Replace ChaoticAlgorithm for tag sorting with deterministic behaviour

aka: implement the algorithms.

src/stores/room-list/algorithms/tag_sorting/AlphabeticAlgorithm.ts

@@ -17,13 +17,16 @@ limitations under the License.
 import { Room } from "matrix-js-sdk/src/models/room";
 import { TagID } from "../../models";
 import { IAlgorithm } from "./IAlgorithm";
+import { MatrixClientPeg } from "../../../../MatrixClientPeg";
+import * as Unread from "../../../../Unread";
 
 /**
- * A demonstration to test the API surface.
- * TODO: Remove this before landing
+ * Sorts rooms according to the browser's determination of alphabetic.
  */
-export class ChaoticAlgorithm implements IAlgorithm {
+export class AlphabeticAlgorithm implements IAlgorithm {
     public async sortRooms(rooms: Room[], tagId: TagID): Promise<Room[]> {
-        return rooms;
+        return rooms.sort((a, b) => {
+            return a.name.localeCompare(b.name);
+        });
     }
 }

src/stores/room-list/algorithms/tag_sorting/RecentAlgorithm.ts

@@ -0,0 +1,81 @@
+/*
+Copyright 2020 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import { Room } from "matrix-js-sdk/src/models/room";
+import { TagID } from "../../models";
+import { IAlgorithm } from "./IAlgorithm";
+import { MatrixClientPeg } from "../../../../MatrixClientPeg";
+import * as Unread from "../../../../Unread";
+
+/**
+ * Sorts rooms according to the last event's timestamp in each room that seems
+ * useful to the user.
+ */
+export class RecentAlgorithm implements IAlgorithm {
+    public async sortRooms(rooms: Room[], tagId: TagID): Promise<Room[]> {
+        // We cache the timestamp lookup to avoid iterating forever on the timeline
+        // of events. This cache only survives a single sort though.
+        // We wouldn't need this if `.sort()` didn't constantly try and compare all
+        // of the rooms to each other.
+
+        // TODO: We could probably improve the sorting algorithm here by finding changes.
+        // For example, if we spent a little bit of time to determine which elements have
+        // actually changed (probably needs to be done higher up?) then we could do an
+        // insertion sort or similar on the limited set of changes.
+
+        const tsCache: { [roomId: string]: number } = {};
+        const getLastTs = (r: Room) => {
+            if (tsCache[r.roomId]) {
+                return tsCache[r.roomId];
+            }
+
+            const ts = (() => {
+                // Apparently we can have rooms without timelines, at least under testing
+                // environments. Just return MAX_INT when this happens.
+                if (!r || !r.timeline) {
+                    return Number.MAX_SAFE_INTEGER;
+                }
+
+                for (let i = r.timeline.length - 1; i >= 0; --i) {
+                    const ev = r.timeline[i];
+                    if (!ev.getTs()) continue; // skip events that don't have timestamps (tests only?)
+
+                    // TODO: Don't assume we're using the same client as the peg
+                    if (ev.getSender() === MatrixClientPeg.get().getUserId()
+                        || Unread.eventTriggersUnreadCount(ev)) {
+                        return ev.getTs();
+                    }
+                }
+
+                // we might only have events that don't trigger the unread indicator,
+                // in which case use the oldest event even if normally it wouldn't count.
+                // This is better than just assuming the last event was forever ago.
+                if (r.timeline.length && r.timeline[0].getTs()) {
+                    return r.timeline[0].getTs();
+                } else {
+                    return Number.MAX_SAFE_INTEGER;
+                }
+            })();
+
+            tsCache[r.roomId] = ts;
+            return ts;
+        };
+
+        return rooms.sort((a, b) => {
+            return getLastTs(a) - getLastTs(b);
+        });
+    }
+}

src/stores/room-list/algorithms/tag_sorting/index.ts

@@ -14,16 +14,17 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import { ChaoticAlgorithm } from "./ChaoticAlgorithm";
 import { SortAlgorithm } from "../models";
 import { ManualAlgorithm } from "./ManualAlgorithm";
 import { IAlgorithm } from "./IAlgorithm";
 import { TagID } from "../../models";
 import { Room } from "matrix-js-sdk/src/models/room";
+import { RecentAlgorithm } from "./RecentAlgorithm";
+import { AlphabeticAlgorithm } from "./AlphabeticAlgorithm";
 
 const ALGORITHM_INSTANCES: { [algorithm in SortAlgorithm]: IAlgorithm } = {
-    [SortAlgorithm.Recent]: new ChaoticAlgorithm(),
-    [SortAlgorithm.Alphabetic]: new ChaoticAlgorithm(),
+    [SortAlgorithm.Recent]: new RecentAlgorithm(),
+    [SortAlgorithm.Alphabetic]: new AlphabeticAlgorithm(),
     [SortAlgorithm.Manual]: new ManualAlgorithm(),
 };