/**
 * @license Copyright (c) 2003-2013, CKSource - Frederico Knabben. All rights reserved.
 * For licensing, see LICENSE.html or http://ckeditor.com/license
 */

/**
 * @fileOverview Defines the {@link CKEDITOR.ajax} object, which holds ajax methods for
 *		data loading.
 */

(function() {
	CKEDITOR.plugins.add( 'ajax', {
		requires: 'xml'
	});

	/**
	 * Ajax methods for data loading.
	 *
	 * @class
	 * @singleton
	 */
	CKEDITOR.ajax = (function() {
		var createXMLHttpRequest = function() {
				// In IE, using the native XMLHttpRequest for local files may throw
				// "Access is Denied" errors.
				if ( !CKEDITOR.env.ie || location.protocol != 'file:' )
					try {
					return new XMLHttpRequest();
				} catch ( e ) {}

				try {
					return new ActiveXObject( 'Msxml2.XMLHTTP' );
				} catch ( e ) {}
				try {
					return new ActiveXObject( 'Microsoft.XMLHTTP' );
				} catch ( e ) {}

				return null;
			};

		var checkStatus = function( xhr ) {
				// HTTP Status Codes:
				//	 2xx : Success
				//	 304 : Not Modified
				//	   0 : Returned when running locally (file://)
				//	1223 : IE may change 204 to 1223 (see http://dev.jquery.com/ticket/1450)

				return ( xhr.readyState == 4 && ( ( xhr.status >= 200 && xhr.status < 300 ) || xhr.status == 304 || xhr.status === 0 || xhr.status == 1223 ) );
			};

		var getResponseText = function( xhr ) {
				if ( checkStatus( xhr ) )
					return xhr.responseText;
				return null;
			};

		var getResponseXml = function( xhr ) {
				if ( checkStatus( xhr ) ) {
					var xml = xhr.responseXML;
					return new CKEDITOR.xml( xml && xml.firstChild ? xml : xhr.responseText );
				}
				return null;
			};

		var load = function( url, callback, getResponseFn ) {
				var async = !!callback;

				var xhr = createXMLHttpRequest();

				if ( !xhr )
					return null;

				xhr.open( 'GET', url, async );

				if ( async ) {
					// TODO: perform leak checks on this closure.
					xhr.onreadystatechange = function() {
						if ( xhr.readyState == 4 ) {
							callback( getResponseFn( xhr ) );
							xhr = null;
						}
					};
				}

				xhr.send( null );

				return async ? '' : getResponseFn( xhr );
			};

		return {
			/**
			 * Loads data from an URL as plain text.
			 *
			 *		// Load data synchronously.
			 *		var data = CKEDITOR.ajax.load( 'somedata.txt' );
			 *		alert( data );
			 *
			 *		// Load data asynchronously.
			 *		var data = CKEDITOR.ajax.load( 'somedata.txt', function( data ) {
			 *			alert( data );
			 *		} );
			 *
			 * @param {String} url The URL from which load data.
			 * @param {Function} [callback] A callback function to be called on
			 * data load. If not provided, the data will be loaded
			 * synchronously.
			 * @returns {String} The loaded data. For asynchronous requests, an
			 * empty string. For invalid requests, `null`.
			 */
			load: function( url, callback ) {
				return load( url, callback, getResponseText );
			},

			/**
			 * Loads data from an URL as XML.
			 *
			 *		// Load XML synchronously.
			 *		var xml = CKEDITOR.ajax.loadXml( 'somedata.xml' );
			 *		alert( xml.getInnerXml( '//' ) );
			 *
			 *		// Load XML asynchronously.
			 *		var data = CKEDITOR.ajax.loadXml( 'somedata.xml', function( xml ) {
			 *			alert( xml.getInnerXml( '//' ) );
			 *		} );
			 *
			 * @param {String} url The URL from which load data.
			 * @param {Function} [callback] A callback function to be called on
			 * data load. If not provided, the data will be loaded synchronously.
			 * @returns {CKEDITOR.xml} An XML object holding the loaded data. For asynchronous requests, an
			 * empty string. For invalid requests, `null`.
			 */
			loadXml: function( url, callback ) {
				return load( url, callback, getResponseXml );
			}
		};
	})();

})();