Factor out shield display rules into one file

src/utils/ShieldUtils.ts

@@ -0,0 +1,45 @@
+import DMRoomMap from './DMRoomMap';
+
+/* For now, a cut-down type spec for the client */
+interface Client {
+    getUserId: () => string;
+    checkUserTrust: (userId: string) => {
+        isCrossSigningVerified: () => boolean
+    };
+    getStoredDevicesForUser: (userId: string) => Promise<[{ deviceId: string }]>;
+    checkDeviceTrust: (userId: string, deviceId: string) => {
+        isVerified: () => boolean
+    }
+}
+
+export async function shieldStatusForMembership(client: Client, room) {
+    const members = (await room.getEncryptionTargetMembers()).map(({userId}) => userId);
+    const inDMMap = !!DMRoomMap.shared().getUserIdForRoomId(room.roomId);
+
+    const verified = [];
+    const unverified = [];
+    members.filter((userId) => userId !== client.getUserId())
+        .forEach((userId) => {
+            (client.checkUserTrust(userId).isCrossSigningVerified() ?
+            verified : unverified).push(userId);
+        });
+
+    /* Check all verified user devices. */
+    /* Don't alarm if no other users are verified  */
+    const includeUser = (verified.length > 0) &&    // Don't alarm for self in rooms where nobody else is verified
+                        !inDMMap &&                 // Don't alarm for self in DMs with other users
+                        (members.length != 2) || // Don't alarm for self in 1:1 chats with other users
+                        (members.length == 1);   // Do alarm for self if we're alone in a room
+    const targets = includeUser ? [...verified, client.getUserId()] : verified;
+    for (const userId of targets) {
+        const devices = await client.getStoredDevicesForUser(userId);
+        const anyDeviceNotVerified = devices.some(({deviceId}) => {
+            return !client.checkDeviceTrust(userId, deviceId).isVerified();
+        });
+        if (anyDeviceNotVerified) {
+            return "warning";
+        }
+    }
+
+    return unverified.length === 0 ? "verified" : "normal";
+}