    /**
     * @class Ext.Direct
     * @extends Ext.util.Observable
     * <p><b><u>Overview</u></b></p>
     *
     * <p>Ext.Direct aims to streamline communication between the client and server
     * by providing a single interface that reduces the amount of common code
     * typically required to validate data and handle returned data packets
     * (reading data, error conditions, etc).</p>
     *
     * <p>The Ext.direct namespace includes several classes for a closer integration
     * with the server-side. The Ext.data namespace also includes classes for working
     * with Ext.data.Stores which are backed by data from an Ext.Direct method.</p>
     *
     * <p><b><u>Specification</u></b></p>
     *
     * <p>For additional information consult the
     * <a href="http://extjs.com/products/extjs/direct.php">Ext.Direct Specification</a>.</p>
     *
     * <p><b><u>Providers</u></b></p>
     *
     * <p>Ext.Direct uses a provider architecture, where one or more providers are
     * used to transport data to and from the server. There are several providers
     * that exist in the core at the moment:</p><div class="mdetail-params"><ul>
     *
     * <li>{@link Ext.direct.JsonProvider JsonProvider} for simple JSON operations</li>
     * <li>{@link Ext.direct.PollingProvider PollingProvider} for repeated requests</li>
     * <li>{@link Ext.direct.RemotingProvider RemotingProvider} exposes server side
     * on the client.</li>
     * </ul></div>
     *
     * <p>A provider does not need to be invoked directly, providers are added via
     * {@link Ext.Direct}.{@link Ext.Direct#add add}.</p>
     *
     * <p><b><u>Router</u></b></p>
     *
     * <p>Ext.Direct utilizes a "router" on the server to direct requests from the client
     * to the appropriate server-side method. Because the Ext.Direct API is completely
     * platform-agnostic, you could completely swap out a Java based server solution
     * and replace it with one that uses C# without changing the client side JavaScript
     * at all.</p>
     *
     * <p><b><u>Server side events</u></b></p>
     *
     * <p>Custom events from the server may be handled by the client by adding
     * listeners, for example:</p>
     * <pre><code>
    {"type":"event","name":"message","data":"Successfully polled at: 11:19:30 am"}

    // add a handler for a 'message' event sent by the server
    Ext.Direct.on('message', function(e){
        out.append(String.format('&lt;p>&lt;i>{0}&lt;/i>&lt;/p>', e.data));
                out.el.scrollTo('t', 100000, true);
    });
     * </code></pre>
     * @singleton
     */
    Ext.Direct = Ext.extend(Ext.util.Observable, {
        /**
         * Each event type implements a getData() method. The default event types are:
         * <div class="mdetail-params"><ul>
         * <li><b><tt>event</tt></b> : Ext.Direct.Event</li>
         * <li><b><tt>exception</tt></b> : Ext.Direct.ExceptionEvent</li>
         * <li><b><tt>rpc</tt></b> : Ext.Direct.RemotingEvent</li>
         * </ul></div>
         * @property eventTypes
         * @type Object
         */

        /**
         * Four types of possible exceptions which can occur:
         * <div class="mdetail-params"><ul>
         * <li><b><tt>Ext.Direct.exceptions.TRANSPORT</tt></b> : 'xhr'</li>
         * <li><b><tt>Ext.Direct.exceptions.PARSE</tt></b> : 'parse'</li>
         * <li><b><tt>Ext.Direct.exceptions.LOGIN</tt></b> : 'login'</li>
         * <li><b><tt>Ext.Direct.exceptions.SERVER</tt></b> : 'exception'</li>
         * </ul></div>
         * @property exceptions
         * @type Object
         */
        exceptions: {
            TRANSPORT: 'xhr',
            PARSE: 'parse',
            LOGIN: 'login',
            SERVER: 'exception'
        },

        // private
        constructor: function(){
            this.addEvents(
                /**
                 * @event event
                 * Fires after an event.
                 * @param {event} e The {@link Ext.Direct#eventTypes Ext.Direct.Event type} that occurred.
                 * @param {Ext.direct.Provider} provider The {@link Ext.direct.Provider Provider}.
                 */
                'event',
                /**
                 * @event exception
                 * Fires after an event exception.
                 * @param {event} e The {@link Ext.Direct#eventTypes Ext.Direct.Event type} that occurred.
                 */
                'exception'
            );
            this.transactions = {};
            this.providers = {};
        },

        /**
         * Adds an Ext.Direct Provider and creates the proxy or stub methods to execute server-side methods.
         * If the provider is not already connected, it will auto-connect.
         * <pre><code>
    var pollProv = new Ext.direct.PollingProvider({
        url: 'php/poll2.php'
    });

    Ext.Direct.addProvider(
        {
            "type":"remoting",       // create a {@link Ext.direct.RemotingProvider}
            "url":"php\/router.php", // url to connect to the Ext.Direct server-side router.
            "actions":{              // each property within the actions object represents a Class
                "TestAction":[       // array of methods within each server side Class
                {
                    "name":"doEcho", // name of method
                    "len":1
                },{
                    "name":"multiply",
                    "len":1
                },{
                    "name":"doForm",
                    "formHandler":true, // handle form on server with Ext.Direct.Transaction
                    "len":1
                }]
            },
            "namespace":"myApplication",// namespace to create the Remoting Provider in
        },{
            type: 'polling', // create a {@link Ext.direct.PollingProvider}
            url:  'php/poll.php'
        },
        pollProv // reference to previously created instance
    );
         * </code></pre>
         * @param {Object/Array} provider Accepts either an Array of Provider descriptions (an instance
         * or config object for a Provider) or any number of Provider descriptions as arguments.  Each
         * Provider description instructs Ext.Direct how to create client-side stub methods.
         */
        addProvider : function(provider){
            var a = arguments;
            if(a.length > 1){
                for(var i = 0, len = a.length; i < len; i++){
                    this.addProvider(a[i]);
                }
                return;
            }

            // if provider has not already been instantiated
            if(!provider.events){
                provider = new Ext.Direct.PROVIDERS[provider.type](provider);
            }
            provider.id = provider.id || Ext.id();
            this.providers[provider.id] = provider;

            provider.on('data', this.onProviderData, this);
            provider.on('exception', this.onProviderException, this);

            if(!provider.isConnected()){
                provider.connect();
            }

            return provider;
        },

        /**
         * Retrieve a {@link Ext.direct.Provider provider} by the
         * <b><tt>{@link Ext.direct.Provider#id id}</tt></b> specified when the provider is
         * {@link #addProvider added}.
         * @param {String} id Unique identifier assigned to the provider when calling {@link #addProvider}
         */
        getProvider : function(id){
            return this.providers[id];
        },

        removeProvider : function(id){
            var provider = id.id ? id : this.providers[id];
            provider.un('data', this.onProviderData, this);
            provider.un('exception', this.onProviderException, this);
            delete this.providers[provider.id];
            return provider;
        },

        addTransaction: function(t){
            this.transactions[t.tid] = t;
            return t;
        },

        removeTransaction: function(t){
            delete this.transactions[t.tid || t];
            return t;
        },

        getTransaction: function(tid){
            return this.transactions[tid.tid || tid];
        },

        onProviderData : function(provider, e){
            if(Ext.isArray(e)){
                for(var i = 0, len = e.length; i < len; i++){
                    this.onProviderData(provider, e[i]);
                }
                return;
            }
            if(e.name && e.name != 'event' && e.name != 'exception'){
                this.fireEvent(e.name, e);
            }else if(e.type == 'exception'){
                this.fireEvent('exception', e);
            }
            this.fireEvent('event', e, provider);
        },

        createEvent : function(response, extraProps){
            return new Ext.Direct.eventTypes[response.type](Ext.apply(response, extraProps));
        }
    });
    // overwrite impl. with static instance
    Ext.Direct = new Ext.Direct();

    Ext.Direct.TID = 1;
    Ext.Direct.PROVIDERS = {};