// Copyright 2011 Google Inc. All Rights Reserved.

/**
* @fileoverview A simple script to automatically track Facebook and Twitter
* buttons using Google Analytics social tracking feature.
* @author api.nickm@google.com (Nick Mihailovski)
*/


/**
* Namespace.
* @type {Object}.
*/
var _ga = _ga || {};


/**
* Ensure global _gaq Google Anlaytics queue has be initialized.
* @type {Array}
*/
var _gaq = _gaq || [];


/**
* Helper method to track social features. This assumes all the social
* scripts / apis are loaded synchronously. If they are loaded async,
* you might need to add the nextwork specific tracking call to the
* a callback once the network's script has loaded.
* @param {string} opt_pageUrl An optional URL to associate the social
*     tracking with a particular page.
* @param {string} opt_trackerName An optional name for the tracker object.
*/
_ga.trackSocial = function(opt_pageUrl, opt_trackerName) {
	_ga.trackFacebook(opt_pageUrl, opt_trackerName);
	_ga.trackTwitter(opt_pageUrl, opt_trackerName);
};


/**
* Tracks Facebook likes, unlikes and sends by suscribing to the Facebook
* JSAPI event model. Note: This will not track facebook buttons using the
* iFrame method.
* @param {string} opt_pageUrl An optional URL to associate the social
*     tracking with a particular page.
* @param {string} opt_trackerName An optional name for the tracker object.
*/
_ga.trackFacebook = function(opt_pageUrl, opt_trackerName) {
	var trackerName = _ga.buildTrackerName_(opt_trackerName);
	try {
		if (FB && FB.Event && FB.Event.subscribe) {
			FB.Event.subscribe('edge.create', function(targetUrl) {
				_gaq.push([trackerName + '_trackSocial', 'facebook', 'like', targetUrl, opt_pageUrl]);
			});
			FB.Event.subscribe('edge.remove', function(targetUrl) {
				_gaq.push([trackerName + '_trackSocial', 'facebook', 'unlike', targetUrl, opt_pageUrl]);
			});
			FB.Event.subscribe('message.send', function(targetUrl) {
				_gaq.push([trackerName + '_trackSocial', 'facebook', 'send', targetUrl, opt_pageUrl]);
			});
		}
	} catch (e) { }
};


/**
* Returns the normalized tracker name configuration parameter.
* @param {string} opt_trackerName An optional name for the tracker object.
* @return {string} If opt_trackerName is set, then the value appended with
*     a . Otherwise an empty string.
* @private
*/
_ga.buildTrackerName_ = function(opt_trackerName) {
	return opt_trackerName ? opt_trackerName + '.' : '';
};


/**
* Tracks everytime a user clicks on a tweet button from Twitter.
* This subscribes to the Twitter JS API event mechanism to listen for
* clicks coming from this page. Details here:
* http://dev.twitter.com/pages/intents-events#click
* This method should be called once the twitter API has loaded.
* @param {string} opt_pageUrl An optional URL to associate the social
*     tracking with a particular page.
* @param {string} opt_trackerName An optional name for the tracker object.
*/
_ga.trackTwitter = function(opt_pageUrl, opt_trackerName) {
	var trackerName = _ga.buildTrackerName_(opt_trackerName);
	try {
		if (twttr && twttr.events && twttr.events.bind) {
			twttr.events.bind('tweet', function(event) {
				if (event) {
					var targetUrl; // Default value is undefined.
					if (event.target && event.target.nodeName == 'IFRAME') {
						targetUrl = _ga.extractParamFromUri_(event.target.src, 'url');
					}
					_gaq.push([trackerName + '_trackSocial', 'twitter', 'tweet', targetUrl, opt_pageUrl]);
				}
			});
		}
	} catch (e) { }
};


/**
* Extracts a query parameter value from a URI.
* @param {string} uri The URI from which to extract the parameter.
* @param {string} paramName The name of the query paramater to extract.
* @return {string} The un-encoded value of the query paramater. underfined
*     if there is no URI parameter.
* @private
*/
_ga.extractParamFromUri_ = function(uri, paramName) {
	if (!uri) {
		return;
	}
	var uri = uri.split('#')[0];  // Remove anchor.
	var parts = uri.split('?');  // Check for query params.
	if (parts.length == 1) {
		return;
	}
	var query = decodeURI(parts[1]);

	// Find url param.
	paramName += '=';
	var params = query.split('&');
	for (var i = 0, param; param = params[i]; ++i) {
		if (param.indexOf(paramName) === 0) {
			return unescape(param.split('=')[1]);
		}
	}
	return;
};