// 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)
{
  // 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)
    {
      try
      {
        if (elem.selectedIndex > 0)
        {
          loadXMLDoc(elem.options[elem.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;
    }
  }
}