// JavaScript Document
/**
*	@fileoverview Simple example that shows how to encapsulate 
*	XMLHTTPRequestCalls
*
*	@author Mike Chambers (mesh@adobe.com)
*/



/**
*	Constructor for the class.
*
*	@param {String} dataURL The path to the data that the class
*	will load (OPTIONAL)
*
*	@constructor
*/
function MessageLoader(outerContainerID, dataURL)
{
	this._outerContainer = document.getElementById(outerContainerID);
	
	if(dataURL != undefined)
	{
		this._dataURL = dataURL;
	}
	
	this._writeContainer();
}

//where to load the data from
MessageLoader.prototype._dataURL = "data.txt";

//var to hold an instance of the XMLHTTPRequest object
MessageLoader.prototype._request = undefined;

MessageLoader.prototype._outerContainer = undefined;

//ID for the html div we will create to display the data
MessageLoader.prototype._containerID = "innerContainer";

//name of the css class for the HTML container
MessageLoader.prototype._containerClass = "ml_container";

/**************** Public APIs **********************/


/**
*	Tells the class to load its data and render the results.
*/
MessageLoader.prototype.load = function()
{
	//get a new XMLHTTPRequest and store it in an instance var.
	this._request = this._getXMLHTTPRequest();
	
	//set the var so we can scope the callback
	var _this = this;
	
	//callback will be an anonymous function that calls back into our class
	//this allows the call back in which we handle the response (_onData())
	// to have the correct scope.
	this._request.onreadystatechange = function(){_this._onData()};
	this._request.open("GET", this._generateDataUrl(), true);
	this._request.send(null);
}

/***************Private Rendering APIs ********************/

//writes the top level div for the class / widget
MessageLoader.prototype._writeContainer = function()
{
	//styles should be in external CSS
	//document.write("<div id='"+this._containerID+"' class='"+this._containerClass+"'></div>");
	var innerContainer = document.createElement("div");
		innerContainer.setAttribute("id", this._containerID);
		innerContainer.setAttribute("class", this._containerClass);
		
		//need this for IE
		innerContainer.setAttribute("className", this._containerClass);
		
	this._outerContainer.appendChild(innerContainer);
	
}

//renders the entire widget
MessageLoader.prototype._render = function(title)
{
	var content = document.getElementById(this._containerID);
		content.appendChild(document.createTextNode(title));
}

/***************Private Data Loading Handlers*******************/

//return the URL from which the data will be loaded
MessageLoader.prototype._generateDataUrl = function()
{
	return this._dataURL;
}


//callback for when the data is loaded from the server
MessageLoader.prototype._onData = function()
{
	if(this._request.readyState == 4)
	{
		if(this._request.status == "200")
		{
			this._render(this._request.responseText);
			
			//if the onDraw callback has been defined
			//call it to let the listener know
			//that we are done creating the list
			if(this.onDraw != undefined)
			{
				this.onDraw();
			}
		}
		else
		{	
			//check if an error callback handler has been defined
			if(this.onError != undefined)
			{
				//pass an object to the callback handler with info
				//about the error
				this.onError({status:this_request.status, 
						statusText:this._request.statusText});
			}
		}
		
		//clean up
		delete this._request;
	}
}

/***************Private Data Util Functions ********************/


//returns an XMLHTTPRequest instance (based on browser)
MessageLoader.prototype._getXMLHTTPRequest = function()
{
	var xmlHttp;
	try
	{
		xmlHttp = new ActiveXObject("Msxml2.XMLHttp");
	}
	catch(e)
	{
		try
		{
			xmlHttp = new ActiveXObject("Microsoft.XMLHttp");
		}
		catch(e2)
		{
		}
	}
	
	if(xmlHttp == undefined && (typeof XMLHttpRequest != 'undefined'))
	{
		xmlHttp = new XMLHttpRequest();
	}
	
	return xmlHttp;
}