/* This script will pull in an xml file of all cites for a given state that was chosen
 * from a states drop down list. The xml files are in the /xml directory and are created
 * once a day via a cronjob
*/

// 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", "/xml/" + url + ".xml", 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", "/xml/" + url + ".xml", 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) {
            clearTopicList();
            buildTopicList();
        }
        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 loadDoc(evt) {
function loadDoc(item) {
    // equalize W3C/IE event models to get event object
	// evt = (evt) ? evt : ((window.event) ? window.event : null);

    // if (evt) {
        // equalize W3C/IE models to get event target reference
        // var elem = (evt.target) ? evt.target : ((evt.srcElement) ? evt.srcElement : null);

        // if (elem) {
		if (item) {
            try {
                if (item.selectedIndex > 0) {
                    loadXMLDoc(item.options[item.selectedIndex].value);
                }
            }
            catch(e) {
                var msg = (typeof e == "string") ? e : ((e.message) ? e.message : "Unknown Error");
                alert("Unable to get XML data:\n" + msg);
                return;
            }
        }
    // }
}

// 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"; }
}

// empty Topics select list content
function clearTopicList() {
    var select = document.getElementById("topics");

    while (select.length > 0) { select.remove(0); }
}

// 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);
}

// fill Topics select list with items from the current XML document
function buildTopicList() {
    var select = document.getElementById("topics");
    var items = req.responseXML.getElementsByTagName("item");

    // loop through <item> elements, and add each nested <title> element to Topics select element
    for (var i = 0; i < items.length; i++) {
        appendToSelect(select, getElementTextNS("", "title", items[i], 0), document.createTextNode(getElementTextNS("", "title", items[i], 0)));
    }

    // clear detail display
    //document.getElementById("details").innerHTML = "";
}

// 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;
        }
    }
}