import std.algorithm, std.conv, std.datetime, std.file, std.json;
import onedrive;
static import log;

private long fragmentSize = 10 * 2^^20; // 10 MiB

struct UploadSession
{
	private OneDriveApi onedrive;
	private bool verbose;
	// https://dev.onedrive.com/resources/uploadSession.htm
	private JSONValue session;
	// path where to save the session
	private string sessionFilePath;

	this(OneDriveApi onedrive, string sessionFilePath)
	{
		assert(onedrive);
		this.onedrive = onedrive;
		this.sessionFilePath = sessionFilePath;
		this.verbose = verbose;
	}

	JSONValue upload(string localPath, const(char)[] parentDriveId, const(char)[] parentId, const(char)[] filename, const(char)[] eTag = null)
	{
		session = onedrive.createUploadSession(parentDriveId, parentId, filename, eTag);
		session["localPath"] = localPath;
		save();
		return upload();
	}

	/* Restore the previous upload session.
	 * Returns true if the session is valid. Call upload() to resume it.
	 * Returns false if there is no session or the session is expired. */
	bool restore()
	{
		if (exists(sessionFilePath)) {
			log.vlog("Trying to restore the upload session ...");
			session = readText(sessionFilePath).parseJSON();
			auto expiration =  SysTime.fromISOExtString(session["expirationDateTime"].str);
			if (expiration < Clock.currTime()) {
				log.vlog("The upload session is expired");
				return false;
			}
			if (!exists(session["localPath"].str)) {
				log.vlog("The file does not exist anymore");
				return false;
			}
			// request the session status
			JSONValue response;
			try {
				response = onedrive.requestUploadStatus(session["uploadUrl"].str);
			} catch (OneDriveException e) {
				if (e.httpStatusCode == 400) {
					log.vlog("Upload session not found");
					return false;
				} else {
					throw e;
				}
			}
			session["expirationDateTime"] = response["expirationDateTime"];
			session["nextExpectedRanges"] = response["nextExpectedRanges"];
			if (session["nextExpectedRanges"].array.length == 0) {
				log.vlog("The upload session is completed");
				return false;
			}
			return true;
		}
		return false;
	}

	JSONValue upload()
	{
		long offset = session["nextExpectedRanges"][0].str.splitter('-').front.to!long;
		long fileSize = getSize(session["localPath"].str);
		JSONValue response;
		while (true) {
			long fragSize = fragmentSize < fileSize - offset ? fragmentSize : fileSize - offset;
			log.vlog("Uploading fragment: ", offset, "-", offset + fragSize, "/", fileSize);
			response = onedrive.uploadFragment(
				session["uploadUrl"].str,
				session["localPath"].str,
				offset,
				fragSize,
				fileSize
			);
			offset += fragmentSize;
			if (offset >= fileSize) break;
			// update the session
			session["expirationDateTime"] = response["expirationDateTime"];
			session["nextExpectedRanges"] = response["nextExpectedRanges"];
			save();
		}
		// upload complete
		remove(sessionFilePath);
		return response;
	}

	private void save()
	{
		std.file.write(sessionFilePath, session.toString());
	}
}