/*
 * Returns an new XMLHttpRequest object, or false if the browser
 * doesn't support it
 */
function newXMLHttpRequest() 
{
	var xmlreq = false;

	// Create XMLHttpRequest object in non-Microsoft browsers
	if (window.XMLHttpRequest) 
	{
		xmlreq = new XMLHttpRequest();
	} 
	else if (window.ActiveXObject) 
	{
		try 
		{
			// Try to create XMLHttpRequest in later versions of Internet Explorer
			xmlreq = new ActiveXObject("Msxml2.XMLHTTP");
		} 
		catch (e1) 
		{
			// Failed to create required ActiveXObject
			try 
			{
				// Try version supported by older versions of Internet Explorer
				xmlreq = new ActiveXObject("Microsoft.XMLHTTP");
			} 
			catch (e2) 
			{
				// Unable to create an XMLHttpRequest by any means
				xmlreq = false;
			}
		}
	}

	return xmlreq;
}

/*
 * Returns a function that waits for the specified XMLHttpRequest
 * to complete, then passes it XML response to the given handler function.
 * req - The XMLHttpRequest whose state is changing
 * responseXmlHandler - Function to pass the XML response to
 */
function getReadyStateHandler(req, responseXmlHandler) 
{
	// Return an anonymous function that listens to the XMLHttpRequest instance
	return function () {

		// If the request's status is "complete"
		if (req.readyState == 4) 
		{
			// Check that we received a successful response from the server
			if (req.status == 200) 
			{
				// Pass the XML payload of the response to the handler function.
				responseXmlHandler(req.responseXML);
			} 
			else 
			{
				// An HTTP problem has occurred
				alert("HTTP error occurs in Calendar! \nPlease contact with webmaster and try again later.");
			}
		}
	}
}

function sendStandardRequest(responseXmlHandler, url, params)
{
	var req = newXMLHttpRequest();
	req.onreadystatechange = getReadyStateHandler(req, responseXmlHandler);
	req.open("POST", url, true);
	req.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
	req.send(params);
}