/**
 * Retrieve and Parse RSS Feeds
 * @author gabe@fijiwebdesign.com
 * @copyright www.fijiwebdesign.com
 * @license Creative-Commons 2.0
 * @version $Id$
 */
RSSClient = function() {
	// sad, but we need this to call our instance from global scope
	this._id = new String('instance_'+new Date().getTime());
	RSSClient[this._id] = this;
};
RSSClient.prototype = {
	
	/**
	 * JSON proxy url
	 */
	proxy: 'http://json-proxy.jgate.de/',
	

	/**
	 * Attach an Event Listener
	 * @param {HTMLElement} el DOM Node
	 * @param {String} type Event Type
	 * @param {Function} fn Event listener
	 * @param {Bool}
	 */
	addEvent: function(el, type, fn, useCapture) {
		if (el.addEventListener) {
			el.addEventListener(type, fn, useCapture);
		} else if (el.attachEvent) {
			el.attachEvent('on' + type, fn);
		} else {
			el['on' + type] = fn;
		}
	},
	
	/**
	 * Attach a Script Element to the DOM
	 * @param {String} src URL of script
	 */
	addScript: function(src) {
		var head = document.getElementsByTagName('head')[0];
		var script = document.createElement('script');
		script.type = 'text/javascript';
		script.src = src;
		head.appendChild(script);
	},
	
	/**
	 * Convert String XML to DOM XML Object
	 * @param {String} strXML
	 */
	textToXML: function(strXML) {
		var xmlDoc = null;
		try {
			xmlDoc = (document.all)?new ActiveXObject("Microsoft.XMLDOM"):new DOMParser();
			xmlDoc.async = false;
		} catch(e) {throw new Error("XML Parser could not be instantiated");}
		var out;
		try {
			if(document.all) {
				out = (xmlDoc.loadXML(strXML))?xmlDoc:false;
			} else {  
				out = xmlDoc.parseFromString(strXML, "text/xml");
			}
		} catch(e) { throw new Error("Error parsing XML string"); }
		return out;
	},
	
	/**
	 * Retrieve an RSS Feed
	 * @param {Object} url
	 */
	getRSS: function(url, callback) {
		var self = this;
		self._callback = callback;
		self.callback = function(str) {
			var xml = self.textToXML(str);
			self._callback(xml);
		};
		var proxy = this.proxy+'?url='+encodeURIComponent(url)+'&callback=RSSClient.'+this._id+'.callback';
		this.addScript(proxy);
	},
	
	/**
	 * Add observer of client load
	 */
	onload: function(fn) {
		this.addEvent(window, 'load', fn);
	}
}