Add more functionality to the room list vm (#29402)

* Add more vm functionality

- Listen for updates from the store
- Provide a method to open rooms

* Write test

src/components/viewmodels/roomlist/RoomListViewModel.tsx

@@ -5,14 +5,26 @@ SPDX-License-Identifier: AGPL-3.0-only OR GPL-3.0-only OR LicenseRef-Element-Com
 Please see LICENSE files in the repository root for full details.
 */
 
+import { useCallback, useState } from "react";
+
 import type { Room } from "matrix-js-sdk/src/matrix";
+import type { ViewRoomPayload } from "../../../dispatcher/payloads/ViewRoomPayload";
 import RoomListStoreV3 from "../../../stores/room-list-v3/RoomListStoreV3";
+import { useEventEmitter } from "../../../hooks/useEventEmitter";
+import { LISTS_UPDATE_EVENT } from "../../../stores/room-list/RoomListStore";
+import dispatcher from "../../../dispatcher/dispatcher";
+import { Action } from "../../../dispatcher/actions";
 
 export interface RoomListViewState {
     /**
      * A list of rooms to be displayed in the left panel.
      */
     rooms: Room[];
+
+    /**
+     * Open the room having given roomId.
+     */
+    openRoom: (roomId: string) => void;
 }
 
 /**
@@ -20,6 +32,20 @@ export interface RoomListViewState {
  * @see {@link RoomListViewState} for more information about what this view model returns.
  */
 export function useRoomListViewModel(): RoomListViewState {
-    const rooms = RoomListStoreV3.instance.getSortedRooms();
-    return { rooms };
+    const [rooms, setRooms] = useState(RoomListStoreV3.instance.getSortedRoomsInActiveSpace());
+
+    useEventEmitter(RoomListStoreV3.instance, LISTS_UPDATE_EVENT, () => {
+        const newRooms = RoomListStoreV3.instance.getSortedRoomsInActiveSpace();
+        setRooms(newRooms);
+    });
+
+    const openRoom = useCallback((roomId: string): void => {
+        dispatcher.dispatch<ViewRoomPayload>({
+            action: Action.ViewRoom,
+            room_id: roomId,
+            metricsTrigger: "RoomList",
+        });
+    }, []);
+
+    return { rooms, openRoom };
 }

test/unit-tests/components/viewmodels/roomlist/RoomListViewModel-test.tsx

@@ -0,0 +1,62 @@
+/*
+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 { range } from "lodash";
+import { act, renderHook, waitFor } from "jest-matrix-react";
+
+import RoomListStoreV3 from "../../../../../src/stores/room-list-v3/RoomListStoreV3";
+import { mkStubRoom } from "../../../../test-utils";
+import { LISTS_UPDATE_EVENT } from "../../../../../src/stores/room-list/SlidingRoomListStore";
+import { useRoomListViewModel } from "../../../../../src/components/viewmodels/roomlist/RoomListViewModel";
+import dispatcher from "../../../../../src/dispatcher/dispatcher";
+import { Action } from "../../../../../src/dispatcher/actions";
+
+describe("RoomListViewModel", () => {
+    function mockAndCreateRooms() {
+        const rooms = range(10).map((i) => mkStubRoom(`foo${i}:matrix.org`, `Foo ${i}`, undefined));
+        jest.spyOn(RoomListStoreV3.instance, "getSortedRoomsInActiveSpace").mockImplementation(() => [...rooms]);
+        return rooms;
+    }
+
+    it("should return a list of rooms", async () => {
+        const rooms = mockAndCreateRooms();
+        const { result: vm } = renderHook(() => useRoomListViewModel());
+
+        expect(vm.current.rooms).toHaveLength(10);
+        for (const room of rooms) {
+            expect(vm.current.rooms).toContain(room);
+        }
+    });
+
+    it("should update list of rooms on event from room list store", async () => {
+        const rooms = mockAndCreateRooms();
+        const { result: vm } = renderHook(() => useRoomListViewModel());
+
+        const newRoom = mkStubRoom("bar:matrix.org", "Bar", undefined);
+        rooms.push(newRoom);
+        act(() => RoomListStoreV3.instance.emit(LISTS_UPDATE_EVENT));
+
+        await waitFor(() => {
+            expect(vm.current.rooms).toContain(newRoom);
+        });
+    });
+
+    it("should dispatch view room action on openRoom", async () => {
+        const rooms = mockAndCreateRooms();
+        const { result: vm } = renderHook(() => useRoomListViewModel());
+
+        const fn = jest.spyOn(dispatcher, "dispatch");
+        act(() => vm.current.openRoom(rooms[7].roomId));
+        expect(fn).toHaveBeenCalledWith(
+            expect.objectContaining({
+                action: Action.ViewRoom,
+                room_id: rooms[7].roomId,
+                metricsTrigger: "RoomList",
+            }),
+        );
+    });
+});