var xmlHttp = createXmlHttpRequestObject();
// holds the remote server address and parameters
// variables that establish how often to access the server
var statupdateInterval = 7; // how many seconds to wait to get new message
var errorRetryInterval = 30; // seconds to wait after server error
// when set to true, display detailed error messages

// creates an XMLHttpRequest instance
function createXmlHttpRequestObject()
{
	// will store the reference to the XMLHttpRequest object
	var xmlHttp;
	
	// this should work for all browsers except IE6 and older
	try
	{
		// try to create XMLHttpRequest object
		xmlHttp = new XMLHttpRequest();
	}
	catch(e)
	{
		// assume IE6 or older
		var XmlHttpVersions = new Array("MSXML2.XMLHTTP.6.0","MSXML2.XMLHTTP.5.0","MSXML2.XMLHTTP.4.0","MSXML2.XMLHTTP.3.0","MSXML2.XMLHTTP","Microsoft.XMLHTTP");
		
		// try every prog id until one works
		for (var i=0; i < XmlHttpVersions.length && !xmlHttp; i++)
		{
			try
			{
				// try to create XMLHttpRequest object
				xmlHttp = new ActiveXObject(XmlHttpVersions[i]);
			}
			catch (e) {}
		}
	}
	// return the created object or display an error message
	if (!xmlHttp)
	{
		alert("Error creating the XMLHttpRequest object.");
	}
	else
	{
		return xmlHttp;
	}
}


// read a file from the server
function process()
{
	// only continue if xmlHttp isn't void
	if (!xmlHttp)
	{
		return;
	}
	// don't try to make server requests if the XMLHttpObject is busy
	if (!(xmlHttp.readyState == 0 || xmlHttp.readyState == 4))
	{
		alert("Can't connect to server, please try again later. ");
	}	
	else
	{
		// try to connect to the server
		try
		{
			// initiate the asynchronous HTTP request
			xmlHttp.open("GET", "./getUrgentPetitions.php", true);
			xmlHttp.onreadystatechange = handleRequestStateChange;
			xmlHttp.send(null);
		}
		catch (e)
		{
			alert("Can't connect to server:\n" + e.toString());
		}
	}
}


// function called when the state of the HTTP request changes
function handleRequestStateChange()
{
	// when readyState is 4, we are ready to read the server response
	if (xmlHttp.readyState == 4)
	{
		// continue only if HTTP status is "OK"
		if (xmlHttp.status == 200)
		{
			try
			{
				// do something with the response from the server
				handleServerResponse();
			}
			catch(e)
			{
				// display error message
				alert("Error reading the response: " + e.toString());
			}
		}
		else
		{
			// display status message
			alert("There was a problem retrieving the data:\n" +
			xmlHttp.statusText);
		}
	}
}

// handles the response received from the server
function handleServerResponse()
{
	// retrieve the server's response packaged as an XML DOM object
	var response = xmlHttp.responseText;
			
	targetDiv = document.getElementById("urgent");
	targetDiv.innerHTML = response; 			

	// repeat on every statupdateInterval seconde
	setTimeout("process()", statupdateInterval * 1000);
}