Implement third-party invite waiting room (#10229)

src/utils/room/shouldEncryptRoomWithSingle3rdPartyInvite.ts

@@ -0,0 +1,48 @@
+/*
+Copyright 2023 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 { MatrixEvent, Room } from "matrix-js-sdk/src/matrix";
+
+import DMRoomMap from "../DMRoomMap";
+import { privateShouldBeEncrypted } from "../rooms";
+
+/**
+ * Tests whether a DM room with exactly one third-party invite should be encrypted.
+ * If it should be encrypted, the third-party invitation event is also returned.
+ */
+export const shouldEncryptRoomWithSingle3rdPartyInvite = (
+    room: Room,
+): { shouldEncrypt: true; inviteEvent: MatrixEvent } | { shouldEncrypt: false; inviteEvent?: undefined } => {
+    // encryption not promoted via .well-known
+    if (!privateShouldBeEncrypted()) return { shouldEncrypt: false };
+
+    // not a DM room
+    if (!DMRoomMap.shared().getRoomIds().has(room.roomId)) return { shouldEncrypt: false };
+
+    // more than one room member / invite
+    if (room.getInvitedAndJoinedMemberCount() !== 1) return { shouldEncrypt: false };
+
+    const thirdPartyInvites = room.currentState.getStateEvents("m.room.third_party_invite") || [];
+
+    if (thirdPartyInvites.length === 1) {
+        return {
+            shouldEncrypt: true,
+            inviteEvent: thirdPartyInvites[0],
+        };
+    }
+
+    return { shouldEncrypt: false };
+};