/**
* Constructor of the Ajax (Asynchronous JavaScript + XML) object
* Object realize communication between web page and server using JavaScript
* and browser abilities.
* Works in Mozilla 1.0, Safari 1.2, Opera 8.0 and Internet Explorer 5.0
*
* @author  Dmitry Baranovskiy  <Dmitry.Baranovskiy@optus.com.au>
*
* @return object
* @access public
*/

TAjax = function()
{

  this.isIE = false;
  this.responseXML = null;
  this.temp = null;

  this.pool = Array();
  this.inProcess = false;

/**
* sends request and loads content by URL using method
* content should have type "application/xml"
* @param  url        URL
* @param  parameters    parameters of the request ['var1=value1&var2=value2&var3=...']
* @param  method      'POST' or 'GET'
*
* @return void
* @access public
*/
  this.send = function(url, parameters, method, func)
  {
    if (typeof parameters == "undefined" || parameters == "") parameters = null;
    if (typeof func == "undefined" || func == "") func = null;
    if (typeof method == "undefined" || method == "") method = "GET";
    else method = method.toUpperCase();

    if (method == "GET" && parameters != null) {
      url += "?" + parameters;
      parameters = null;
    }

    if (this.inProcess) {
      var request = new Object();
      request.url = url;
      request.parameters = parameters;
      request.method = method;
      request.func = func;
      this.pool.push(request);
      return false;
    }

    this.inProcess = true;

    if (func != null) {
      this.temp = this.process;
      this.process = func;
    }

    if (window.XMLHttpRequest) {
      Global_XMLHttp_Request = new XMLHttpRequest();
      Global_XMLHttp_Request.onreadystatechange = processReqChange;
      Global_XMLHttp_Request.open(method, url, true);
      if (method == "POST") {
        Global_XMLHttp_Request.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
      }
      Global_XMLHttp_Request.send(parameters);
    } else if (window.ActiveXObject) {
      this.isIE = true;
      Global_XMLHttp_Request = new ActiveXObject("Microsoft.XMLHTTP");
      if (Global_XMLHttp_Request) {
        Global_XMLHttp_Request.onreadystatechange = processReqChange;
        Global_XMLHttp_Request.open(method, url, true);
        if (method == "POST") {
          Global_XMLHttp_Request.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
        }
        if (parameters == null) {
          Global_XMLHttp_Request.send();
        }
        else {
          Global_XMLHttp_Request.send(parameters);
        }
      }
    }
    this.onsend();
    return true;

  }


/**
* check is browser supports XMLHttp object
*
* @return boolean
* @access public
*/
  this.isBrowserOk = function()
  {
    try {
      if (window.XMLHttpRequest) return true;
      if (window.ActiveXObject) return true;
      return false;
    }
    catch(e) {
      return false;
    }

  }//end isBrowserOk


/**
* return XMLHttpRequest object
*
* @return object
* @access public
*/
  this.request = function()
  {
    return Global_XMLHttp_Request;

  }//end request


/**
* process XML receiving
*
* @return void
* @access public
*/
  this.process = function()
  {
    //do nothing

  }//end process


/**
* returns content of the response
*
* @return String
* @access public
*/
  this.getXML = function()
  {
    return Global_XMLHttp_Request.responseText;

  }//end getXML


/**
* returns content of the response
*
* @return String
* @access public
*/
  this.getXMLobject = function()
  {
    return Global_XMLHttp_Request.responseXML;

  }//end getXML


/**
* will be called on error in processing (could be overwriten)
*
* @param  message    error message
*
* @return String
* @access public
*/
  this.processError = function(message)
  {
    //do nothing;
    alert(message);
  }//end processError


/**
* will be called on error in receiving (could be overwriten)
*
* @param  message    error message
* @param  status    status code
*
* @return String
* @access public
*/
  this.receiveError = function(message, status)
  {
    //do nothing;
    alert(message + "|" + status)
  }//end receiveError


/**
* will be called on send (could be overwriten)
*
* @return String
* @access public
*/
  this.onsend = function()
  {
    //do nothing;
  }//end receiveError


/**
* will be called on load (could be overwriten)
*
* @return String
* @access public
*/
  this.onload = function()
  {
    //do nothing;
  }//end receiveError


/**
* sends form data via XMLHttp
*
* @param  formid    form id
* @param  func    handler
*
* @return void
* @access public
*/
  this.submitForm = function(formid, func)
  {
    if (typeof formid == "object") {
      var form = formid;
    } else {
      var form = document.getElementById(formid);
    }
    var post = "";
    for (var i = 0; i < form.length; i++) {
      post += ((form.elements[i].id == "")?(form.elements[i].name):(form.elements[i].id)) + "=" + form.elements[i].value + "&";
    }

    this.send(form.action, post, form.method, func);

  }


/**
* sends form data via XMLHttp
*
* @param  divid    div id
* @param  url      content URL
*
* @return void
* @access public
*/
  this.loadContent = function(divid, url)
  {
    if (document.getElementById(divid) == null) {
      return false;
    }
    var func = function()
    {
      document.getElementById(divid).innerHTML = this.getXML();
    }
    this.send(url, "", "", func);
    return true;

  }
}


/**
* handle onreadystatechange event of request object
*
* @return void
* @access public
*/
function processReqChange() {
    // only if req shows "loaded"
    if (Global_XMLHttp_Request.readyState == 4) {
      // only if "OK"
      if (Global_XMLHttp_Request.status == 200) {
        Ajax.responseXML = Global_XMLHttp_Request.responseXML;
        try {
          Ajax.inProcess = false;
          Ajax.onload();
          Ajax.process();
          if (Ajax.temp != null) {
            Ajax.process  = Ajax.temp;
            Ajax.temp    = null;
          }
          if (Ajax.pool.length > 0) {
            var request = Ajax.pool.shift();
            Ajax.send(request.url, request.parameters, request.method, request.func);
          }
        }
        catch (e) {
          Ajax.processError(e.message);
        }
       } else {
         Ajax.receiveError(Global_XMLHttp_Request.statusText, Global_XMLHttp_Request.status);
       }
    }

  }


// global request and XML document objects
var Global_XMLHttp_Request = null;

// if no XMLHttp variable created, create it.
if (typeof Ajax == "undefined") Ajax = new TAjax();