phaser/src/loader/LoaderPlugin.js

/**
 * @author       Richard Davey <rich@photonstorm.com>
 * @copyright    2018 Photon Storm Ltd.
 * @license      {@link https://github.com/photonstorm/phaser/blob/master/license.txt|MIT License}
 */

var Class = require('../utils/Class');
var CONST = require('./const');
var CustomSet = require('../structs/Set');
var EventEmitter = require('eventemitter3');
var FileTypesManager = require('./FileTypesManager');
var GetFastValue = require('../utils/object/GetFastValue');
var PluginCache = require('../plugins/PluginCache');
var XHRSettings = require('./XHRSettings');

/**
 * @classdesc
 * The Loader handles loading all external content such as Images, Sounds, Texture Atlases and data files.
 * You typically interact with it via `this.load` in your Scene. Scenes can have a `preload` method, which is always
 * called before the Scenes `create` method, allowing you to preload assets that the Scene may need.
 *
 * If you call any `this.load` methods from outside of `Scene.preload` then you need to start the Loader going
 * yourself by calling `Loader.start()`. It's only automatically started during the Scene preload.
 *
 * The Loader uses a combination of tag loading (eg. Audio elements) and XHR and provides progress and completion events.
 * Files are loaded in parallel by default. The amount of concurrent connections can be controlled in your Game Configuration.
 *
 * Once the Loader has started loading you are still able to add files to it. These can be injected as a result of a loader
 * event, the type of file being loaded (such as a pack file) or other external events. As long as the Loader hasn't finished
 * simply adding a new file to it, while running, will ensure it's added into the current queue.
 *
 * Every Scene has its own instance of the Loader and they are bound to the Scene in which they are created. However,
 * assets loaded by the Loader are placed into global game-level caches. For example, loading an XML file will place that
 * file inside `Game.cache.xml`, which is accessible from every Scene in your game, no matter who was responsible
 * for loading it. The same is true of Textures. A texture loaded in one Scene is instantly available to all other Scenes
 * in your game.
 *
 * The Loader works by using custom File Types. These are stored in the FileTypesManager, which injects them into the Loader
 * when it's instantiated. You can create your own custom file types by extending either the File or MultiFile classes.
 * See those files for more details.
 *
 * @class LoaderPlugin
 * @extends Phaser.Events.EventEmitter
 * @memberOf Phaser.Loader
 * @constructor
 * @since 3.0.0
 *
 * @param {Phaser.Scene} scene - The Scene which owns this Loader instance.
 */
var LoaderPlugin = new Class({

    Extends: EventEmitter,

    initialize:

    function LoaderPlugin (scene)
    {
        EventEmitter.call(this);

        var gameConfig = scene.sys.game.config;
        var sceneConfig = scene.sys.settings.loader;

        /**
         * The Scene which owns this Loader instance.
         *
         * @name Phaser.Loader.LoaderPlugin#scene
         * @type {Phaser.Scene}
         * @protected
         * @since 3.0.0
         */
        this.scene = scene;

        /**
         * A reference to the Scene Systems.
         *
         * @name Phaser.Loader.LoaderPlugin#systems
         * @type {Phaser.Scenes.Systems}
         * @protected
         * @since 3.0.0
         */
        this.systems = scene.sys;

        /**
         * A reference to the global Cache Manager.
         *
         * @name Phaser.Loader.LoaderPlugin#cacheManager
         * @type {Phaser.Cache.CacheManager}
         * @protected
         * @since 3.7.0
         */
        this.cacheManager = scene.sys.cache;

        /**
         * A reference to the global Texture Manager.
         *
         * @name Phaser.Loader.LoaderPlugin#textureManager
         * @type {Phaser.Textures.TextureManager}
         * @protected
         * @since 3.7.0
         */
        this.textureManager = scene.sys.textures;

        //  Inject the available filetypes into the Loader
        FileTypesManager.install(this);

        /**
         * An optional prefix that is automatically prepended to the start of every file key.
         * If prefix was `MENU.` and you load an image with the key 'Background' the resulting key would be `MENU.Background`.
         * You can set this directly, or call `Loader.setPrefix()`. It will then affect every file added to the Loader
         * from that point on. It does _not_ change any file already in the load queue.
         *
         * @name Phaser.Loader.LoaderPlugin#prefix
         * @type {string}
         * @default ''
         * @since 3.7.0
         */
        this.prefix = '';

        /**
         * The value of `path`, if set, is placed before any _relative_ file path given. For example:
         *
         * ```javascript
         * this.load.path = "images/sprites/";
         * this.load.image("ball", "ball.png");
         * this.load.image("tree", "level1/oaktree.png");
         * this.load.image("boom", "http://server.com/explode.png");
         * ```
         *
         * Would load the `ball` file from `images/sprites/ball.png` and the tree from
         * `images/sprites/level1/oaktree.png` but the file `boom` would load from the URL
         * given as it's an absolute URL.
         *
         * Please note that the path is added before the filename but *after* the baseURL (if set.)
         *
         * If you set this property directly then it _must_ end with a "/". Alternatively, call `setPath()` and it'll do it for you.
         *
         * @name Phaser.Loader.LoaderPlugin#path
         * @type {string}
         * @default ''
         * @since 3.0.0
         */
        this.path = '';

        /**
         * If you want to append a URL before the path of any asset you can set this here.
         * 
         * Useful if allowing the asset base url to be configured outside of the game code.
         * 
         * If you set this property directly then it _must_ end with a "/". Alternatively, call `setBaseURL()` and it'll do it for you.
         *
         * @name Phaser.Loader.LoaderPlugin#baseURL
         * @type {string}
         * @default ''
         * @since 3.0.0
         */
        this.baseURL = '';

        this.setBaseURL(GetFastValue(sceneConfig, 'baseURL', gameConfig.loaderBaseURL));

        this.setPath(GetFastValue(sceneConfig, 'path', gameConfig.loaderPath));

        this.setPrefix(GetFastValue(sceneConfig, 'prefix', gameConfig.loaderPrefix));

        /**
         * The number of concurrent / parallel resources to try and fetch at once.
         *
         * Old browsers limit 6 requests per domain; modern ones, especially those with HTTP/2 don't limit it at all.
         *
         * The default is 32 but you can change this in your Game Config, or by changing this property before the Loader starts.
         *
         * @name Phaser.Loader.LoaderPlugin#maxParallelDownloads
         * @type {integer}
         * @since 3.0.0
         */
        this.maxParallelDownloads = GetFastValue(sceneConfig, 'maxParallelDownloads', gameConfig.loaderMaxParallelDownloads);

        /**
         * xhr specific global settings (can be overridden on a per-file basis)
         *
         * @name Phaser.Loader.LoaderPlugin#xhr
         * @type {XHRSettingsObject}
         * @since 3.0.0
         */
        this.xhr = XHRSettings(
            GetFastValue(sceneConfig, 'responseType', gameConfig.loaderResponseType),
            GetFastValue(sceneConfig, 'async', gameConfig.loaderAsync),
            GetFastValue(sceneConfig, 'user', gameConfig.loaderUser),
            GetFastValue(sceneConfig, 'password', gameConfig.loaderPassword),
            GetFastValue(sceneConfig, 'timeout', gameConfig.loaderTimeout)
        );

        /**
         * The crossOrigin value applied to loaded images. Very often this needs to be set to 'anonymous'.
         *
         * @name Phaser.Loader.LoaderPlugin#crossOrigin
         * @type {string}
         * @since 3.0.0
         */
        this.crossOrigin = GetFastValue(sceneConfig, 'crossOrigin', gameConfig.loaderCrossOrigin);

        /**
         * The total number of files to load. It may not always be accurate because you may add to the Loader during the process
         * of loading, especially if you load a Pack File. Therefore this value can change, but in most cases remains static.
         *
         * @name Phaser.Loader.LoaderPlugin#totalToLoad
         * @type {integer}
         * @default 0
         * @since 3.0.0
         */
        this.totalToLoad = 0;

        /**
         * The progress of the current load queue, as a float value between 0 and 1.
         * This is updated automatically as files complete loading.
         * Note that it is possible for this value to go down again if you add content to the current load queue during a load.
         *
         * @name Phaser.Loader.LoaderPlugin#progress
         * @type {float}
         * @default 0
         * @since 3.0.0
         */
        this.progress = 0;

        /**
         * Files are placed in this Set when they're added to the Loader via `addFile`.
         * 
         * They are moved to the `inflight` Set when they start loading, and assuming a successful
         * load, to the `queue` Set for further processing.
         *
         * By the end of the load process this Set will be empty.
         *
         * @name Phaser.Loader.LoaderPlugin#list
         * @type {Phaser.Structs.Set.<Phaser.Loader.File>}
         * @since 3.0.0
         */
        this.list = new CustomSet();

        /**
         * Files are stored in this Set while they're in the process of being loaded.
         * 
         * Upon a successful load they are moved to the `queue` Set.
         * 
         * By the end of the load process this Set will be empty.
         *
         * @name Phaser.Loader.LoaderPlugin#inflight
         * @type {Phaser.Structs.Set.<Phaser.Loader.File>}
         * @since 3.0.0
         */
        this.inflight = new CustomSet();

        /**
         * Files are stored in this Set while they're being processed.
         * 
         * If the process is successful they are moved to their final destination, which could be
         * a Cache or the Texture Manager.
         * 
         * At the end of the load process this Set will be empty.
         *
         * @name Phaser.Loader.LoaderPlugin#queue
         * @type {Phaser.Structs.Set.<Phaser.Loader.File>}
         * @since 3.0.0
         */
        this.queue = new CustomSet();

        /**
         * A temporary Set in which files are stored after processing,
         * awaiting destruction at the end of the load process.
         *
         * @name Phaser.Loader.LoaderPlugin#_deleteQueue
         * @type {Phaser.Structs.Set.<Phaser.Loader.File>}
         * @private
         * @since 3.7.0
         */
        this._deleteQueue = new CustomSet();

        /**
         * The total number of files that failed to load during the most recent load.
         * This value is reset when you call `Loader.start`.
         *
         * @name Phaser.Loader.LoaderPlugin#totalFailed
         * @type {integer}
         * @default 0
         * @since 3.7.0
         */
        this.totalFailed = 0;

        /**
         * The total number of files that successfully loaded during the most recent load.
         * This value is reset when you call `Loader.start`.
         *
         * @name Phaser.Loader.LoaderPlugin#totalComplete
         * @type {integer}
         * @default 0
         * @since 3.7.0
         */
        this.totalComplete = 0;

        /**
         * The current state of the Loader.
         *
         * @name Phaser.Loader.LoaderPlugin#state
         * @type {integer}
         * @readOnly
         * @since 3.0.0
         */
        this.state = CONST.LOADER_IDLE;

        scene.sys.events.once('boot', this.boot, this);
        scene.sys.events.on('start', this.pluginStart, this);
    },

    /**
     * This method is called automatically, only once, when the Scene is first created.
     * Do not invoke it directly.
     *
     * @method Phaser.Loader.LoaderPlugin#boot
     * @private
     * @since 3.5.1
     */
    boot: function ()
    {
        this.systems.events.once('destroy', this.destroy, this);
    },

    /**
     * This method is called automatically by the Scene when it is starting up.
     * It is responsible for creating local systems, properties and listening for Scene events.
     * Do not invoke it directly.
     *
     * @method Phaser.Loader.LoaderPlugin#pluginStart
     * @private
     * @since 3.5.1
     */
    pluginStart: function ()
    {
        this.systems.events.once('shutdown', this.shutdown, this);
    },

    /**
     * If you want to append a URL before the path of any asset you can set this here.
     * 
     * Useful if allowing the asset base url to be configured outside of the game code.
     * 
     * Once a base URL is set it will affect every file loaded by the Loader from that point on. It does _not_ change any
     * file _already_ being loaded. To reset it, call this method with no arguments.
     *
     * @method Phaser.Loader.LoaderPlugin#setBaseURL
     * @since 3.0.0
     *
     * @param {string} [url] - The URL to use. Leave empty to reset.
     *
     * @return {Phaser.Loader.LoaderPlugin} This Loader object.
     */
    setBaseURL: function (url)
    {
        if (url === undefined) { url = ''; }

        if (url !== '' && url.substr(-1) !== '/')
        {
            url = url.concat('/');
        }

        this.baseURL = url;

        return this;
    },

    /**
     * The value of `path`, if set, is placed before any _relative_ file path given. For example:
     *
     * ```javascript
     * this.load.setPath("images/sprites/");
     * this.load.image("ball", "ball.png");
     * this.load.image("tree", "level1/oaktree.png");
     * this.load.image("boom", "http://server.com/explode.png");
     * ```
     *
     * Would load the `ball` file from `images/sprites/ball.png` and the tree from
     * `images/sprites/level1/oaktree.png` but the file `boom` would load from the URL
     * given as it's an absolute URL.
     *
     * Please note that the path is added before the filename but *after* the baseURL (if set.)
     * 
     * Once a path is set it will then affect every file added to the Loader from that point on. It does _not_ change any
     * file _already_ in the load queue. To reset it, call this method with no arguments.
     *
     * @method Phaser.Loader.LoaderPlugin#setPath
     * @since 3.0.0
     *
     * @param {string} [path] - The path to use. Leave empty to reset.
     *
     * @return {Phaser.Loader.LoaderPlugin} This Loader object.
     */
    setPath: function (path)
    {
        if (path === undefined) { path = ''; }

        if (path !== '' && path.substr(-1) !== '/')
        {
            path = path.concat('/');
        }

        this.path = path;

        return this;
    },

    /**
     * An optional prefix that is automatically prepended to the start of every file key.
     * 
     * If prefix was `MENU.` and you load an image with the key 'Background' the resulting key would be `MENU.Background`.
     * 
     * Once a prefix is set it will then affect every file added to the Loader from that point on. It does _not_ change any
     * file _already_ in the load queue. To reset it, call this method with no arguments.
     *
     * @method Phaser.Loader.LoaderPlugin#setPrefix
     * @since 3.7.0
     *
     * @param {string} [prefix] - The prefix to use. Leave empty to reset.
     *
     * @return {Phaser.Loader.LoaderPlugin} This Loader object.
     */
    setPrefix: function (prefix)
    {
        if (prefix === undefined) { prefix = ''; }

        this.prefix = prefix;

        return this;
    },

    /**
     * Sets the Cross Origin Resource Sharing value used when loading files.
     * 
     * Files can override this value on a per-file basis by specifying an alternative `crossOrigin` value in their file config.
     * 
     * Once CORs is set it will then affect every file loaded by the Loader from that point on, as long as they don't have
     * their own CORs setting. To reset it, call this method with no arguments.
     *
     * For more details about CORs see https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS
     *
     * @method Phaser.Loader.LoaderPlugin#setCORS
     * @since 3.0.0
     *
     * @param {string} [crossOrigin] - The value to use for the `crossOrigin` property in the load request.
     *
     * @return {Phaser.Loader.LoaderPlugin} This Loader object.
     */
    setCORS: function (crossOrigin)
    {
        this.crossOrigin = crossOrigin;

        return this;
    },

    /**
     * This event is fired when a Loader successfully begins to load its queue.
     * 
     * @event Phaser.Loader.LoaderPlugin#addFileEvent
     * @param {string} key - The key of the file that was added.
     * @param {string} type - The type of the file that was added.
     * @param {Phaser.Loader.LoaderPlugin} loader - The Loader that had the file added to it.
     * @param {Phaser.Loader.File} loader - The File object that was added to the Loader.
     */

    /**
     * Adds a file, or array of files, into the load queue.
     *
     * The file must be an instance of `Phaser.Loader.File`, or a class that extends it. The Loader will check that the key
     * used by the file won't conflict with any other key either in the loader, the inflight queue or the target cache.
     * If allowed it will then add the file into the pending list, read for the load to start. Or, if the load has already
     * started, ready for the next batch of files to be pulled from the list to the inflight queue.
     *
     * You should not normally call this method directly, but rather use one of the Loader methods like `image` or `atlas`,
     * however you can call this as long as the file given to it is well formed.
     *
     * @method Phaser.Loader.LoaderPlugin#addFile
     * @fires Phaser.Loader.LoaderPlugin#addFileEvent
     * @since 3.0.0
     *
     * @param {(Phaser.Loader.File|Phaser.Loader.File[])} file - The file, or array of files, to be added to the load queue.
     */
    addFile: function (file)
    {
        if (!Array.isArray(file))
        {
            file = [ file ];
        }

        for (var i = 0; i < file.length; i++)
        {
            var item = file[i];

            //  Does the file already exist in the cache or texture manager?
            //  Or will it conflict with a file already in the queue or inflight?
            if (!this.keyExists(item))
            {
                this.list.set(item);

                this.emit('addfile', item.key, item.type, this, item);

                if (this.isLoading())
                {
                    this.totalToLoad++;
                    this.updateProgress();
                }
            }
        }
    },

    /**
     * Checks the key and type of the given file to see if it will conflict with anything already
     * in a Cache, the Texture Manager, or the list or inflight queues.
     *
     * @method Phaser.Loader.LoaderPlugin#keyExists
     * @since 3.7.0
     *
     * @param {Phaser.Loader.File} file - The file to check the key of.
     *
     * @return {boolean} `true` if adding this file will cause a cache or queue conflict, otherwise `false`.
     */
    keyExists: function (file)
    {
        var keyConflict = file.hasCacheConflict();

        if (!keyConflict)
        {
            this.list.iterate(function (item)
            {
                if (item.type === file.type && item.key === file.key)
                {
                    keyConflict = true;

                    return false;
                }

            });
        }

        if (!keyConflict && this.isLoading())
        {
            this.inflight.iterate(function (item)
            {
                if (item.type === file.type && item.key === file.key)
                {
                    keyConflict = true;

                    return false;
                }

            });

            this.queue.iterate(function (item)
            {
                if (item.type === file.type && item.key === file.key)
                {
                    keyConflict = true;

                    return false;
                }

            });
        }

        return keyConflict;
    },

    /**
     * Takes a well formed, fully parsed pack file object and adds its entries into the load queue. Usually you do not call
     * this method directly, but instead use `Loader.pack` and supply a path to a JSON file that holds the
     * pack data. However, if you've got the data prepared you can pass it to this method.
     *
     * You can also provide an optional key. If you do then it will only add the entries from that part of the pack into
     * to the load queue. If not specified it will add all entries it finds. For more details about the pack file format
     * see the `LoaderPlugin.pack` method.
     *
     * @method Phaser.Loader.LoaderPlugin#addPack
     * @since 3.7.0
     *
     * @param {any} data - The Pack File data to be parsed and each entry of it to added to the load queue.
     * @param {string} [packKey] - An optional key to use from the pack file data.
     *
     * @return {boolean} `true` if any files were added to the queue, otherwise `false`.
     */
    addPack: function (pack, packKey)
    {
        //  if no packKey provided we'll add everything to the queue
        if (packKey && pack.hasOwnProperty(packKey))
        {
            pack = { packKey: pack[packKey] };
        }

        var total = 0;

        //  Store the loader settings in case this pack replaces them
        var currentBaseURL = this.baseURL;
        var currentPath = this.path;
        var currentPrefix = this.prefix;

        //  Here we go ...
        for (var key in pack)
        {
            var config = pack[key];

            //  Any meta data to process?
            var baseURL = GetFastValue(config, 'baseURL', currentBaseURL);
            var path = GetFastValue(config, 'path', currentPath);
            var prefix = GetFastValue(config, 'prefix', currentPrefix);
            var files = GetFastValue(config, 'files', null);
            var defaultType = GetFastValue(config, 'defaultType', 'void');

            if (Array.isArray(files))
            {
                this.setBaseURL(baseURL);
                this.setPath(path);
                this.setPrefix(prefix);

                for (var i = 0; i < files.length; i++)
                {
                    var file = files[i];
                    var type = (file.hasOwnProperty('type')) ? file.type : defaultType;

                    if (this[type])
                    {
                        this[type](file);
                        total++;
                    }
                }
            }
        }

        //  Reset the loader settings
        this.setBaseURL(currentBaseURL);
        this.setPath(currentPath);
        this.setPrefix(currentPrefix);

        return (total > 0);
    },

    /**
     * Is the Loader actively loading, or processing loaded files?
     *
     * @method Phaser.Loader.LoaderPlugin#isLoading
     * @since 3.0.0
     *
     * @return {boolean} `true` if the Loader is busy loading or processing, otherwise `false`.
     */
    isLoading: function ()
    {
        return (this.state === CONST.LOADER_LOADING || this.state === CONST.LOADER_PROCESSING);
    },

    /**
     * Is the Loader ready to start a new load?
     *
     * @method Phaser.Loader.LoaderPlugin#isReady
     * @since 3.0.0
     *
     * @return {boolean} `true` if the Loader is ready to start a new load, otherwise `false`.
     */
    isReady: function ()
    {
        return (this.state === CONST.LOADER_IDLE || this.state === CONST.LOADER_COMPLETE);
    },

    /**
     * This event is fired when a Loader successfully begins to load its queue.
     * 
     * @event Phaser.Loader.LoaderPlugin#startEvent
     * @param {Phaser.Loader.LoaderPlugin} loader - The Loader instance that started.
     */

    /**
     * Starts the Loader running. This will reset the progress and totals and then emit a `start` event.
     * If there is nothing in the queue the Loader will immediately complete, otherwise it will start
     * loading the first batch of files.
     *
     * The Loader is started automatically if the queue is populated within your Scenes `preload` method.
     *
     * However, outside of this, you need to call this method to start it.
     *
     * If the Loader is already running this method will simply return.
     *
     * @method Phaser.Loader.LoaderPlugin#start
     * @fires Phaser.Loader.LoaderPlugin#startEvent
     * @since 3.0.0
     */
    start: function ()
    {
        if (!this.isReady())
        {
            return;
        }

        this.progress = 0;

        this.totalFailed = 0;
        this.totalComplete = 0;
        this.totalToLoad = this.list.size;

        this.emit('start', this);

        if (this.list.size === 0)
        {
            this.loadComplete();
        }
        else
        {
            this.state = CONST.LOADER_LOADING;

            this.inflight.clear();
            this.queue.clear();

            this.updateProgress();

            this.checkLoadQueue();
        }
    },

    /**
     * This event is fired when the Loader updates its progress, typically as a result of
     * a file having completed loading.
     * 
     * @event Phaser.Loader.LoaderPlugin#progressEvent
     * @param {float} progress - The current progress of the load. A value between 0 and 1.
     */

    /**
     * Called automatically during the load process.
     * It updates the `progress` value and then emits a progress event, which you can use to
     * display a loading bar in your game.
     *
     * @method Phaser.Loader.LoaderPlugin#updateProgress
     * @fires Phaser.Loader.LoaderPlugin#progressEvent
     * @since 3.0.0
     */
    updateProgress: function ()
    {
        this.progress = 1 - ((this.list.size + this.inflight.size) / this.totalToLoad);

        this.emit('progress', this.progress);
    },

    /**
     * An internal method called by the Loader.
     * 
     * It will check to see if there are any more files in the pending list that need loading, and if so it will move
     * them from the list Set into the inflight Set, set their CORs flag and start them loading.
     * 
     * It will carrying on doing this for each file in the pending list until it runs out, or hits the max allowed parallel downloads.
     *
     * @method Phaser.Loader.LoaderPlugin#checkLoadQueue
     * @private
     * @since 3.7.0
     */
    checkLoadQueue: function ()
    {
        this.list.each(function (file)
        {
            if (file.state === CONST.FILE_POPULATED || (file.state === CONST.FILE_PENDING && this.inflight.size < this.maxParallelDownloads))
            {
                this.inflight.set(file);

                this.list.delete(file);

                //  If the file doesn't have its own crossOrigin set,
                //  we'll use the Loaders (which is undefined by default)
                if (!file.crossOrigin)
                {
                    file.crossOrigin = this.crossOrigin;
                }

                file.load();
            }

            if (this.inflight.size === this.maxParallelDownloads)
            {
                //  Tells the Set iterator to abort
                return false;
            }

        }, this);
    },

    /**
     * This event is fired when the a file successfully completes loading, _before_ it is processed.
     * 
     * @event Phaser.Loader.LoaderPlugin#loadEvent
     * @param {Phaser.Loader.File} file - The file that has completed loading.
     */

    /**
     * This event is fired when the a file errors during load.
     * 
     * @event Phaser.Loader.LoaderPlugin#loadErrorEvent
     * @param {Phaser.Loader.File} file - The file that has failed to load.
     */

    /**
     * An internal method called automatically by the XHRLoader belong to a File.
     * 
     * This method will remove the given file from the inflight Set and update the load progress.
     * If the file was successful its `onProcess` method is called, otherwise it is added to the delete queue.
     *
     * @method Phaser.Loader.LoaderPlugin#nextFile
     * @fires Phaser.Loader.LoaderPlugin#loadEvent
     * @fires Phaser.Loader.LoaderPlugin#loadErrorEvent
     * @since 3.0.0
     *
     * @param {Phaser.Loader.File} file - The File that just finished loading, or errored during load.
     * @param {boolean} success - `true` if the file loaded successfully, otherwise `false`.
     */
    nextFile: function (file, success)
    {
        this.inflight.delete(file);

        this.updateProgress();

        if (success)
        {
            this.totalComplete++;

            this.queue.set(file);

            this.emit('load', file);

            file.onProcess();
        }
        else
        {
            this.totalFailed++;

            this._deleteQueue.set(file);

            this.emit('loaderror', file);
        }

        if (this.list.size > 0)
        {
            this.checkLoadQueue();
        }
    },

    /**
     * An internal method that is called automatically by the File when it has finished processing.
     *
     * If the process was successful, and the File isn't part of a MultiFile, its `addToCache` method is called.
     *
     * It this then removed from the queue. If there are more files to load, `checkLoadQueue` is called, otherwise `loadComplete` is.
     *
     * @method Phaser.Loader.LoaderPlugin#fileProcessComplete
     * @since 3.7.0
     *
     * @param {Phaser.Loader.File} file - The file that has finished processing.
     */
    fileProcessComplete: function (file)
    {
        //  This file has failed, so move it to the failed Set
        if (file.state === CONST.FILE_ERRORED)
        {
            if (file.multiFile)
            {
                file.multiFile.onFileFailed(file);
            }
        }
        else if (file.state === CONST.FILE_COMPLETE)
        {
            if (file.multiFile)
            {
                if (file.multiFile.isReadyToProcess())
                {
                    //  If we got here then all files the link file needs are ready to add to the cache
                    file.multiFile.addToCache();
                }
            }
            else
            {
                //  If we got here, then the file processed, so let it add itself to its cache
                file.addToCache();
            }
        }

        //  Remove it from the queue
        this.queue.delete(file);

        //  Nothing left to do?
        if (this.list.size === 0 && this.inflight.size === 0 && this.queue.size === 0)
        {
            this.loadComplete();
        }
        else
        {
            //  In case we've added to the list by processing this file
            this.checkLoadQueue();
        }
    },

    /**
     * This event is fired when the Loader has finished loading everything and the queue is empty.
     * By this point every loaded file will now be in its associated cache and ready for use.
     * 
     * @event Phaser.Loader.LoaderPlugin#completeEvent
     * @param {Phaser.Loader.File} file - The file that has failed to load.
     */

    /**
     * Called at the end when the load queue is exhausted and all files have either loaded or errored.
     * By this point every loaded file will now be in its associated cache and ready for use.
     *
     * Also clears down the Sets, puts progress to 1 and clears the deletion queue.
     *
     * @method Phaser.Loader.LoaderPlugin#loadComplete
     * @fires Phaser.Loader.LoaderPlugin#completeEvent
     * @since 3.7.0
     */
    loadComplete: function ()
    {
        this.emit('loadcomplete', this);

        this.list.clear();
        this.inflight.clear();
        this.queue.clear();

        this.progress = 1;

        this.state = CONST.LOADER_COMPLETE;

        //  Call 'destroy' on each file ready for deletion
        this._deleteQueue.iterateLocal('destroy');

        this._deleteQueue.clear();

        this.emit('complete', this, this.totalComplete, this.totalFailed);
    },

    /**
     * Adds a File into the pending-deletion queue.
     *
     * @method Phaser.Loader.LoaderPlugin#flagForRemoval
     * @since 3.7.0
     * 
     * @param {Phaser.Loader.File} file - The File to be queued for deletion when the Loader completes.
     */
    flagForRemoval: function (file)
    {
        this._deleteQueue.set(file);
    },

    /**
     * Converts the given JSON data into a file that the browser then prompts you to download so you can save it locally.
     *
     * The data must be well formed JSON and ready-parsed, not a JavaScript object.
     *
     * @method Phaser.Loader.LoaderPlugin#saveJSON
     * @since 3.0.0
     *
     * @param {*} data - The JSON data, ready parsed.
     * @param {string} [filename=file.json] - The name to save the JSON file as.
     *
     * @return {Phaser.Loader.LoaderPlugin} This Loader plugin.
     */
    saveJSON: function (data, filename)
    {
        return this.save(JSON.stringify(data), filename);
    },

    /**
     * Causes the browser to save the given data as a file to its default Downloads folder.
     * 
     * Creates a DOM level anchor link, assigns it as being a `download` anchor, sets the href
     * to be an ObjectURL based on the given data, and then invokes a click event.
     *
     * @method Phaser.Loader.LoaderPlugin#save
     * @since 3.0.0
     *
     * @param {*} data - The data to be saved. Will be passed through URL.createObjectURL.
     * @param {string} [filename=file.json] - The filename to save the file as.
     * @param {string} [filetype=application/json] - The file type to use when saving the file. Defaults to JSON.
     *
     * @return {Phaser.Loader.LoaderPlugin} This Loader plugin.
     */
    save: function (data, filename, filetype)
    {
        if (filename === undefined) { filename = 'file.json'; }
        if (filetype === undefined) { filetype = 'application/json'; }

        var blob = new Blob([ data ], { type: filetype });

        var url = URL.createObjectURL(blob);

        var a = document.createElement('a');

        a.download = filename;
        a.textContent = 'Download ' + filename;
        a.href = url;
        a.click();

        return this;
    },

    /**
     * Resets the Loader.
     *
     * This will clear all lists and reset the base URL, path and prefix.
     *
     * Warning: If the Loader is currently downloading files, or has files in its queue, they will be aborted.
     *
     * @method Phaser.Loader.LoaderPlugin#reset
     * @since 3.0.0
     */
    reset: function ()
    {
        this.list.clear();
        this.inflight.clear();
        this.queue.clear();

        var gameConfig = this.systems.game.config;
        var sceneConfig = this.systems.settings.loader;

        this.setBaseURL(GetFastValue(sceneConfig, 'baseURL', gameConfig.loaderBaseURL));
        this.setPath(GetFastValue(sceneConfig, 'path', gameConfig.loaderPath));
        this.setPrefix(GetFastValue(sceneConfig, 'prefix', gameConfig.loaderPrefix));

        this.state = CONST.LOADER_IDLE;
    },

    /**
     * The Scene that owns this plugin is shutting down.
     * We need to kill and reset all internal properties as well as stop listening to Scene events.
     *
     * @method Phaser.Loader.LoaderPlugin#shutdown
     * @private
     * @since 3.0.0
     */
    shutdown: function ()
    {
        this.reset();

        this.state = CONST.LOADER_SHUTDOWN;

        this.systems.events.off('shutdown', this.shutdown, this);
    },

    /**
     * The Scene that owns this plugin is being destroyed.
     * We need to shutdown and then kill off all external references.
     *
     * @method Phaser.Loader.LoaderPlugin#destroy
     * @private
     * @since 3.0.0
     */
    destroy: function ()
    {
        this.shutdown();

        this.state = CONST.LOADER_DESTROYED;

        this.systems.events.off('start', this.pluginStart, this);

        this.list = null;
        this.inflight = null;
        this.queue = null;

        this.scene = null;
        this.systems = null;
        this.textureManager = null;
        this.cacheManager = null;
    }

});

PluginCache.register('Loader', LoaderPlugin, 'load');

module.exports = LoaderPlugin;