implement room grid view model

src/domain/session/RoomGridViewModel.js

@@ -0,0 +1,89 @@
+/*
+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 {ViewModel} from "../ViewModel.js";
+
+export class RoomGridViewModel extends ViewModel {
+    constructor(options) {
+        super(options);
+        this._width = options.width;
+        this._height = options.height;
+        this._selectedIndex = 0;
+        this._viewModels = [];
+    }
+
+    roomViewModelAt(idx) {
+        return this._viewModels[idx]?.vm;
+    }
+
+    get focusedIndex() {
+        return this._selectedIndex;
+    }
+
+    setFocusedIndex(idx) {
+        const oldItem = this._viewModels[this._selectedIndex];
+        oldItem?.tileVM?.close();
+        this._selectedIndex = idx;
+        const newItem = this._viewModels[this._selectedIndex];
+        if (newItem) {
+            newItem.vm.focus();
+            newItem.tileVM.open();
+        }
+        this.emitChange("focusedIndex");
+    }
+    get width() {
+        return this._width;
+    }
+
+    get height() {
+        return this._height;
+    }
+
+    /**
+     * Sets a pair of room and room tile view models at the current index
+     * @param {RoomViewModel} vm
+     * @param {RoomTileViewModel} tileVM
+     * @package
+     */
+    setRoomViewModel(vm, tileVM) {
+        const old = this._viewModels[this._selectedIndex];
+        this.disposeTracked(old?.vm);
+        old?.tileVM?.close();
+        this._viewModels[this._selectedIndex] = {vm: this.track(vm), tileVM};
+        this.emitChange(`${this._selectedIndex}`);
+    }
+
+    /**
+     * @package
+     */
+    hasRoomId(roomId) {
+        return this._viewModels.some(vms => vms?.vm._room.id === roomId);
+    }
+    
+    /**
+     * Returns the first set of room and room tile vm,
+     * and untracking them so they are not owned by this view model anymore.
+     * @package
+     */
+    getAndUntrackFirst() {
+        for (const item of this._viewModels) {
+            if (item) {
+                this.untrack(item.vm);
+                return item;
+            }
+        }
+    }
+}