// jXHR.js (JSON-P XHR)

// v0.1 (c) Kyle Simpson

// MIT License

(function(global){

	var SETTIMEOUT = global.setTimeout, // for better compression

		doc = global.document,

		callback_counter = 0;

	global.jXHR = function() {

		var script_url,

			script_loaded,

			jsonp_callback,

			scriptElem,

			publicAPI = null;

		function removeScript() { try { scriptElem.parentNode.removeChild(scriptElem); } catch (err) { } }

		function reset() {

			script_loaded = false;

			script_url = "";

			removeScript();

			scriptElem = null;

			fireReadyStateChange(0);

		}

		function ThrowError(msg) {

			try { publicAPI.onerror.call(publicAPI,msg,script_url); } catch (err) { throw new Error(msg); }

		}

		function handleScriptLoad() {

			if ((this.readyState && this.readyState!=="complete" && this.readyState!=="loaded") || script_loaded) { return; }

			this.onload = this.onreadystatechange = null; // prevent memory leak

			script_loaded = true;

			if (publicAPI.readyState !== 4) ThrowError("Script failed to load ["+script_url+"].");

			removeScript();

		}

		function fireReadyStateChange(rs,args) {

			args = args || [];

			publicAPI.readyState = rs;

			if (typeof publicAPI.onreadystatechange === "function") publicAPI.onreadystatechange.apply(publicAPI,args);

		}

		publicAPI = {

			onerror:null,

			onreadystatechange:null,

			readyState:0,

			open:function(method,url){

				reset();

				internal_callback = "cb"+(callback_counter++);

				(function(icb){

					global.jXHR[icb] = function() {

						try { fireReadyStateChange.call(publicAPI,4,arguments); }

						catch(err) {

							publicAPI.readyState = -1;

							ThrowError("Script failed to run ["+script_url+"].");

						}

						global.jXHR[icb] = null;

					};

				})(internal_callback);

				script_url = url.replace(/=\?/,"=jXHR."+internal_callback);

				fireReadyStateChange(1);

			},

			send:function(){

				SETTIMEOUT(function(){

					scriptElem = doc.createElement("script");

					scriptElem.setAttribute("type","text/javascript");

					scriptElem.onload = scriptElem.onreadystatechange = function(){handleScriptLoad.call(scriptElem);};

					scriptElem.setAttribute("src",script_url);

					doc.getElementsByTagName("head")[0].appendChild(scriptElem);

				},0);

				fireReadyStateChange(2);

			},

			setRequestHeader:function(){}, // noop

			getResponseHeader:function(){return "";}, // basically noop

			getAllResponseHeaders:function(){return [];} // ditto

		};

		reset();

		return publicAPI;

	};

})(window);