/*
Script: XHR.js
        Contains the basic XMLHttpRequest Class Wrapper.

License:
        MIT-style license.
*/

/*
Class: XHR
        Basic XMLHttpRequest Wrapper.

Arguments:
        options - an object with options names as keys. See options below.

Options:
        method - 'post' or 'get' - the protocol for the request; optional, defaults to 'post'.
        async - boolean: asynchronous option; true uses asynchronous requests. Defaults to true.
        encoding - the encoding, defaults to utf-8.
        autoCancel - cancels the already running request if another one is sent. defaults to false.
        headers - accepts an object, that will be set to request headers.

Events:
        onRequest - function to execute when the XHR request is fired.
        onSuccess - function to execute when the XHR request completes.
        onStateChange - function to execute when the state of the XMLHttpRequest changes.
        onFailure - function to execute when the state of the XMLHttpRequest changes.

Properties:
        running - true if the request is running.
        response - object, text and xml as keys. You can access this property in the onSuccess event.

Example:
        >var myXHR = new XHR({method: 'get'}).send('http://site.com/requestHandler.php', 'name=john&lastname=dorian');
*/

var XHR = new Class({

        options: {
                method: 'post',
                async: true,
                onRequest: Class.empty,
                onSuccess: Class.empty,
                onFailure: Class.empty,
                urlEncoded: true,
                encoding: 'utf-8',
                autoCancel: false,
                headers: {}
        },

        setTransport: function(){
                this.transport = (window.XMLHttpRequest) ? new XMLHttpRequest() : (window.ie ? new ActiveXObject('Microsoft.XMLHTTP') : false);
                return this;
        },

        initialize: function(options){
                this.setTransport().setOptions(options);
                this.options.isSuccess = this.options.isSuccess || this.isSuccess;
                this.headers = {};
                if (this.options.urlEncoded && this.options.method == 'post'){
                        var encoding = (this.options.encoding) ? '; charset=' + this.options.encoding : '';
                        this.setHeader('Content-type', 'application/x-www-form-urlencoded' + encoding);
                }
                if (this.options.initialize) this.options.initialize.call(this);
        },

        onStateChange: function(){
                if (this.transport.readyState != 4 || !this.running) return;
                this.running = false;
                var status = 0;
                try {status = this.transport.status;} catch(e){};
                if (this.options.isSuccess.call(this, status)) this.onSuccess();
                else this.onFailure();
                this.transport.onreadystatechange = Class.empty;
        },

        isSuccess: function(status){
                return ((status >= 200) && (status < 300));
        },

        onSuccess: function(){
                this.response = {
                        'text': this.transport.responseText,
                        'xml': this.transport.responseXML
                };
                this.fireEvent('onSuccess', [this.response.text, this.response.xml]);
                this.callChain();
        },

        onFailure: function(){
                this.fireEvent('onFailure', this.transport);
        },

        /*
        Property: setHeader
                Add/modify an header for the request. It will not override headers from the options.

        Example:
                >var myXhr = new XHR(url, {method: 'get', headers: {'X-Request': 'JSON'}});
                >myXhr.setHeader('Last-Modified','Sat, 1 Jan 2005 05:00:00 GMT');
        */

        setHeader: function(name, value){
                this.headers[name] = value;
                return this;
        },

        /*
        Property: send
                Opens the XHR connection and sends the data. Data has to be null or a string.

        Example:
                >var myXhr = new XHR({method: 'post'});
                >myXhr.send(url, querystring);
                >
                >var syncXhr = new XHR({async: false, method: 'post'});
                >syncXhr.send(url, null);
                >
        */

        send: function(url, data){
                if (this.options.autoCancel) this.cancel();
                else if (this.running) return this;
                this.running = true;
                if (data && this.options.method == 'get'){
                        url = url + (url.contains('?') ? '&' : '?') + data;
                        data = null;
                }
                this.transport.open(this.options.method.toUpperCase(), url, this.options.async);
                this.transport.onreadystatechange = this.onStateChange.bind(this);
                if ((this.options.method == 'post') && this.transport.overrideMimeType) this.setHeader('Connection', 'close');
                $extend(this.headers, this.options.headers);
                for (var type in this.headers) try {this.transport.setRequestHeader(type, this.headers[type]);} catch(e){};
                this.fireEvent('onRequest');
                this.transport.send($pick(data, null));
                return this;
        },

        /*
        Property: cancel
                Cancels the running request. No effect if the request is not running.

        Example:
                >var myXhr = new XHR({method: 'get'}).send(url);
                >myXhr.cancel();
        */

        cancel: function(){
                if (!this.running) return this;
                this.running = false;
                this.transport.abort();
                this.transport.onreadystatechange = Class.empty;
                this.setTransport();
                this.fireEvent('onCancel');
                return this;
        }

});

XHR.implement(new Chain, new Events, new Options);