Add a UI feature to disable advanced encryption options

src/settings/controllers/OrderedMultiController.ts

@@ -0,0 +1,54 @@
+/*
+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 SettingController from "./SettingController";
+import { SettingLevel } from "../SettingLevel";
+
+/**
+ * Allows for multiple controllers to affect a setting. The first controller
+ * provided to this class which overrides the setting value will affect
+ * the value - other controllers are not called. Change notification handlers
+ * are proxied through to all controllers.
+ *
+ * Similarly, the first controller which indicates that a setting is disabled
+ * will be used - other controllers will not be considered.
+ */
+export class OrderedMultiController extends SettingController {
+    constructor(public readonly controllers: SettingController[]) {
+        super();
+    }
+
+    public getValueOverride(level: SettingLevel, roomId: string, calculatedValue: any, calculatedAtLevel: SettingLevel): any {
+        for (const controller of this.controllers) {
+            const override = controller.getValueOverride(level, roomId, calculatedValue, calculatedAtLevel);
+            if (override !== undefined && override !== null) return override;
+        }
+        return null; // no override
+    }
+
+    public onChange(level: SettingLevel, roomId: string, newValue: any) {
+        for (const controller of this.controllers) {
+            controller.onChange(level, roomId, newValue);
+        }
+    }
+
+    public get settingDisabled(): boolean {
+        for (const controller of this.controllers) {
+            if (controller.settingDisabled) return true;
+        }
+        return false;
+    }
+}