Cache.js

define([
	'dojo/_base/array',
	'dojo/when',
	'dojo/_base/declare',
	'dojo/_base/lang',
	'./Store',
	'./Memory',
	'./QueryResults'
], function (arrayUtil, when, declare, lang, Store, Memory, QueryResults) {

	// module:
	//		dstore/Cache


	function cachingQuery(type) {
		// ensure querying creates a parallel caching store query
		return function () {
			var subCollection = this.inherited(arguments);
			var cachingCollection = this.cachingCollection || this.cachingStore;
			subCollection.cachingCollection = cachingCollection[type].apply(cachingCollection, arguments);
			subCollection.isValidFetchCache = this.canCacheQuery === true || this.canCacheQuery(type, arguments);
			return subCollection;
		};
	}

	function init (store) {
		if (!store.cachingStore) {
			store.cachingStore = new Memory();
		}

		store.cachingStore.Model = store.Model;
		store.cachingStore.idProperty = store.idProperty;
	}
	var CachePrototype = {
		cachingStore: null,
		constructor: function () {
			init(this);
		},
		canCacheQuery: function (method, args) {
			// summary:
			//		Indicates if a queried (filter, sort, etc.) collection should using caching
			return false;
		},
		isAvailableInCache: function () {
			// summary:
			//		Indicates if the collection's cachingCollection is a viable source
			//		for a fetch
			return (this.isValidFetchCache && (this.allLoaded || this.fetchRequest)) ||
					this._parent && this._parent.isAvailableInCache();
		},
		fetch: function () {
			return this._fetch(arguments);
		},
		fetchRange: function () {
			return this._fetch(arguments, true);
		},
		_fetch: function (args, isRange) {
			// if the data is available in the cache (via any parent), we use fetch from the caching store
			var cachingStore = this.cachingStore;
			var cachingCollection = this.cachingCollection || cachingStore;
			var store = this;
			var available = this.isAvailableInCache();
			if (available) {
				return new QueryResults(when(available, function () {
					// need to double check to make sure the flag hasn't been cleared
					// and we really have all data loaded
					if (store.isAvailableInCache()) {
						return isRange ?
							cachingCollection.fetchRange(args[0]) :
							cachingCollection.fetch();
					} else {
						return store.inherited(args);
					}
				}));
			}
			var results = this.fetchRequest = this.inherited(args);
			when(results, function (results) {
				var allLoaded = !isRange;
				store.fetchRequest = null;
				// store each object before calling the callback
				arrayUtil.forEach(results, function (object) {
					// store each object before calling the callback
					if (!store.isLoaded || store.isLoaded(object)) {
						if (cachingStore.putSync) {
							// if putSync is available (from the memory store),
							// use that as it is about 40x faster
							cachingStore.putSync(object);
						} else {
							cachingStore.put(object);
						}
					} else {
						// if anything is not loaded, we can't consider them all loaded
						allLoaded = false;
					}
				});
				if (allLoaded) {
					store.allLoaded = true;
				}

				return results;
			},function(err) {
				store.fetchRequest=null; //reset requesting flag
				if(err) {
					throw err;
				}
				throw new Error("Error fetching data from master-store");
			});
			return results;
		},
		// TODO: for now, all forEach() calls delegate to fetch(), but that may be different
		// with IndexedDB, so we may need to intercept forEach as well (and hopefully not
		// double load elements.
		// isValidFetchCache: boolean
		//		This flag indicates if a previous fetch can be used as a cache for subsequent
		//		fetches (in this collection, or downstream).
		isValidFetchCache: false,
		get: function (id, directives) {
			var cachingStore = this.cachingStore;
			var masterGet = this.getInherited(arguments);
			var masterStore = this;
			// if everything is being loaded, we always wait for that to finish
			return when(this.fetchRequest, function () {
				return when(cachingStore.get(id), function (result) {
					if (result !== undefined) {
						return result;
					} else if (masterGet) {
						return when(masterGet.call(masterStore, id, directives), function (result) {
							if (result) {
								cachingStore.put(result, {id: id});
							}
							return result;
						});
					}
				});
			});
		},
		add: function (object, directives) {
			var cachingStore = this.cachingStore;
			return when(this.inherited(arguments), function (result) {
				// now put result in cache (note we don't do add, because add may have
				// called put() and already added it)
				var cachedPutResult =
					cachingStore.put(result && typeof result === 'object' ? result : object, directives);
				// the result from the add should be dictated by the master store and be unaffected by the cachingStore,
				// unless the master store doesn't implement add
				return result || cachedPutResult;
			});
		},
		put: function (object, directives) {
			// first update the cache, we are going to assume the update is valid while we wait to
			// hear from the master store
			var cachingStore = this.cachingStore;
			cachingStore.put(object, directives);
			return when(this.inherited(arguments)).then(function (result) {
				// now put result in cache
				var cachedPutResult =
					cachingStore.put(result && typeof result === 'object' ? result : object, directives);
				// the result from the put should be dictated by the master store and be unaffected by the cachingStore,
				// unless the master store doesn't implement put
				return result || cachedPutResult;
			}, function (exception) {
				// Assuming a rejection of a promise invalidates the local cache
				cachingStore.remove((directives && directives.id) || cachingStore.getIdentity(object));
				if(exception) {
					throw exception;	
				}
				throw new Error("Failed to put() object to master-store");
			});
		},
		remove: function (id, directives) {
			var cachingStore = this.cachingStore;
			return when(this.inherited(arguments), function (result) {
				return when(cachingStore.remove(id, directives), function () {
					return result;
				});
			});
		},
		evict: function (id) {
			// summary:
			//		Evicts an object from the cache
			// any eviction means that we don't have everything loaded anymore
			this.allLoaded = false;
			return this.cachingStore.remove(id);
		},
		invalidate: function () {
			// summary:
			//		Invalidates this collection's cache as being a valid source of
			//		future fetches
			this.allLoaded = false;
		},
		_createSubCollection: function () {
			var subCollection = this.inherited(arguments);
			subCollection._parent = this;
			return subCollection;
		},

		sort: cachingQuery('sort'),
		filter: cachingQuery('filter'),
		select: cachingQuery('select'),

		_getQuerierFactory: function (type) {
			var cachingStore = this.cachingStore;
			return this.inherited(arguments) || lang.hitch(cachingStore, cachingStore._getQuerierFactory(type));
		}
	};
	var Cache = declare(null, CachePrototype);
	Cache.create = function (target, properties) {
		// create a delegate of an existing store with caching
		// functionality mixed in
		target = declare.safeMixin(lang.delegate(target), CachePrototype);
		declare.safeMixin(target, properties);
		// we need to initialize it since the constructor won't have been called
		init(target);
		return target;
	};
	return Cache;
});