    /**
     * @author Ed Spencer
     * @class Ext.data.proxy.Ajax
     * @extends Ext.data.proxy.Server
     *
     * <p>AjaxProxy is one of the most widely-used ways of getting data into your application. It uses AJAX requests to
     * load data from the server, usually to be placed into a {@link Ext.data.Store Store}. Let's take a look at a typical
     * setup. Here we're going to set up a Store that has an AjaxProxy. To prepare, we'll also set up a
     * {@link Ext.data.Model Model}:</p>
     *
    <pre><code>
    Ext.define('User', {
        extend: 'Ext.data.Model',
        fields: ['id', 'name', 'email']
    });

    //The Store contains the AjaxProxy as an inline configuration
    var store = new Ext.data.Store({
        model: 'User',
        proxy: {
            type: 'ajax',
            url : 'users.json'
        }
    });

    store.load();
    </code></pre>
     *
     * <p>Our example is going to load user data into a Store, so we start off by defining a {@link Ext.data.Model Model}
     * with the fields that we expect the server to return. Next we set up the Store itself, along with a {@link #proxy}
     * configuration. This configuration was automatically turned into an Ext.data.proxy.Ajax instance, with the url we
     * specified being passed into AjaxProxy's constructor. It's as if we'd done this:</p>
     *
    <pre><code>
    new Ext.data.proxy.Ajax({
        url: 'users.json',
        model: 'User',
        reader: 'json'
    });
    </code></pre>
     *
     * <p>A couple of extra configurations appeared here - {@link #model} and {@link #reader}. These are set by default
     * when we create the proxy via the Store - the Store already knows about the Model, and Proxy's default
     * {@link Ext.data.reader.Reader Reader} is {@link Ext.data.reader.Json JsonReader}.</p>
     *
     * <p>Now when we call store.load(), the AjaxProxy springs into action, making a request to the url we configured
     * ('users.json' in this case). As we're performing a read, it sends a GET request to that url (see {@link #actionMethods}
     * to customize this - by default any kind of read will be sent as a GET request and any kind of write will be sent as a
     * POST request).</p>
     *
     * <p><u>Limitations</u></p>
     *
     * <p>AjaxProxy cannot be used to retrieve data from other domains. If your application is running on http://domainA.com
     * it cannot load data from http://domainB.com because browsers have a built-in security policy that prohibits domains
     * talking to each other via AJAX.</p>
     *
     * <p>If you need to read data from another domain and can't set up a proxy server (some software that runs on your own
     * domain's web server and transparently forwards requests to http://domainB.com, making it look like they actually came
     * from http://domainA.com), you can use {@link Ext.data.proxy.JsonP} and a technique known as JSON-P (JSON with
     * Padding), which can help you get around the problem so long as the server on http://domainB.com is set up to support
     * JSON-P responses. See {@link Ext.data.proxy.JsonP JsonPProxy}'s introduction docs for more details.</p>
     *
     * <p><u>Readers and Writers</u></p>
     *
     * <p>AjaxProxy can be configured to use any type of {@link Ext.data.reader.Reader Reader} to decode the server's response. If
     * no Reader is supplied, AjaxProxy will default to using a {@link Ext.data.reader.Json JsonReader}. Reader configuration
     * can be passed in as a simple object, which the Proxy automatically turns into a {@link Ext.data.reader.Reader Reader}
     * instance:</p>
     *
    <pre><code>
    var proxy = new Ext.data.proxy.Ajax({
        model: 'User',
        reader: {
            type: 'xml',
            root: 'users'
        }
    });

    proxy.getReader(); //returns an {@link Ext.data.reader.Xml XmlReader} instance based on the config we supplied
    </code></pre>
     *
     * <p><u>Url generation</u></p>
     *
     * <p>AjaxProxy automatically inserts any sorting, filtering, paging and grouping options into the url it generates for
     * each request. These are controlled with the following configuration options:</p>
     *
     * <ul style="list-style-type: disc; padding-left: 20px;">
     *     <li>{@link #pageParam} - controls how the page number is sent to the server
     *     (see also {@link #startParam} and {@link #limitParam})</li>
     *     <li>{@link #sortParam} - controls how sort information is sent to the server</li>
     *     <li>{@link #groupParam} - controls how grouping information is sent to the server</li>
     *     <li>{@link #filterParam} - controls how filter information is sent to the server</li>
     * </ul>
     *
     * <p>Each request sent by AjaxProxy is described by an {@link Ext.data.Operation Operation}. To see how we can
     * customize the generated urls, let's say we're loading the Proxy with the following Operation:</p>
     *
    <pre><code>
    var operation = new Ext.data.Operation({
        action: 'read',
        page  : 2
    });
    </code></pre>
     *
     * <p>Now we'll issue the request for this Operation by calling {@link #read}:</p>
     *
    <pre><code>
    var proxy = new Ext.data.proxy.Ajax({
        url: '/users'
    });

    proxy.read(operation); //GET /users?page=2
    </code></pre>
     *
     * <p>Easy enough - the Proxy just copied the page property from the Operation. We can customize how this page data is
     * sent to the server:</p>
     *
    <pre><code>
    var proxy = new Ext.data.proxy.Ajax({
        url: '/users',
        pagePage: 'pageNumber'
    });

    proxy.read(operation); //GET /users?pageNumber=2
    </code></pre>
     *
     * <p>Alternatively, our Operation could have been configured to send start and limit parameters instead of page:</p>
     *
    <pre><code>
    var operation = new Ext.data.Operation({
        action: 'read',
        start : 50,
        limit : 25
    });

    var proxy = new Ext.data.proxy.Ajax({
        url: '/users'
    });

    proxy.read(operation); //GET /users?start=50&limit=25
    </code></pre>
     *
     * <p>Again we can customize this url:</p>
     *
    <pre><code>
    var proxy = new Ext.data.proxy.Ajax({
        url: '/users',
        startParam: 'startIndex',
        limitParam: 'limitIndex'
    });

    proxy.read(operation); //GET /users?startIndex=50&limitIndex=25
    </code></pre>
     *
     * <p>AjaxProxy will also send sort and filter information to the server. Let's take a look at how this looks with a
     * more expressive Operation object:</p>
     *
    <pre><code>
    var operation = new Ext.data.Operation({
        action: 'read',
        sorters: [
            new Ext.util.Sorter({
                property : 'name',
                direction: 'ASC'
            }),
            new Ext.util.Sorter({
                property : 'age',
                direction: 'DESC'
            })
        ],
        filters: [
            new Ext.util.Filter({
                property: 'eyeColor',
                value   : 'brown'
            })
        ]
    });
    </code></pre>
     *
     * <p>This is the type of object that is generated internally when loading a {@link Ext.data.Store Store} with sorters
     * and filters defined. By default the AjaxProxy will JSON encode the sorters and filters, resulting in something like
     * this (note that the url is escaped before sending the request, but is left unescaped here for clarity):</p>
     *
    <pre><code>
    var proxy = new Ext.data.proxy.Ajax({
        url: '/users'
    });

    proxy.read(operation); //GET /users?sort=[{"property":"name","direction":"ASC"},{"property":"age","direction":"DESC"}]&filter=[{"property":"eyeColor","value":"brown"}]
    </code></pre>
     *
     * <p>We can again customize how this is created by supplying a few configuration options. Let's say our server is set
     * up to receive sorting information is a format like "sortBy=name#ASC,age#DESC". We can configure AjaxProxy to provide
     * that format like this:</p>
     *
     <pre><code>
     var proxy = new Ext.data.proxy.Ajax({
         url: '/users',
         sortParam: 'sortBy',
         filterParam: 'filterBy',

         //our custom implementation of sorter encoding - turns our sorters into "name#ASC,age#DESC"
         encodeSorters: function(sorters) {
             var length   = sorters.length,
                 sortStrs = [],
                 sorter, i;

             for (i = 0; i < length; i++) {
                 sorter = sorters[i];

                 sortStrs[i] = sorter.property + '#' + sorter.direction
             }

             return sortStrs.join(",");
         }
     });

     proxy.read(operation); //GET /users?sortBy=name#ASC,age#DESC&filterBy=[{"property":"eyeColor","value":"brown"}]
     </code></pre>
     *
     * <p>We can also provide a custom {@link #encodeFilters} function to encode our filters.</p>
     *
     * @constructor
     *
     * <p>Note that if this HttpProxy is being used by a {@link Ext.data.Store Store}, then the
     * Store's call to {@link #load} will override any specified <tt>callback</tt> and <tt>params</tt>
     * options. In this case, use the Store's {@link Ext.data.Store#events events} to modify parameters,
     * or react to loading events. The Store's {@link Ext.data.Store#baseParams baseParams} may also be
     * used to pass parameters known at instantiation time.</p>
     *
     * <p>If an options parameter is passed, the singleton {@link Ext.Ajax} object will be used to make
     * the request.</p>
     */
    Ext.define('Ext.data.proxy.Ajax', {
        requires: ['Ext.util.MixedCollection', 'Ext.Ajax'],
        extend: 'Ext.data.proxy.Server',
        alias: 'proxy.ajax',
        alternateClassName: ['Ext.data.HttpProxy', 'Ext.data.AjaxProxy'],

        /**
         * @property actionMethods
         * Mapping of action name to HTTP request method. In the basic AjaxProxy these are set to 'GET' for 'read' actions and 'POST'
         * for 'create', 'update' and 'destroy' actions. The {@link Ext.data.proxy.Rest} maps these to the correct RESTful methods.
         */
        actionMethods: {
            create : 'POST',
            read   : 'GET',
            update : 'POST',
            destroy: 'POST'
        },

        /**
         * @cfg {Object} headers Any headers to add to the Ajax request. Defaults to <tt>undefined</tt>.
         */

        /**
         * @ignore
         */
        doRequest: function(operation, callback, scope) {
            var writer  = this.getWriter(),
                request = this.buildRequest(operation, callback, scope);

            if (operation.allowWrite()) {
                request = writer.write(request);
            }

            Ext.apply(request, {
                headers       : this.headers,
                timeout       : this.timeout,
                scope         : this,
                callback      : this.createRequestCallback(request, operation, callback, scope),
                method        : this.getMethod(request),
                disableCaching: false // explicitly set it to false, ServerProxy handles caching
            });

            Ext.Ajax.request(request);

            return request;
        },

        /**
         * Returns the HTTP method name for a given request. By default this returns based on a lookup on {@link #actionMethods}.
         * @param {Ext.data.Request} request The request object
         * @return {String} The HTTP method to use (should be one of 'GET', 'POST', 'PUT' or 'DELETE')
         */
        getMethod: function(request) {
            return this.actionMethods[request.action];
        },

        /**
         * @private
         * TODO: This is currently identical to the JsonPProxy version except for the return function's signature. There is a lot
         * of code duplication inside the returned function so we need to find a way to DRY this up.
         * @param {Ext.data.Request} request The Request object
         * @param {Ext.data.Operation} operation The Operation being executed
         * @param {Function} callback The callback function to be called when the request completes. This is usually the callback
         * passed to doRequest
         * @param {Object} scope The scope in which to execute the callback function
         * @return {Function} The callback function
         */
        createRequestCallback: function(request, operation, callback, scope) {
            var me = this;

            return function(options, success, response) {
                me.processResponse(success, operation, request, response, callback, scope);
            };
        }
    }, function() {
        //backwards compatibility, remove in Ext JS 5.0
        Ext.data.HttpProxy = this;
    });