Add a Backbone model for the local storage of the browser

The LocalStorageModel makes possible to use the local storage of the
browser as a Backbone model, for example, with a Marionette view.

It is introduced to be used in a later commit as a bridge between the
local storage of the browser and an EditableTextLabel for the name of
the guest.

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>

js/models/localstoragemodel.js

@@ -0,0 +1,69 @@
+/* global Backbone, OCA */
+
+/**
+ *
+ * @copyright Copyright (c) 2017, Daniel Calviño Sánchez (danxuliu@gmail.com)
+ *
+ * @license GNU AGPL version 3 or any later version
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+(function(OCA, Backbone) {
+	'use strict';
+
+	OCA.SpreedMe = OCA.SpreedMe || {};
+	OCA.SpreedMe.Models = OCA.SpreedMe.Models || {};
+
+	/**
+	 * Model for the local storage of the browser.
+	 *
+	 * This makes possible to use the local storage of the browser as a Backbone
+	 * model, for example, with a Marionette view.
+	 *
+	 * The local storage keys to handle must be specified in the "attributes"
+	 * parameter of the constructor.
+	 */
+	var LocalStorageModel = Backbone.Model.extend({
+		isNew: function() {
+			return false;
+		},
+		sync: function(method, model, options) {
+			if (method !== 'read' && method !== 'update') {
+				throw 'Method not supported by LocalStorageModel: ' + method;
+			}
+
+			var response = {};
+
+			if (method === 'read') {
+				response = _.clone(model.attributes);
+				_.each(response, function(value, attribute) {
+					response[attribute] = localStorage.getItem(attribute);
+				});
+			} else {
+				_.each(model.attributes, function(value, attribute) {
+					localStorage.setItem(attribute, value);
+				});
+			}
+
+			if (_.isFunction(options.success)) {
+				options.success.call(this, response);
+			}
+		}
+	});
+
+	OCA.SpreedMe.Models.LocalStorageModel = LocalStorageModel;
+
+})(OCA, Backbone);