//  Holds an instance of XMLHttpRequest  Page 415 #3
var xmlHttp = createXmlHttpRequestObject();
//  Display error messages (true) or degrade to non-AJAX behavior (false)
var showErrors = true;
//  Contains the link or form clicked or submitted by the visitor
var actionObject = '';
//  This is true when the Place Order button is clicked, false otherwise
var placingOrder = false;
//  Creates an XMLHttpRequest instance
function createXmlHttpRequestObject()   
{
   //  Will store the XMLHttpRequest object
   var xmlHttp;
   //  Create the XMLHttpRequest object
   try
   {
      //  Try to create native 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 id until one works
	  for (i = 0; i < XmlHttpVersions.length && !xmlHttp; i++)
	  {
	     try
		 {
		    //  Try to create XMLHttpRequest object
			xmlHttp = new ActiveXObject(XmlHttpVersions[i]);
		 }
		 catch (e) {}  //  Ignore potential error
	  }
   }
   //  If the XMLHttpRequest object was created successfully, return it
   if (xmlHttp)
      {
         return xmlHttp;
      }
      //  If an error happened, pass it to handleError
   else
      {
         handleError("Error creating the XMLHttpRequest object.");
      }
}   	  	  	  	 		 	  
//  Displays an the error message or degrades to non-AJAX behavior
function handleError($message)
{
   //  Ignore errors if showErrors is false
   if (showErrors)
   {
	  //  Display error message
	  alert("Error encountered: \n" + $message);
	  return false;
   }
   //  Fall back to non-AJAX behavior
   else if (!actionObject.tagName)
   {
      return true;
   }
   //  Fall back to non-AJAX behavior by following the link
   else if (actionObject.tagName == 'A')
   {
      window.location = actionObject.href;
   }
   //  Fall back to non-AJAX behavior by submitting the form
   else if (actionObject.tagName == 'FORM')
   {
      actionObject.submit();
   }
}
//  Adds a product to the shopping cart
function addProductToCart(form)
{
   //  Display "Updating" message
   document.getElementById('updating').style.visibility = 'visible';
   //  Degrade to classical form submit if XMLHttprequest is not available
   if (!xmlHttp) return true;
      //  Create the URL we open asynchronously
      request = form.action + '&AjaxRequest';
      params = null;
      //  obtain selected attributes
      formSelects = form.getElementsByTagName('SELECT');
      if (formSelects)
      {
		 for (i = 0; i < formSelects.length; i++)
		 {
            params += '&' + formSelects[i].name + '=';
	        selected_index = formSelects[i].selectedIndex;
	        params += encodeURIComponent(formSelects[i][selected_index].text);
         }
      }
      //  Try to connect to the server
      try
      {
         //  Continue only if the XMLHttpRequest object isn't busy
	     if (xmlHttp.readyState == 4 || xmlHttp.readyState == 0)
	     {
	        //  Make a server request to validate the extracted data
		    xmlHttp.open("POST", request);
		    xmlHttp.setRequestHeader("Content-Type",
		                             "application/x-www-form-urlencoded");
	        xmlHttp.onreadystatechange = addToCartStateChange;
		    xmlHttp.send(params);
	     }
      }
      catch (e)
      {
         //  Handle error
	     handleError(e.toString());
      }
      //  Stop classical form submit if AJAX action succeeded
      return false;
}
//  Function that retrieves the HTTP response
function addToCartStateChange()
{
   //  When readyState is 4, we also read the server response
   if (xmlHttp.readyState == 4)
   {
      //  Continue only if HTTP status is "OK"
 	  if (xmlHttp.status == 200)
	  {
	     try
	   	 {
		    updateCartSummary();
		 }
		 catch (e)
		 {
		    handleError(e.toString());
		 }
	  }
	  else
	  {
	     handleError(xmlHttp.statusText);
	  }
   }
}
//  Process server's response
function updateCartSummary()
{
   //  Read the response
   response = xmlHttp.responseText;
   //  Server error?
   if (response.indexOf("ERRNO") >= 0 || response.indexOf("error") >= 0)
   {
      handleError(response);
   }
   else
   {
      //  Extract the contents of the cart_summary div element
 	  var cartSummaryRegEx = /^<div class="box" id="cart-summary">([\s\S]*)<\/div>$/m;
	  matches = cartSummaryRegEx.exec(response);
	  response = matches[1];
	  //  Update the cart summary box and hide the Loading message
	  document.getElementById("cart-summary").innerHTML = response;
	  //  Hide the "Updating ..." message
	  document.getElementById('updating').style.visibility = 'hidden';
   }
}
//  Called on shopping cart update actions  Page 427 #2
function executeCartAction(obj)
{
    //  Degrade to classical form submit for Place Order action  Page 440 #3
	if (placingOrder) return true;
    //  Display "Updating..." message
	document.getElementById('updating').style.visibility = 'visible';
	//  Degrade to classical form submit if XMLHttpRequest is not available
	if (!xmlHttp) return true;
	//  Save object reference
	actionObject = obj;
	//  Initialize response and parameters
	response = '';
	params = '';
	//  If a link was clicked we get its href attribute
	if (obj.tagName == 'A')
	{
		url = obj.href + '&AjaxRequest';
	}
	//  If the form was submitted we get its elements
	else
	{
		url = obj.action + '&AjaxRequest';
		formElements = obj.getElementsByTagName('INPUT');
		if (formElements)
		{
			for (i = 0; i < formElements.length; i++)
			{
				if (formElements[i].name != 'place_order')
				{
					params += '&' + formElements[i].name + '=';
					params += encodeURIComponent(formElements[i].value);
				}
			}
		}
	}
     	//  Try to connect to the server
	   try
	   {
		  //  Make server request only if the XMLHttpRequest object isn't busy
		  if (xmlHttp.readyState == 4 || xmlHttp.readyState == 0)
		  {
			  xmlHttp.open("POST", url, true);
			  xmlHttp.setRequestHeader("Content-Type",
									   "application/x-www-form-urlencoded");
			  xmlHttp.onreadystatechange = cartActionStateChange;
			  xmlHttp.send(params);
		  }
	   }
	   catch (e)
	   {
		  //  Handle error
		  handleError(e.toString());
	   }
	   //  Stop classical form submit if AJAX action succeeded
	   return false;
}
//  Function that retrieves the HTTP response
function cartActionStateChange()
{
	//  When readyState is 4, we also read the server response
	if (xmlHttp.readyState == 4)
	{
		//  Continue only if HTTP status is "OK"
		if (xmlHttp.status == 200)
		{
			try
			{
				//  Read the response
				response = xmlHttp.responseText;
				//  Server error?
				if (response.indexOf("ERRNO") >= 0 || response.indexOf("error") >= 0)
				{
					handleError(response);
				}
				else
				{
					//  Update the cart
					document.getElementById("contents").innerHTML = response;
					//  Hide the "Updating..." message
					document.getElementById('updating').style.visibility = 'hidden';
				}
			}
			catch (e)
			{
				//  Handle error
				handleError(e.toString());
			}
		}
		else
		{
			//  Handle error
			handleError(xmlHttp.statusText);
		}
	}
}