// global flag
var isIE = false;

// global request and XML document objects
var req;

// retrieve XML document (reusable generic function);
// parameter is URL string (relative or complete) to
// an .xml file whose Content-Type is a valid XML
// type, such as text/xml; XML source must be from
// same domain as HTML file
function loadXMLDoc(url) 
{
    // branch for native XMLHttpRequest object
    if (window.XMLHttpRequest) {
        req = new XMLHttpRequest();
        req.onreadystatechange = processReqChange;
        req.open("GET", url, true);
        req.send(null);
    // branch for IE/Windows ActiveX version
    } else if (window.ActiveXObject) {
        isIE = true;
        req = new ActiveXObject("Microsoft.XMLHTTP");
        if (req) {
            req.onreadystatechange = processReqChange;
            req.open("GET", url, true);
            req.send();
        }
    }
}

// handle onreadystatechange event of req object
function processReqChange() {
    // only if req shows "loaded"
    if (req.readyState == 4) 
    {
        // only if "OK"
        if (req.status == 200) 
        {
            setGalleryText();
        } else {
           alert("There was a problem retrieving the XML data:\n" +
               req.statusText);
        }
    }
}

// invoked by "Category" select element change;
// loads chosen XML document, clears Topics select
// element, loads new items into Topics select element
function loadGalleryText(id)
{
   try 
   {
       loadXMLDoc("getGalleryText.php?id="+id);
   }
   catch(e)
   {
       var msg = (typeof e == "string") ? e : ((e.message) ? e.message : "Unknown Error");
       alert("Unable to get XML data:\n" + msg);
       return;
   }
}

function setGalleryText()
{
   var items = req.responseXML.getElementsByTagName("item");
   var text = getElementTextNS("", "text", items[0], 0)
   var elem = document.getElementById('gallery_text');
   //alert(text)
   elem.innerHTML = text;
}

// retrieve text of an XML document element, including
// elements using namespaces
function getElementTextNS(prefix, local, parentElem, index) {
    var result = "";
    if (prefix && isIE) {
        // IE/Windows way of handling namespaces
        result = parentElem.getElementsByTagName(prefix + ":" + local)[index];
    } else {
        // the namespace versions of this method 
        // (getElementsByTagNameNS()) operate
        // differently in Safari and Mozilla, but both
        // return value with just local name, provided 
        // there aren't conflicts with non-namespace element
        // names
        result = parentElem.getElementsByTagName(local)[index];
    }
    if (result) {
        // get text, accounting for possible
        // whitespace (carriage return) text nodes 
        if (result.childNodes.length > 1) {
            return result.childNodes[1].nodeValue;
        } else {
            return result.firstChild.nodeValue;         
        }
    } else {
        return "n/a";
    }
}