openedTab = false;
http_request = false;
destinationLayer = '';

function navigate(activeTab, panelName)
{
    for (t = 0; t < 5; t++)
    {
		if (t == activeTab)
		{
            /* This if prevents a user from clicking on an already 'opened' tab,
            so it doesn't generate unnecessary XHR's.*/
            
            if ((document.getElementById('TD' + t).style.backgroundImage != 'url(img/darkTab.gif)') || !openedTab)
            {
                openedTab = true;
                
                document.getElementById('TD' + t).style.backgroundImage='url(img/darkTab.gif)';
                document.getElementById('TD' + t).style.cursor='text';
                                
                retrieveData(panelName + 'Main', 'http://localhost:8080/dbwtk/code/echoTabs.php', 'POST', true, 'tab=' + t, 'setLayerContent');
                
                retrieveData(panelName + 'Buttons', 'http://localhost:8080/dbwtk/code/echoButtons.php', 'POST', true, 'tab=' + t, 'setLayerContent');
            }
		}
		else
		{
			document.getElementById('TD' + t).style.backgroundImage='url(img/lightTab.gif)';
            document.getElementById('TD' + t).style.cursor='pointer';
		}
    }
}

function retrieveData(toLayer, requestURL, requestMethod, requestAsynchronous, requestData, returnFunction)
{
    http_request = false;
    destinationLayer = toLayer; // Defines the value of this global so the right layer is populated
    
    if (window.XMLHttpRequest)
    {
        http_request = new XMLHttpRequest();
        
        if (http_request.overrideMimeType)
        {
            http_request.overrideMimeType('text/xml');
        }
    }
    else if (window.ActiveXObject)
    {
        try
        {
            http_request = new ActiveXObject("Msxml2.XMLHTTP")
        }
        catch(e)
        {
            try
            {
                http_request = new ActiveXObject("Microsoft.XMLHTTP")
            }
            catch(e)
            {
            }
        }
    }
    
    if (!http_request)
    {
        alert('Your browser is not equiped to use this tool.');
    }
    
    http_request.onreadystatechange = eval(returnFunction);
    http_request.open(requestMethod, requestURL, requestAsynchronous);
    http_request.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
    http_request.send(requestData);
}

function setLayerContent()
{
    functionStatus = false;
    
    xmlReturn = '';
    
	if (http_request.readyState == 4)
	{
		if (http_request.status == 200)
		{
			xmlReturn = http_request.responseText;
            functionStatus = true;
            
            alert(http_request.responseText);
		}
		else
		{
			alert('AJAX request error.');
            functionStatus = false;
		}
	}
	
    document.getElementById(destinationLayer).innerHTML = xmlReturn;
	
	return functionStatus;
}