( function ( mw, $ ) {
	var pageVisibility = mw.popups.pageVisibility,
		checkin = {
			/**
			 * Checkin times - Fibonacci numbers
			 *
			 * Exposed for testing only.
			 *
			 * @type {number[]}
			 * @private
			 */
			CHECKIN_TIMES: [ 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233,
				377, 610, 987, 1597, 2584, 4181, 6765 ],
			/**
			 * Have checkin actions been setup already?
			 *
			 * Exposed for testing only.
			 *
			 * @private
			 * @type {boolean}
			 */
			haveCheckinActionsBeenSetup: false
		};

	/**
	 * A customized `setTimeout` function that takes page visibility into account
	 *
	 * If the document is not visible to the user, e.g. browser window is minimized,
	 * then pause the time. Otherwise execute `callback` after `delay` milliseconds.
	 * The callback won't be executed if the browser does not suppor the page visibility
	 * API.
	 *
	 * Exposed for testing only.
	 *
	 * @see https://www.w3.org/TR/page-visibility/#dom-document-hidden
	 * @private
	 * @param {Function} callback Function to call when the time is up
	 * @param {number} delay The number of milliseconds to wait before executing the callback
	 */
	checkin.setVisibleTimeout = function ( callback, delay ) {
		var hiddenPropertyName = pageVisibility.getDocumentHiddenPropertyName( document ),
			visibilityChangeEventName = pageVisibility.getDocumentVisibilitychangeEventName( document ),
			timeoutId,
			lastStartedAt;

		if ( !hiddenPropertyName || !visibilityChangeEventName ) {
			return;
		}

		/**
		 * Execute the callback and turn off listening to the visibilitychange event
		 */
		function done() {
			callback();
			$( document ).off( visibilityChangeEventName, visibilityChangeHandler );
		}

		/**
		 * Pause or resume the timer depending on the page visibility state
		 */
		function visibilityChangeHandler() {
			var millisecondsPassed;

			// Pause the timer if the page is hidden ...
			if ( pageVisibility.isDocumentHidden( document ) ) {
				// ... and only if the timer has started.
				// Timer may not have been started if the document opened in a
				// hidden tab for example. The timer will be started when the
				// document is visible to the user.
				if ( lastStartedAt ) {
					millisecondsPassed = new Date().getTime() - lastStartedAt;
					delay = Math.max( 0, delay - millisecondsPassed );
					clearTimeout( timeoutId );
				}
			} else {
				lastStartedAt = new Date().getTime();
				timeoutId = setTimeout( done, delay );
			}
		}

		visibilityChangeHandler();

		$( document ).on( visibilityChangeEventName, visibilityChangeHandler );
	};

	/**
	 * Perform the passed `checkin` action at the predefined times
	 *
	 * Actions are setup only once no matter how many times this function is
	 * called. Ideally this function should be called once.
	 *
	 * @see checkin.CHECKIN_TIMES
	 * @param {Function} checkinAction
	 */
	checkin.setupActions = function( checkinAction ) {
		var timeIndex = 0,
			timesLength = checkin.CHECKIN_TIMES.length,
			time,  // current checkin time
			nextTime;  // the checkin time that will be logged next

		if ( checkin.haveCheckinActionsBeenSetup ) {
			return;
		}

		/**
		 * Execute the checkin action with the current checkin time
		 *
		 * If more checkin times are left, then setup a timer to log the next one.
		 */
		function setup() {
			time = checkin.CHECKIN_TIMES[ timeIndex ];
			checkinAction( time );

			timeIndex += 1;
			if ( timeIndex < timesLength ) {
				nextTime = checkin.CHECKIN_TIMES[ timeIndex ];
				// Execute the callback after the number of seconds left till the
				// next checkin time.
				checkin.setVisibleTimeout( setup, ( nextTime - time ) * 1000 );
			}
		}

		checkin.setVisibleTimeout( setup, checkin.CHECKIN_TIMES[ timeIndex ] * 1000 );

		checkin.haveCheckinActionsBeenSetup = true;
	};

	mw.popups.checkin = checkin;

}( mediaWiki, jQuery ) );