/*!
 * VisualEditor MediaWiki TargetLoader.
 *
 * @copyright 2011-2015 VisualEditor Team and others; see AUTHORS.txt
 * @license The MIT License (MIT); see LICENSE.txt
 */

/**
 * Target loader.
 *
 * Light-weight loader that loads ResourceLoader modules for VisualEditor
 * and HTML and page data from the API. Also handles plugin registration.
 *
 * @class mw.libs.ve.targetLoader
 * @singleton
 */
( function () {
	var prefName, prefValue,
		conf = mw.config.get( 'wgVisualEditorConfig' ),
		pluginCallbacks = [],
		modules = [
			'ext.visualEditor.mwcore',
			'ext.visualEditor.mwlink',
			'ext.visualEditor.data',
			'ext.visualEditor.mwreference',
			'ext.visualEditor.mwtransclusion',
			'ext.visualEditor.language',
			'ext.visualEditor.icons'
		]
			// Add modules from $wgVisualEditorPluginModules
			.concat( conf.pluginModules );

	// Add preference modules
	for ( prefName in conf.preferenceModules ) {
		prefValue = mw.user.options.get( prefName );
		// Check "0" (T89513)
		if ( prefValue && prefValue !== '0' ) {
			modules.push( conf.preferenceModules[prefName] );
		}
	}

	mw.libs.ve = mw.libs.ve || {};

	mw.libs.ve.targetLoader = {
		/**
		 * Add a plugin module or callback.
		 *
		 * If a module name is passed, that module will be loaded alongside the other modules.
		 *
		 * If a callback is passed, it will be executed after the modules have loaded. The callback
		 * may optionally return a jQuery.Promise; if it does, loading won't be complete until
		 * that promise is resolved.
		 *
		 * @param {string|Function} plugin Plugin module name or callback
		 */
		addPlugin: function ( plugin ) {
			if ( typeof plugin === 'string' ) {
				modules.push( plugin );
			} else if ( $.isFunction( plugin ) ) {
				pluginCallbacks.push( plugin );
			}
		},

		/**
		 * Load modules needed for VisualEditor, as well as plugins.
		 *
		 * This loads the base VE modules as well as any registered plugin modules.
		 * Once those are loaded, any registered plugin callbacks are executed,
		 * and we wait for all promises returned by those callbacks to resolve.
		 *
		 * @return {jQuery.Promise} Promise resolved when the loading process is complete
		 */
		loadModules: function () {
			ve.track( 'trace.moduleLoad.enter' );
			return mw.loader.using( modules )
				.then( function () {
					ve.track( 'trace.moduleLoad.exit' );
					pluginCallbacks.push( ve.init.platform.getInitializedPromise.bind( ve.init.platform ) );
					// Execute plugin callbacks and collect promises
					return $.when.apply( $, pluginCallbacks.map( function ( callback ) {
						return callback();
					} ) );
				} );
		},

		/**
		 * Request the page HTML and various metadata from the MediaWiki API and Parsoid.
		 * @return {jQuery.Promise} Abortable promise resolved with a JSON object
		 */
		requestPageData: function ( pageName, oldid, targetName ) {
			var start, apiXhr, restbaseXhr, apiPromise, restbasePromise, dataPromise,
				data = {
					action: 'visualeditor',
					paction: conf.restbaseUrl ? 'metadata' : 'parse',
					page: pageName,
					uselang: mw.config.get( 'wgUserLanguage' )
				};

			// Only request the API to explicitly load the currently visible revision if we're restoring
			// from oldid. Otherwise we should load the latest version. This prevents us from editing an
			// old version if an edit was made while the user was viewing the page and/or the user is
			// seeing (slightly) stale cache.
			if ( oldid !== undefined ) {
				data.oldid = oldid;
			}
			// Load DOM
			start = ve.now();
			ve.track( 'trace.apiLoad.enter' );

			apiXhr = new mw.Api().get( data );
			apiPromise = apiXhr.then( function ( data, jqxhr ) {
				ve.track( 'trace.apiLoad.exit' );
				ve.track( 'mwtiming.performance.system.apiLoad', {
					bytes: $.byteLength( jqxhr.responseText ),
					duration: ve.now() - start,
					cacheHit: /hit/i.test( jqxhr.getResponseHeader( 'X-Cache' ) ),
					targetName: targetName
				} );
				return data;
			} );

			if ( conf.restbaseUrl ) {
				ve.track( 'trace.restbaseLoad.enter' );
				restbaseXhr = $.ajax( {
					url: conf.restbaseUrl + encodeURIComponent( pageName ) +
						( oldid === undefined ? '' : '/' + oldid ),
					type: 'GET',
					dataType: 'text'
				} );
				restbasePromise = restbaseXhr.then(
					function ( data, status, jqxhr ) {
						ve.track( 'trace.restbaseLoad.exit' );
						ve.track( 'mwtiming.performance.system.restbaseLoad', {
							bytes: $.byteLength( jqxhr.responseText ),
							duration: ve.now() - start,
							targetName: targetName
						} );
						return data;
					},
					function ( response ) {
						if ( response.status === 404 ) {
							// Page does not exist, so let the user start with a blank document.
							return $.Deferred().resolve( '' ).promise();
						} else {
							mw.log.warn( 'One of the load requests failed (unhandled).' );
						}
					}
				);

				dataPromise = $.when( apiPromise, restbasePromise )
					.then( function ( apiData, restbaseHtml ) {
						if ( apiData.visualeditor ) {
							apiData.visualeditor.content = restbaseHtml;
						}
						return apiData;
					} )
					.promise( { abort: function () {
						apiXhr.abort();
						restbaseXhr.abort();
					} } );
			} else {
				dataPromise = apiPromise.promise( { abort: apiXhr.abort } );
			}

			return dataPromise;
		}
	};
}() );