Add VoIP user mapper

The accompanying element-web PR with the config documentation should
explain what this is & why. Internally, this breaks the assumption
that call.roomId is the room that the call appears in for the user.
call.roomId may now be a 'virtual' room while the react SDK actually
displays it in a different room. React SDK always stores the calls
under the user-facing rooms, and provides a function to get the
user-facing room for a given call.

src/VoipUserMapper.ts

@@ -0,0 +1,77 @@
+/*
+Copyright 2021 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 { ensureDMExists, findDMForUser } from './createRoom';
+import { MatrixClientPeg } from "./MatrixClientPeg";
+import DMRoomMap from "./utils/DMRoomMap";
+import SdkConfig from "./SdkConfig";
+
+// Functions for mapping users & rooms for the voip_mxid_translate_pattern
+// config option
+
+export function voipUserMapperEnabled(): boolean {
+    return SdkConfig.get()['voip_mxid_translate_pattern'] !== undefined;
+}
+
+function userToVirtualUser(userId: string, templateString?: string): string {
+    if (templateString === undefined) templateString = SdkConfig.get()['voip_mxid_translate_pattern'];
+    if (!templateString) return null;
+    return templateString.replace('${mxid}', encodeURIComponent(userId).replace(/%/g, '=').toLowerCase());
+}
+
+function virtualUserToUser(userId: string, templateString?: string): string {
+    if (templateString === undefined) templateString = SdkConfig.get()['voip_mxid_translate_pattern'];
+    if (!templateString) return null;
+
+    const regexString = templateString.replace('${mxid}', '(.+)');
+
+    const match = userId.match('^' + regexString + '$');
+    if (!match) return null;
+
+    return decodeURIComponent(match[1].replace(/=/g, '%'));
+}
+
+async function getOrCreateVirtualRoomForUser(userId: string):Promise<string> {
+    const virtualUser = userToVirtualUser(userId);
+    if (!virtualUser) return null;
+
+    return await ensureDMExists(MatrixClientPeg.get(), virtualUser);
+}
+
+export async function getOrCreateVirtualRoomForRoom(roomId: string):Promise<string> {
+    const user = DMRoomMap.shared().getUserIdForRoomId(roomId);
+    if (!user) return null;
+    return getOrCreateVirtualRoomForUser(user);
+}
+
+export function roomForVirtualRoom(roomId: string):string {
+    const virtualUser = DMRoomMap.shared().getUserIdForRoomId(roomId);
+    if (!virtualUser) return null;
+    const realUser = virtualUserToUser(virtualUser);
+    const room = findDMForUser(MatrixClientPeg.get(), realUser);
+    if (room) {
+        return room.roomId;
+    } else {
+        return null;
+    }
+}
+
+export function isVirtualRoom(roomId: string):boolean {
+    const virtualUser = DMRoomMap.shared().getUserIdForRoomId(roomId);
+    if (!virtualUser) return null;
+    const realUser = virtualUserToUser(virtualUser);
+    return Boolean(realUser);
+}