// global flag
var isIE = false;

// global request and XML document objects
var req;


// The callback when the XMLHttpRequest
var onComplete = null; // has completed
var onError    = null; // has failed

// 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 sendRequest(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) {
            if (onComplete !== null) {
				var ct    = req.getResponseHeader('Content-Type').split(";")[0];
				var isXml = (ct == "text/xml") || (ct.substr(ct.length-4, 4) == "+xml");
				onComplete(isXml ? req.responseXML : req.responseText);
			}
         } else {
            if (onError !== null) {
                onError(req.statusText);
            } else {
                window.alert("There was a problem retrieving the XML data:\n" + req.status + ": " + req.statusText);
			}
         }
    }
}

// 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";
    }
}

// add item to select element the less
// elegant, but compatible way.
function appendToSelect(select, value, content) {
    var opt;
    opt = document.createElement("option");
    opt.value = value;
    opt.appendChild(content);
    select.appendChild(opt);
}

// display details retrieved from XML document
function showDetail(evt) {
    evt = (evt) ? evt : ((window.event) ? window.event : null);
    var item, content, div;
    if (evt) {
        var select = (evt.target) ? evt.target : ((evt.srcElement) ? evt.srcElement : null);
        if (select && select.options.length > 1) {
            // copy <content:encoded> element text for
            // the selected item
            item = req.responseXML.getElementsByTagName("item")[select.value];
            content = getElementTextNS("content", "encoded", item, 0);
            div = document.getElementById("details");
            div.innerHTML = "";
            // blast new HTML content into "details" <div>
            div.innerHTML = content;
        }
    }
}