/* AjaxRequest encapsulates AJAX functionality into a javascript class.
 * The aim of this is to make it easier for a developer to handle
 * data in the form of TEXT or XML from an asynchronous AJAX, or a synchronous
 * call from the XMLHttpRequest object.
 */

AjaxRequest.prototype._request;			// holds the XMLHttpRequest object

AjaxRequest.prototype._response;		// holds the response in the form of
																						// TEXT from the XMLHttpRequest request









/**
 * constructor.  This just sets up this instance's XMLHttpRequest request 
 * instance.
 */
function AjaxRequest() {
	if (window.XMLHttpRequest)
		this._request = new XMLHttpRequest();  //for cool people
	else if (window.ActiveXObject)
		this._request = new ActiveXObject("Microsoft.XMLHTTP");	//for IE users
	else
		return null;
}



AjaxRequest.prototype.abort = function() {
	this._onDataRetrieved = false;
	this._request.abort();
}



/**
 * asyncRequest is called when you want to make an ASYNCHRONOUS request
 * to the XMLHttpRequest object.  This is also known as AJAX.  The javascript
 * continues to run and DOES NOT wait for data to be returned.
 *
 * @param method	String - HTML method to GET or POST parameters to a page.
 * @param url			String - URL to request data from.
 * @param params	String - parameters to GET/POST from/to that URL.  Should take 
 *								the form: "param1=x1&param2=x2&..."  NOTICE: NO LEADING "?"!!
 * @param onData	this is the callback function the coder wishes to execute
 *										once data is returned from the AJAX request.
 */
AjaxRequest.prototype.asyncRequest = function(method, url, params, onData) {

	/* i have to emulate overloading here since you can't do that in javascript.
	 * this is necessary because the user could specify a callback, but no parameters.
	 * In this case, the javascript would think that the callback is the parameter(s)
	 * due to the order of arguments in this method's signature.
	 */
	 

	 
	 
	 //check to see if the third argument is a function (onData) or not
	 if (arguments.length == 3) {
	 
		if (typeof arguments[2] == 'function') {
			onData = arguments[2];
			params = false;
		}
	 }

	//this is the function you want to be called once the data is returned
	if (onData) this.onData = onData;

	//determines whether you want to post or get the parameters
	method ? method = method.toUpperCase() : method = "GET";
	
	//the url to request from
	var fullURL = url;
	

	
	if (method =="GET") {
		//HTML method is GET
		
		//stick the parameters onto the end of the URL
		if (params) fullURL += "?" + params;
		
		//this is the textbook AJAX call
		this._request.open(method, fullURL, true);

		//ANOTHER IE bug... have to set onreadystatechange after open so we can reuse _request
		//this allows the call back to know see the instance of AjaxRequest that called it.
		var _this = this;
		this._request.onreadystatechange = function() {if (_this._onDataRetrieved) _this._onDataRetrieved()};
		
		//we aren't POSTing any parameters so there's nothing to send.
		this._request.send(null);   
		
	} else if (method == "POST") {
		//HTML method is POST
		
		//here is the AJAX call
		this._request.open(method, fullURL , true);
		
		//ANOTHER IE bug... have to set onreadystatechange after open so we can reuse _request
		//this allows the call back to know see the instance of AjaxRequest that called it.
		var _this = this;
		this._request.onreadystatechange = function() {if (_this._onDataRetrieved) _this._onDataRetrieved()};
				
		
		//if there are any parameters, we post them here via the send method.
		if (params) {
		
			//set some request headers for our POSTed parameters
			this._request.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
			this._request.setRequestHeader('Connection', 'close');		
			this._request.setRequestHeader('Content-length', params.length);
			this._request.send(params);
			
		} else {
		
			//no parameters specified
			this._request.send(null);
		}
	}
}









/**
 * syncRequest is called when you want to make a SYNCHRONOUS request
 * to the XMLHttpRequest object. The JAVASCRIPT STOPS EXECUTION UNTIL DATA IS
 * IS RETURNED FROM THE REQUEST.  NOTICE: This will cause the browser to freeze 
 * until data is retrieved.
 *
 * @param method	String - HTML method to GET or POST parameters to a page.
 * @param url			String - URL to request data from.
 * @param params	String - parameters to GET/POST from/to that URL.  Should take 
 *								the form: "param1=x1&param2=x2&..."  NOTICE: NO LEADING "?"!!
 */
AjaxRequest.prototype.syncRequest = function(method, url, params) {
	
	//determines whether you want to post or get the parameters
	method ? method = method.toUpperCase() : method = "GET";
	
	//the url to request from
	var fullURL = url;
	
	if (method =="GET") {
		//HTML method is GET
	
		//stick the parameters at the end of the url
		if (params) fullURL += "?" + params;
		
		//this is the synchronous call that freezes up your browser while it waits
		//for data to return
		this._request.open(method, fullURL, false);
		
		//we aren't POSTing any parameters so there's nothing to send.
		this._request.send(null);   
	
	} else if (method == "POST") {
		//HTML method is POST{
		
		//this is the synchronous call that freezes up your browser while it waits
		//for data to return
		this._request.open(method, fullURL , false);
		
		//if there are any parameters, we post them here via the send method.
		if (params) {
		
			//set some request headers for our POSTed parameters
			this._request.setRequestHeader("Cache-Control","no-store");
			this._request.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
			this._request.setRequestHeader('Connection', 'close');		
			this._request.setRequestHeader('Content-length', params.length);
			this._request.send(params);
		} else {
		
			//no parameters specified
			this._request.send(null);
		}
	}

	//perform the call back since the request call has by now returned.
	if (this._onDataRetrieved) this._onDataRetrieved();
}









/**
 * _onDataRetrieved is called by both async and sync requests.  This call reads the
 * returned data from the XMLHttpRequest instance and puts it in to a string.
 * If there is a callback function specified (only from an AJAX (async) request),
 * the callback is executed here.
 */
AjaxRequest.prototype._onDataRetrieved = function() {
	if (this._request.readyState == 4) {
		if (this._request.status == 200) {
		
			//get the data in String form from request
			this._response = this._request.responseText;
			
			//the onData callback (FOR AJAX (async) CALLS ONLY)
			if (this.onData) {
				this.onData();
				this.onData = '';
			}
			
		} else {
		
			//there was an error retrieving the data, there are several-
			//see: http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html
			this._response = "An error occurred retrieving data: " + this._request.status;
			
		}
	}
}










/**
 * getReponseText returns the data retrieved from the request in the form of a 
 * String.
 *
 * @return	the response from the XMLHttpRequest request as a String.
 */
AjaxRequest.prototype.getResponseText = function() {
	return this._response;
}









/**
 * getResponseXML transforms the data returned from the request into an XML
 * document.  Make sure it is valid XML returned in the first place.
 *
 * @return	data retrieved from request in form of an XML document.
 */
AjaxRequest.prototype.getResponseXML = function() {
    
	var theDocument = false;	//this will be the XML document

	if (window.XMLHttpRequest) {		//for everyone else
	
		try {
			
			//parse the request String to form an XML document.
			var parser = new DOMParser();
			theDocument = parser.parseFromString(this._response, "text/xml");
			
		} catch (e) {
		
			//oops. something went wrong in your parsing.
			alert("Error parsing XML.");
			
			return false;
		}

	} if (window.ActiveXObject) {		//for IE users......
		
		try {

			//parse the request String to form an XML document.
			theDocument = new ActiveXObject("Microsoft.XMLDOM");
			theDocument.async = false;
			theDocument.loadXML(this._response);
			
		} catch (e) {
		
			//oops. something went wrong in your parsing.		
			alert("Error parsing XML.");
			
			return false;
		}
	}

	return theDocument;
}