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rECNO/resources/subscribing/ext.centralNotice.kvStoreMaintenance.js
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ext.centralNotice.kvStoreMaintenance.js
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			/**
			* Module for maintenance of items in kvStore. During idle time, it checks the
			* expiry times of items and removes those that expired a specified "leeway"
			* time ago.
			*
			* This module provides an API at mw.centralNotice.kvStoreMaintenance.
			*/
			( function ( $, mw ) {
			var now = Math.round( ( new Date() ).getTime() / 1000 ),
			cn,

			// Regex to find kvStore localStorage keys. Must correspond with PREFIX
			// in ext.centralNotice.kvStore.js.
			PREFIX_REGEX = /^CentralNoticeKV/,

			// Time past expiry before actually removing items: 1 day (in seconds).
			// (This should prevent race conditions among browser tabs.)
			LEEWAY_FOR_REMOVAL = 86400,

			// Maximum number of keys to process at a time.
			MAX_BATCH_SIZE = 10,

			// Maximum number of items to process on any given pageview.
			// This ensures we don't block the browser too much when we prepare the
			// arrays of keys and batch functions.
			MAX_ITEMS_TO_PROCESS = 60;

			function makeRemoveExpiredBatchFunction( keys ) {
			return function() {

			var n, key, rawValue, value;

			for ( n = 0; n < keys.length; n++ ) {
			key = keys[n];

			// Operate only on localStorage items used by the kvStore
			if ( !PREFIX_REGEX.test( key ) ) {
			continue;
			}

			rawValue = localStorage.getItem( key );

			// The item might have been removed since we retrieved the key
			if ( rawValue === null ) {
			continue;
			}

			try {
			value = JSON.parse( rawValue );
			} catch ( e ) {
			// Remove any unparseable items and maybe set an error
			localStorage.removeItem( key );

			if ( cn.kvStore ) {
			cn.kvStore.setMaintenanceError( key );
			}

			continue;
			}

			if ( !value.expiry \|\|
			( value.expiry + LEEWAY_FOR_REMOVAL ) < now ) {

			localStorage.removeItem( key );
			}
			}
			};
			}

			// Don't assume mw.centralNotice has or hasn't been initialized
			mw.centralNotice = cn = ( mw.centralNotice \|\| {} );

			/**
			* Public API
			*/
			cn.kvStoreMaintenance = {

			/**
			* Schedule the batched removal of expired KVStore items.
			*/
			removeExpiredItemsWhenIdle: function () {

			var funcs, keys, i, stopBefore, key,
			j = 0,
			keysToProcess;

			if ( !window.localStorage \|\| localStorage.length === 0) {
			return;
			}

			// We don't know how many batches we'll get through before the user
			// navigates away, and there may be more localStorage items than
			// MAX_ITEMS_TO_PROCESS. So we choose a random key index to start
			// at, and wrap around until we've collected all keys, or the
			// maximum number.
			// This way we're likely to get to all items eventually, even if
			// there are a lot of them and/or each pageview is very quick.
			i = Math.floor( Math.random() * localStorage.length );
			stopBefore =
			( i + Math.min( MAX_ITEMS_TO_PROCESS, localStorage.length ) )
			% localStorage.length;

			// Build an array of localStorage keys
			keys = [];
			do {
			key = localStorage.key( i );

			// Don't assume that the number of keys hasn't changed and that
			// the key exists.
			if ( key !== null ) {
			keys.push( key );
			}

			i++;
			if ( i === localStorage.length ) {
			i = i - localStorage.length;
			}
			} while ( i !== stopBefore );

			// Build an array of functions to process the keys in batches
			funcs = [];
			while ( j < keys.length ) {
			keysToProcess = keys.slice( j,
			Math.min( keys.length, j + MAX_BATCH_SIZE ) );

			funcs.push( makeRemoveExpiredBatchFunction( keysToProcess ) );
			j += MAX_BATCH_SIZE;
			}

			cn.doIdleWork( funcs );
			}
			};

			} )( jQuery, mediaWiki );