// 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;
}

// read a file from the server
function process( date_start, days_count, room_count, language, id_group, adults, children )
{
  // 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", "ajax/availability_checker.php?date_start="+date_start+"&days_count="+days_count+"&room_count="+room_count+"&lg="+language+'&id_group='+id_group+'&adults='+adults+'&children='+children, 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()
{
  // read the message from the server
  var xmlResponse = xmlHttp.responseXML;
  var elSubmit = document.getElementById('firstStepSubmit');
  // obtain the XML's document element
  xmlRoot = xmlResponse.documentElement;  
  
  // obtain arrays with book titles and ISBNs
  freeroomArray = xmlRoot.getElementsByTagName("freeroom");
  messageArray = xmlRoot.getElementsByTagName("message");
  
  freeroom = freeroomArray.item(0).firstChild.data;
  message = messageArray.item(0).firstChild.data;
  
  
  if ( freeroom=='yes' ) {
    disableSend( false );
  } else {
    disableSend( true );
  }

  document.getElementById('ajaxMessage').innerHTML=message;
}