/**
 * Projects exported for the Web expose the :js:class:`Engine` class to the JavaScript environment, that allows
 * fine control over the engine's start-up process.
 *
 * This API is built in an asynchronous manner and requires basic understanding
 * of `Promises <https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Using_promises>`__.
 *
 * @module Engine
 * @header HTML5 shell class reference
 */
const Engine = (function () {
	const preloader = new Preloader();

	let loadPromise = null;
	let loadPath = '';
	let initPromise = null;

	/**
	 * @classdesc The ``Engine`` class provides methods for loading and starting exported projects on the Web. For default export
	 * settings, this is already part of the exported HTML page. To understand practical use of the ``Engine`` class,
	 * see :ref:`Custom HTML page for Web export <doc_customizing_html5_shell>`.
	 *
	 * @description Create a new Engine instance with the given configuration.
	 *
	 * @global
	 * @constructor
	 * @param {EngineConfig} initConfig The initial config for this instance.
	 */
	function Engine(initConfig) { // eslint-disable-line no-shadow
		this.config = new InternalConfig(initConfig);
		this.rtenv = null;
	}

	/**
	 * Load the engine from the specified base path.
	 *
	 * @param {string} basePath Base path of the engine to load.
	 * @returns {Promise} A Promise that resolves once the engine is loaded.
	 *
	 * @function Engine.load
	 */
	Engine.load = function (basePath) {
		if (loadPromise == null) {
			loadPath = basePath;
			loadPromise = preloader.loadPromise(`${loadPath}.wasm`);
			requestAnimationFrame(preloader.animateProgress);
		}
		return loadPromise;
	};

	/**
	 * Unload the engine to free memory.
	 *
	 * This method will be called automatically depending on the configuration. See :js:attr:`unloadAfterInit`.
	 *
	 * @function Engine.unload
	 */
	Engine.unload = function () {
		loadPromise = null;
	};

	/**
	 * Check whether WebGL is available. Optionally, specify a particular version of WebGL to check for.
	 *
	 * @param {number=} [majorVersion=1] The major WebGL version to check for.
	 * @returns {boolean} If the given major version of WebGL is available.
	 * @function Engine.isWebGLAvailable
	 */
	Engine.isWebGLAvailable = function (majorVersion = 1) {
		try {
			return !!document.createElement('canvas').getContext(['webgl', 'webgl2'][majorVersion - 1]);
		} catch (e) { /* Not available */ }
		return false;
	};

	/**
	 * Safe Engine constructor, creates a new prototype for every new instance to avoid prototype pollution.
	 * @ignore
	 * @constructor
	 */
	function SafeEngine(initConfig) {
		const proto = /** @lends Engine.prototype */ {
			/**
			 * Initialize the engine instance. Optionally, pass the base path to the engine to load it,
			 * if it hasn't been loaded yet. See :js:meth:`Engine.load`.
			 *
			 * @param {string=} basePath Base path of the engine to load.
			 * @return {Promise} A ``Promise`` that resolves once the engine is loaded and initialized.
			 */
			init: function (basePath) {
				if (initPromise) {
					return initPromise;
				}
				if (loadPromise == null) {
					if (!basePath) {
						initPromise = Promise.reject(new Error('A base path must be provided when calling `init` and the engine is not loaded.'));
						return initPromise;
					}
					Engine.load(basePath);
				}
				preloader.setProgressFunc(this.config.onProgress);
				let config = this.config.getModuleConfig(loadPath, loadPromise);
				const me = this;
				initPromise = new Promise(function (resolve, reject) {
					Godot(config).then(function (module) {
						module['initFS'](me.config.persistentPaths).then(function (fs_err) {
							me.rtenv = module;
							if (me.config.unloadAfterInit) {
								Engine.unload();
							}
							resolve();
							config = null;
						});
					});
				});
				return initPromise;
			},

			/**
			 * Load a file so it is available in the instance's file system once it runs. Must be called **before** starting the
			 * instance.
			 *
			 * If not provided, the ``path`` is derived from the URL of the loaded file.
			 *
			 * @param {string|ArrayBuffer} file The file to preload.
			 *
			 * If a ``string`` the file will be loaded from that path.
			 *
			 * If an ``ArrayBuffer`` or a view on one, the buffer will used as the content of the file.
			 *
			 * @param {string=} path Path by which the file will be accessible. Required, if ``file`` is not a string.
			 *
			 * @returns {Promise} A Promise that resolves once the file is loaded.
			 */
			preloadFile: function (file, path) {
				return preloader.preload(file, path);
			},

			/**
			 * Start the engine instance using the given override configuration (if any).
			 * :js:meth:`startGame <Engine.prototype.startGame>` can be used in typical cases instead.
			 *
			 * This will initialize the instance if it is not initialized. For manual initialization, see :js:meth:`init <Engine.prototype.init>`.
			 * The engine must be loaded beforehand.
			 *
			 * Fails if a canvas cannot be found on the page, or not specified in the configuration.
			 *
			 * @param {EngineConfig} override An optional configuration override.
			 * @return {Promise} Promise that resolves once the engine started.
			 */
			start: function (override) {
				this.config.update(override);
				const me = this;
				return me.init().then(function () {
					if (!me.rtenv) {
						return Promise.reject(new Error('The engine must be initialized before it can be started'));
					}

					let config = {};
					try {
						config = me.config.getGodotConfig(function () {
							me.rtenv = null;
						});
					} catch (e) {
						return Promise.reject(e);
					}
					// Godot configuration.
					me.rtenv['initConfig'](config);

					// Preload GDNative libraries.
					const libs = [];
					me.config.gdnativeLibs.forEach(function (lib) {
						libs.push(me.rtenv['loadDynamicLibrary'](lib, { 'loadAsync': true }));
					});
					return Promise.all(libs).then(function () {
						return new Promise(function (resolve, reject) {
							preloader.preloadedFiles.forEach(function (file) {
								me.rtenv['copyToFS'](file.path, file.buffer);
							});
							preloader.preloadedFiles.length = 0; // Clear memory
							me.rtenv['callMain'](me.config.args);
							initPromise = null;
							resolve();
						});
					});
				});
			},

			/**
			 * Start the game instance using the given configuration override (if any).
			 *
			 * This will initialize the instance if it is not initialized. For manual initialization, see :js:meth:`init <Engine.prototype.init>`.
			 *
			 * This will load the engine if it is not loaded, and preload the main pck.
			 *
			 * This method expects the initial config (or the override) to have both the :js:attr:`executable` and :js:attr:`mainPack`
			 * properties set (normally done by the editor during export).
			 *
			 * @param {EngineConfig} override An optional configuration override.
			 * @return {Promise} Promise that resolves once the game started.
			 */
			startGame: function (override) {
				this.config.update(override);
				// Add main-pack argument.
				const exe = this.config.executable;
				const pack = this.config.mainPack || `${exe}.pck`;
				this.config.args = ['--main-pack', pack].concat(this.config.args);
				// Start and init with execName as loadPath if not inited.
				const me = this;
				return Promise.all([
					this.init(exe),
					this.preloadFile(pack, pack),
				]).then(function () {
					return me.start.apply(me);
				});
			},

			/**
			 * Create a file at the specified ``path`` with the passed as ``buffer`` in the instance's file system.
			 *
			 * @param {string} path The location where the file will be created.
			 * @param {ArrayBuffer} buffer The content of the file.
			 */
			copyToFS: function (path, buffer) {
				if (this.rtenv == null) {
					throw new Error('Engine must be inited before copying files');
				}
				this.rtenv['copyToFS'](path, buffer);
			},

			/**
			 * Request that the current instance quit.
			 *
			 * This is akin the user pressing the close button in the window manager, and will
			 * have no effect if the engine has crashed, or is stuck in a loop.
			 *
			 */
			requestQuit: function () {
				if (this.rtenv) {
					this.rtenv['request_quit']();
				}
			},
		};

		Engine.prototype = proto;
		// Closure compiler exported instance methods.
		Engine.prototype['init'] = Engine.prototype.init;
		Engine.prototype['preloadFile'] = Engine.prototype.preloadFile;
		Engine.prototype['start'] = Engine.prototype.start;
		Engine.prototype['startGame'] = Engine.prototype.startGame;
		Engine.prototype['copyToFS'] = Engine.prototype.copyToFS;
		Engine.prototype['requestQuit'] = Engine.prototype.requestQuit;
		// Also expose static methods as instance methods
		Engine.prototype['load'] = Engine.load;
		Engine.prototype['unload'] = Engine.unload;
		Engine.prototype['isWebGLAvailable'] = Engine.isWebGLAvailable;
		return new Engine(initConfig);
	}

	// Closure compiler exported static methods.
	SafeEngine['load'] = Engine.load;
	SafeEngine['unload'] = Engine.unload;
	SafeEngine['isWebGLAvailable'] = Engine.isWebGLAvailable;

	return SafeEngine;
}());
if (typeof window !== 'undefined') {
	window['Engine'] = Engine;
}
