/*!
 * Ext JS Library 3.0.0
 * Copyright(c) 2006-2009 Ext JS, LLC
 * licensing@extjs.com
 * http://www.extjs.com/license
 */
/**
 * @class Ext.data.ScriptTagProxy
 * @extends Ext.data.DataProxy
 * An implementation of Ext.data.DataProxy that reads a data object from a URL which may be in a domain
 * other than the originating domain of the running page.<br>
 * <p>
 * <b>Note that if you are retrieving data from a page that is in a domain that is NOT the same as the originating domain
 * of the running page, you must use this class, rather than HttpProxy.</b><br>
 * <p>
 * The content passed back from a server resource requested by a ScriptTagProxy <b>must</b> be executable JavaScript
 * source code because it is used as the source inside a &lt;script> tag.<br>
 * <p>
 * In order for the browser to process the returned data, the server must wrap the data object
 * with a call to a callback function, the name of which is passed as a parameter by the ScriptTagProxy.
 * Below is a Java example for a servlet which returns data for either a ScriptTagProxy, or an HttpProxy
 * depending on whether the callback name was passed:
 * <p>
 * <pre><code>
boolean scriptTag = false;
String cb = request.getParameter("callback");
if (cb != null) {
    scriptTag = true;
    response.setContentType("text/javascript");
} else {
    response.setContentType("application/x-json");
}
Writer out = response.getWriter();
if (scriptTag) {
    out.write(cb + "(");
}
out.print(dataBlock.toJsonString());
if (scriptTag) {
    out.write(");");
}
</code></pre>
 *
 * @constructor
 * @param {Object} config A configuration object.
 */
Ext.data.ScriptTagProxy = function(config){
    Ext.apply(this, config);

    Ext.data.ScriptTagProxy.superclass.constructor.call(this, config);

    this.head = document.getElementsByTagName("head")[0];

    /**
     * @event loadexception
     * <b>Deprecated</b> in favor of 'exception' event.
     * Fires if an exception occurs in the Proxy during data loading.  This event can be fired for one of two reasons:
     * <ul><li><b>The load call timed out.</b>  This means the load callback did not execute within the time limit
     * specified by {@link #timeout}.  In this case, this event will be raised and the
     * fourth parameter (read error) will be null.</li>
     * <li><b>The load succeeded but the reader could not read the response.</b>  This means the server returned
     * data, but the configured Reader threw an error while reading the data.  In this case, this event will be
     * raised and the caught error will be passed along as the fourth parameter of this event.</li></ul>
     * Note that this event is also relayed through {@link Ext.data.Store}, so you can listen for it directly
     * on any Store instance.
     * @param {Object} this
     * @param {Object} options The loading options that were specified (see {@link #load} for details).  If the load
     * call timed out, this parameter will be null.
     * @param {Object} arg The callback's arg object passed to the {@link #load} function
     * @param {Error} e The JavaScript Error object caught if the configured Reader could not read the data.
     * If the remote request returns success: false, this parameter will be null.
     */
};

Ext.data.ScriptTagProxy.TRANS_ID = 1000;

Ext.extend(Ext.data.ScriptTagProxy, Ext.data.DataProxy, {
    /**
     * @cfg {String} url The URL from which to request the data object.
     */
    /**
     * @cfg {Number} timeout (optional) The number of milliseconds to wait for a response. Defaults to 30 seconds.
     */
    timeout : 30000,
    /**
     * @cfg {String} callbackParam (Optional) The name of the parameter to pass to the server which tells
     * the server the name of the callback function set up by the load call to process the returned data object.
     * Defaults to "callback".<p>The server-side processing must read this parameter value, and generate
     * javascript output which calls this named function passing the data object as its only parameter.
     */
    callbackParam : "callback",
    /**
     *  @cfg {Boolean} nocache (optional) Defaults to true. Disable caching by adding a unique parameter
     * name to the request.
     */
    nocache : true,

    /**
     * HttpProxy implementation of DataProxy#doRequest
     * @param {String} action
     * @param {Ext.data.Record/Ext.data.Record[]} rs If action is <tt>read</tt>, rs will be null
     * @param {Object} params An object containing properties which are to be used as HTTP parameters
     * for the request to the remote server.
     * @param {Ext.data.DataReader} reader The Reader object which converts the data
     * object into a block of Ext.data.Records.
     * @param {Function} callback The function into which to pass the block of Ext.data.Records.
     * The function must be passed <ul>
     * <li>The Record block object</li>
     * <li>The "arg" argument from the load function</li>
     * <li>A boolean success indicator</li>
     * </ul>
     * @param {Object} scope The scope in which to call the callback
     * @param {Object} arg An optional argument which is passed to the callback as its second parameter.
     */
    doRequest : function(action, rs, params, reader, callback, scope, arg) {
        var p = Ext.urlEncode(Ext.apply(params, this.extraParams));

        var url = this.buildUrl(action, rs);
        if (!url) {
            throw new Ext.data.Api.Error('invalid-url', url);
        }
        url = Ext.urlAppend(url, p);

        if(this.nocache){
            url = Ext.urlAppend(url, '_dc=' + (new Date().getTime()));
        }
        var transId = ++Ext.data.ScriptTagProxy.TRANS_ID;
        var trans = {
            id : transId,
            action: action,
            cb : "stcCallback"+transId,
            scriptId : "stcScript"+transId,
            params : params,
            arg : arg,
            url : url,
            callback : callback,
            scope : scope,
            reader : reader
        };
        window[trans.cb] = this.createCallback(action, rs, trans);
        url += String.format("&{0}={1}", this.callbackParam, trans.cb);
        if(this.autoAbort !== false){
            this.abort();
        }

        trans.timeoutId = this.handleFailure.defer(this.timeout, this, [trans]);

        var script = document.createElement("script");
        script.setAttribute("src", url);
        script.setAttribute("type", "text/javascript");
        script.setAttribute("id", trans.scriptId);
        this.head.appendChild(script);

        this.trans = trans;
    },

    // @private createCallback
    createCallback : function(action, rs, trans) {
        var self = this;
        return function(res) {
            self.trans = false;
            self.destroyTrans(trans, true);
            if (action === Ext.data.Api.actions.read) {
                self.onRead.call(self, action, trans, res);
            } else {
                self.onWrite.call(self, action, trans, res, rs);
            }
        };
    },
    /**
     * Callback for read actions
     * @param {String} action [Ext.data.Api.actions.create|read|update|destroy]
     * @param {Object} trans The request transaction object
     * @param {Object} res The server response
     * @private
     */
    onRead : function(action, trans, res) {
        var result;
        try {
            result = trans.reader.readRecords(res);
        }catch(e){
            // @deprecated: fire loadexception
            this.fireEvent("loadexception", this, trans, res, e);

            this.fireEvent('exception', this, 'response', action, trans, res, e);
            trans.callback.call(trans.scope||window, null, trans.arg, false);
            return;
        }
        if (result.success === false) {
            // @deprecated: fire old loadexception for backwards-compat.
            this.fireEvent('loadexception', this, trans, res);

            this.fireEvent('exception', this, 'remote', action, trans, res, null);
        } else {
            this.fireEvent("load", this, res, trans.arg);
        }
        trans.callback.call(trans.scope||window, result, trans.arg, result.success);
    },
    /**
     * Callback for write actions
     * @param {String} action [Ext.data.Api.actions.create|read|update|destroy]
     * @param {Object} trans The request transaction object
     * @param {Object} res The server response
     * @private
     */
    onWrite : function(action, trans, res, rs) {
        var reader = trans.reader;
        try {
            // though we already have a response object here in STP, run through readResponse to catch any meta-data exceptions.
            reader.readResponse(action, res);
        } catch (e) {
            this.fireEvent('exception', this, 'response', action, trans, res, e);
            trans.callback.call(trans.scope||window, null, res, false);
            return;
        }
        if(!res[reader.meta.successProperty] === true){
            this.fireEvent('exception', this, 'remote', action, trans, res, rs);
            trans.callback.call(trans.scope||window, null, res, false);
            return;
        }
        this.fireEvent("write", this, action, res[reader.meta.root], res, rs, trans.arg );
        trans.callback.call(trans.scope||window, res[reader.meta.root], res, true);
    },

    // private
    isLoading : function(){
        return this.trans ? true : false;
    },

    /**
     * Abort the current server request.
     */
    abort : function(){
        if(this.isLoading()){
            this.destroyTrans(this.trans);
        }
    },

    // private
    destroyTrans : function(trans, isLoaded){
        this.head.removeChild(document.getElementById(trans.scriptId));
        clearTimeout(trans.timeoutId);
        if(isLoaded){
            window[trans.cb] = undefined;
            try{
                delete window[trans.cb];
            }catch(e){}
        }else{
            // if hasn't been loaded, wait for load to remove it to prevent script error
            window[trans.cb] = function(){
                window[trans.cb] = undefined;
                try{
                    delete window[trans.cb];
                }catch(e){}
            };
        }
    },

    // private
    handleFailure : function(trans){
        this.trans = false;
        this.destroyTrans(trans, false);
        if (trans.action === Ext.data.Api.actions.read) {
            // @deprecated firing loadexception
            this.fireEvent("loadexception", this, null, trans.arg);
        }

        this.fireEvent('exception', this, 'response', trans.action, {
            response: null,
            options: trans.arg
        });
        trans.callback.call(trans.scope||window, null, trans.arg, false);
    },

    // inherit docs
    destroy: function(){
        this.abort();
        Ext.data.ScriptTagProxy.superclass.destroy.call(this);
    }
});