// holds an instance of XMLHttpRequest
var xmlHttp = createXmlHttpRequestObject();

// creates an XMLHttpRequest instance
function createXmlHttpRequestObject() 
{
  // will store the reference to the XMLHttpRequest object
  var xmlHttp;
  // this should work for all browsers except IE6 and older
  try
  {
    // try to create XMLHttpRequest object
    xmlHttp = new XMLHttpRequest();
  }
  catch(e)
  {
    // assume IE6 or older
    var XmlHttpVersions = new Array("MSXML2.XMLHTTP.6.0",
                                    "MSXML2.XMLHTTP.5.0",
                                    "MSXML2.XMLHTTP.4.0",
                                    "MSXML2.XMLHTTP.3.0",
                                    "MSXML2.XMLHTTP",
                                    "Microsoft.XMLHTTP");
    // try every prog id until one works
 
    for (var i=0; i<XmlHttpVersions.length && !xmlHttp; i++) 
    {
      try 
      { 
        // try to create XMLHttpRequest object
        xmlHttp = new ActiveXObject(XmlHttpVersions[i]);
      } 
      catch (e) {}
    }
  }
  // return the created object or display an error message
  if (!xmlHttp)
    alert("Error creating the XMLHttpRequest object.");
  else 
    return xmlHttp;
}
function get_families()
{
    if ( document.getElementById('family_quickselect_status').innerHTML == 'uninitialized' )
    {
        document.getElementById('family_quickselect_status').innerHTML = 'loading';
        var family_list = document.getElementById('family_quickselect');
        if ( family_list )
        {
            clearOptions(family_list);
            addToOptionList(family_list, '', 'loading...');
        }
        connect_to_server()
    }

}
// read a file from the server
function connect_to_server()
{
  // only continue if xmlHttp isn't void
  if ( xmlHttp )
  {
    // try to connect to the server
    try
    {
      // initiate reading a file from the server
      xmlHttp.open("GET", "get_families.php", true);
      xmlHttp.onreadystatechange = handleRequestStateChange;
      xmlHttp.send(null);
    }
    // display the error in case of failure
    catch (e)
    {
      alert("Can't connect to server:\n" + e.toString());
    }
  }
}


// function called when the state of the HTTP request changes
function handleRequestStateChange() 
{
  // when readyState is 4, we are ready to read the server response
  if (xmlHttp.readyState == 4) 
  {
    // continue only if HTTP status is "OK"
    if (xmlHttp.status == 200) 
    {
      try
      {
        // do something with the response from the server
        handleServerResponse();
      }
      catch(e)
      {
        // display error message
        alert("Error reading the response: " + e.toString());
      }
    } 
    else
    {
      // display status message
      alert("There was a problem retrieving the data:\n" + 
            xmlHttp.statusText);
 
    }
  }
}

// handles the response received from the server
function handleServerResponse()
{
  document.getElementById('family_quickselect_status').innerHTML = 'populated';
  
  // read the message from the server
  var xmlResponse = xmlHttp.responseXML;
  // catching potential errors with IE and Opera
  if (!xmlResponse || !xmlResponse.documentElement)
    throw("Invalid XML structure:\n" + xmlHttp.responseText);
  // catching potential errors with Firefox
  var rootNodeName = xmlResponse.documentElement.nodeName;
  if (rootNodeName == "parsererror") throw("Invalid XML structure");
  // obtain the XML's document element
  xmlRoot = xmlResponse.documentElement;  
  // obtain arrays with family names and ids 
  familyArray = xmlRoot.getElementsByTagName("n");
  idArray = xmlRoot.getElementsByTagName("i");
  // generate HTML output
  var html = "";  

  var family_select = document.getElementById('family_quickselect');
  if ( family_select )
  {
    clearOptions(family_select);
    addToOptionList(family_select, '', 'Choose a Family');
      for (var i=0; i<familyArray.length; i++)
      {
        addToOptionList(family_select, idArray.item(i).firstChild.data, familyArray.item(i).firstChild.data);
      }
  }
}

function clearOptions(OptionList) {

   // Always clear an option list from the last entry to the first
   for (x = OptionList.length; x >= 0; x = x - 1) {
      OptionList[x] = null;
   }
}


function addToOptionList(OptionList, OptionValue, OptionText) {
   // Add option to the bottom of the list
   OptionList[OptionList.length] = new Option(OptionText, OptionValue);
}