Bring back the little green men without slowness

Introduces a singleton DMRoomMap that subscribes to account data to keep itself up to date so we don't have to keep doing the map inversion for each room tile.

src/Lifecycle.js

@@ -22,6 +22,7 @@ import Notifier from './Notifier'
 import UserActivity from './UserActivity';
 import Presence from './Presence';
 import dis from './dispatcher';
+import DMRoomMap from './utils/DMRoomMap';
 
 /**
  * Called at startup, to attempt to build a logged-in Matrix session. It tries
@@ -317,6 +318,7 @@ export function startMatrixClient() {
     Notifier.start();
     UserActivity.start();
     Presence.start();
+    DMRoomMap.shared().start();
 
     MatrixClientPeg.start();
 }
@@ -354,6 +356,7 @@ export function stopMatrixClient() {
     Notifier.stop();
     UserActivity.stop();
     Presence.stop();
+    DMRoomMap.shared().stop();
     var cli = MatrixClientPeg.get();
     if (cli) {
         cli.stopClient();

src/components/views/rooms/RoomTile.js

@@ -70,8 +70,7 @@ module.exports = React.createClass({
     },
 
     _isDirectMessageRoom: function(roomId) {
-        const dmRoomMap = new DMRoomMap(MatrixClientPeg.get());
-        var dmRooms = dmRoomMap.getUserIdForRoomId(roomId);
+        var dmRooms = DMRoomMap.shared().getUserIdForRoomId(roomId);
         if (dmRooms) {
             return true;
         } else {
@@ -277,11 +276,9 @@ module.exports = React.createClass({
         var RoomAvatar = sdk.getComponent('avatars.RoomAvatar');
 
         var directMessageIndicator;
-        // Temporarily turning off the LGM badges as isDirectMessageRoom is horribly unperformant
-        // - see https://github.com/vector-im/vector-web/issues/2343
-        // if (this._isDirectMessageRoom(this.props.room.roomId)) {
-        //     directMessageIndicator = <img src="img/icon_person.svg" className="mx_RoomTile_dm" width="11" height="13" alt="dm"/>;
-        // }
+        if (this._isDirectMessageRoom(this.props.room.roomId)) {
+         directMessageIndicator = <img src="img/icon_person.svg" className="mx_RoomTile_dm" width="11" height="13" alt="dm"/>;
+        }
 
         // These props are injected by React DnD,
         // as defined by your `collect` function above:

src/utils/DMRoomMap.js

@@ -14,16 +14,25 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
+import MatrixClientPeg from '../MatrixClientPeg';
+
 /**
  * Class that takes a Matrix Client and flips the m.direct map
  * so the operation of mapping a room ID to which user it's a DM
  * with can be performed efficiently.
+ *
+ * With 'start', this can also keep itself up to date over time.
  */
 export default class DMRoomMap {
     constructor(matrixClient) {
         this.matrixClient = matrixClient;
         this.roomToUser = null;
 
+        // XXX: Force-bind the event handler method because it
+        // doesn't call it with our object as the 'this'
+        // (use a static property arrow function for this when we can)
+        this._onAccountData = this._onAccountData.bind(this);
+
         const mDirectEvent = matrixClient.getAccountData('m.direct');
         if (!mDirectEvent) {
             this.userToRooms = {};
@@ -32,6 +41,34 @@ export default class DMRoomMap {
         }
     }
 
+    /**
+     * Returns a shared instance of the class
+     * that uses the singleton matrix client
+     * The shared instance must be started before use.
+     */
+    static shared() {
+        if (!DMRoomMap._sharedInstance) {
+            DMRoomMap._sharedInstance = new DMRoomMap(MatrixClientPeg.get());
+        }
+        return DMRoomMap._sharedInstance;
+    }
+
+    start() {
+        this._populateRoomToUser();
+        this.matrixClient.on("accountData", this._onAccountData);
+    }
+
+    stop() {
+        this.matrixClient.removeListener("accountData", this._onAccountData);
+    }
+
+    _onAccountData(ev) {
+        this.userToRooms = this.matrixClient.getAccountData('m.direct').getContent();
+        if (ev.getType() == 'm.direct') {
+            this._populateRoomToUser();
+        }
+    }
+
     getDMRoomsForUserId(userId) {
         // Here, we return the empty list if there are no rooms,
         // since the number of conversations you have with this user is zero.