Live location sharing - update beacon tile with latest location (#8265)

* add useBeacon hook

Signed-off-by: Kerry Archibald <kerrya@element.io>

* update message tile types to work with function comp with ref

Signed-off-by: Kerry Archibald <kerrya@element.io>

* use beacon hook in beacon body

Signed-off-by: Kerry Archibald <kerrya@element.io>

* update beacon body with (textual) latest locations, test

Signed-off-by: Kerry Archibald <kerrya@element.io>

* language in comment

Signed-off-by: Kerry Archibald <kerrya@element.io>

* comments

Signed-off-by: Kerry Archibald <kerrya@element.io>

* copyright

Signed-off-by: Kerry Archibald <kerrya@element.io>

src/utils/beacon/index.ts

@@ -16,3 +16,4 @@ limitations under the License.
 
 export * from './duration';
 export * from './geolocation';
+export * from './useBeacon';

src/utils/beacon/useBeacon.ts

@@ -0,0 +1,72 @@
+/*
+Copyright 2022 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 { useContext, useEffect, useState } from "react";
+import {
+    Beacon,
+    BeaconEvent,
+    MatrixEvent,
+    getBeaconInfoIdentifier,
+} from "matrix-js-sdk/src/matrix";
+
+import MatrixClientContext from "../../contexts/MatrixClientContext";
+import { useEventEmitterState } from "../../hooks/useEventEmitter";
+
+export const useBeacon = (beaconInfoEvent: MatrixEvent): Beacon | undefined => {
+    const matrixClient = useContext(MatrixClientContext);
+    const [beacon, setBeacon] = useState<Beacon>();
+
+    useEffect(() => {
+        const roomId = beaconInfoEvent.getRoomId();
+        const beaconIdentifier = getBeaconInfoIdentifier(beaconInfoEvent);
+
+        const room = matrixClient.getRoom(roomId);
+        const beaconInstance = room.currentState.beacons.get(beaconIdentifier);
+
+        // TODO could this be less stupid?
+
+        // Beacons are identified by their `state_key`,
+        // where `state_key` is always owner mxid for access control.
+        // Thus, only one beacon is allowed per-user per-room.
+        // See https://github.com/matrix-org/matrix-spec-proposals/pull/3672
+        // When a user creates a new beacon any previous
+        // beacon is replaced and should assume a 'stopped' state
+        // Here we check that this event is the latest beacon for this user
+        // If it is not the beacon instance is set to undefined.
+        // Retired beacons don't get a beacon instance.
+        if (beaconInstance?.beaconInfoId === beaconInfoEvent.getId()) {
+            setBeacon(beaconInstance);
+        } else {
+            setBeacon(undefined);
+        }
+    }, [beaconInfoEvent, matrixClient]);
+
+    // beacon update will fire when this beacon is superceded
+    // check the updated event id for equality to the matrix event
+    const beaconInstanceEventId = useEventEmitterState(
+        beacon,
+        BeaconEvent.Update,
+        () => beacon?.beaconInfoId,
+    );
+
+    useEffect(() => {
+        if (beaconInstanceEventId && beaconInstanceEventId !== beaconInfoEvent.getId()) {
+            setBeacon(undefined);
+        }
+    }, [beaconInstanceEventId, beaconInfoEvent]);
+
+    return beacon;
+};