// holds an instance of XMLHttpRequest
var xmlHttp = createXmlHttpRequestObject();
// how many seconds between updates
var timeout_sec = 60;

// 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()
{
  // only continue if xmlHttp isn't void
  if (xmlHttp)
  {
    // try to connect to the server
    try
    {
      // initiate the asynchronous HTTP request
      xmlHttp.open("GET", "user_info.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());
	  setTimeout('process()', timeout_sec*1000); // 1000 = one second
    }
  }
}

// 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()
{
  // retrieve the server's response packaged as an XML DOM object
  var xmlResponse = xmlHttp.responseXML;
  responseText = "";
  // catching potential errors with IE and Opera
  if (!xmlResponse || !xmlResponse.documentElement)
  {
//    throw("Invalid XML structure (1):\n" + xmlHttp.responseText);
  }
  else
  {
	  // catching potential errors with Firefox
	  var rootNodeName = xmlResponse.documentElement.nodeName;
	  if (rootNodeName == "parsererror")
	  {
//		throw("Invalid XML structure (2):\n" + xmlHttp.responseText);
	  }
	  else
	  {
		  // getting the root element (the document element)
		  xmlRoot = xmlResponse.documentElement;
		  // testing that we received the XML document we expect
		  if (rootNodeName != "response" || !xmlRoot.firstChild)
		  {
		//	throw("Invalid XML structure (3):\n" + xmlHttp.responseText);
		  }
		  else
		  {
			  // the value we need to display is the child of the root <response> element
			  responseText = xmlRoot.firstChild.data;
		  }
	  }
  }
  // display the user message
  myDiv = document.getElementById("User_info");
  myDiv.innerHTML = responseText;
  // restart sequence
  setTimeout('process()', timeout_sec*1000); // 1000 = one second
}