Implement filtering within skip list

src/stores/room-list-v3/RoomListStoreV3.ts

@@ -8,6 +8,7 @@ Please see LICENSE files in the repository root for full details.
 import type { EmptyObject, Room } from "matrix-js-sdk/src/matrix";
 import type { MatrixDispatcher } from "../../dispatcher/dispatcher";
 import type { ActionPayload } from "../../dispatcher/payloads";
+import type { Filter } from "./skip-list/filters";
 import { AsyncStoreWithClient } from "../AsyncStoreWithClient";
 import SettingsStore from "../../settings/SettingsStore";
 import { VisibilityProvider } from "../room-list/filters/VisibilityProvider";
@@ -16,10 +17,12 @@ import { LISTS_UPDATE_EVENT } from "../room-list/RoomListStore";
 import { RoomSkipList } from "./skip-list/RoomSkipList";
 import { RecencySorter } from "./skip-list/sorters/RecencySorter";
 import { AlphabeticSorter } from "./skip-list/sorters/AlphabeticSorter";
+import { FavouriteFilter } from "./skip-list/filters/FavouriteFilter";
 
 export class RoomListStoreV3Class extends AsyncStoreWithClient<EmptyObject> {
     private roomSkipList?: RoomSkipList;
     private readonly msc3946ProcessDynamicPredecessor: boolean;
+    private filters: Filter[] = [new FavouriteFilter()];
 
     public constructor(dispatcher: MatrixDispatcher) {
         super(dispatcher);
@@ -54,7 +57,7 @@ export class RoomListStoreV3Class extends AsyncStoreWithClient<EmptyObject> {
     protected async onReady(): Promise<any> {
         if (this.roomSkipList?.initialized || !this.matrixClient) return;
         const sorter = new RecencySorter(this.matrixClient.getSafeUserId());
-        this.roomSkipList = new RoomSkipList(sorter);
+        this.roomSkipList = new RoomSkipList(sorter, this.filters);
         const rooms = this.getRooms();
         this.roomSkipList.seed(rooms);
         this.emit(LISTS_UPDATE_EVENT);

src/stores/room-list-v3/skip-list/RoomNode.ts

@@ -6,6 +6,7 @@ Please see LICENSE files in the repository root for full details.
 */
 
 import type { Room } from "matrix-js-sdk/src/matrix";
+import type { Filter, Filters } from "./filters";
 
 /**
  * Room skip list stores room nodes.
@@ -26,4 +27,18 @@ export class RoomNode {
      * eg: previous[i] gives the previous room node from this room node in level i.
      */
     public previous: RoomNode[] = [];
+
+    /**
+     * Aggregates all the filters that apply to this room.
+     * eg: if filters[Filter.FavouriteFilter] is true, then this room is a favourite
+     * room.
+     */
+    public filters: Map<Filters, boolean> = new Map();
+
+    public calculateFilters(filters: Filter[]): void {
+        for (const filter of filters) {
+            const matchesFilter = filter.matches(this.room);
+            this.filters.set(filter.key, matchesFilter);
+        }
+    }
 }

src/stores/room-list-v3/skip-list/RoomSkipList.ts

@@ -7,6 +7,7 @@ Please see LICENSE files in the repository root for full details.
 
 import type { Room } from "matrix-js-sdk/src/matrix";
 import type { Sorter } from "./sorters";
+import type { Filter, Filters } from "./filters";
 import { RoomNode } from "./RoomNode";
 import { shouldPromote } from "./utils";
 import { Level } from "./Level";
@@ -20,7 +21,10 @@ export class RoomSkipList implements Iterable<Room> {
     private roomNodeMap: Map<string, RoomNode> = new Map();
     public initialized: boolean = false;
 
-    public constructor(private sorter: Sorter) {}
+    public constructor(
+        private sorter: Sorter,
+        private filters: Filter[] = [],
+    ) {}
 
     private reset(): void {
         this.levels = [new Level(0)];
@@ -35,6 +39,7 @@ export class RoomSkipList implements Iterable<Room> {
         const sortedRoomNodes = this.sorter.sort(rooms).map((room) => new RoomNode(room));
         let currentLevel = this.levels[0];
         for (const node of sortedRoomNodes) {
+            node.calculateFilters(this.filters);
             currentLevel.setNext(node);
             this.roomNodeMap.set(node.room.roomId, node);
         }
@@ -81,6 +86,7 @@ export class RoomSkipList implements Iterable<Room> {
         this.removeRoom(room);
 
         const newNode = new RoomNode(room);
+        newNode.calculateFilters(this.filters);
         this.roomNodeMap.set(room.roomId, newNode);
 
         /**
@@ -159,6 +165,10 @@ export class RoomSkipList implements Iterable<Room> {
         return new SortedRoomIterator(this.levels[0].head!);
     }
 
+    public getFiltered(filterKeys: Filters[]): SortedFilteredIterator {
+        return new SortedFilteredIterator(this.levels[0].head!, filterKeys);
+    }
+
     /**
      * The number of rooms currently in the skip list.
      */
@@ -179,3 +189,26 @@ class SortedRoomIterator implements Iterator<Room> {
         };
     }
 }
+
+class SortedFilteredIterator implements Iterator<Room> {
+    public constructor(
+        private current: RoomNode,
+        private filterKeys: Filters[],
+    ) {}
+
+    public [Symbol.iterator](): SortedFilteredIterator {
+        return this;
+    }
+
+    public next(): IteratorResult<Room> {
+        let current = this.current;
+        while (current && this.filterKeys.some((key) => !current.filters.get(key))) {
+            current = current.next[0];
+        }
+        if (!current) return { value: undefined, done: true };
+        this.current = current.next[0];
+        return {
+            value: current.room,
+        };
+    }
+}

src/stores/room-list-v3/skip-list/filters/FavouriteFilter.ts

@@ -0,0 +1,20 @@
+/*
+Copyright 2025 New Vector Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR GPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE files in the repository root for full details.
+*/
+import type { Room } from "matrix-js-sdk/src/matrix";
+import type { Filter } from ".";
+import { Filters } from ".";
+import { DefaultTagID } from "../../../room-list/models";
+
+export class FavouriteFilter implements Filter {
+    public matches(room: Room): boolean {
+        return !!room.tags[DefaultTagID.Favourite];
+    }
+
+    public get key(): Filters.FavouriteFilter {
+        return Filters.FavouriteFilter;
+    }
+}

src/stores/room-list-v3/skip-list/filters/index.ts

@@ -0,0 +1,25 @@
+/*
+Copyright 2025 New Vector Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR GPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE files in the repository root for full details.
+*/
+
+import type { Room } from "matrix-js-sdk/src/matrix";
+
+export const enum Filters {
+    FavouriteFilter,
+}
+
+export interface Filter {
+    /**
+     * Boolean return value indicates whether this room satisfies
+     * the filter condition.
+     */
+    matches(room: Room): boolean;
+
+    /**
+     * An unique string used to identify a given filter.
+     */
+    key: Filters;
+}