/**

 * Heartbeat API

 *

 * Heartbeat is a simple server polling API that sends XHR requests to

 * the server every 15 - 60 seconds and triggers events (or callbacks) upon

 * receiving data. Currently these 'ticks' handle transports for post locking,

 * login-expiration warnings, autosave, and related tasks while a user is logged in.

 *

 * Available PHP filters (in ajax-actions.php):

 * - heartbeat_received

 * - heartbeat_send

 * - heartbeat_tick

 * - heartbeat_nopriv_received

 * - heartbeat_nopriv_send

 * - heartbeat_nopriv_tick

 * @see wp_ajax_nopriv_heartbeat(), wp_ajax_heartbeat()

 *

 * Custom jQuery events:

 * - heartbeat-send

 * - heartbeat-tick

 * - heartbeat-error

 * - heartbeat-connection-lost

 * - heartbeat-connection-restored

 * - heartbeat-nonces-expired

 *

 * @since 3.6.0

 * @output wp-includes/js/heartbeat.js

 */

( function( $, window, undefined ) {

	/**

	 * Constructs the Heartbeat API.

	 *

	 * @since 3.6.0

	 *

	 * @returns {Object} An instance of the Heartbeat class.

	 * @constructor

	 */

	var Heartbeat = function() {

		var $document = $(document),

			settings = {

				// Suspend/resume.

				suspend: false,

				// Whether suspending is enabled.

				suspendEnabled: true,

				// Current screen id, defaults to the JS global 'pagenow' when present

				// (in the admin) or 'front'.

				screenId: '',

				// XHR request URL, defaults to the JS global 'ajaxurl' when present.

				url: '',

				// Timestamp, start of the last connection request.

				lastTick: 0,

				// Container for the enqueued items.

				queue: {},

				// Connect interval (in seconds).

				mainInterval: 60,

				// Used when the interval is set to 5 sec. temporarily.

				tempInterval: 0,

				// Used when the interval is reset.

				originalInterval: 0,

				// Used to limit the number of AJAX requests.

				minimalInterval: 0,

				// Used together with tempInterval.

				countdown: 0,

				// Whether a connection is currently in progress.

				connecting: false,

				// Whether a connection error occurred.

				connectionError: false,

				// Used to track non-critical errors.

				errorcount: 0,

				// Whether at least one connection has been completed successfully.

				hasConnected: false,

				// Whether the current browser window is in focus and the user is active.

				hasFocus: true,

				// Timestamp, last time the user was active. Checked every 30 sec.

				userActivity: 0,

				// Flag whether events tracking user activity were set.

				userActivityEvents: false,

				// Timer that keeps track of how long a user has focus.

				checkFocusTimer: 0,

				// Timer that keeps track of how long needs to be waited before connecting to

				// the server again.

				beatTimer: 0

			};

		/**

		 * Sets local variables and events, then starts the heartbeat.

		 *

		 * @access private

		 *

		 * @since 3.8.0

		 *

		 * @returns {void}

		 */

		function initialize() {

			var options, hidden, visibilityState, visibilitychange;

			if ( typeof window.pagenow === 'string' ) {

				settings.screenId = window.pagenow;

			}

			if ( typeof window.ajaxurl === 'string' ) {

				settings.url = window.ajaxurl;

			}

			// Pull in options passed from PHP.

			if ( typeof window.heartbeatSettings === 'object' ) {

				options = window.heartbeatSettings;

				// The XHR URL can be passed as option when window.ajaxurl is not set.

				if ( ! settings.url && options.ajaxurl ) {

					settings.url = options.ajaxurl;

				}

				/*

				 * The interval can be from 15 to 120 sec. and can be set temporarily to 5 sec.

				 * It can be set in the initial options or changed later through JS and/or

				 * through PHP.

				 */

				if ( options.interval ) {

					settings.mainInterval = options.interval;

					if ( settings.mainInterval < 15 ) {

						settings.mainInterval = 15;

					} else if ( settings.mainInterval > 120 ) {

						settings.mainInterval = 120;

					}

				}

				/*

				 * Used to limit the number of AJAX requests. Overrides all other intervals if

				 * they are shorter. Needed for some hosts that cannot handle frequent requests

				 * and the user may exceed the allocated server CPU time, etc. The minimal

				 * interval can be up to 600 sec. however setting it to longer than 120 sec.

				 * will limit or disable some of the functionality (like post locks). Once set

				 * at initialization, minimalInterval cannot be changed/overridden.

				 */

				if ( options.minimalInterval ) {

					options.minimalInterval = parseInt( options.minimalInterval, 10 );

					settings.minimalInterval = options.minimalInterval > 0 && options.minimalInterval <= 600 ? options.minimalInterval * 1000 : 0;

				}

				if ( settings.minimalInterval && settings.mainInterval < settings.minimalInterval ) {

					settings.mainInterval = settings.minimalInterval;

				}

				// 'screenId' can be added from settings on the front end where the JS global

				// 'pagenow' is not set.

				if ( ! settings.screenId ) {

					settings.screenId = options.screenId || 'front';

				}

				if ( options.suspension === 'disable' ) {

					settings.suspendEnabled = false;

				}

			}

			// Convert to milliseconds.

			settings.mainInterval = settings.mainInterval * 1000;

			settings.originalInterval = settings.mainInterval;

			/*

			 * Switch the interval to 120 seconds by using the Page Visibility API.

			 * If the browser doesn't support it (Safari < 7, Android < 4.4, IE < 10), the

			 * interval will be increased to 120 seconds after 5 minutes of mouse and keyboard

			 * inactivity.

			 */

			if ( typeof document.hidden !== 'undefined' ) {

				hidden = 'hidden';

				visibilitychange = 'visibilitychange';

				visibilityState = 'visibilityState';

			} else if ( typeof document.msHidden !== 'undefined' ) { // IE10

				hidden = 'msHidden';

				visibilitychange = 'msvisibilitychange';

				visibilityState = 'msVisibilityState';

			} else if ( typeof document.webkitHidden !== 'undefined' ) { // Android

				hidden = 'webkitHidden';

				visibilitychange = 'webkitvisibilitychange';

				visibilityState = 'webkitVisibilityState';

			}

			if ( hidden ) {

				if ( document[hidden] ) {

					settings.hasFocus = false;

				}

				$document.on( visibilitychange + '.wp-heartbeat', function() {

					if ( document[visibilityState] === 'hidden' ) {

						blurred();

						window.clearInterval( settings.checkFocusTimer );

					} else {

						focused();

						if ( document.hasFocus ) {

							settings.checkFocusTimer = window.setInterval( checkFocus, 10000 );

						}

					}

				});

			}

			// Use document.hasFocus() if available.

			if ( document.hasFocus ) {

				settings.checkFocusTimer = window.setInterval( checkFocus, 10000 );

			}

			$(window).on( 'unload.wp-heartbeat', function() {

				// Don't connect anymore.

				settings.suspend = true;

				// Abort the last request if not completed.

				if ( settings.xhr && settings.xhr.readyState !== 4 ) {

					settings.xhr.abort();

				}

			});

			// Check for user activity every 30 seconds.

			window.setInterval( checkUserActivity, 30000 );

			// Start one tick after DOM ready.

			$document.ready( function() {

				settings.lastTick = time();

				scheduleNextTick();

			});

		}

		/**

		 * Returns the current time according to the browser.

		 *

		 * @access private

		 *

		 * @since 3.6.0

		 *

		 * @returns {number} Returns the current time.

		 */

		function time() {

			return (new Date()).getTime();

		}

		/**

		 * Checks if the iframe is from the same origin.

		 *

		 * @access private

		 *

		 * @since 3.6.0

		 *

		 * @returns {boolean} Returns whether or not the iframe is from the same origin.

		 */

		function isLocalFrame( frame ) {

			var origin, src = frame.src;

			/*

			 * Need to compare strings as WebKit doesn't throw JS errors when iframes have

			 * different origin. It throws uncatchable exceptions.

			 */

			if ( src && /^https?:\/\//.test( src ) ) {

				origin = window.location.origin ? window.location.origin : window.location.protocol + '//' + window.location.host;

				if ( src.indexOf( origin ) !== 0 ) {

					return false;

				}

			}

			try {

				if ( frame.contentWindow.document ) {

					return true;

				}

			} catch(e) {}

			return false;

		}

		/**

		 * Checks if the document's focus has changed.

		 *

		 * @access private

		 *

		 * @since 4.1.0

		 *

		 * @returns {void}

		 */

		function checkFocus() {

			if ( settings.hasFocus && ! document.hasFocus() ) {

				blurred();

			} else if ( ! settings.hasFocus && document.hasFocus() ) {

				focused();

			}

		}

		/**

		 * Sets error state and fires an event on XHR errors or timeout.

		 *

		 * @access private

		 *

		 * @since 3.8.0

		 *

		 * @param {string} error  The error type passed from the XHR.

		 * @param {number} status The HTTP status code passed from jqXHR

		 *                        (200, 404, 500, etc.).

		 *

		 * @returns {void}

		 */

		function setErrorState( error, status ) {

			var trigger;

			if ( error ) {

				switch ( error ) {

					case 'abort':

						// Do nothing.

						break;

					case 'timeout':

						// No response for 30 sec.

						trigger = true;

						break;

					case 'error':

						if ( 503 === status && settings.hasConnected ) {

							trigger = true;

							break;

						}

						/* falls through */

					case 'parsererror':

					case 'empty':

					case 'unknown':

						settings.errorcount++;

						if ( settings.errorcount > 2 && settings.hasConnected ) {

							trigger = true;

						}

						break;

				}

				if ( trigger && ! hasConnectionError() ) {

					settings.connectionError = true;

					$document.trigger( 'heartbeat-connection-lost', [error, status] );

					wp.hooks.doAction( 'heartbeat.connection-lost', error, status );

				}

			}

		}

		/**

		 * Clears the error state and fires an event if there is a connection error.

		 *

		 * @access private

		 *

		 * @since 3.8.0

		 *

		 * @returns {void}

		 */

		function clearErrorState() {

			// Has connected successfully.

			settings.hasConnected = true;

			if ( hasConnectionError() ) {

				settings.errorcount = 0;

				settings.connectionError = false;

				$document.trigger( 'heartbeat-connection-restored' );

				wp.hooks.doAction( 'heartbeat.connection-restored' );

			}

		}

		/**

		 * Gathers the data and connects to the server.

		 *

		 * @access private

		 *