    /**
     * @author Ed Spencer
     * @class Ext.data.proxy.JsonP
     * @extends Ext.data.proxy.Server
     *
     * <p>JsonPProxy is useful when you need to load data from a domain other than the one your application is running
     * on. If your application is running on http://domainA.com it cannot use {@link Ext.data.proxy.Ajax Ajax} to load its
     * data from http://domainB.com because cross-domain ajax requests are prohibited by the browser.</p>
     *
     * <p>We can get around this using a JsonPProxy. JsonPProxy injects a &lt;script&gt; tag into the DOM whenever
     * an AJAX request would usually be made. Let's say we want to load data from http://domainB.com/users - the script tag
     * that would be injected might look like this:</p>
     *
    <pre><code>
    &lt;script src="http://domainB.com/users?callback=someCallback"&gt;&lt;/script&gt;
    </code></pre>
     *
     * <p>When we inject the tag above, the browser makes a request to that url and includes the response as if it was any
     * other type of JavaScript include. By passing a callback in the url above, we're telling domainB's server that we
     * want to be notified when the result comes in and that it should call our callback function with the data it sends
     * back. So long as the server formats the response to look like this, everything will work:</p>
     *
    <pre><code>
    someCallback({
        users: [
            {
                id: 1,
                name: "Ed Spencer",
                email: "ed@sencha.com"
            }
        ]
    });
    </code></pre>
     *
     * <p>As soon as the script finishes loading, the 'someCallback' function that we passed in the url is called with the
     * JSON object that the server returned.</p>
     *
     * <p>JsonPProxy takes care of all of this automatically. It formats the url you pass, adding the callback
     * parameter automatically. It even creates a temporary callback function, waits for it to be called and then puts
     * the data into the Proxy making it look just like you loaded it through a normal {@link Ext.data.proxy.Ajax AjaxProxy}.
     * Here's how we might set that up:</p>
     *
    <pre><code>
    Ext.define('User', {
        extend: 'Ext.data.Model',
        fields: ['id', 'name', 'email']
    });

    var store = new Ext.data.Store({
        model: 'User',
        proxy: {
            type: 'jsonp',
            url : 'http://domainB.com/users'
        }
    });

    store.load();
    </code></pre>
     *
     * <p>That's all we need to do - JsonPProxy takes care of the rest. In this case the Proxy will have injected a
     * script tag like this:
     *
    <pre><code>
    &lt;script src="http://domainB.com/users?callback=stcCallback001" id="stcScript001"&gt;&lt;/script&gt;
    </code></pre>
     *
     * <p><u>Customization</u></p>
     *
     * <p>Most parts of this script tag can be customized using the {@link #callbackParam}, {@link #callbackPrefix} and
     * {@link #scriptIdPrefix} configurations. For example:
     *
    <pre><code>
    var store = new Ext.data.Store({
        model: 'User',
        proxy: {
            type: 'jsonp',
            url : 'http://domainB.com/users',
            callbackParam: 'theCallbackFunction',
            callbackPrefix: 'ABC',
            scriptIdPrefix: 'injectedScript'
        }
    });

    store.load();
    </code></pre>
     *
     * <p>Would inject a script tag like this:</p>
     *
    <pre><code>
    &lt;script src="http://domainB.com/users?theCallbackFunction=ABC001" id="injectedScript001"&gt;&lt;/script&gt;
    </code></pre>
     *
     * <p><u>Implementing on the server side</u></p>
     *
     * <p>The remote server side needs to be configured to return data in this format. Here are suggestions for how you
     * might achieve this using Java, PHP and ASP.net:</p>
     *
     * <p>Java:</p>
     *
    <pre><code>
    boolean jsonP = false;
    String cb = request.getParameter("callback");
    if (cb != null) {
        jsonP = true;
        response.setContentType("text/javascript");
    } else {
        response.setContentType("application/x-json");
    }
    Writer out = response.getWriter();
    if (jsonP) {
        out.write(cb + "(");
    }
    out.print(dataBlock.toJsonString());
    if (jsonP) {
        out.write(");");
    }
    </code></pre>
     *
     * <p>PHP:</p>
     *
    <pre><code>
    $callback = $_REQUEST['callback'];

    // Create the output object.
    $output = array('a' => 'Apple', 'b' => 'Banana');

    //start output
    if ($callback) {
        header('Content-Type: text/javascript');
        echo $callback . '(' . json_encode($output) . ');';
    } else {
        header('Content-Type: application/x-json');
        echo json_encode($output);
    }
    </code></pre>
     *
     * <p>ASP.net:</p>
     *
    <pre><code>
    String jsonString = "{success: true}";
    String cb = Request.Params.Get("callback");
    String responseString = "";
    if (!String.IsNullOrEmpty(cb)) {
        responseString = cb + "(" + jsonString + ")";
    } else {
        responseString = jsonString;
    }
    Response.Write(responseString);
    </code></pre>
     *
     */
    Ext.define('Ext.data.proxy.JsonP', {
        extend: 'Ext.data.proxy.Server',
        alternateClassName: 'Ext.data.ScriptTagProxy',
        alias: ['proxy.jsonp', 'proxy.scripttag'],
        requires: ['Ext.data.JsonP'],

        defaultWriterType: 'base',

        /**
         * @cfg {String} callbackKey (Optional) See {@link Ext.data.JsonP#callbackKey}.
         */
        callbackKey : 'callback',

        /**
         * @cfg {String} recordParam
         * The param name to use when passing records to the server (e.g. 'records=someEncodedRecordString').
         * Defaults to 'records'
         */
        recordParam: 'records',

        /**
         * @cfg {Boolean} autoAppendParams True to automatically append the request's params to the generated url. Defaults to true
         */
        autoAppendParams: true,

        constructor: function(){
            this.addEvents(
                /**
                 * @event exception
                 * Fires when the server returns an exception
                 * @param {Ext.data.proxy.Proxy} this
                 * @param {Ext.data.Request} request The request that was sent
                 * @param {Ext.data.Operation} operation The operation that triggered the request
                 */
                'exception'
            );
            this.callParent(arguments);
        },

        /**
         * @private
         * Performs the read request to the remote domain. JsonPProxy does not actually create an Ajax request,
         * instead we write out a <script> tag based on the configuration of the internal Ext.data.Request object
         * @param {Ext.data.Operation} operation The {@link Ext.data.Operation Operation} object to execute
         * @param {Function} callback A callback function to execute when the Operation has been completed
         * @param {Object} scope The scope to execute the callback in
         */
        doRequest: function(operation, callback, scope) {
            //generate the unique IDs for this request
            var me      = this,
                writer  = me.getWriter(),
                request = me.buildRequest(operation),
                params = request.params;

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

            //apply JsonPProxy-specific attributes to the Request
            Ext.apply(request, {
                callbackKey: me.callbackKey,
                timeout: me.timeout,
                scope: me,
                disableCaching: false, // handled by the proxy
                callback: me.createRequestCallback(request, operation, callback, scope)
            });

            // prevent doubling up
            if (me.autoAppendParams) {
                request.params = {};
            }

            request.jsonp = Ext.data.JsonP.request(request);
            // restore on the request
            request.params = params;
            operation.setStarted();
            me.lastRequest = request;

            return request;
        },

        /**
         * @private
         * Creates and returns the function that is called when the request has completed. The returned function
         * should accept a Response object, which contains the response to be read by the configured Reader.
         * The third argument is the callback that should be called after the request has been completed and the Reader has decoded
         * the response. This callback will typically be the callback passed by a store, e.g. in proxy.read(operation, theCallback, scope)
         * theCallback refers to the callback argument received by this function.
         * See {@link #doRequest} for details.
         * @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(success, response, errorType) {
                delete me.lastRequest;
                me.processResponse(success, operation, request, response, callback, scope);
            };
        },

        // inherit docs
        setException: function(operation, response) {
            operation.setException(operation.request.jsonp.errorType);
        },

        /**
         * Generates a url based on a given Ext.data.Request object. Adds the params and callback function name to the url
         * @param {Ext.data.Request} request The request object
         * @return {String} The url
         */
        buildUrl: function(request) {
            var me      = this,
                url     = me.callParent(arguments),
                params  = Ext.apply({}, request.params),
                filters = params.filters,
                records,
                filter, i;

            delete params.filters;

            if (me.autoAppendParams) {
                url = Ext.urlAppend(url, Ext.Object.toQueryString(params));
            }

            if (filters && filters.length) {
                for (i = 0; i < filters.length; i++) {
                    filter = filters[i];

                    if (filter.value) {
                        url = Ext.urlAppend(url, filter.property + "=" + filter.value);
                    }
                }
            }

            //if there are any records present, append them to the url also
            records = request.records;

            if (Ext.isArray(records) && records.length > 0) {
                url = Ext.urlAppend(url, Ext.String.format("{0}={1}", me.recordParam, me.encodeRecords(records)));
            }

            return url;
        },

        //inherit docs
        destroy: function() {
            this.abort();
            this.callParent();
        },

        /**
         * Aborts the current server request if one is currently running
         */
        abort: function() {
            var lastRequest = this.lastRequest;
            if (lastRequest) {
                Ext.data.JsonP.abort(lastRequest.jsonp);
            }
        },

        /**
         * Encodes an array of records into a string suitable to be appended to the script src url. This is broken
         * out into its own function so that it can be easily overridden.
         * @param {Array} records The records array
         * @return {String} The encoded records string
         */
        encodeRecords: function(records) {
            var encoded = "",
                i = 0,
                len = records.length;

            for (; i < len; i++) {
                encoded += Ext.Object.toQueryString(records[i].data);
            }

            return encoded;
        }
    });