/*!
 * VisualEditor MediaWiki Initialization LinkCache class.
 *
 * @copyright 2011-2014 VisualEditor Team and others; see AUTHORS.txt
 * @license The MIT License (MIT); see LICENSE.txt
 */
( function () {
	/*global mw */

	/**
	 * MediaWiki link status cache.
	 *
	 * Used to track how to style links to a given page based on their existence status etc.
	 *
	 * @class
	 *
	 * @constructor
	 */
	ve.init.mw.LinkCache = function VeInitMwLinkCache() {
		// Mixin constructor
		OO.EventEmitter.call( this );

		this.cache = {}; // Keys are page names, values are deferreds
		this.queue = []; // Array of page names queued to be looked up
		this.schedule = ve.debounce( this.processQueue.bind( this ), 0 );
	};

	OO.mixinClass( ve.init.mw.LinkCache, OO.EventEmitter );

	// TODO maybe factor out generic parts into ve.StatusCache or whatever
	// TODO unit tests

	/**
	 * Fired when a new entry is added to the cache.
	 * @event add
	 * @param {Object} entries Cache entries that were added. Object mapping names to data objects.
	 */

	/**
	 * Look up data about a page in the cache. If the data about this page is already in the cache,
	 * this returns an already-resolved promise. Otherwise, it returns a pending promise and schedules
	 * an API call to retrieve the data.
	 *
	 * @param {string} name Normalized page title
	 * @returns {jQuery.Promise} Promise that will be resolved with the data once it's available
	 */
	ve.init.mw.LinkCache.prototype.get = function ( name ) {
		if ( !Object.prototype.hasOwnProperty.call( this.cache, name ) ) {
			this.cache[name] = $.Deferred();
			this.queue.push( name );
			this.schedule();
		}
		return this.cache[name].promise();
	};

	/**
	 * Add entries to the cache.
	 * @param {Object} entries Object keyed by page title, with the values being data objects
	 * @fires add
	 */
	ve.init.mw.LinkCache.prototype.set = function ( entries ) {
		var name;
		for ( name in entries ) {
			if ( !Object.prototype.hasOwnProperty.call( this.cache, name ) ) {
				this.cache[name] = $.Deferred();
			}
			this.cache[name].resolve( entries[name] );
		}
		this.emit( 'add', ve.getObjectKeys( entries ) );
	};

	// TODO should reuse ve.dm.MWInternalLinkAnnotation#getLookupTitle once factored out
	function normalizeTitle( name ) {
		var title = mw.Title.newFromText( name );
		if ( !title ) {
			return name;
		}
		return title.getPrefixedText();
	}

	/**
	 * Perform any scheduled API requests.
	 * @private
	 * @fires add
	 */
	ve.init.mw.LinkCache.prototype.processQueue = function () {
		var subqueue, queue, queueCopy, linkCache = this;

		function rejectSubqueue() {
			var i, len;
			for ( i = 0, len = subqueue.length; i < len; i++ ) {
				linkCache.cache[subqueue[i]].reject();
			}
		}

		function processData( data ) {
			var pageid, info, dfd, pages = data.query && data.query.pages || {};
			for ( pageid in pages ) {
				info = {
					'missing': pages[pageid].missing !== undefined
				};
				dfd = linkCache.cache[pages[pageid].title];
				if ( dfd ) {
					dfd.resolve( info );
				}
			}
			// Reject everything in subqueue; this will only reject the ones
			// that weren't already resolved above, because .reject() on an
			// already resolved Deferred is a no-op.
			rejectSubqueue();
		}

		queue = this.queue;
		queueCopy = queue.slice();
		this.queue = [];
		while ( queue.length ) {
			subqueue = queue.splice( 0, 50 ).map( normalizeTitle );
			ve.init.target.constructor.static.apiRequest( {
				'action': 'query',
				'prop': 'info',
				'titles': subqueue.join( '|' )
			} )
				.done( processData )
				.fail( rejectSubqueue );
		}
		this.emit( 'add', queueCopy );
	};

} () );