var xmlHttp = createXmlHttpRequestObject();
var serverAddress = "check.php";
var showErrors = true;
var cache = new Array();

function createXmlHttpRequestObject()
{
    var xmlHttp;
    try
    {
        xmlHttp = new XMLHttpRequest();
    }
    catch(e)
    {
        var XmlHttpVersions = new Array("MSXML2.XMLHTTP.6.0",
                                        "MSXML2.XMLHTTP.5.0",
                                        "MSXML2.XMLHTTP.4.0",
                                        "MSXML2.XMLHTTP.3.0",
                                        "MSXML2.XMLHTTP",
                                        "Microsoft.XMLHTTP");

        for(var i = 0; i < XmlHttpVersions.length && !xmlHttp; i++)
        {
            try
            {
                xmlHttp = new ActiveXObject(XmlHttpVersions[i]);
            }
            catch(e)
            { }
        }
    }
    if(!xmlHttp)
    {    displayError("Error creating XMLHttpRequest object.");    }
    else
    {    return xmlHttp;    }
}

function displayError($message)
{
    if(showErrors)
    {
        showErrors = false;
        alert("Error Encountered: \n" + $message);
        setTimeout("validate();", 10000);
    }
}

function validate(inputValue, fieldID)
{
    if(xmlHttp)
    {
        if(fieldID)
        {
            inputValue = encodeURIComponent(inputValue);
            fieldID = encodeURIComponent(fieldID);
            cache.push("inputValue=" + inputValue + "&fieldID=" + fieldID);
        }

        try
        {
            if((xmlHttp.readyState == 4 || xmlHttp.readyState == 0) && cache.length > 0)
            {
                var cacheEntry = cache.shift();
                xmlHttp.open("POST", serverAddress, true);
                xmlHttp.setRequestHeader("Content-Type", "application/x-www-form-urlencoded; charset=UTF-8");
                xmlHttp.onreadystatechange = handleRequestStateChange;
                xmlHttp.send(cacheEntry);
            }
        }
        catch(e)
        {
            displayError(e.toString());
        }
    }
}

function handleRequestStateChange()
{
    if(xmlHttp.readyState == 4)
    {
        if(xmlHttp.status == 200)
        {
            try
            {
                readResponse();
            }
            catch(e)
            {
                displayError(e.toString());
            }
        }
        else
        {
            displayError(xmlHttp.statusText);
        }
    }
}

function readResponse()
{
    var response = xmlHttp.responseText;
    if(response.indexOf("ERRNO") >= 0 || response.indexOf("error:") >= 0 || response.length == 0)
    {    throw(response.length == 0 ? "Server error." : response);  }
    responseXml = xmlHttp.responseXML;
    xmlDoc = responseXml.documentElement;
    result = xmlDoc.getElementsByTagName("result")[0].firstChild.data;
    fieldID = xmlDoc.getElementsByTagName("fieldid")[0].firstChild.data;
    message = document.getElementById(fieldID + "Failed");
    message.className = (result == "0") ? "error" : "hidden";
    setTimeout("validate();", 500);
}