessionFilePath)) {
			remove(threadUploadSessionFilePath);
		}
		
		// Return the session upload response
		return uploadResponse;
	}
	
	// Delete an item on OneDrive
	void uploadDeletedItem(Item itemToDelete, string path) {
			
		// Are we in a situation where we HAVE to keep the data online - do not delete the remote object
		if (noRemoteDelete) {
			if ((itemToDelete.type == ItemType.dir)) {
				// Do not process remote directory delete
				log.vlog("Skipping remote directory delete as --upload-only & --no-remote-delete configured");
			} else {
				// Do not process remote file delete
				log.vlog("Skipping remote file delete as --upload-only & --no-remote-delete configured");
			}
		} else {
			
			// Is this a --download-only operation?
			if (!appConfig.getValueBool("download_only")) {
				// Process the delete - delete the object online
				log.log("Deleting item from OneDrive: ", path);
				bool flagAsBigDelete = false;
				
				Item[] children;
				ulong itemsToDelete;
			
				if ((itemToDelete.type == ItemType.dir)) {
					// Query the database - how many objects will this remove?
					children = getChildren(itemToDelete.driveId, itemToDelete.id);
					// Count the returned items + the original item (1)
					itemsToDelete = count(children) + 1;
					log.vdebug("Number of items online to delete: ", itemsToDelete);
				} else {
					itemsToDelete = 1;
				}
				
				// A local delete of a file|folder when using --monitor  will issue a inotify event, which will trigger the local & remote data immediately be deleted
				// The user may also be --sync process, so we are checking if something was deleted between application use
				if (itemsToDelete >= appConfig.getValueLong("classify_as_big_delete")) {
					// A big delete has been detected
					flagAsBigDelete = true;
					if (!appConfig.getValueBool("force")) {
						log.error("ERROR: An attempt to remove a large volume of data from OneDrive has been detected. Exiting client to preserve data on OneDrive");
						log.error("ERROR: To delete a large volume of data use --force or increase the config value 'classify_as_big_delete' to a larger value");
						// Must exit here to preserve data on online 
						exit(-1);
					}
				}
				
				// Are we in a --dry-run scenario?
				if (!dryRun) {
					// We are not in a dry run scenario
					log.vdebug("itemToDelete: ", itemToDelete);
					
					// Create new OneDrive API Instance
					OneDriveApi uploadDeletedItemOneDriveApiInstance;
					uploadDeletedItemOneDriveApiInstance = new OneDriveApi(appConfig);
					uploadDeletedItemOneDriveApiInstance.initialise();
				
					// what item are we trying to delete?
					log.vdebug("Attempting to delete this single item id: ", itemToDelete.id, " from drive: ", itemToDelete.driveId);
					try {
						// perform the delete via the default OneDrive API instance
						uploadDeletedItemOneDriveApiInstance.deleteById(itemToDelete.driveId, itemToDelete.id);
						// Shutdown API
						uploadDeletedItemOneDriveApiInstance.shutdown();
						// Free object and memory
						object.destroy(uploadDeletedItemOneDriveApiInstance);
					} catch (OneDriveException e) {
						if (e.httpStatusCode == 404) {
							// item.id, item.eTag could not be found on the specified driveId
							log.vlog("OneDrive reported: The resource could not be found to be deleted.");
						}
					}
					
					// Delete the reference in the local database
					itemDB.deleteById(itemToDelete.driveId, itemToDelete.id);
					if (itemToDelete.remoteId != null) {
						// If the item is a remote item, delete the reference in the local database
						itemDB.deleteById(itemToDelete.remoteDriveId, itemToDelete.remoteId);
					}
				} else {
					// log that this is a dry-run activity
					log.log("dry run - no delete activity");
				}
			} else {
				// --download-only operation, we are not uploading any delete event to OneDrive
				log.vdebug("Not pushing local delete to Microsoft OneDrive due to --download-only being used");
			}
		}
	}
	
	// Get the children of an item id from the database
	Item[] getChildren(string driveId, string id) {
				
		Item[] children;
		children ~= itemDB.selectChildren(driveId, id);
		foreach (Item child; children) {
			if (child.type != ItemType.file) {
				// recursively get the children of this child
				children ~= getChildren(child.driveId, child.id);
			}
		}
		return children;
	}
	
	// Perform a 'reverse' delete of all child objects on OneDrive
	void performReverseDeletionOfOneDriveItems(Item[] children, Item itemToDelete) {
		
		// Log what is happening
		log.vdebug("Attempting a reverse delete of all child objects from OneDrive");
		
		// Create a new API Instance for this thread and initialise it
		OneDriveApi performReverseDeletionOneDriveApiInstance;
		performReverseDeletionOneDriveApiInstance = new OneDriveApi(appConfig);
		performReverseDeletionOneDriveApiInstance.initialise();
		
		foreach_reverse (Item child; children) {
			// Log the action
			log.vdebug("Attempting to delete this child item id: ", child.id, " from drive: ", child.driveId);
			// perform the delete via the default OneDrive API instance
			performReverseDeletionOneDriveApiInstance.deleteById(child.driveId, child.id, child.eTag);
			// delete the child reference in the local database
			itemDB.deleteById(child.driveId, child.id);
		}
		// Log the action
		log.vdebug("Attempting to delete this parent item id: ", itemToDelete.id, " from drive: ", itemToDelete.driveId);
		// Perform the delete via the default OneDrive API instance
		performReverseDeletionOneDriveApiInstance.deleteById(itemToDelete.driveId, itemToDelete.id, itemToDelete.eTag);
		// Shutdown API instance
		performReverseDeletionOneDriveApiInstance.shutdown();
		// Free object and memory
		object.destroy(performReverseDeletionOneDriveApiInstance);
	}
	
	// Create a fake OneDrive response suitable for use with saveItem
	JSONValue createFakeResponse(const(string) path) {
		
		import std.digest.sha;
		// Generate a simulated JSON response which can be used
		// At a minimum we need:
		// 1. eTag
		// 2. cTag
		// 3. fileSystemInfo
		// 4. file or folder. if file, hash of file
		// 5. id
		// 6. name
		// 7. parent reference
		
		string fakeDriveId = appConfig.defaultDriveId;
		string fakeRootId = appConfig.defaultRootId;
		SysTime mtime = timeLastModified(path).toUTC();
		
		// Need to update the 'fakeDriveId' & 'fakeRootId' with elements from the --dry-run database
		// Otherwise some calls to validate objects will fail as the actual driveId being used is invalid
		string parentPath = dirName(path);
		Item databaseItem;
		
		if (parentPath != ".") {
			// Not a 'root' parent
			// For each driveid in the existing driveIDsArray 
			foreach (searchDriveId; driveIDsArray) {
				log.vdebug("FakeResponse: searching database for: ", searchDriveId, " ", parentPath);
				if (itemDB.selectByPath(parentPath, searchDriveId, databaseItem)) {
					log.vdebug("FakeResponse: Found Database Item: ", databaseItem);
					fakeDriveId = databaseItem.driveId;
					fakeRootId = databaseItem.id;
				}
			}
		}
		
		// real id / eTag / cTag are different format for personal / business account
		auto sha1 = new SHA1Digest();
		ubyte[] fakedOneDriveItemValues = sha1.digest(path);
		
		JSONValue fakeResponse;
		
		if (isDir(path)) {
			// path is a directory
			fakeResponse = [
							"id": JSONValue(toHexString(fakedOneDriveItemValues)),
							"cTag": JSONValue(toHexString(fakedOneDriveItemValues)),
							"eTag": JSONValue(toHexString(fakedOneDriveItemValues)),
							"fileSystemInfo": JSONValue([
														"createdDateTime": mtime.toISOExtString(),
														"lastModifiedDateTime": mtime.toISOExtString()
														]),
							"name": JSONValue(baseName(path)),
							"parentReference": JSONValue([
														"driveId": JSONValue(fakeDriveId),
														"driveType": JSONValue(appConfig.accountType),
														"id": JSONValue(fakeRootId)
														]),
							"folder": JSONValue("")
							];
		} else {
			// path is a file
			// compute file hash - both business and personal responses use quickXorHash
			string quickXorHash = computeQuickXorHash(path);
	
			fakeResponse = [
							"id": JSONValue(toHexString(fakedOneDriveItemValues)),
							"cTag": JSONValue(toHexString(fakedOneDriveItemValues)),
							"eTag": JSONValue(toHexString(fakedOneDriveItemValues)),
							"fileSystemInfo": JSONValue([
														"createdDateTime": mtime.toISOExtString(),
														"lastModifiedDateTime": mtime.toISOExtString()
														]),
							"name": JSONValue(baseName(path)),
							"parentReference": JSONValue([
														"driveId": JSONValue(fakeDriveId),
														"driveType": JSONValue(appConfig.accountType),
														"id": JSONValue(fakeRootId)
														]),
							"file": JSONValue([
												"hashes":JSONValue([
																	"quickXorHash": JSONValue(quickXorHash)
																	])
												
												])
							];
		}
						
		log.vdebug("Generated Fake OneDrive Response: ", fakeResponse);
		return fakeResponse;
	}
	
	// Save JSON item details into the item database
	void saveItem(JSONValue jsonItem) {
			
		// jsonItem has to be a valid object
		if (jsonItem.type() == JSONType.object) {
			// Check if the response JSON has an 'id', otherwise makeItem() fails with 'Key not found: id'
			if (hasId(jsonItem)) {
				// Are we in a --upload-only & --remove-source-files scenario?
				// We do not want to add the item to the database in this situation as there is no local reference to the file post file deletion
				// If the item is a directory, we need to add this to the DB, if this is a file, we dont add this, the parent path is not in DB, thus any new files in this directory are not added
				if ((uploadOnly) && (localDeleteAfterUpload) && (isItemFile(jsonItem))) {
					// Log that we skipping adding item to the local DB and the reason why
					log.vdebug("Skipping adding to database as --upload-only & --remove-source-files configured");
				} else {
					// What is the JSON item we are trying to create a DB record with?
					log.vdebug("saveItem - creating DB item from this JSON: ", jsonItem);
					// Takes a JSON input and formats to an item which can be used by the database
					Item item = makeItem(jsonItem);
					
					// Is this JSON item a 'root' item?
					if ((isItemRoot(jsonItem)) && (item.name == "root")) {
						log.vdebug("Updating DB Item object with correct values as this is a 'root' object");
						item.parentId = null; 	// ensures that this database entry has no parent
						// Check for parentReference
						if (hasParentReference(jsonItem)) {
							// Set the correct item.driveId
							log.vdebug("ROOT JSON Item HAS parentReference .... setting item.driveId = jsonItem['parentReference']['driveId'].str");
							item.driveId = jsonItem["parentReference"]["driveId"].str;
						}
						
						// We only should be adding our account 'root' to the database, not shared folder 'root' items
						if (item.driveId != appConfig.defaultDriveId) {
							// Shared Folder drive 'root' object .. we dont want this item
							log.vdebug("NOT adding 'remote root' object to database: ", item);
							return;
						}
					}
					
					// Add to the local database
					log.vdebug("Adding to database: ", item);
					itemDB.upsert(item);
					
					// If we have a remote drive ID, add this to our list of known drive id's
					if (!item.remoteDriveId.empty) {
						// Keep the driveIDsArray with unique entries only
						if (!canFind(driveIDsArray, item.remoteDriveId)) {
							// Add this drive id to the array to search with
							driveIDsArray ~= item.remoteDriveId;
						}
					}
				}
			} else {
				// log error
				log.error("ERROR: OneDrive response missing required 'id' element");
				log.error("ERROR: ", jsonItem);
			}
		} else {
			// log error
			log.error("ERROR: An error was returned from OneDrive and the resulting response is not a valid JSON object");
			log.error("ERROR: Increase logging verbosity to assist determining why.");
		}
	}
	
	// Wrapper function for makeDatabaseItem so we can check to ensure that the item has the required hashes
	Item makeItem(JSONValue onedriveJSONItem) {
			
		// Make the DB Item from the JSON data provided
		Item newDatabaseItem = makeDatabaseItem(onedriveJSONItem);
		
		// Is this a 'file' item that has not been deleted? Deleted items have no hash
		if ((newDatabaseItem.type == ItemType.file) && (!isItemDeleted(onedriveJSONItem))) {
			// Does this item have a file size attribute?
			if (hasFileSize(onedriveJSONItem)) {
				// Is the file size greater than 0?
				if (onedriveJSONItem["size"].integer > 0) {
					// Does the DB item have any hashes as per the API provided JSON data?
					if ((newDatabaseItem.quickXorHash.empty) && (newDatabaseItem.sha256Hash.empty)) {
						// Odd .. there is no hash for this item .. why is that?
						// Is there a 'file' JSON element?
						if ("file" in onedriveJSONItem) {
							// Microsoft OneDrive OneNote objects will report as files but have 'application/msonenote' and 'application/octet-stream' as mime types
							if ((isMicrosoftOneNoteMimeType1(onedriveJSONItem)) || (isMicrosoftOneNoteMimeType2(onedriveJSONItem))) {
								// Debug log output that this is a potential OneNote object
								log.vdebug("This item is potentially an associated Microsoft OneNote Object Item");
							} else {
								// Not a Microsoft OneNote Mime Type Object ..
								string apiWarningMessage = "WARNING: OneDrive API inconsistency - this file does not have any hash: ";
								// This is computationally expensive .. but we are only doing this if there are no hashses provided
								bool parentInDatabase = itemDB.idInLocalDatabase(newDatabaseItem.driveId, newDatabaseItem.parentId);
								// Is the parent id in the database?
								if (parentInDatabase) {
									// This is again computationally expensive .. calculate this item path to advise the user the actual path of this item that has no hash
									string newItemPath = computeItemPath(newDatabaseItem.driveId, newDatabaseItem.parentId) ~ "/" ~ newDatabaseItem.name;
									log.log(apiWarningMessage, newItemPath);
								} else {
									// Parent is not in the database .. why?
									// Check if the parent item had been skipped .. 
									if (newDatabaseItem.parentId in skippedItems) {
										log.vdebug(apiWarningMessage, "newDatabaseItem.parentId listed within skippedItems");
									} else {
										// Use the item ID .. there is no other reference available, parent is not being skipped, so we should have been able to calculate this - but we could not
										log.log(apiWarningMessage, newDatabaseItem.id);
									}
								}
							}
						}	
					}
				} else {
					// zero file size
					log.vdebug("This item file is zero size - potentially no hash provided by the OneDrive API");
				}
			}
		}
		
		// Return the new database item
		return newDatabaseItem;
	}
	
	// Print the fileDownloadFailures and fileUploadFailures arrays if they are not empty
	void displaySyncFailures() {
			
		// Were there any file download failures?
		if (!fileDownloadFailures.empty) {
			// There are download failures ...
			log.log("\nFailed items to download from OneDrive: ", fileDownloadFailures.length);
			foreach(failedFileToDownload; fileDownloadFailures) {
				// List the detail of the item that failed to download
				log.logAndNotify("Failed to download: ", failedFileToDownload);
				
				// Is this failed item in the DB? It should not be ..
				Item downloadDBItem;
				// Need to check all driveid's we know about, not just the defaultDriveId
				foreach (searchDriveId; driveIDsArray) {
					if (itemDB.selectByPath(failedFileToDownload, searchDriveId, downloadDBItem)) {
						// item was found in the DB
						log.error("ERROR: Failed Download Path found in database, must delete this item from the database .. it should not be in there if it failed to download");
						// Process the database entry removal. In a --dry-run scenario, this is being done against a DB copy
						itemDB.deleteById(downloadDBItem.driveId, downloadDBItem.id);
						if (downloadDBItem.remoteDriveId != null) {
							// delete the linked remote folder
							itemDB.deleteById(downloadDBItem.remoteDriveId, downloadDBItem.remoteId);
						}	
					}
				}
			}
			// Set the flag
			syncFailures = true;
		}
		
		// Were there any file upload failures?
		if (!fileUploadFailures.empty) {
			// There are download failures ...
			log.log("\nFailed items to upload to OneDrive: ", fileUploadFailures.length);
			foreach(failedFileToUpload; fileUploadFailures) {
				// List the path of the item that failed to upload
				log.logAndNotify("Failed to upload: ", failedFileToUpload);
				
				// Is this failed item in the DB? It should not be ..
				Item uploadDBItem;
				// Need to check all driveid's we know about, not just the defaultDriveId
				foreach (searchDriveId; driveIDsArray) {
					if (itemDB.selectByPath(failedFileToUpload, searchDriveId, uploadDBItem)) {
						// item was found in the DB
						log.error("ERROR: Failed Upload Path found in database, must delete this item from the database .. it should not be in there if it failed to upload");
						// Process the database entry removal. In a --dry-run scenario, this is being done against a DB copy
						itemDB.deleteById(uploadDBItem.driveId, uploadDBItem.id);
						if (uploadDBItem.remoteDriveId != null) {
							// delete the linked remote folder
							itemDB.deleteById(uploadDBItem.remoteDriveId, uploadDBItem.remoteId);
						}	
					}
				}
			}
			// Set the flag
			syncFailures = true;
		}
	}
	
	// Generate a /delta compatible response - for use when we cant actually use /delta
	// This is required when the application is configured to use National Azure AD deployments as these do not support /delta queries
	// The same technique can also be used when we are using --single-directory. The parent objects up to the single directory target can be added,
	// then once the target of the --single-directory request is hit, all of the children of that path can be queried, giving a much more focused
	// JSON response which can then be processed, negating the need to continuously traverse the tree and 'exclude' items
	JSONValue generateDeltaResponse(string pathToQuery = null) {
			
		// JSON value which will be responded with
		JSONValue selfGeneratedDeltaResponse;
		
		// Function variables
		Item searchItem;
		JSONValue rootData;
		JSONValue driveData;
		JSONValue pathData;
		JSONValue topLevelChildren;
		JSONValue[] childrenData;
		string nextLink;
		
		// Was a path to query passed in?
		if (pathToQuery.empty) {
			// Will query for the 'root'
			pathToQuery = ".";
		}
		
		// Create new OneDrive API Instance
		OneDriveApi generateDeltaResponseOneDriveApiInstance;
		generateDeltaResponseOneDriveApiInstance = new OneDriveApi(appConfig);
		generateDeltaResponseOneDriveApiInstance.initialise();
		
		if (!singleDirectoryScope) {
			// In a --resync scenario, there is no DB data to query, so we have to query the OneDrive API here to get relevant details
			try {
				// Query the OneDrive API
				pathData = generateDeltaResponseOneDriveApiInstance.getPathDetails(pathToQuery);
				// Is the path on OneDrive local or remote to our account drive id?
				if (isItemRemote(pathData)) {
					// The path we are seeking is remote to our account drive id
					searchItem.driveId = pathData["remoteItem"]["parentReference"]["driveId"].str;
					searchItem.id = pathData["remoteItem"]["id"].str;
				} else {
					// The path we are seeking is local to our account drive id
					searchItem.driveId = pathData["parentReference"]["driveId"].str;
					searchItem.id = pathData["id"].str;
				}
			} catch (OneDriveException e) {
				// Display error message
				displayOneDriveErrorMessage(e.msg, getFunctionName!({}));
				// Must exit here
				generateDeltaResponseOneDriveApiInstance.shutdown();
				// Free object and memory
				object.destroy(generateDeltaResponseOneDriveApiInstance);
				exit(-1);
			}
		} else {
			// When setSingleDirectoryScope() was called, the following were set to the correct items, even if the path was remote:
			// - singleDirectoryScopeDriveId
			// - singleDirectoryScopeItemId
			// Reuse these prior set values
			searchItem.driveId = singleDirectoryScopeDriveId;
			searchItem.id = singleDirectoryScopeItemId;
		}
		
		// Before we get any data from the OneDrive API, flag any child object in the database as out-of-sync for this driveId & and object id
		// Downgrade ONLY files associated with this driveId and idToQuery
		log.vdebug("Downgrading all children for this searchItem.driveId (" ~ searchItem.driveId ~ ") and searchItem.id (" ~ searchItem.id ~ ") to an out-of-sync state");
		auto drivePathChildren = getChildren(searchItem.driveId, searchItem.id);
		if (count(drivePathChildren) > 0) {
			// Children to process and flag as out-of-sync	
			foreach (drivePathChild; drivePathChildren) {
				// Flag any object in the database as out-of-sync for this driveId & and object id
				log.vdebug("Downgrading item as out-of-sync: ", drivePathChild.id);
				itemDB.downgradeSyncStatusFlag(drivePathChild.driveId, drivePathChild.id);
			}
		}
		
		// Get drive details for the provided driveId
		try {
			driveData = generateDeltaResponseOneDriveApiInstance.getPathDetailsById(searchItem.driveId, searchItem.id);
		} catch (OneDriveException exception) {
			log.vdebug("driveData = generateDeltaResponseOneDriveApiInstance.getPathDetailsById(searchItem.driveId, searchItem.id) generated a OneDriveException");
			
			string thisFunctionName = getFunctionName!({});
			// HTTP request returned status code 408,429,503,504
			if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 429) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
				// Handle the 429
				if (exception.httpStatusCode == 429) {
					// HTTP request returned status code 429 (Too Many Requests). We need to leverage the response Retry-After HTTP header to ensure minimum delay until the throttle is removed.
					handleOneDriveThrottleRequest(generateDeltaResponseOneDriveApiInstance);
					log.vdebug("Retrying original request that generated the OneDrive HTTP 429 Response Code (Too Many Requests) - attempting to retry ", thisFunctionName);
				}
				// re-try the specific changes queries
				if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
					// 408 - Request Time Out
					// 503 - Service Unavailable
					// 504 - Gateway Timeout
					// Transient error - try again in 30 seconds
					auto errorArray = splitLines(exception.msg);
					log.log(errorArray[0], " when attempting to query path details on OneDrive - retrying applicable request in 30 seconds");
					log.vdebug(thisFunctionName, " previously threw an error - retrying");
					// The server, while acting as a proxy, did not receive a timely response from the upstream server it needed to access in attempting to complete the request. 
					log.vdebug("Thread sleeping for 30 seconds as the server did not receive a timely response from the upstream server it needed to access in attempting to complete the request");
					Thread.sleep(dur!"seconds"(30));
				}
				// re-try original request - retried for 429, 503, 504 - but loop back calling this function 
				log.vdebug("Retrying Function: ", thisFunctionName);
				generateDeltaResponse(pathToQuery);
			} else {
				// Default operation if not 408,429,503,504 errors
				// display what the error is
				displayOneDriveErrorMessage(exception.msg, thisFunctionName);
			}
		}
		
		// Was a valid JSON response for 'driveData' provided?
		if (driveData.type() == JSONType.object) {
		
			// Dynamic output for a non-verbose run so that the user knows something is happening
			if (log.verbose == 0) {
				if (!appConfig.surpressLoggingOutput) {
					log.fileOnly("Fetching items from the OneDrive API for Drive ID: ", searchItem.driveId);
					// Use the dots to show the application is 'doing something'
					write("Fetching items from the OneDrive API for Drive ID: ", searchItem.driveId, " .");
				}
			} else {
				log.vlog("Generating a /delta response from the OneDrive API for Drive ID: ", searchItem.driveId);
			}
		
			// Process this initial JSON response
			if (!isItemRoot(driveData)) {
				// Get root details for the provided driveId
				try {
					rootData = generateDeltaResponseOneDriveApiInstance.getDriveIdRoot(searchItem.driveId);
				} catch (OneDriveException exception) {
					log.vdebug("rootData = onedrive.getDriveIdRoot(searchItem.driveId) generated a OneDriveException");
					
					string thisFunctionName = getFunctionName!({});
					// HTTP request returned status code 408,429,503,504
					if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 429) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
						// Handle the 429
						if (exception.httpStatusCode == 429) {
							// HTTP request returned status code 429 (Too Many Requests). We need to leverage the response Retry-After HTTP header to ensure minimum delay until the throttle is removed.
							handleOneDriveThrottleRequest(generateDeltaResponseOneDriveApiInstance);
							log.vdebug("Retrying original request that generated the OneDrive HTTP 429 Response Code (Too Many Requests) - attempting to retry ", thisFunctionName);
						}
						// re-try the specific changes queries
						if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
							// 408 - Request Time Out
							// 503 - Service Unavailable
							// 504 - Gateway Timeout
							// Transient error - try again in 30 seconds
							auto errorArray = splitLines(exception.msg);
							log.log(errorArray[0], " when attempting to query drive root details on OneDrive - retrying applicable request in 30 seconds");
							log.vdebug(thisFunctionName, " previously threw an error - retrying");
							// The server, while acting as a proxy, did not receive a timely response from the upstream server it needed to access in attempting to complete the request. 
							log.vdebug("Thread sleeping for 30 seconds as the server did not receive a timely response from the upstream server it needed to access in attempting to complete the request");
							Thread.sleep(dur!"seconds"(30));
						}
						// re-try original request - retried for 429, 503, 504 - but loop back calling this function 
						log.log("Retrying Query: rootData = generateDeltaResponseOneDriveApiInstance.getDriveIdRoot(searchItem.driveId)");
						rootData = generateDeltaResponseOneDriveApiInstance.getDriveIdRoot(searchItem.driveId);
					} else {
						// Default operation if not 408,429,503,504 errors
						// display what the error is
						displayOneDriveErrorMessage(exception.msg, thisFunctionName);
					}
				}
				// Add driveData JSON data to array
				log.vlog("Adding OneDrive root details for processing");
				childrenData ~= rootData;
			}
			
			// Add driveData JSON data to array
			log.vlog("Adding OneDrive folder details for processing");
			childrenData ~= driveData;
		} else {
			// driveData is an invalid JSON object
			writeln("CODING TO DO: The query of OneDrive API to getPathDetailsById generated an invalid JSON response - thus we cant build our own /delta simulated response ... how to handle?");
			// Must exit here
			generateDeltaResponseOneDriveApiInstance.shutdown();
			// Free object and memory
			object.destroy(generateDeltaResponseOneDriveApiInstance);
			exit(-1);
		}
		
		// For each child object, query the OneDrive API
		for (;;) {
			// query top level children
			try {
				topLevelChildren = generateDeltaResponseOneDriveApiInstance.listChildren(searchItem.driveId, searchItem.id, nextLink);
			} catch (OneDriveException exception) {
				// OneDrive threw an error
				log.vdebug("------------------------------------------------------------------");
				log.vdebug("Query Error: topLevelChildren = generateDeltaResponseOneDriveApiInstance.listChildren(searchItem.driveId, searchItem.id, nextLink)");
				log.vdebug("driveId:   ", searchItem.driveId);
				log.vdebug("idToQuery: ", searchItem.id);
				log.vdebug("nextLink:  ", nextLink);
				
				string thisFunctionName = getFunctionName!({});
				// HTTP request returned status code 408,429,503,504
				if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 429) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
					// Handle the 429
					if (exception.httpStatusCode == 429) {
						// HTTP request returned status code 429 (Too Many Requests). We need to leverage the response Retry-After HTTP header to ensure minimum delay until the throttle is removed.
						handleOneDriveThrottleRequest(generateDeltaResponseOneDriveApiInstance);
						log.vdebug("Retrying original request that generated the OneDrive HTTP 429 Response Code (Too Many Requests) - attempting to retry topLevelChildren = generateDeltaResponseOneDriveApiInstance.listChildren(searchItem.driveId, searchItem.id, nextLink)");
					}
					// re-try the specific changes queries
					if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
						// 408 - Request Time Out
						// 503 - Service Unavailable
						// 504 - Gateway Timeout
						// Transient error - try again in 30 seconds
						auto errorArray = splitLines(exception.msg);
						log.log(errorArray[0], " when attempting to query OneDrive top level drive children on OneDrive - retrying applicable request in 30 seconds");
						log.vdebug("generateDeltaResponseOneDriveApiInstance.listChildren(searchItem.driveId, searchItem.id, nextLink) previously threw an error - retrying");
						// The server, while acting as a proxy, did not receive a timely response from the upstream server it needed to access in attempting to complete the request. 
						log.vdebug("Thread sleeping for 30 seconds as the server did not receive a timely response from the upstream server it needed to access in attempting to complete the request");
						Thread.sleep(dur!"seconds"(30));
					}
					// re-try original request - retried for 429, 503, 504 - but loop back calling this function 
					//log.vdebug("Retrying Query: generateDeltaResponseOneDriveApiInstance.listChildren(searchItem.driveId, searchItem.id, nextLink)");
					//topLevelChildren = generateDeltaResponseOneDriveApiInstance.listChildren(searchItem.driveId, searchItem.id, nextLink);
					
					log.vdebug("Retrying Function: ", thisFunctionName);
					generateDeltaResponse(pathToQuery);
					
				} else {
					// Default operation if not 408,429,503,504 errors
					// display what the error is
					displayOneDriveErrorMessage(exception.msg, thisFunctionName);
				}
			}
			
			// process top level children
			log.vlog("Adding ", count(topLevelChildren["value"].array), " OneDrive items for processing from the OneDrive 'root' folder");
			foreach (child; topLevelChildren["value"].array) {
				// Check for any Client Side Filtering here ... we should skip querying the OneDrive API for 'folders' that we are going to just process and skip anyway.
				// This avoids needless calls to the OneDrive API, and potentially speeds up this process.
				if (!checkJSONAgainstClientSideFiltering(child)) {
					// add this child to the array of objects
					childrenData ~= child;
					// is this child a folder?
					if (isItemFolder(child)) {
						// We have to query this folders children if childCount > 0
						if (child["folder"]["childCount"].integer > 0){
							// This child folder has children
							string childIdToQuery = child["id"].str;
							string childDriveToQuery = child["parentReference"]["driveId"].str;
							auto childParentPath = child["parentReference"]["path"].str.split(":");
							string folderPathToScan = childParentPath[1] ~ "/" ~ child["name"].str;
							
							string pathForLogging;
							// Are we in a --single-directory situation? If we are, the path we are using for logging needs to use the input path as a base
							if (singleDirectoryScope) {
								pathForLogging = appConfig.getValueString("single_directory") ~ "/" ~ child["name"].str;
							} else {
								pathForLogging = child["name"].str;
							}
							
							// Query the children of this item
							JSONValue[] grandChildrenData = queryForChildren(childDriveToQuery, childIdToQuery, folderPathToScan, pathForLogging);
							foreach (grandChild; grandChildrenData.array) {
								// add the grandchild to the array
								childrenData ~= grandChild;
							}
						}
					}
				}
			}
			// If a collection exceeds the default page size (200 items), the @odata.nextLink property is returned in the response 
			// to indicate more items are available and provide the request URL for the next page of items.
			if ("@odata.nextLink" in topLevelChildren) {
				// Update nextLink to next changeSet bundle
				log.vdebug("Setting nextLink to (@odata.nextLink): ", nextLink);
				nextLink = topLevelChildren["@odata.nextLink"].str;
			} else break;
		}
		
		if (log.verbose == 0) {
			// Dynamic output for a non-verbose run so that the user knows something is happening
			if (!appConfig.surpressLoggingOutput) {
				writeln();
			}
		}
		
		// Craft response from all returned JSON elements
		selfGeneratedDeltaResponse = [
						"@odata.context": JSONValue("https://graph.microsoft.com/v1.0/$metadata#Collection(driveItem)"),
						"value": JSONValue(childrenData.array)
						];
		
		// Shutdown API
		generateDeltaResponseOneDriveApiInstance.shutdown();
		// Free object and memory
		object.destroy(generateDeltaResponseOneDriveApiInstance);
		
		// Return the generated JSON response
		return selfGeneratedDeltaResponse;
	}
	
	// Query the OneDrive API for the specified child id for any children objects
	JSONValue[] queryForChildren(string driveId, string idToQuery, string childParentPath, string pathForLogging) {
				
		// function variables
		JSONValue thisLevelChildren;
		JSONValue[] thisLevelChildrenData;
		string nextLink;
		
		// Create new OneDrive API Instance
		OneDriveApi queryChildrenOneDriveApiInstance;
		queryChildrenOneDriveApiInstance = new OneDriveApi(appConfig);
		queryChildrenOneDriveApiInstance.initialise();
		
		for (;;) {
			// query this level children
			try {
				thisLevelChildren = queryThisLevelChildren(driveId, idToQuery, nextLink, queryChildrenOneDriveApiInstance);
			} catch (OneDriveException exception) {
				
				writeln("CODING TO DO: EXCEPTION HANDLING NEEDED: thisLevelChildren = queryThisLevelChildren(driveId, idToQuery, nextLink, queryChildrenOneDriveApiInstance)");
			
			}
			
			if (log.verbose == 0) {
				// Dynamic output for a non-verbose run so that the user knows something is happening
				if (!appConfig.surpressLoggingOutput) {
					write(".");
				}
			}
			
			// Was a valid JSON response for 'thisLevelChildren' provided?
			if (thisLevelChildren.type() == JSONType.object) {
				// process this level children
				if (!childParentPath.empty) {
					// We dont use childParentPath to log, as this poses an information leak risk.
					// The full parent path of the child, as per the JSON might be:
					//   /Level 1/Level 2/Level 3/Child Shared Folder/some folder/another folder
					// But 'Child Shared Folder' is what is shared, thus '/Level 1/Level 2/Level 3/' is a potential information leak if logged.
					// Plus, the application output now shows accuratly what is being shared - so that is a good thing.
					log.vlog("Adding ", count(thisLevelChildren["value"].array), " OneDrive items for processing from ", pathForLogging);
				}
				foreach (child; thisLevelChildren["value"].array) {
					// Check for any Client Side Filtering here ... we should skip querying the OneDrive API for 'folders' that we are going to just process and skip anyway.
					// This avoids needless calls to the OneDrive API, and potentially speeds up this process.
					if (!checkJSONAgainstClientSideFiltering(child)) {
						// add this child to the array of objects
						thisLevelChildrenData ~= child;
						// is this child a folder?
						if (isItemFolder(child)){
							// We have to query this folders children if childCount > 0
							if (child["folder"]["childCount"].integer > 0){
								// This child folder has children
								string childIdToQuery = child["id"].str;
								string childDriveToQuery = child["parentReference"]["driveId"].str;
								auto grandchildParentPath = child["parentReference"]["path"].str.split(":");
								string folderPathToScan = grandchildParentPath[1] ~ "/" ~ child["name"].str;
								string newLoggingPath = pathForLogging ~ "/" ~ child["name"].str;
								JSONValue[] grandChildrenData = queryForChildren(childDriveToQuery, childIdToQuery, folderPathToScan, newLoggingPath);
								foreach (grandChild; grandChildrenData.array) {
									// add the grandchild to the array
									thisLevelChildrenData ~= grandChild;
								}
							}
						}
					}
				}
				// If a collection exceeds the default page size (200 items), the @odata.nextLink property is returned in the response 
				// to indicate more items are available and provide the request URL for the next page of items.
				if ("@odata.nextLink" in thisLevelChildren) {
					// Update nextLink to next changeSet bundle
					nextLink = thisLevelChildren["@odata.nextLink"].str;
					log.vdebug("Setting nextLink to (@odata.nextLink): ", nextLink);
				} else break;
			
			} else {
				// Invalid JSON response when querying this level children
				log.vdebug("INVALID JSON response when attempting a retry of parent function - queryForChildren(driveId, idToQuery, childParentPath, pathForLogging)");
				// retry thisLevelChildren = queryThisLevelChildren
				log.vdebug("Thread sleeping for an additional 30 seconds");
				Thread.sleep(dur!"seconds"(30));
				log.vdebug("Retry this call thisLevelChildren = queryThisLevelChildren(driveId, idToQuery, nextLink, queryChildrenOneDriveApiInstance)");
				thisLevelChildren = queryThisLevelChildren(driveId, idToQuery, nextLink, queryChildrenOneDriveApiInstance);
			}
		}
		
		// Shutdown API instance
		queryChildrenOneDriveApiInstance.shutdown();
		// Free object and memory
		object.destroy(queryChildrenOneDriveApiInstance);
		
		// return response
		return thisLevelChildrenData;
	}
	
	// Query the OneDrive API for the child objects for this element
	JSONValue queryThisLevelChildren(string driveId, string idToQuery, string nextLink, OneDriveApi queryChildrenOneDriveApiInstance) {
		
		// function variables 
		JSONValue thisLevelChildren;
		
		// query children
		try {
			// attempt API call
			log.vdebug("Attempting Query: thisLevelChildren = queryChildrenOneDriveApiInstance.listChildren(driveId, idToQuery, nextLink)");
			thisLevelChildren = queryChildrenOneDriveApiInstance.listChildren(driveId, idToQuery, nextLink);
			log.vdebug("Query 'thisLevelChildren = queryChildrenOneDriveApiInstance.listChildren(driveId, idToQuery, nextLink)' performed successfully");
		} catch (OneDriveException exception) {
			// OneDrive threw an error
			log.vdebug("------------------------------------------------------------------");
			log.vdebug("Query Error: thisLevelChildren = queryChildrenOneDriveApiInstance.listChildren(driveId, idToQuery, nextLink)");
			log.vdebug("driveId: ", driveId);
			log.vdebug("idToQuery: ", idToQuery);
			log.vdebug("nextLink: ", nextLink);
			
			string thisFunctionName = getFunctionName!({});
			// HTTP request returned status code 408,429,503,504
			if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 429) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
				// Handle the 429
				if (exception.httpStatusCode == 429) {
					// HTTP request returned status code 429 (Too Many Requests). We need to leverage the response Retry-After HTTP header to ensure minimum delay until the throttle is removed.
					handleOneDriveThrottleRequest(queryChildrenOneDriveApiInstance);
					log.vdebug("Retrying original request that generated the OneDrive HTTP 429 Response Code (Too Many Requests) - attempting to retry ", thisFunctionName);
				}
				// re-try the specific changes queries
				if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
					// 408 - Request Time Out
					// 503 - Service Unavailable
					// 504 - Gateway Timeout
					// Transient error - try again in 30 seconds
					auto errorArray = splitLines(exception.msg);
					log.log(errorArray[0], " when attempting to query OneDrive drive item children - retrying applicable request in 30 seconds");
					log.vdebug("thisLevelChildren = queryChildrenOneDriveApiInstance.listChildren(driveId, idToQuery, nextLink) previously threw an error - retrying");
					// The server, while acting as a proxy, did not receive a timely response from the upstream server it needed to access in attempting to complete the request. 
					log.vdebug("Thread sleeping for 30 seconds as the server did not receive a timely response from the upstream server it needed to access in attempting to complete the request");
					Thread.sleep(dur!"seconds"(30));
				}
				// re-try original request - retried for 429, 503, 504 - but loop back calling this function 
				log.vdebug("Retrying Function: ", thisFunctionName);
				queryThisLevelChildren(driveId, idToQuery, nextLink, queryChildrenOneDriveApiInstance);
				
			} else {
				// Default operation if not 408,429,503,504 errors
				// display what the error is
				displayOneDriveErrorMessage(exception.msg, thisFunctionName);
			}
		}
				
		// return response
		return thisLevelChildren;
	}
	
	// Traverses the provided path online, via the OneDrive API, following correct parent driveId and itemId elements across the account
	// to find if this full path exists. If this path exists online, the last item in the object path will be returned as a full JSON item.
	//
	// If the createPathIfMissing = false + no path exists online, a null invalid JSON item will be returned.
	// If the createPathIfMissing = true + no path exists online, the requested path will be created in the correct location online. The resulting
	// response to the directory creation will then be returned.
	//
	// This function also ensures that each path in the requested path actually matches the requested element to ensure that the OneDrive API response
	// is not falsely matching a 'case insensitive' match to the actual request which is a POSIX compliance issue.
	JSONValue queryOneDriveForSpecificPathAndCreateIfMissing(string thisNewPathToSearch, bool createPathIfMissing) {
		
		// function variables
		JSONValue getPathDetailsAPIResponse;
		string currentPathTree;
		Item parentDetails;
		JSONValue topLevelChildren;
		string nextLink;
		bool directoryFoundOnline = false;
		bool posixIssue = false;
		
		// Create a new API Instance for this thread and initialise it
		OneDriveApi queryOneDriveForSpecificPath;
		queryOneDriveForSpecificPath = new OneDriveApi(appConfig);
		queryOneDriveForSpecificPath.initialise();
		
		foreach (thisFolderName; pathSplitter(thisNewPathToSearch)) {
			log.vdebug("Testing for the existance online of this folder path: ", thisFolderName);
			directoryFoundOnline = false;
			
			// If this is '.' this is the account root
			if (thisFolderName == ".") {
				currentPathTree = thisFolderName;
			} else {
				currentPathTree = currentPathTree ~ "/" ~ thisFolderName;
			}
			
			log.vdebug("Attempting to query OneDrive for this path: ", currentPathTree);
			
			// What query do we use?
			if (thisFolderName == ".") {
				// Query the root, set the right details
				try {
					getPathDetailsAPIResponse = queryOneDriveForSpecificPath.getPathDetails(currentPathTree);
					parentDetails = makeItem(getPathDetailsAPIResponse);
					// Save item to the database
					saveItem(getPathDetailsAPIResponse);
					directoryFoundOnline = true;
				} catch (OneDriveException exception) {
				
					string thisFunctionName = getFunctionName!({});
					// HTTP request returned status code 408,429,503,504
					if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 429) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
						// Handle the 429
						if (exception.httpStatusCode == 429) {
							// HTTP request returned status code 429 (Too Many Requests). We need to leverage the response Retry-After HTTP header to ensure minimum delay until the throttle is removed.
							handleOneDriveThrottleRequest(queryOneDriveForSpecificPath);
							log.vdebug("Retrying original request that generated the OneDrive HTTP 429 Response Code (Too Many Requests) - attempting to retry ", thisFunctionName);
						}
						// re-try the specific changes queries
						if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
							// 408 - Request Time Out
							// 503 - Service Unavailable
							// 504 - Gateway Timeout
							// Transient error - try again in 30 seconds
							auto errorArray = splitLines(exception.msg);
							log.log(errorArray[0], " when attempting to query path on OneDrive - retrying applicable request in 30 seconds");
							log.vdebug(thisFunctionName, " previously threw an error - retrying");
							// The server, while acting as a proxy, did not receive a timely response from the upstream server it needed to access in attempting to complete the request. 
							log.vdebug("Thread sleeping for 30 seconds as the server did not receive a timely response from the upstream server it needed to access in attempting to complete the request");
							Thread.sleep(dur!"seconds"(30));
						}
						// re-try original request - retried for 429, 503, 504 - but loop back calling this function 
						log.vdebug("Retrying Function: ", thisFunctionName);
						queryOneDriveForSpecificPathAndCreateIfMissing(thisNewPathToSearch, createPathIfMissing);	
					} else {
						// Default operation if not 408,429,503,504 errors
						// display what the error is
						displayOneDriveErrorMessage(exception.msg, thisFunctionName);
					}	
				}
			} else {
				// Ensure we have a valid driveId to search here
				if (parentDetails.driveId.empty) {
					parentDetails.driveId = appConfig.defaultDriveId;
				}
				
				// If the prior JSON 'getPathDetailsAPIResponse' is on this account driveId .. then continue to use getPathDetails
				if (parentDetails.driveId == appConfig.defaultDriveId) {
				
					try {
						// Query OneDrive API for this path
						getPathDetailsAPIResponse = queryOneDriveForSpecificPath.getPathDetails(currentPathTree);
						// Portable Operating System Interface (POSIX) testing of JSON response from OneDrive API
						performPosixTest(thisFolderName, getPathDetailsAPIResponse["name"].str);
						// No POSIX issue with requested path element
						parentDetails = makeItem(getPathDetailsAPIResponse);
						// Save item to the database
						saveItem(getPathDetailsAPIResponse);
						directoryFoundOnline = true;
						
						// Is this JSON a remote object
						if (isItemRemote(getPathDetailsAPIResponse)) {
							// Remote Directory .. need a DB Tie Item
							log.vdebug("Creating a DB TIE for this Shared Folder");
							// New DB Tie Item to bind the 'remote' path to our parent path
							Item tieDBItem;
							// Set the name
							tieDBItem.name = parentDetails.name;
							// Set the correct item type
							tieDBItem.type = ItemType.dir;
							// Set the right elements using the 'remote' of the parent as the 'actual' for this DB Tie
							tieDBItem.driveId = parentDetails.remoteDriveId;
							tieDBItem.id = parentDetails.remoteId;
							// Set the correct mtime
							tieDBItem.mtime = parentDetails.mtime;
							// Add tie DB record to the local database
							log.vdebug("Adding tie DB record to database: ", tieDBItem);
							itemDB.upsert(tieDBItem);
							// Update parentDetails to use the DB Tie record
							parentDetails = tieDBItem;
						}
						
					} catch (OneDriveException exception) {
						if (exception.httpStatusCode == 404) {
							directoryFoundOnline = false;
						} else {
						
							string thisFunctionName = getFunctionName!({});
							// HTTP request returned status code 408,429,503,504
							if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 429) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
								// Handle the 429
								if (exception.httpStatusCode == 429) {
									// HTTP request returned status code 429 (Too Many Requests). We need to leverage the response Retry-After HTTP header to ensure minimum delay until the throttle is removed.
									handleOneDriveThrottleRequest(queryOneDriveForSpecificPath);
									log.vdebug("Retrying original request that generated the OneDrive HTTP 429 Response Code (Too Many Requests) - attempting to retry ", thisFunctionName);
								}
								// re-try the specific changes queries
								if ((exception.httpStatusCode == 408) || (exception.httpStatusCode == 503) || (exception.httpStatusCode == 504)) {
									// 408 - Request Time Out
									// 503 - Service Unavailable
									// 504 - Gateway Timeout
									// Transient error - try again in 30 seconds
									auto errorArray = splitLines(exception.msg);
									log.log(errorArray[0], " when attempting to query path on OneDrive - retrying applicable request in 30 seconds");
									log.vdebug(thisFunctionName, " previously threw an error - retrying");
									// The server, while acting as a proxy, did not receive a timely response from the upstream server it needed to access in attempting to complete the request. 
									log.vdebug("Thread sleeping for 30 seconds as the server did not receive a timely response from the upstream server it needed to access in attempting to complete the request");
									Thread.sleep(dur!"seconds"(30));
								}
								// re-try original request - retried for 429, 503, 504 - but loop back calling this function 
								log.vdebug("Retrying Function: ", thisFunctionName);
								queryOneDriveForSpecificPathAndCreateIfMissing(thisNewPathToSearch, createPathIfMissing);
							} else {
								// Default operation if not 408,429,503,504 errors
								// display what the error is
								displayOneDriveErrorMessage(exception.msg, thisFunctionName);
							}
						}
					}
				} else {
					// parentDetails.driveId is not the account drive id - thus will be a remote shared item
					log.vdebug("This parent directory is a remote object this next path will be on a remote drive");
					// For this parentDetails.driveId, parentDetails.id object, query the OneDrive API for it's children
					for (;;) {
						// Query this remote object for its children
						topLevelChildren = queryOneDriveForSpecificPath.listChildren(parentDetails.driveId, parentDetails.id, nextLink);
						// Process each child
						foreach (child; topLevelChildren["value"].array) {
							// Is this child a folder?
							if (isItemFolder(child)) {
								// Is this the child folder we are looking for, and is a POSIX match?
								if (child["name"].str == thisFolderName) {
									// EXACT MATCH including case sensitivity: Flag that we found the folder online 
									directoryFoundOnline = true;
									// Use these details for the next entry path
									getPathDetailsAPIResponse = child;
									parentDetails = makeItem(getPathDetailsAPIResponse);
									// Save item to the database
									saveItem(getPathDetailsAPIResponse);
									// No need to continue searching
									break;
								} else {
									string childAsLower = toLower(child["name"].str);
									string thisFolderNameAsLower = toLower(thisFolderName);
									if (childAsLower == thisFolderNameAsLower) {	
										// This is a POSIX 'case in-sensitive match' ..... 
										// Local item name has a 'case-insensitive match' to an existing item on OneDrive
										posixIssue = true;
										throw new posixException(thisFolderName, child["name"].str);
									}
								}
							}
						}
						
						if (directoryFoundOnline) {
							// We found the folder, no need to continue searching nextLink data
							break;
						}
						
						// If a collection exceeds the default page size (200 items), the @odata.nextLink property is returned in the response 
						// to indicate more items are available and provide the request URL for the next page of items.
						if ("@odata.nextLink" in topLevelChildren) {
							// Update nextLink to next changeSet bundle
							log.vdebug("Setting nextLink to (@odata.nextLink): ", nextLink);
							nextLink = topLevelChildren["@odata.nextLink"].str;
						} else break;
					}
				}
			}
			
			// If we did not find the folder, we need to create this folder
			if (!directoryFoundOnline) {
				// Folder not found online
				// Set any response to be an invalid JSON item
				getPathDetailsAPIResponse = null;
				// Was there a POSIX issue?
				if (!posixIssue) {
					// No POSIX issue
					if (createPathIfMissing) {
						// Create this path as it is missing on OneDrive online and there is no POSIX issue with a 'case-insensitive match'
						log.vdebug("FOLDER NOT FOUND ONLINE AND WE ARE REQUESTED TO CREATE IT");
						log.vdebug("Create folder on this drive:             ", parentDetails.driveId);
						log.vdebug("Create folder as a child on this object: ", parentDetails.id);
						log.vdebug("Create this folder name:                 ", thisFolderName);
						
						JSONValue newDriveItem = [
								"name": JSONValue(thisFolderName),
								"folder": parseJSON("{}")
						];
					
						JSONValue createByIdAPIResponse;
						// Submit the creation request
						// Fix for https://github.com/skilion/onedrive/issues/356
						if (!dryRun) {
							try {
								// Attempt to create a new folder on the configured parent driveId & parent id
								createByIdAPIResponse = queryOneDriveForSpecificPath.createById(parentDetails.driveId, parentDetails.id, newDriveItem);
								// Is the response a valid JSON object - validation checking done in saveItem
								saveItem(createByIdAPIResponse);
								// Set getPathDetailsAPIResponse to createByIdAPIResponse
								getPathDetailsAPIResponse = createByIdAPIResponse;
							} catch (OneDriveException e) {
								// 409 - API Race Condition
								if (e.httpStatusCode == 409) {
									// When we attempted to create it, OneDrive responded that it now already exists
									log.vlog("OneDrive reported that ", thisFolderName, " already exists .. OneDrive API race condition");
								} else {
									// some other error from OneDrive was returned - display what it is
									log.error("OneDrive generated an error when creating this path: ", thisFolderName);
									displayOneDriveErrorMessage(e.msg, getFunctionName!({}));
								}
							}
						} else {
							// Simulate a successful 'directory create' & save it to the dryRun database copy
							// The simulated response has to pass 'makeItem' as part of saveItem
							auto fakeResponse = createFakeResponse(thisNewPathToSearch);
							// Save item to the database
							saveItem(fakeResponse);
						}
					}
				}
			}
		}
		
		// Shutdown API instance
		queryOneDriveForSpecificPath.shutdown();
		// Free object and memory
		object.destroy(queryOneDriveForSpecificPath);
		
		// Output our search results
		log.vdebug("queryOneDriveForSpecificPathAndCreateIfMissing.getPathDetailsAPIResponse = ", getPathDetailsAPIResponse);
		return getPathDetailsAPIResponse;
	}
	
	// Delete an item by it's path
	// This function is only used in --monitor mode and --remove-directory directive
	void deleteByPath(string path) {
		
		// function variables
		Item dbItem;
		
		// Need to check all driveid's we know about, not just the defaultDriveId
		bool itemInDB = false;
		foreach (searchDriveId; driveIDsArray) {
			if (itemDB.selectByPath(path, searchDriveId, dbItem)) {
				// item was found in the DB
				itemInDB = true;
				break;
			}
		}
		
		// Was the item found in the database?
		if (!itemInDB) {
			// path to delete is not in the local database ..
			// was this a --remove-directory attempt?
			if (!appConfig.getValueBool("monitor")) {
				// --remove-directory deletion attempt
				log.error("The item to delete is not in the local database - unable to delete online");
				return;
			} else {
				// normal use .. --monitor being used
				throw new SyncException("The item to delete is not in the local database");
			}
		}
		
		// This needs to be enforced as we have to know the parent id of the object being deleted
		if (dbItem.parentId == null) {
			// the item is a remote folder, need to do the operation on the parent
			enforce(itemDB.selectByPathWithoutRemote(path, appConfig.defaultDriveId, dbItem));
		}
		
		try {
			if (noRemoteDelete) {
				// do not process remote delete
				log.vlog("Skipping remote delete as --upload-only & --no-remote-delete configured");
			} else {
				uploadDeletedItem(dbItem, path);
			}
		} catch (OneDriveException e) {
			if (e.httpStatusCode == 404) {
				log.log(e.msg);
			} else {
				// display what the error is
				displayOneDriveErrorMessage(e.msg, getFunctionName!({}));
			}
		}
	}
	
	// https://docs.microsoft.com/en-us/onedrive/developer/rest-api/api/driveitem_move
	// This function is only called in monitor mode when an move event is coming from
	// inotify and we try to move the item.
	void uploadMoveItem(string oldPath, string newPath) {
		// Log that we are doing a move
		log.log("Moving ", oldPath, " to ", newPath);
		// Is this move unwanted?
		bool unwanted = false;
		// Item variables
		Item oldItem, newItem, parentItem;
		
		// This not a Client Side Filtering check, nor a Microsoft Check, but is a sanity check that the path provided is UTF encoded correctly
		// Check the std.encoding of the path against: Unicode 5.0, ASCII, ISO-8859-1, ISO-8859-2, WINDOWS-1250, WINDOWS-1251, WINDOWS-1252
		if (!unwanted) {
			if(!isValid(newPath)) {
				// Path is not valid according to https://dlang.org/phobos/std_encoding.html
				log.logAndNotify("Skipping item - invalid character encoding sequence: ", newPath);
				unwanted = true;
			}
		}
		
		// Check this path against the Client Side Filtering Rules
		// - check_nosync
		// - skip_dotfiles
		// - skip_symlinks
		// - skip_file
		// - skip_dir
		// - sync_list
		// - skip_size
		if (!unwanted) {
			unwanted = checkPathAgainstClientSideFiltering(newPath);
		}
		
		// Check against Microsoft OneDrive restriction and limitations about Windows naming files
		if (!unwanted) {
			unwanted = checkPathAgainstMicrosoftNamingRestrictions(newPath);
		}
		
		// 'newPath' has passed client side filtering validation
		if (!unwanted) {
		
			if (!itemDB.selectByPath(oldPath, appConfig.defaultDriveId, oldItem)) {
				// The old path|item is not synced with the database, upload as a new file
				log.log("Moved local item was not in-sync with local databse - uploading as new item");
				uploadNewFile(newPath);
				return;
			}
		
			if (oldItem.parentId == null) {
				// the item is a remote folder, need to do the operation on the parent
				enforce(itemDB.selectByPathWithoutRemote(oldPath, appConfig.defaultDriveId, oldItem));
			}
		
			if (itemDB.selectByPath(newPath, appConfig.defaultDriveId, newItem)) {
				// the destination has been overwritten
				log.log("Moved local item overwrote an existing item - deleting old online item");
				uploadDeletedItem(newItem, newPath);
			}
			
			if (!itemDB.selectByPath(dirName(newPath), appConfig.defaultDriveId, parentItem)) {
				// the parent item is not in the database
				throw new SyncException("Can't move an item to an unsynced directory");
			}
		
			if (oldItem.driveId != parentItem.driveId) {
				// items cannot be moved between drives
				uploadDeletedItem(oldItem, oldPath);
				
				// what sort of move is this?
				if (isFile(newPath)) {
					// newPath is a file
					uploadNewFile(newPath);
				} else {
					// newPath is a directory
					scanLocalFilesystemPathForNewData(newPath);
				}
			} else {
				if (!exists(newPath)) {
					// is this --monitor use?
					if (appConfig.getValueBool("monitor")) {
						log.vlog("uploadMoveItem target has disappeared: ", newPath);
						return;
					}
				}
			
				// Configure the modification JSON item
				SysTime mtime;
				if (appConfig.getValueBool("monitor")) {
					// Use the newPath modified timestamp
					mtime = timeLastModified(newPath).toUTC();
				} else {
					// Use the current system time
					mtime = Clock.currTime().toUTC();
				}
								
				JSONValue data = [
					"name": JSONValue(baseName(newPath)),
					"parentReference": JSONValue([
						"id": parentItem.id
					]),
					"fileSystemInfo": JSONValue([
						"lastModifiedDateTime": mtime.toISOExtString()
					])
				];
				
				// Perform the move operation on OneDrive
				JSONValue response;
				
				// Create a new API Instance for this thread and initialise it
				OneDriveApi movePathOnlineApiInstance;
				movePathOnlineApiInstance = new OneDriveApi(appConfig);
				movePathOnlineApiInstance.initialise();
				
				try {
					response = movePathOnlineApiInstance.updateById(oldItem.driveId, oldItem.id, data, oldItem.eTag);
				} catch (OneDriveException e) {
					if (e.httpStatusCode == 412) {
						// OneDrive threw a 412 error, most likely: ETag does not match current item's value
						// Retry without eTag
						log.vdebug("File Move Failed - OneDrive eTag / cTag match issue");
						log.vlog("OneDrive returned a 'HTTP 412 - Precondition Failed' when attempting to move the file - gracefully handling error");
						string nullTag = null;
						// move the file but without the eTag
						response = movePathOnlineApiInstance.updateById(oldItem.driveId, oldItem.id, data, nullTag);
					}
				} 
				// Shutdown API instance
				movePathOnlineApiInstance.shutdown();
				// Free object and memory
				object.destroy(movePathOnlineApiInstance);
				
				// save the move response from OneDrive in the database
				// Is the response a valid JSON object - validation checking done in saveItem
				saveItem(response);
			}
		} else {
			// Moved item is unwanted
			log.log("Item has been moved to a location that is excluded from sync operations. Removing item from OneDrive");
			uploadDeletedItem(oldItem, oldPath);
		}
	}
	
	// Perform integrity validation of the file that was uploaded
	bool performUploadIntegrityValidationChecks(JSONValue uploadResponse, string localFilePath, ulong localFileSize) {
	
		bool integrityValid = false;
	
		if (!disableUploadValidation) {
			// Integrity validation has not been disabled (this is the default so we are always integrity checking our uploads)
			if (uploadResponse.type() == JSONType.object) {
				// Provided JSON is a valid JSON	
				ulong uploadFileSize = uploadResponse["size"].integer;
				string uploadFileHash = uploadResponse["file"]["hashes"]["quickXorHash"].str;
				string localFileHash = computeQuickXorHash(localFilePath);
				
				if ((localFileSize == uploadFileSize) && (localFileHash == uploadFileHash)) {
					// Uploaded file integrity intact
					log.vdebug("Uploaded local file matches reported online size and hash values");
					integrityValid = true;
				} else {
					// Upload integrity failure .. what failed?
					// There are 2 scenarios where this happens:
					// 1. Failed Transfer
					// 2. Upload file is going to a SharePoint Site, where Microsoft enriches the file with additional metadata with no way to disable
					log.logAndNotify("WARNING: Uploaded file integrity failure for: ", localFilePath);
					
					// What integrity failed - size?
					if (localFileSize != uploadFileSize) {
						log.vlog("WARNING: Uploaded file integrity failure - Size Mismatch");
					}
					// What integrity failed - hash?
					if (localFileHash != uploadFileHash) {
						log.vlog("WARNING: Uploaded file integrity failure - Hash Mismatch");
					}
					
					// What account type is this?
					if (appConfig.accountType != "personal") {
						// Not a personal account, thus the integrity failure is most likely due to SharePoint
						log.vlog("CAUTION: Microsoft SharePoint enhances files after you upload them, which means this file may now have technical differences from your local copy, resulting in an integrity issue.");
						log.vlog("See: https://github.com/OneDrive/onedrive-api-docs/issues/935 for further details");
					}
					// How can this be disabled?
					log.log("To disable the integrity checking of uploaded files use --disable-upload-validation");
				}
			} else {
				log.log("Upload file validation unable to be performed: input JSON was invalid");
				log.log("WARNING: Skipping upload integrity check for: ", localFilePath);
			}
		} else {
			// We are bypassing integrity checks due to --disable-upload-validation
			log.vdebug("Upload file validation disabled due to --disable-upload-validation");
			log.vlog("WARNING: Skipping upload integrity check for: ", localFilePath);
		}
		
		// Is the file integrity online valid?
		return integrityValid;
	}
	
	// Query Office 365 SharePoint Shared Library site name to obtain it's Drive ID
	void querySiteCollectionForDriveID(string sharepointLibraryNameToQuery) {
		// Steps to get the ID:
		// 1. Query https://graph.microsoft.com/v1.0/sites?search= with the name entered
		// 2. Evaluate the response. A valid response will contain the description and the id. If the response comes back with nothing, the site name cannot be found or no access
		// 3. If valid, use the returned ID and query the site drives
		//		https://graph.microsoft.com/v1.0/sites/<site_id>/drives
		// 4. Display Shared Library Name & Drive ID
		
		string site_id;
		string drive_id;
		bool found = false;
		JSONValue siteQuery;
		string nextLink;
		string[] siteSearchResults;
		
		// Create a new API Instance for this thread and initialise it
		OneDriveApi querySharePointLibraryNameApiInstance;
		querySharePointLibraryNameApiInstance = new OneDriveApi(appConfig);
		querySharePointLibraryNameApiInstance.initialise();
		
		// The account type must not be a personal account type
		if (appConfig.accountType == "personal") {
			log.error("ERROR: A OneDrive Personal Account cannot be used with --get-sharepoint-drive-id. Please re-authenticate your client using a OneDrive Business Account.");
			return;
		}
		
		// What query are we performing?
		writeln();
		log.log("Office 365 Library Name Query: ", sharepointLibraryNameToQuery);
		
		for (;;) {
			try {
				siteQuery = querySharePointLibraryNameApiInstance.o365SiteSearch(nextLink);
			} catch (OneDriveException e) {
				log.error("ERROR: Query of OneDrive for Office 365 Library Name failed");
				// Forbidden - most likely authentication scope needs to be updated
				if (e.httpStatusCode == 403) {
					log.error("ERROR: Authentication scope needs to be updated. Use --reauth and re-authenticate client.");
					return;
				}
				// Requested resource cannot be found
				if (e.httpStatusCode == 404) {
					string siteSearchUrl;
					if (nextLink.empty) {
						siteSearchUrl = querySharePointLibraryNameApiInstance.getSiteSearchUrl();
					} else {
						siteSearchUrl = nextLink;
					}
					// log the error
					log.error("ERROR: Your OneDrive Account and Authentication Scope cannot access this OneDrive API: ", siteSearchUrl);
					log.error("ERROR: To resolve, please discuss this issue with whomever supports your OneDrive and SharePoint environment.");
					return;
				}
				// HTTP request returned status code 429 (Too Many Requests)
				if (e.httpStatusCode == 429) {
					// HTTP request returned status code 429 (Too Many Requests). We need to leverage the response Retry-After HTTP header to ensure minimum delay until the throttle is removed.
					handleOneDriveThrottleRequest(querySharePointLibraryNameApiInstance);
					log.vdebug("Retrying original request that generated the OneDrive HTTP 429 Response Code (Too Many Requests) - attempting to query OneDrive drive children");
				}
				// HTTP request returned status code 504 (Gateway Timeout) or 429 retry
				if ((e.httpStatusCode == 429) || (e.httpStatusCode == 504)) {
					// re-try the specific changes queries	
					if (e.httpStatusCode == 504) {
						log.log("OneDrive returned a 'HTTP 504 - Gateway Timeout' when attempting to query Sharepoint Sites - retrying applicable request");
						log.vdebug("siteQuery = onedrive.o365SiteSearch(nextLink) previously threw an error - retrying");
						// The server, while acting as a proxy, did not receive a timely response from the upstream server it needed to access in attempting to complete the request. 
						log.vdebug("Thread sleeping for 30 seconds as the server did not receive a timely response from the upstream server it needed to access in attempting to complete the request");
						Thread.sleep(dur!"seconds"(30));
					}
					// re-try original request - retried for 429 and 504
					try {
						log.vdebug("Retrying Query: siteQuery = onedrive.o365SiteSearch(nextLink)");
						siteQuery = querySharePointLibraryNameApiInstance.o365SiteSearch(nextLink);
						log.vdebug("Query 'siteQuery = onedrive.o365SiteSearch(nextLink)' performed successfully on re-try");
					} catch (OneDriveException e) {
						// display what the error is
						log.vdebug("Query Error: siteQuery = onedrive.o365SiteSearch(nextLink) on re-try after delay");
						// error was not a 504 this time
						displayOneDriveErrorMessage(e.msg, getFunctionName!({}));
						return;
					}
				} else {
					// display what the error is
					displayOneDriveErrorMessage(e.msg, getFunctionName!({}));
					return;
				}
			}
			
			// is siteQuery a valid JSON object & contain data we can use?
			if ((siteQuery.type() == JSONType.object) && ("value" in siteQuery)) {
				// valid JSON object
				log.vdebug("O365 Query Response: ", siteQuery);
				
				foreach (searchResult; siteQuery["value"].array) {
					// Need an 'exclusive' match here with sharepointLibraryNameToQuery as entered
					log.vdebug("Found O365 Site: ", searchResult);
					
					// 'displayName' and 'id' have to be present in the search result record in order to query the site
					if (("displayName" in searchResult) && ("id" in searchResult)) {
						if (sharepointLibraryNameToQuery == searchResult["displayName"].str){
							// 'displayName' matches search request
							site_id = searchResult["id"].str;
							JSONValue siteDriveQuery;
							
							try {
								siteDriveQuery = querySharePointLibraryNameApiInstance.o365SiteDrives(site_id);
							} catch (OneDriveException e) {
								log.error("ERROR: Query of OneDrive for Office Site ID failed");
								// display what the error is
								displayOneDriveErrorMessage(e.msg, getFunctionName!({}));
								return;
							}
							
							// is siteDriveQuery a valid JSON object & contain data we can use?
							if ((siteDriveQuery.type() == JSONType.object) && ("value" in siteDriveQuery)) {
								// valid JSON object
								foreach (driveResult; siteDriveQuery["value"].array) {
									// Display results
									writeln("-----------------------------------------------");
									log.vdebug("Site Details: ", driveResult);
									found = true;
									writeln("Site Name:    ", searchResult["displayName"].str);
									writeln("Library Name: ", driveResult["name"].str);
									writeln("drive_id:     ", driveResult["id"].str);
									writeln("Library URL:  ", driveResult["webUrl"].str);
								}
								// closeout
								writeln("-----------------------------------------------");
							} else {
								// not a valid JSON object
								log.error("ERROR: There was an error performing this operation on OneDrive");
								log.error("ERROR: Increase logging verbosity to assist determining why.");
								return;
							}
						}
					} else {
						// 'displayName', 'id' or ''webUrl' not present in JSON results for a specific site
						string siteNameAvailable = "Site 'name' was restricted by OneDrive API permissions";
						bool displayNameAvailable = false;
						bool idAvailable = false;
						if ("name" in searchResult) siteNameAvailable = searchResult["name"].str;
						if ("displayName" in searchResult) displayNameAvailable = true;
						if ("id" in searchResult) idAvailable = true;
						
						// Display error details for this site data
						writeln();
						log.error("ERROR: SharePoint Site details not provided for: ", siteNameAvailable);
						log.error("ERROR: The SharePoint Site results returned from OneDrive API do not contain the required items to match. Please check your permissions with your site administrator.");
						log.error("ERROR: Your site security settings is preventing the following details from being accessed: 'displayName' or 'id'");
						log.vlog(" - Is 'displayName' available = ", displayNameAvailable);
						log.vlog(" - Is 'id' available          = ", idAvailable);
						log.error("ERROR: To debug this further, please increase verbosity (--verbose or --verbose --verbose) to provide further insight as to what details are actually being returned.");
					}
				}
				
				if(!found) {
					// The SharePoint site we are searching for was not found in this bundle set
					// Add to siteSearchResults so we can display what we did find
					string siteSearchResultsEntry;
					foreach (searchResult; siteQuery["value"].array) {
						// We can only add the displayName if it is available
						if ("displayName" in searchResult) {
							// Use the displayName
							siteSearchResultsEntry = " * " ~ searchResult["displayName"].str;
							siteSearchResults ~= siteSearchResultsEntry;
						} else {
							// Add, but indicate displayName unavailable, use id
							if ("id" in searchResult) {
								siteSearchResultsEntry = " * " ~ "Unknown displayName (Data not provided by API), Site ID: " ~ searchResult["id"].str;
								siteSearchResults ~= siteSearchResultsEntry;
							} else {
								// displayName and id unavailable, display in debug log the entry
								log.vdebug("Bad SharePoint Data for site: ", searchResult);
							}
						}
					}
				}
			} else {
				// not a valid JSON object
				log.error("ERROR: There was an error performing this operation on OneDrive");
				log.error("ERROR: Increase logging verbosity to assist determining why.");
				return;
			}
			
			// If a collection exceeds the default page size (200 items), the @odata.nextLink property is returned in the response 
			// to indicate more items are available and provide the request URL for the next page of items.
			if ("@odata.nextLink" in siteQuery) {
				// Update nextLink to next set of SharePoint library names
				nextLink = siteQuery["@odata.nextLink"].str;
				log.vdebug("Setting nextLink to (@odata.nextLink): ", nextLink);
			} else break;
		}
		
		// Was the intended target found?
		if(!found) {
			
			// Was the search a wildcard?
			if (sharepointLibraryNameToQuery != "*") {
				// Only print this out if the search was not a wildcard
				writeln();
				log.error("ERROR: The requested SharePoint site could not be found. Please check it's name and your permissions to access the site.");
			}
			// List all sites returned to assist user
			writeln();
			log.log("The following SharePoint site names were returned:");
			foreach (searchResultEntry; siteSearchResults) {
				// list the display name that we use to match against the user query
				log.log(searchResultEntry);
			}
		}
		
		// Shutdown API instance
		querySharePointLibraryNameApiInstance.shutdown();
		// Free object and memory
		object.destroy(querySharePointLibraryNameApiInstance);
	}
	
	// Query the sync status of the client and the local system
	void queryOneDriveForSyncStatus(string pathToQueryStatusOn) {
	
		// Query the account driveId and rootId to get the /delta JSON information
		// Process that JSON data for relevancy
		
		// Function variables
		ulong downloadSize = 0;
		string deltaLink = null;
		string driveIdToQuery = appConfig.defaultDriveId;
		string itemIdToQuery = appConfig.defaultRootId;
		JSONValue deltaChanges;
		
		// Array of JSON items
		JSONValue[] jsonItemsArray;
		
		// Query Database for a potential deltaLink starting point
		deltaLink = itemDB.getDeltaLink(driveIdToQuery, itemIdToQuery);
		
		write("Querying the change status of Drive ID: ", driveIdToQuery, " .");
		// Query the OenDrive API using the applicable details, following nextLink if applicable
		
		// Create a new API Instance for querying /delta and initialise it
		OneDriveApi getDeltaQueryOneDriveApiInstance;
		getDeltaQueryOneDriveApiInstance = new OneDriveApi(appConfig);
		getDeltaQueryOneDriveApiInstance.initialise();
		
		for (;;) {
			// Add a processing '.'
			write(".");
		
			// Get the /delta changes via the OneDrive API
			// getDeltaChangesByItemId has the re-try logic for transient errors
			deltaChanges = getDeltaChangesByItemId(driveIdToQuery, itemIdToQuery, deltaLink, getDeltaQueryOneDriveApiInstance);
			
			// If the initial deltaChanges response is an invalid JSON object, keep trying ..
			if (deltaChanges.type() != JSONType.object) {
				while (deltaChanges.type() != JSONType.object) {
					// Handle the invalid JSON response adn retry
					log.vdebug("ERROR: Query of the OneDrive API via deltaChanges = getDeltaChangesByItemId() returned an invalid JSON response");
					deltaChanges = getDeltaChangesByItemId(driveIdToQuery, itemIdToQuery, deltaLink, getDeltaQueryOneDriveApiInstance);
				}
			}
			
			// We have a valid deltaChanges JSON array. This means we have at least 200+ JSON items to process.
			// The API response however cannot be run in parallel as the OneDrive API sends the JSON items in the order in which they must be processed
			foreach (onedriveJSONItem; deltaChanges["value"].array) {
				// is the JSON a root object - we dont want to count this
				if (!isItemRoot(onedriveJSONItem)) {
					// Files are the only item that we want to calculate
					if (isItemFile(onedriveJSONItem)) {
						// JSON item is a file
						// Is the item filtered out due to client side filtering rules?
						if (!checkJSONAgainstClientSideFiltering(onedriveJSONItem)) {
							// Is the path of this JSON item 'in-scope' or 'out-of-scope' ?
							if (pathToQueryStatusOn != "/") {
								// We need to check the path of this item against pathToQueryStatusOn
								string thisItemPath = "";
								if (("path" in onedriveJSONItem["parentReference"]) != null) {
									// If there is a parent reference path, try and use it
									string selfBuiltPath = onedriveJSONItem["parentReference"]["path"].str ~ "/" ~ onedriveJSONItem["name"].str;
									
									// Check for ':' and split if present
									auto splitIndex = selfBuiltPath.indexOf(":");
									if (splitIndex != -1) {
										// Keep only the part after ':'
										selfBuiltPath = selfBuiltPath[splitIndex + 1 .. $];
									}
									
									// Check for HTML entities (e.g., '%20' for space) in source JSON
									if (selfBuiltPath.canFind("%")) {
										log.error("CAUTION:    Microsoft OneDrive API sent a JSON element containing HTML entities. This will cause issues performing pattern matching and potentially cause this path not to sync.");
										log.error("WORKAROUND: A possible workaround is to rename this item online: " ~ selfBuiltPath);
										log.error("See: https://github.com/OneDrive/onedrive-api-docs/issues/1765 for further details");
									}
									
									// Set thisItemPath to the self built path
									thisItemPath = selfBuiltPath;
								} else {
									// no parent reference path available
									thisItemPath = onedriveJSONItem["name"].str;
								}
								// can we find 'pathToQueryStatusOn' in 'thisItemPath' ?
								if (canFind(thisItemPath, pathToQueryStatusOn)) {
									// Add this to the array for processing
									jsonItemsArray ~= onedriveJSONItem;
								}
							} else {
								// We are not doing a --single-directory check
								// Add this to the array for processing
								jsonItemsArray ~= onedriveJSONItem;
							}
						}
					}
				}
			}
			
			// The response may contain either @odata.deltaLink or @odata.nextLink
			if ("@odata.deltaLink" in deltaChanges) {
				deltaLink = deltaChanges["@odata.deltaLink"].str;
				log.vdebug("Setting next deltaLink to (@odata.deltaLink): ", deltaLink);
			}
			
			// Update deltaLink to next changeSet bundle
			if ("@odata.nextLink" in deltaChanges) {	
				deltaLink = deltaChanges["@odata.nextLink"].str;
				log.vdebug("Setting next deltaLink to (@odata.nextLink): ", deltaLink);
			}
			else break;
		}
		// Needed after printing out '....' when fetching changes from OneDrive API
		writeln();
		
		// Are there any JSON items to process?
		if (count(jsonItemsArray) != 0) {
			// There are items to process
			foreach (onedriveJSONItem; jsonItemsArray.array) {
			
				// variables we need
				string thisItemParentDriveId;
				string thisItemId;
				string thisItemHash;
				bool existingDBEntry = false;
				
				// Is this file a remote item (on a shared folder) ?
				if (isItemRemote(onedriveJSONItem)) {
					// remote drive item
					thisItemParentDriveId = onedriveJSONItem["remoteItem"]["parentReference"]["driveId"].str;
					thisItemId = onedriveJSONItem["id"].str;
				} else {
					// standard drive item
					thisItemParentDriveId = onedriveJSONItem["parentReference"]["driveId"].str;
					thisItemId = onedriveJSONItem["id"].str;
				}
				
				// Get the file hash
				thisItemHash = onedriveJSONItem["file"]["hashes"]["quickXorHash"].str;
				
				// Check if the item has been seen before
				Item existingDatabaseItem;
				existingDBEntry = itemDB.selectById(thisItemParentDriveId, thisItemId, existingDatabaseItem);
				
				if (existingDBEntry) {
					// item exists in database .. do the database details match the JSON record?
					if (existingDatabaseItem.quickXorHash != thisItemHash) {
						// file hash is different, will trigger a download event
						downloadSize = downloadSize + onedriveJSONItem["size"].integer;
					} 
				} else {
					// item does not exist in the database
					// this item has already passed client side filtering rules (skip_dir, skip_file, sync_list)
					downloadSize = downloadSize + onedriveJSONItem["size"].integer;
				}
			}
		}
			
		// Was anything detected that would constitute a download?
		if (downloadSize > 0) {
			// we have something to download
			if (pathToQueryStatusOn != "/") {
				writeln("The selected local directory via --single-directory is out of sync with Microsoft OneDrive");
			} else {
				writeln("The configured local 'sync_dir' directory is out of sync with Microsoft OneDrive");
			}
			writeln("Approximate data to download from Microsoft OneDrive: ", (downloadSize/1024), " KB");
		} else {
			// No changes were returned
			writeln("There are no pending changes from Microsoft OneDrive; your local directory matches the data online.");
		}
	}
	
	// Query OneDrive for file details of a given path, returning either the 'webURL' or 'lastModifiedBy' JSON facet
	void queryOneDriveForFileDetails(string inputFilePath, string runtimePath, string outputType) {
	
		// Calculate the full local file path
		string fullLocalFilePath = buildNormalizedPath(buildPath(runtimePath, inputFilePath));
		
		// Query if file is valid locally
		if (exists(fullLocalFilePath)) {
			// search drive_id list
			string[] distinctDriveIds = itemDB.selectDistinctDriveIds();
			bool pathInDB = false;
			Item dbItem;
			
			foreach (searchDriveId; distinctDriveIds) {
				// Does this path exist in the database, use the 'inputFilePath'
				if (itemDB.selectByPath(inputFilePath, searchDriveId, dbItem)) {
					// item is in the database
					pathInDB = true;
					JSONValue fileDetailsFromOneDrive;
				
					// Create a new API Instance for this thread and initialise it
					OneDriveApi queryOneDriveForFileDetailsApiInstance;
					queryOneDriveForFileDetailsApiInstance = new OneDriveApi(appConfig);
					queryOneDriveForFileDetailsApiInstance.initialise();
					
					try {
						fileDetailsFromOneDrive = queryOneDriveForFileDetailsApiInstance.getPathDetailsById(dbItem.driveId, dbItem.id);
					} catch (OneDriveException exception) {
						// display what the error is
						displayOneDriveErrorMessage(exception.msg, getFunctionName!({}));
						return;
					}
					
					// Is the API response a valid JSON file?
					if (fileDetailsFromOneDrive.type() == JSONType.object) {
					
						// debug output of response
						log.vdebug("API Response: ", fileDetailsFromOneDrive);
						
						// What sort of response to we generate
						// --get-file-link response
						if (outputType == "URL") {
							if ((fileDetailsFromOneDrive.type() == JSONType.object) && ("webUrl" in fileDetailsFromOneDrive)) {
								// Valid JSON object
								writeln();
								writeln("WebURL: ", fileDetailsFromOneDrive["webUrl"].str);
							}
						}
						
						// --modified-by response
						if (outputType == "ModifiedBy") {
							if ((fileDetailsFromOneDrive.type() == JSONType.object) && ("lastModifiedBy" in fileDetailsFromOneDrive)) {
								// Valid JSON object
								writeln();
								writeln("Last modified:    ", fileDetailsFromOneDrive["lastModifiedDateTime"].str);
								writeln("Last modified by: ", fileDetailsFromOneDrive["lastModifiedBy"]["user"]["displayName"].str);
								// if 'email' provided, add this to the output
								if ("email" in fileDetailsFromOneDrive["lastModifiedBy"]["user"]) {
									writeln("Email Address:    ", fileDetailsFromOneDrive["lastModifiedBy"]["user"]["email"].str);
								}
							}
						}
						
						// --create-share-link response
						if (outputType == "ShareableLink") {
						
							JSONValue accessScope;
							JSONValue createShareableLinkResponse;
							string thisDriveId = fileDetailsFromOneDrive["parentReference"]["driveId"].str;
							string thisItemId = fileDetailsFromOneDrive["id"].str;
							string fileShareLink;
							bool writeablePermissions = appConfig.getValueBool("with_editing_perms");
							
							// What sort of shareable link is required?
							if (writeablePermissions) {
								// configure the read-write access scope
								accessScope = [
									"type": "edit",
									"scope": "anonymous"
								];
							} else {
								// configure the read-only access scope (default)
								accessScope = [
									"type": "view",
									"scope": "anonymous"
								];
							}
							
							// Try and create the shareable file link
							try {
								createShareableLinkResponse = queryOneDriveForFileDetailsApiInstance.createShareableLink(thisDriveId, thisItemId, accessScope);
							} catch (OneDriveException exception) {
								// display what the error is
								displayOneDriveErrorMessage(exception.msg, getFunctionName!({}));
								return;
							}
							
							// Is the API response a valid JSON file?
							if ((createShareableLinkResponse.type() == JSONType.object) && ("link" in createShareableLinkResponse)) {
								// Extract the file share link from the JSON response
								fileShareLink = createShareableLinkResponse["link"]["webUrl"].str;
								writeln("File Shareable Link: ", fileShareLink);
								if (writeablePermissions) {
									writeln("Shareable Link has read-write permissions - use and provide with caution"); 
								}
							}
						}
					}
					
					// Shutdown the API access
					queryOneDriveForFileDetailsApiInstance.shutdown();
					// Free object and memory
					object.destroy(queryOneDriveForFileDetailsApiInstance);
				}
			}
			
			// was path found?
			if (!pathInDB) {
				// File has not been synced with OneDrive
				log.error("Selected path has not been synced with OneDrive: ", inputFilePath);
			}
		} else {
			// File does not exist locally
			log.error("Selected path not found on local system: ", inputFilePath);
		}
	}
	
	// Query OneDrive for the quota details
	void queryOneDriveForQuotaDetails() {
		// This function is similar to getRemainingFreeSpace() but is different in data being analysed and output method
		JSONValue currentDriveQuota;
		string driveId;

		if (appConfig.getValueString("drive_id").length) {
			driveId = appConfig.getValueString("drive_id");
		} else {
			driveId = appConfig.defaultDriveId;
		}
		
		try {
			// Create a new OneDrive API instance
			OneDriveApi getCurrentDriveQuotaApiInstance;
			getCurrentDriveQuotaApiInstance = new OneDriveApi(appConfig);
			getCurrentDriveQuotaApiInstance.initialise();
			log.vdebug("Seeking available quota for this drive id: ", driveId);
			currentDriveQuota = getCurrentDriveQuotaApiInstance.getDriveQuota(driveId);
			// Shut this API instance down
			getCurrentDriveQuotaApiInstance.shutdown();
			// Free object and memory
			object.destroy(getCurrentDriveQuotaApiInstance);
		} catch (OneDriveException e) {
			log.vdebug("currentDriveQuota = onedrive.getDriveQuota(driveId) generated a OneDriveException");
		}
		
		// validate that currentDriveQuota is a JSON value
		if (currentDriveQuota.type() == JSONType.object) {
			// was 'quota' in response?
			if ("quota" in currentDriveQuota) {
		
				// debug output of response
				log.vdebug("currentDriveQuota: ", currentDriveQuota);
				
				// human readable output of response
				string deletedValue = "Not Provided";
				string remainingValue = "Not Provided";
				string stateValue = "Not Provided";
				string totalValue = "Not Provided";
				string usedValue = "Not Provided";
			
				// Update values
				if ("deleted" in currentDriveQuota["quota"]) {
					deletedValue = byteToGibiByte(currentDriveQuota["quota"]["deleted"].integer);
				}
				
				if ("remaining" in currentDriveQuota["quota"]) {
					remainingValue = byteToGibiByte(currentDriveQuota["quota"]["remaining"].integer);
				}
				
				if ("state" in currentDriveQuota["quota"]) {
					stateValue = currentDriveQuota["quota"]["state"].str;
				}
				
				if ("total" in currentDriveQuota["quota"]) {
					totalValue = byteToGibiByte(currentDriveQuota["quota"]["total"].integer);
				}
				
				if ("used" in currentDriveQuota["quota"]) {
					usedValue = byteToGibiByte(currentDriveQuota["quota"]["used"].integer);
				}
				
				writeln("Microsoft OneDrive quota information as reported for this Drive ID: ", driveId);
				writeln();
				writeln("Deleted:   ", deletedValue, " GB (", currentDriveQuota["quota"]["deleted"].integer, " bytes)");
				writeln("Remaining: ", remainingValue, " GB (", currentDriveQuota["quota"]["remaining"].integer, " bytes)");
				writeln("State:     ", stateValue);
				writeln("Total:     ", totalValue, " GB (", currentDriveQuota["quota"]["total"].integer, " bytes)");
				writeln("Used:      ", usedValue, " GB (", currentDriveQuota["quota"]["used"].integer, " bytes)");
				writeln();
			} else {
				writeln("Microsoft OneDrive quota information is being restricted for this Drive ID: ", driveId);
			}
	
		} 
	}
	
	// Query the system for session_upload.* files
	bool checkForInterruptedSessionUploads() {
	
		bool interruptedUploads = false;
		ulong interruptedUploadsCount;
		
		// Scan the filesystem for the files we are interested in, build up interruptedUploadsSessionFiles array
		foreach (sessionFile; dirEntries(appConfig.configDirName, "session_upload.*", SpanMode.shallow)) {
			// calculate the full path
			string tempPath = buildNormalizedPath(buildPath(appConfig.configDirName, sessionFile));
			// add to array
			interruptedUploadsSessionFiles ~= [tempPath];
		}
		
		// Count all 'session_upload' files in appConfig.configDirName
		//interruptedUploadsCount = count(dirEntries(appConfig.configDirName, "session_upload.*", SpanMode.shallow));
		interruptedUploadsCount = count(interruptedUploadsSessionFiles);
		if (interruptedUploadsCount != 0) {
			interruptedUploads = true;
		}
		
		// return if there are interrupted uploads to process
		return interruptedUploads;
	}
	
	// Process interrupted 'session_upload' files
	void processForInterruptedSessionUploads() {
		// For each upload_session file that has been found, process the data to ensure it is still valid
		foreach (sessionFilePath; interruptedUploadsSessionFiles) {
			if (!validateUploadSessionFileData(sessionFilePath)) {
				// Remove upload_session file as it is invalid
				// upload_session file file contains an error - cant resume this session
				log.vlog("Restore file upload session failed - cleaning up resumable session data file: ", sessionFilePath);
				if (exists(sessionFilePath)) {
					if (!dryRun) {
						remove(sessionFilePath);
					}
				}
			}
		}
		
		// At this point we should have an array of JSON items to resume uploading
		if (count(jsonItemsToResumeUpload) > 0) {
			// there are valid items to resume upload
		
			// Lets deal with all the JSON items that need to be reumed for upload in a batch process
			ulong batchSize = appConfig.concurrentThreads;
			ulong batchCount = (jsonItemsToResumeUpload.length + batchSize - 1) / batchSize;
			ulong batchesProcessed = 0;
			
			foreach (chunk; jsonItemsToResumeUpload.chunks(batchSize)) {
				// send an array containing 'appConfig.concurrentThreads' (16) JSON items to resume upload
				resumeSessionUploadsInParallel(chunk);
			}
		}
	}
	
	bool validateUploadSessionFileData(string sessionFilePath) {
		
		JSONValue sessionFileData;

		// Try and read the text from the session file as a JSON array
		try {
			sessionFileData = readText(sessionFilePath).parseJSON();
		} catch (JSONException e) {
			log.vdebug("SESSION-RESUME: Invalid JSON data in: ", sessionFilePath);
			return false;
		}
		
		// Does the file we wish to resume uploading exist locally still?
		if ("localPath" in sessionFileData) {
			string sessionLocalFilePath = sessionFileData["localPath"].str;
			log.vdebug("SESSION-RESUME: sessionLocalFilePath: ", sessionLocalFilePath);
		
			// Does the file exist?
			if (!exists(sessionLocalFilePath)) {
				log.vlog("The local file to upload does not exist locally anymore");
				return false;
			}
			
			// Can we read the file?
			if (!readLocalFile(sessionLocalFilePath)) {
				// filesystem error already returned if unable to read
				return false;
			}
			
		} else {
			log.vdebug("SESSION-RESUME: No localPath data in: ", sessionFilePath);
			return false;
		}
		
		// Check the session data for expirationDateTime
		if ("expirationDateTime" in sessionFileData) {
			auto expiration = SysTime.fromISOExtString(sessionFileData["expirationDateTime"].str);
			if (expiration < Clock.currTime()) {
				log.vlog("The upload session has expired for: ", sessionFilePath);
				return false;
			}
		} else {
			log.vdebug("SESSION-RESUME: No expirationDateTime data in: ", sessionFilePath);
			return false;
		}
		
		// Check the online upload status, using the uloadURL in sessionFileData
		if ("uploadUrl" in sessionFileData) {
			JSONValue response;
			
			// Create a new OneDrive API instance
			OneDriveApi validateUploadSessionFileDataApiInstance;
			validateUploadSessionFileDataApiInstance = new OneDriveApi(appConfig);
			validateUploadSessionFileDataApiInstance.initialise();
			
			try {
				response = validateUploadSessionFileDataApiInstance.requestUploadStatus(sessionFileData["uploadUrl"].str);
			} catch (OneDriveException e) {
				// handle any onedrive error response as invalid
				log.vdebug("SESSION-RESUME: Invalid response when using uploadUrl in: ", sessionFilePath);
				return false;
			}
			
			// Shutdown API instance
			validateUploadSessionFileDataApiInstance.shutdown();
			// Free object and memory
			object.destroy(validateUploadSessionFileDataApiInstance);
			
			// Do we have a valid response from OneDrive?
			if (response.type() == JSONType.object) {
				// Valid JSON object was returned
				if (("expirationDateTime" in response) && ("nextExpectedRanges" in response)) {
					// The 'uploadUrl' is valid, and the response contains elements we need
					sessionFileData["expirationDateTime"] = response["expirationDateTime"];
					sessionFileData["nextExpectedRanges"] = response["nextExpectedRanges"];
					
					if (sessionFileData["nextExpectedRanges"].array.length == 0) {
						log.vlog("The upload session was already completed");
						return false;
					}
				} else {
					log.vdebug("SESSION-RESUME: No expirationDateTime & nextExpectedRanges data in Microsoft OneDrive API response: ", response);
					return false;
				}
			} else {
				// not a JSON object
				log.vlog("Restore file upload session failed - invalid response from Microsoft OneDrive");
				return false;
			}
		} else {
			log.vdebug("SESSION-RESUME: No uploadUrl data in: ", sessionFilePath);
			return false;
		}
		
		// Add 'sessionFilePath' to 'sessionFileData' so that it can be used when we re-use the JSON data to resume the upload
		sessionFileData["sessionFilePath"] = sessionFilePath;
		
		// Add sessionFileData to jsonItemsToResumeUpload as it is now valid
		jsonItemsToResumeUpload ~= sessionFileData;
		return true;
	}
	
	void resumeSessionUploadsInParallel(JSONValue[] array) {
		// This function recieved an array of 16 JSON items to resume upload
		foreach (i, jsonItemToResume; taskPool.parallel(array)) {
			// Take each JSON item and resume upload using the JSON data
			
			JSONValue uploadResponse;
			OneDriveApi uploadFileOneDriveApiInstance;
			uploadFileOneDriveApiInstance = new OneDriveApi(appConfig);
			uploadFileOneDriveApiInstance.initialise();
			
			// Pull out data from this JSON element
			string threadUploadSessionFilePath = jsonItemToResume["sessionFilePath"].str;
			ulong thisFileSizeLocal = getSize(jsonItemToResume["localPath"].str);
			
			// Try to resume the session upload using the provided data
			try {
				uploadResponse = performSessionFileUpload(uploadFileOneDriveApiInstance, thisFileSizeLocal, jsonItemToResume, threadUploadSessionFilePath);
			} catch (OneDriveException exception) {
				writeln("CODING TO DO: Handle an exception when performing a resume session upload");	
			}
			
			// Was the response from the OneDrive API a valid JSON item?
			if (uploadResponse.type() == JSONType.object) {
				// A valid JSON object was returned - session resumption upload sucessful
				
				// Are we in an --upload-only & --remove-source-files scenario?
				// Use actual config values as we are doing an upload session recovery
				if (localDeleteAfterUpload) {
					// Log that we are deleting a local item
					log.log("Removing local file as --upload-only & --remove-source-files configured");
					// are we in a --dry-run scenario?
					if (!dryRun) {
						// No --dry-run ... process local file delete
						// Only perform the delete if we have a valid file path
						if (exists(jsonItemToResume["localPath"].str)) {
							// file exists
							log.vdebug("Removing local file: ", jsonItemToResume["localPath"].str);
							safeRemove(jsonItemToResume["localPath"].str);
						}
					}
					// as file is removed, we have nothing to add to the local database
					log.vdebug("Skipping adding to database as --upload-only & --remove-source-files configured");
				} else {
					// Save JSON item in database
					saveItem(uploadResponse);
				}
			} else {
				// No valid response was returned
				writeln("CODING TO DO: what to do when session upload resumption JSON data is not valid ... nothing ? error message ?");
			}
			
			// Shutdown API instance
			uploadFileOneDriveApiInstance.shutdown();
			// Free object and memory
			object.destroy(uploadFileOneDriveApiInstance);
		}
	}
}