Create MemoryStorage wrapper around mw.SafeStorage

This means we can guarantee we will be able to recover
auto-saves if we don't reload the page.

Change-Id: Ic867ae6df0c949f35cb32ec4b835688778db29ef

extension.json

@@ -70,6 +70,7 @@
 				"CommentItem.js",
 				"HeadingItem.js",
 				"CommentDetails.js",
+				"MemoryStorage.js",
 				"lib/moment-timezone/moment-timezone-with-data-1970-2030.js",
 				{
 					"name": "parser/data.json",

modules/MemoryStorage.js

@@ -0,0 +1,66 @@
+/**
+ * MemoryStorage creates a wrapper around mw.SafeStorage objects, duplicating
+ * their contents in memory, so that even if the underlying storage mechanism
+ * fails (e.g. quote exceeded), the storage can be relied on before the
+ * page has been reloaded.
+ *
+ * @example
+ * var sessionStorage = new MemoryStorage( mw.storage.session.store );
+ * var localStorage = new MemoryStorage( mw.storage.store );
+ *
+ * @class
+ * @extends mw.SafeStorage
+ * @param {Object} store
+ */
+function MemoryStorage() {
+	// Parent constructor
+	MemoryStorage.super.apply( this, arguments );
+
+	this.data = {};
+}
+
+// HACK: SafeStorage is not exposed as a public API, but we can
+// access it as the constructor of mw.storage.
+var SafeStorage = mw.storage.constructor;
+
+/* Inheritance */
+
+OO.inheritClass( MemoryStorage, SafeStorage );
+
+/* Methods */
+
+/**
+ * @inheritdoc
+ */
+MemoryStorage.prototype.get = function ( key ) {
+	if ( Object.prototype.hasOwnProperty.call( this.data, key ) ) {
+		return this.data[ key ];
+	} else {
+		// Parent method
+		return MemoryStorage.super.prototype.get.apply( this, arguments );
+	}
+};
+
+/**
+ * @inheritdoc
+ */
+MemoryStorage.prototype.set = function ( key, value ) {
+	// Parent method
+	MemoryStorage.super.prototype.set.apply( this, arguments );
+
+	this.data[ key ] = value;
+	return true;
+};
+
+/**
+ * @inheritdoc
+ */
+MemoryStorage.prototype.remove = function ( key ) {
+	// Parent method
+	MemoryStorage.super.prototype.remove.apply( this, arguments );
+
+	delete this.data[ key ];
+	return true;
+};
+
+module.exports = MemoryStorage;

modules/controller.js

@@ -5,7 +5,8 @@ var
 	$pageContainer, linksController, lastHighlightComment,
 	featuresEnabled = mw.config.get( 'wgDiscussionToolsFeaturesEnabled' ) || {},
 	seenAutoTopicSubPopup = !!+mw.user.options.get( 'discussiontools-seenautotopicsubpopup' ),
-	storage = mw.storage.session,
+	MemoryStorage = require( './MemoryStorage.js' ),
+	storage = new MemoryStorage( mw.storage.session.store ),
 	Parser = require( './Parser.js' ),
 	ThreadItem = require( './ThreadItem.js' ),
 	CommentItem = require( './CommentItem.js' ),
@@ -1030,5 +1031,6 @@ module.exports = {
 	update: update,
 	checkThreadItemOnPage: checkThreadItemOnPage,
 	getCheckboxesPromise: getCheckboxesPromise,
-	getApi: getApi
+	getApi: getApi,
+	storage: storage
 };

modules/dt.ui.ReplyWidget.js

@@ -45,7 +45,7 @@ function ReplyWidget( commentController, commentDetails, config ) {
 	this.context = contextNode ? contextNode.nodeName.toLowerCase() : 'dl';
 	// TODO: Should storagePrefix include pageName?
 	this.storagePrefix = 'reply/' + threadItem.id;
-	this.storage = mw.storage.session;
+	this.storage = controller.storage;
 	// eslint-disable-next-line no-jquery/no-global-selector
 	this.contentDir = $( '#mw-content-text' ).css( 'direction' );