// Hold an instance of XMLHttpRequest
var xmlHttp = createXmlHttpRequestObject();

// Display error messages (true) or degrade to non-AJAX behavior (false) 
var showErrors = true;

// Contain link or form clicked/submitted by visitor
var actionObject = '';

// True when place order button clicked else flase
var placingOrder = false;

// Create XMLHttpRequest instance
function createXmlHttpRequestObject() {
	// Store XMLHttpRequest object
	var xmlHttp;

	// Create 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 XMLHttpRequest object created successfully, return it 
	if (xmlHttp) {
		return xmlHttp;
	}
	// If error, pass to handleError
	else {
		handleError("Error creating the XMLHttpRequest object.");
	}
}

// Display error message or degrade 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 link
	else if (actionObject.tagName == 'A') {
		window.location = actionObject.href;
	}
	// Fall back to non-AJAX behavior by submitting form
	else if (actionObject.tagName == 'FORM') {
		actionObject.submit();
	}
}

// Add product to shopping cart
function addProductToCart(form) {
	// Display updating message
	document.getElementById('updating').style.visibility = 'visible';

	// Degrade to old skool form submit if XMLHttpRequest not available 
	if (!xmlHttp) return true;

	// Create asynchronous URL
	request = form.action + '&AjaxRequest';
	params = '';

	// 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 connecting to server
	try {
		// Continue only if XMLHttpRequest object not busy
		if (xmlHttp.readyState == 4 || xmlHttp.readyState == 0) {
			// Make server request to validate extracted data
			xmlHttp.open("POST", request, true);
			xmlHttp.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
			xmlHttp.onreadystatechange = addToCartStateChange;
			xmlHttp.send(params);
		}
	}
	catch(e) {
		// Handle error
		handleError(e.toString());
	}

	// Stop old skool form submit if AJAX action succeeded
	return false;
}

// Retrieve HTTP response
function addToCartStateChange() {
	// When readyState 4, also read server response
	if (xmlHttp.readyState == 4) {
		// Continue only if HTTP status okay
		if (xmlHttp.status == 200) {
			try {
				updateCartSummary();
			}
			catch(e) {
				handleError(e.toString());
			}
		}
		else {
			handleError(xmlHttp.statusText);
		}
	}
}

// Process server response
function updateCartSummary() {
	// Read the response
	response = xmlHttp.responseText;

	// Server error?
	if (response.indexOf("ERRNO") >= 0 || response.indexOf("error") >= 0) {
		handleError(response);
	}
	else {
		// Extract content of cart div element
		var cartSummaryRegEx = /^<div class="box base-mini" id="cart-summary">([\s\S]*)<\/div>$/m;
		matches = cartSummaryRegEx.exec(response);
		response = matches[1];

		// Update cart box and hide loading message
		document.getElementById("cart-summary").innerHTML = response;
		// Hide updating message
		document.getElementById('updating').style.visibility = 'hidden';
	}
}

// Called on shopping cart update actions
function executeCartAction(obj) {
	// Degrade to old skool form submit for place order action
	if (placingOrder) return true;

	// Display updating message
	document.getElementById('updating').style.visibility = 'visible';

	// Degrade to old skool form submit if XMLHttpRequest is not available 
	if (!xmlHttp) return true;

	// Save object reference 
	actionObject = obj;

	// Initialise response and parameters
	response = '';
	params = '';

	// If link was clicked, get href attribute
	if (obj.tagName == 'A') {
		url = obj.href + '&AjaxRequest';
	}
	// If form submitted, get 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 connecting to server
	try {
		// Make server request only if 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 old skool form submit if AJAX action succeeded
	return false;
}

// Retrieve HTTP response
function cartActionStateChange() {
	// When readyState 4, read server response
	if (xmlHttp.readyState == 4) {
		// Continue only if HTTP status 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 cart
					document.getElementById("contents").innerHTML = response;
					// Hide updating message
					document.getElementById('updating').style.visibility = 'hidden';
				}
			}
			catch(e) {
				// Handle error
				handleError(e.toString());
			}
		}
		else {
			// Handle error
			handleError(xmlHttp.statusText);
		}
	}
}