function AjaxRequest(url) {
  /** @private */
  var self = this;

  /** @private */
  var xmlHttp = createXMLHttpRequest();

  /** @private */
  var queryString = "";

  /** @private */
  var requestURL = url;

  /** @private */
  var method = "GET";

  /** @private */
  var preRequest = null;

  /** @private */
  var postRequest = null;

  /** @private */
  var debugResponse = false;

  /**
      Return the instance of the XMLHttpRequest object wrapped by this object.
      @return XMLHttpRequest
  */
  this.getXMLHttpRequestObject = function() {
    return xmlHttp;
  }

  /**
    Set the pre-request function. This function will be called prior to 
    sending the Ajax request. The pre-request function is passed a reference
    to this object.
    @param {Function} The function to be called prior to sending the Ajax
    request. The function is passed a refernce of this object.
  */
  this.setPreRequest = function(func) {
      preRequest = func;
  }

  /**
    Set the post-request function. This function will be called after the
    response has been received and after eval() has been called using the 
    XMLHttpRequest object's responseText. The post-request function is passed 
    a reference to this object.
    @param {Function} The function to be called after receiving the Ajax
    response. The function is passed a refernce of this object.
  */
  this.setPostRequest = function(func) {	

    postRequest = func;
	 
  }

  /**
    Send the Ajax request using the POST method. Use with caution -- some
    browsers do not support the POST method with the XMLHttpRequest object.
  */
  this.setUsePOST = function() {
    method = "POST";
  }

  /**
    Send the Ajax request using the GET method, where parameters are sent
    as a query string appended to the URL. This is the default behavior.
  */
  this.setUseGET = function() {
    method = "GET";
  }

  /**
    Enable client-side debugging.  The server's response will be written
    to a text area appended to the bottom of the page.  If parsing is
    performed on the client side, then the results of the parsing operations
    are shown in their own text areas.
  */
  this.setEchoDebugInfo = function() {
    debugResponse = true;
  }

  /**
    Indicate if debugging is enabled.
    @return boolean
  */
  this.isEchoDebugInfo = function() {
    return debugResponse;
  }

  /**
    Set the query string that will be sent to the server. For GET
    requests, the query string is appended to the URL. For POST
    requests, the query string is sent in the request body. This 
    method is useful, for example, if you want to send an XML string
    or JSON string to the server.
    @param {String} qa, the new query string value.
  */
  this.setQueryString = function(qs) {
    queryString = qs;
  }

  /**
    Return the query string.
    @return The query string.
  */
  this.getQueryString = function() {
    return queryString;
  }
  
  
  
  

  /**
    Add all of the form elements under the specified form to the query
    string to be sent to the server as part of the Ajax request. The values
    are automatically encoded.
    @param {String} formID, the value of the id attribute of the form from
    which you wish to accumulate the form values.
  */
  this.addFormElements = function(formID) {
    var formElements = document.getElementById(formID).elements;
    var values = toQueryString(formElements);
    accumulateQueryString(values);
  }

  /** @private */
  function accumulateQueryString(newValues) {
    if(queryString == "") {
      queryString = newValues; 
    } else {
      queryString = queryString + "&" +  newValues;
    }
  }

  /**
    Add the values of the named form elements to the query string to be
    sent to the server as part of the Ajax request. This method takes any 
    number of Strings representing the form elements for wish you wish to 
    accumulate the values. The Strings must be the value of the element's 
    name attribute.<br><br>For example, these are all valid uses:<br>
    <br>ajaxRequest.addNamedFormElements("element-name-1");
    <br>ajaxRequest.addNamedFormElements("element-name-1", "element-name-2", "element-name-3");
  */
  this.addNamedFormElements = function() {
    var elementName = "";
    var namedElements = null;

    for(var i = 0; i < arguments.length; i++) {
      elementName = arguments[i];
      namedElements = document.getElementsByName(elementName);

      elementValues = toQueryString(namedElements);
      accumulateQueryString(elementValues);
    }
  }

  /**
    Add the values of the id'd form elements to the query string to be
    sent to the server as part of the Ajax request. This method takes any 
    number of Strings representing the ids of the form elements for wish you wish to 
    accumulate the values. The Strings must be the value of the element's 
    name attribute.<br><br>For example, these are all valid uses:<br>
    <br>ajaxRequest.addFormElementsById("element-id-1");
    <br>ajaxRequest.addFormElementsById("element-id-1", "element-id-2", "element-id-3");
  */
  this.addFormElementsById = function() {
    var id = "";
    var element = null;
    var elements = new Array();

    for(var h = 0; h < arguments.length; h++) {
      element = document.getElementById(arguments[h]);
      if(element != null) {
        elements[h] = element;
      }
    }

    elementValues = toQueryString(elements);
    accumulateQueryString(elementValues);
  }

  /**
     Send the Ajax request.
  */
  this.sendRequest = function() {
	  
    if(preRequest) {
      preRequest(self);
    }

    var obj = this;
    xmlHttp.onreadystatechange = function () { handleStateChange(self) };

    if(requestURL.indexOf("?") > 0) {
      requestURL = requestURL + "&ts=" + new Date().getTime();
    } else {
      requestURL = requestURL + "?ts=" + new Date().getTime();
    }

    if(method == "GET") {
      if(queryString.length > 0) {
        requestURL = requestURL + "&" + queryString;
      }
      xmlHttp.open(method, requestURL, true);
      xmlHttp.send(null);
	   
    } else {
      xmlHttp.open(method, requestURL, true);
      xmlHttp.setRequestHeader("Content-Type", "application/x-www-form-urlencoded"); 
      xmlHttp.send(queryString);
    }

    if(self.isEchoDebugInfo()) {
      echoRequestParams();
    }
  }

  handleStateChange = function(ajaxRequest) {
    if(ajaxRequest.getXMLHttpRequestObject().readyState != 4) {
		return;
    }
	
    if(ajaxRequest.getXMLHttpRequestObject().status == 200 || ajaxRequest.getXMLHttpRequestObject().status == 0) {
		
      var debug = ajaxRequest.isEchoDebugInfo();
      if(debug) {
        echoResponse(ajaxRequest);
      }
      //var nodes = ajaxRequest.getXMLHttpRequestObject().responseXML.documentElement.childNodes;
      if(postRequest) {

        postRequest(ajaxRequest);
      }
    }
  }

  /** @private */
  function toQueryString(elements) {
    var node = null;
    var qs = "";
    var name = "";

    var tempString = "";
    for(var i = 0; i < elements.length; i++) {
      tempString = "";
      node = elements[i];
      name = node.getAttribute("name");

      if(node.tagName.toLowerCase() == "input") {
        if(node.type.toLowerCase() == "radio" || node.type.toLowerCase() == "checkbox") {
          if(node.checked) {
            tempString = name + "=" + node.value;
          }
        }

        if(node.type.toLowerCase() == "text" || node.type.toLowerCase() == "hidden") {
          tempString = name + "=" + encodeURIComponent(node.value);
        }

        } else if(node.tagName.toLowerCase() == "select") {
          tempString = getSelectedOptions(node);

        } else if(node.tagName.toLowerCase() == "textarea") {
          tempString = name + "=" + encodeURIComponent(node.value);
        }

       if(tempString != "") {
         if(qs == "") {
           qs = tempString;
         } else {
           qs = qs + "&" + tempString;
         }
       }
     }
     return qs;
   }

   /** @private */
   function getSelectedOptions(select) {
     var options = select.options;
     var option = null;
     var qs = "";
     var tempString = "";

     for(var x = 0; x < options.length; x++) {
       tempString = "";
       option = options[x];

       if(option.selected) {
         tempString = select.name + "=" + option.value;
       }

       if(tempString != "") {
         if(qs == "") {
           qs = tempString;
         } else {
           qs = qs + "&" + tempString;
         }
       }
     }
     return qs;
   }

  /** @private */
  function echoResponse(ajaxRequest) {
    var echoTextArea = document.getElementById("debugResponse");
    if(echoTextArea == null) {
      echoTextArea = createDebugTextArea("Server Response:", "debugResponse");
    }
    echoTextArea.value = ajaxRequest.getXMLHttpRequestObject().responseText;
  }

  /** @private */
  function createDebugTextArea(label, id) {
    echoTextArea = document.createElement("textarea");
    echoTextArea.setAttribute("id", id);
    echoTextArea.setAttribute("rows", "15");
    echoTextArea.setAttribute("style", "width:100%");
    echoTextArea.style.cssText = "width:100%";

    document.getElementsByTagName("body")[0].appendChild(document.createTextNode(label));
    document.getElementsByTagName("body")[0].appendChild(echoTextArea);
    return echoTextArea;
  }


  /** @private */
  function echoRequestParams() {
    var qsTextBox = document.getElementById("qsTextBox");
    if(qsTextBox == null) {
        qsTextBox = createDebugTextBox("Query String:", "qsTextBox");
    }
    qsTextBox.value = queryString;

    var urlTextBox = document.getElementById("urlTextBox");
    if(urlTextBox == null) {
        urlTextBox = createDebugTextBox("URL (Includes query string if GET request):", "urlTextBox");
    }
    urlTextBox.value = requestURL;
  }

  /** @private */
  function createDebugTextBox(label, id) {
    textBox = document.createElement("input");
    textBox.setAttribute("type", "text");
    textBox.setAttribute("id", id);
    textBox.setAttribute("style", "width:100%");
    textBox.style.cssText = "width:100%";

    document.getElementsByTagName("body")[0].appendChild(document.createTextNode(label));
    document.getElementsByTagName("body")[0].appendChild(textBox);
    return textBox;
  }
}

/**
    Create an instance of the XMLHttpRequest object, using the appropriate
    method for the type of browser in which this script is running. For Internet
    Explorer, it's an ActiveX object, for all others it's a native JavaScript
    object.
    @return an instance of the XMLHttpRequest object.
*/
function createXMLHttpRequest() {

  if (window.ActiveXObject) {
    return new ActiveXObject("Microsoft.XMLHTTP");
  } else if (window.XMLHttpRequest) {
    return new XMLHttpRequest();
  }
}