/*!
 * VisualEditor tracking methods.
 *
 * @copyright 2011-2013 VisualEditor Team and others; see AUTHORS.txt
 * @license The MIT License (MIT); see LICENSE.txt
 */

( function () {
	var callbacks = $.Callbacks( 'memory' ), queue = [];

	/**
	 * Track an analytic event.
	 *
	 * VisualEditor uses this method internally to track internal changes of state that are of analytic
	 * interest, either because they provide data about how users interact with the editor, or because
	 * they contain exception info, latency measurements, or other metrics that help gauge performance
	 * and reliability. VisualEditor does not transmit these events by default, but it provides a
	 * generic interface for routing these events to an analytics framework.
	 *
	 * @member ve
	 * @param {string} topic Event name
	 * @param {Object} [data] Additional data describing the event, encoded as an object
	 */
	ve.track = function ( topic, data ) {
		queue.push( { topic: topic, timeStamp: ve.now(), data: data } );
		callbacks.fire( queue );
	};

	/**
	 * Register a handler for subset of analytic events, specified by topic
	 *
	 * Handlers will be called once for each tracked event, including any events that fired before the
	 * handler was registered; 'this' is set to a plain object with a 'timeStamp' property indicating
	 * the exact time at which the event fired, a string 'topic' property naming the event, and a
	 * 'data' property which is an object of event-specific data. The event topic and event data are
	 * also passed to the callback as the first and second arguments, respectively.
	 *
	 * @member ve
	 * @param {string} topic Handle events whose name starts with this string prefix
	 * @param {Function} callback Handler to call for each matching tracked event
	 */
	ve.trackSubscribe = function ( topic, callback ) {
		var seen = 0;

		callbacks.add( function ( queue ) {
			var event;
			for ( ; seen < queue.length; seen++ ) {
				event = queue[ seen ];
				if ( event.topic.indexOf( topic ) === 0 ) {
					callback.call( event, event.topic, event.data );
				}
			}
		} );
	};

	/**
	 * Register a handler for all analytic events
	 *
	 * Like ve#trackSubscribe, but binds the callback to all events, regardless of topic.
	 *
	 * @member ve
	 * @param {Function} callback
	 */
	ve.trackSubscribeAll = function ( callback ) {
		ve.trackSubscribe( '', callback );
	};
}() );