// holds an instance of XMLHttpRequest
var xmlHttp = createXmlHttpRequestObject();
// holds the remote server address
var serverAddress = "http://utopiaroadcomics.com/includes/validate.php";
// when set to true, display detailed error messages
var showErrors = true;
// initialize the validation requests cache
var cache = new Array();

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) {} // ignore potential error
			}
		}
		// return the created object or display an error message
		if (!xmlHttp)
			alert("Error creating the XMLHttpRequest object.");
		else
			return xmlHttp;
}

// function that displays an error message
function displayError($message) {
	// ignore errors if showErrors is false
	if (showErrors){
		// turn error displaying Off
		showErrors = false;
		// display error message
		alert("Error encountered: \n" + $message);
		// retry validation after 10 seconds
		setTimeout("validate();", 10000);
	}
}

function validate(inputValue, fieldID) {
	// only continue if xmlHttp isn't void
	if (xmlHttp){
		// if we received non-null parameters, we add them to cache in the
		// form of the query string to be sent to the server for validation
		if (fieldID){
			// encode values for safely adding them to an HTTP request query string
			inputValue = encodeURIComponent(inputValue);
			fieldID = encodeURIComponent(fieldID);
			// add the values to the queue
			cache.push("inputValue=" + inputValue + "&fieldID=" + fieldID);
		}
		// try to connect to the server
		try{
			// continue only if the XMLHttpRequest object isn't busy
			// and the cache is not empty
			if ((xmlHttp.readyState == 4 || xmlHttp.readyState == 0) && cache.length > 0){
				// get a new set of parameters from the cache
				var cacheEntry = cache.shift();
				// make a server request to validate the extracted data
				xmlHttp.open("POST", serverAddress, true);
				xmlHttp.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
				xmlHttp.onreadystatechange = handleRequestStateChange;
				xmlHttp.send(cacheEntry);
			}
		}
		catch (e){
			// display an error when failing to connect to the server
			displayError(e.toString());
		}
	}
}


// function that handles the HTTP response
function handleRequestStateChange(){
	// when readyState is 4, we read the server response
	if (xmlHttp.readyState == 4){
		// continue only if HTTP status is "OK"
		if (xmlHttp.status == 200){
			try{
				// read the response from the server
				readResponse();
			}
			catch(e){
				// display error message
				displayError(e.toString());
			}
		}
		else{
			// display error message
			displayError(xmlHttp.statusText);
		}
	}
}

// read server's response
function readResponse(){
	// retrieve the server's response
	var response = xmlHttp.responseText;
	// server error?
	if (response.indexOf("ERRNO") >= 0 || response.indexOf("error:") >= 0 || response.length == 0)
		throw(response.length == 0 ? "Server error." : response);
		// get response in XML format (assume the response is valid XML)
		responseXml = xmlHttp.responseXML;
		// get the document element
		xmlDoc = responseXml.documentElement;
		result = xmlDoc.getElementsByTagName("result")[0].firstChild.data;
		fieldID = xmlDoc.getElementsByTagName("fieldid")[0].firstChild.data;
		// find the HTML element that displays the error
		message = document.getElementById(fieldID + "Failed");
		// show the error or hide the error
		message.className = (result == "0") ? "error2" : "hidden";
		// call validate() again, in case there are values left in the cache
		setTimeout("validate();", 500);
}

// sets focus on the first field of the form
function setFocus(){
	document.getElementById("txtUsername").focus();
}