"use strict";

const INDEXEDDB_STORAGE_VERSION = 2;
const INDEXEDDB_STORAGE_NAME = "v86-filesystem-storage";
const INDEXEDDB_STORAGE_STORE = "store";
const INDEXEDDB_STORAGE_KEY_PATH = "sha256sum";
const INDEXEDDB_STORAGE_DATA_PATH = "data";
const INDEXEDDB_STORAGE_GET_BLOCK_KEY = (sha256sum, block_number) =>
    block_number === 0 ?  sha256sum : `${sha256sum}-${block_number - 1}`;
const INDEXEDDB_STORAGE_BLOCKSIZE = 4096;

/** @interface */
function FileStorageInterface() {}

/**
 * Read a portion of a file.
 * @param {string} sha256sum
 * @param {number} offset
 * @param {number} count
 * @return {!Promise<Uint8Array>} null if file does not exist.
 */
FileStorageInterface.prototype.read = function(sha256sum, offset, count) {};

/**
 * Add a read-only file to the filestorage.
 * @param {string} sha256sum
 * @param {!Uint8Array} data
 * @return {!Promise}
 */
FileStorageInterface.prototype.set = function(sha256sum, data) {};

/**
 * Call this when the file won't be used soon, e.g. when a file closes or when this immutable
 * version is already out of date. It is used to help prevent accumulation of unused files in
 * memory in the long run for some FileStorage mediums.
 */
FileStorageInterface.prototype.uncache = function(sha256sum) {};

/**
 * @constructor
 * @implements {FileStorageInterface}
 */
function MemoryFileStorage()
{
    /**
     * From sha256sum to file data.
     * @type {Map<string,Uint8Array>}
     */
    this.filedata = new Map();
}

/**
 * @param {string} sha256sum
 * @param {number} offset
 * @param {number} count
 * @return {!Promise<Uint8Array>} null if file does not exist.
 */
MemoryFileStorage.prototype.read = async function(sha256sum, offset, count)
{
    dbg_assert(sha256sum, "MemoryFileStorage read: sha256sum should be a non-empty string");
    const data = this.filedata.get(sha256sum);

    if(!data)
    {
        return null;
    }

    return data.subarray(offset, offset + count);
};

/**
 * @param {string} sha256sum
 * @param {!Uint8Array} data
 */
MemoryFileStorage.prototype.set = async function(sha256sum, data)
{
    dbg_assert(sha256sum, "MemoryFileStorage set: sha256sum should be a non-empty string");
    dbg_assert(!this.filedata.has(sha256sum), "MemoryFileStorage set: Storage should be read-only");

    this.filedata.set(sha256sum, data);
};

/**
 * @param {string} sha256sum
 */
MemoryFileStorage.prototype.uncache = function(sha256sum)
{
    this.filedata.delete(sha256sum);
};

/**
 * Use IndexedDBFileStorage.try_create() instead.
 * @private
 * @constructor
 * @param {!IDBDatabase} db The IndexedDB database opened via init_db().
 * @implements {FileStorageInterface}
 */
function IndexedDBFileStorage(db)
{
    this.db = db;
}

IndexedDBFileStorage.try_create = async function()
{
    if(typeof window === "undefined" || !window.indexedDB)
    {
        throw new Error("IndexedDB is not available");
    }
    const db = await IndexedDBFileStorage.init_db();
    const file_storage = new IndexedDBFileStorage(db);
    return file_storage;
};

/**
 * @return {!Promise<!IDBDatabase>}
 */
IndexedDBFileStorage.init_db = function()
{
    return new Promise((resolve, reject) =>
    {
        const open_request = indexedDB.open(INDEXEDDB_STORAGE_NAME, INDEXEDDB_STORAGE_VERSION);

        open_request.onblocked = event =>
        {
            dbg_log("IndexedDB blocked by an older database version being opened.", LOG_9P);
        };

        open_request.onerror = event =>
        {
            dbg_log("Error opening IndexedDB! Are you in private browsing mode? Error:", LOG_9P);
            dbg_log(open_request.error.toString(), LOG_9P);
            reject(open_request.error);
        };

        /** @suppress{uselessCode} */
        open_request.onupgradeneeded = event =>
        {
            const db = open_request.result;
            if(event.oldVersion < 1)
            {
                // Initial version.
                db.createObjectStore(INDEXEDDB_STORAGE_STORE, { keyPath: INDEXEDDB_STORAGE_KEY_PATH });
            }
            if(event.oldVersion < 2)
            {
                // Version 2 removes total_size and extra_block_count from the base entries.
                // No changes needed, but new files written are not backwards compatible.
            }
        };

        open_request.onsuccess = event =>
        {
            const db = open_request.result;
            db.onabort = event =>
            {
                dbg_assert(false, "IndexedDBFileStorage: transaction aborted unexpectedly");
            };
            db.onclose = event =>
            {
                dbg_assert(false, "IndexedDBFileStorage: connection closed unexpectedly");
            };
            db.onerror = event =>
            {
                const error = event.target.error;
                dbg_log("IndexedDBFileStorage: unexpected error: " + error, LOG_9P);
                throw error;
            };
            db.onversionchange = event =>
            {
                dbg_log("Caution: Another v86 instance might be trying to upgrade the IndexedDB " +
                    "database to a newer version, or a request has been issued to delete the " +
                    "database, but is blocked by this current v86 instance ", LOG_9P);
            };
            resolve(db);
        };
    });
};

/**
 * @private
 * @param {IDBObjectStore} store
 * @param {string} sha256sum
 * @return {!Promise<boolean>}
 */
IndexedDBFileStorage.prototype.db_has_file = function(store, sha256sum)
{
    return new Promise((resolve, reject) =>
    {
        const request = store.count(sha256sum);
        request.onsuccess = event => resolve(/** @type {number} **/ (request.result) > 0);
    });
};

/**
 * @param {string} sha256sum
 * @param {number} offset
 * @param {number} count
 * @return {!Promise<Uint8Array>} null if file does not exist.
 */
IndexedDBFileStorage.prototype.read = function(sha256sum, offset, count)
{
    dbg_assert(sha256sum, "IndexedDBFileStorage read: sha256sum should be a non-empty string");

    const transaction = this.db.transaction(INDEXEDDB_STORAGE_STORE, "readonly");
    transaction.onerror = event =>
    {
        const error = event.target.error;
        dbg_log(`IndexedDBFileStorage read: Error with transaction: ${error}`, LOG_9P);
        throw error;
    };
    const store = transaction.objectStore(INDEXEDDB_STORAGE_STORE);

    const block_number_start = Math.floor(offset / INDEXEDDB_STORAGE_BLOCKSIZE);
    const block_number_end = count > 0 ?
        Math.floor((offset + count - 1) / INDEXEDDB_STORAGE_BLOCKSIZE) :
        block_number_start;

    return new Promise((resolve, reject) =>
    {
        if(block_number_end === 0)
        {
            // Only first block to be read.

            const block_key = INDEXEDDB_STORAGE_GET_BLOCK_KEY(sha256sum, 0);
            const block_request = store.get(block_key);
            block_request.onsuccess = async event =>
            {
                const block_entry = block_request.result;
                if(!block_entry)
                {
                    resolve(null);
                    return;
                }
                const block_data = block_entry[INDEXEDDB_STORAGE_DATA_PATH];
                dbg_assert(block_data instanceof Uint8Array, "IndexedDBFileStorage read: " +
                    `Entry for block-0 without Uint8Array data field.`);
                const chunk = block_data.subarray(offset, offset + count);
                resolve(chunk);
            };
        }
        else if(block_number_start === block_number_end)
        {
            // Only one block to be read.

            const block_offset = block_number_start * INDEXEDDB_STORAGE_BLOCKSIZE;
            const block_key = INDEXEDDB_STORAGE_GET_BLOCK_KEY(sha256sum, block_number_start);
            const block_request = store.get(block_key);
            block_request.onsuccess = async event =>
            {
                const block_entry = block_request.result;
                if(!block_entry)
                {
                    if(!await this.db_has_file(store, sha256sum))
                    {
                        resolve(null);
                    }
                    else
                    {
                        resolve(new Uint8Array(0));
                    }
                    return;
                }
                const block_data = block_entry[INDEXEDDB_STORAGE_DATA_PATH];
                dbg_assert(block_data instanceof Uint8Array, "IndexedDBFileStorage read: " +
                    `Entry for block-${block_number_start} without Uint8Array data field.`);
                const chunk_start = Math.max(0, offset - block_offset);
                const chunk_end = offset + count - block_offset;
                const chunk = block_data.subarray(chunk_start, chunk_end);
                resolve(chunk);
            };
        }
        else
        {
            // Multiple blocks to be read.

            const read_data = new Uint8Array(count);
            let read_count = 0;
            for(let block_number = block_number_start; block_number <= block_number_end; block_number++)
            {
                const block_offset = block_number * INDEXEDDB_STORAGE_BLOCKSIZE;
                const block_key = INDEXEDDB_STORAGE_GET_BLOCK_KEY(sha256sum, block_number);
                const block_request = store.get(block_key);
                block_request.onsuccess = async event =>
                {
                    const block_entry = block_request.result;

                    if(!block_entry)
                    {
                        // If the first requested block doesn't exist, then the remaining blocks
                        // cannot exist.
                        if(block_number === block_number_start)
                        {
                            if(!await this.db_has_file(store, sha256sum))
                            {
                                // Not aborting transaction here because:
                                //  - Abort is treated like an error,
                                //  - AbortError sometimes indicate a different error we want to notice,
                                //  - Most read calls only read a single block anyway.
                                resolve(null);
                            }
                        }

                        return;
                    }

                    const block_data = block_entry[INDEXEDDB_STORAGE_DATA_PATH];
                    dbg_assert(block_data instanceof Uint8Array, "IndexedDBFileStorage read: " +
                        `Entry for block-${block_number} without Uint8Array data field.`);

                    const chunk_start = Math.max(0, offset - block_offset);
                    const chunk_end = offset + count - block_offset;
                    const chunk = block_data.subarray(chunk_start, chunk_end);

                    read_data.set(chunk, block_offset + chunk_start - offset);
                    read_count += chunk.length;
                };
            }

            transaction.oncomplete = event =>
            {
                resolve(read_data.subarray(0, read_count));
            };
        }
    });
};

/**
 * @param {string} sha256sum
 * @param {!Uint8Array} data
 */
IndexedDBFileStorage.prototype.set = function(sha256sum, data)
{
    dbg_assert(sha256sum, "IndexedDBFileStorage set: sha256sum should be a non-empty string");

    const transaction = this.db.transaction(INDEXEDDB_STORAGE_STORE, "readwrite");
    transaction.onerror = event =>
    {
        const error = event.target.error;
        dbg_log(`IndexedDBFileStorage set: Error with transaction: ${error}`, LOG_9P);
        throw error;
    };
    const store = transaction.objectStore(INDEXEDDB_STORAGE_STORE);

    // Ensure at least a single entry is added for empty files.
    const offset_upper_bound = data.length || 1;

    for(let i = 0, offset = 0; offset < offset_upper_bound; i++, offset += INDEXEDDB_STORAGE_BLOCKSIZE)
    {
        const block_key = INDEXEDDB_STORAGE_GET_BLOCK_KEY(sha256sum, i);
        // Note: Without cloning, the entire backing ArrayBuffer is serialized into the database.
        const block_data = data.slice(offset, offset + INDEXEDDB_STORAGE_BLOCKSIZE);
        store.put({
            [INDEXEDDB_STORAGE_KEY_PATH]: block_key,
            [INDEXEDDB_STORAGE_DATA_PATH]: block_data,
        });
    }

    return new Promise((resolve, reject) => {
        transaction.oncomplete = event => resolve();
    });
};

/**
 * @param {string} sha256sum
 */
IndexedDBFileStorage.prototype.uncache = function(sha256sum)
{
    // No-op.
};

/**
 * @constructor
 * @implements {FileStorageInterface}
 * @param {FileStorageInterface} file_storage
 * @param {string} baseurl
 */
function ServerFileStorageWrapper(file_storage, baseurl)
{
    dbg_assert(baseurl, "ServerMemoryFileStorage: baseurl should not be empty");

    this.storage = file_storage;
    this.baseurl = baseurl;
}

/**
 * @param {string} sha256sum
 * @return {!Promise<Uint8Array>}
 */
ServerFileStorageWrapper.prototype.load_from_server = function(sha256sum)
{
    return new Promise((resolve, reject) =>
    {
        v86util.load_file(this.baseurl + sha256sum, { done: buffer =>
        {
            const data = new Uint8Array(buffer);
            this.set(sha256sum, data).then(() => resolve(data));
        }});
    });
};

/**
 * @param {string} sha256sum
 * @param {number} offset
 * @param {number} count
 * @return {!Promise<Uint8Array>}
 */
ServerFileStorageWrapper.prototype.read = async function(sha256sum, offset, count)
{
    const data = await this.storage.read(sha256sum, offset, count);
    if(!data)
    {
        const full_file = await this.load_from_server(sha256sum);
        return full_file.subarray(offset, offset + count);
    }
    return data;
};

/**
 * @param {string} sha256sum
 * @param {!Uint8Array} data
 */
ServerFileStorageWrapper.prototype.set = async function(sha256sum, data)
{
    return await this.storage.set(sha256sum, data);
};

/**
 * @param {string} sha256sum
 */
ServerFileStorageWrapper.prototype.uncache = function(sha256sum)
{
    this.storage.uncache(sha256sum);
};

// Closure Compiler's way of exporting
if(typeof window !== "undefined")
{
    window["MemoryFileStorage"] = MemoryFileStorage;
    window["IndexedDBFileStorage"] = IndexedDBFileStorage;
    window["ServerFileStorageWrapper"] = ServerFileStorageWrapper;
}
else if(typeof module !== "undefined" && typeof module.exports !== "undefined")
{
    module.exports["MemoryFileStorage"] = MemoryFileStorage;
    module.exports["IndexedDBFileStorage"] = IndexedDBFileStorage;
    module.exports["ServerFileStorageWrapper"] = ServerFileStorageWrapper;
}
else if(typeof importScripts === "function")
{
    // web worker
    self["MemoryFileStorage"] = MemoryFileStorage;
    self["IndexedDBFileStorage"] = IndexedDBFileStorage;
    self["ServerFileStorageWrapper"] = ServerFileStorageWrapper;
}