notif: Get token on Android, and send to server

This implements part of zulip#320.

To make an end-to-end demo, we also listen for notification
messages, and just print them to the debug log.

lib/main.dart

@@ -4,6 +4,7 @@ import 'package:flutter/material.dart';
 import 'licenses.dart';
 import 'log.dart';
 import 'model/binding.dart';
+import 'notifications.dart';
 import 'widgets/app.dart';
 
 void main() {
@@ -13,5 +14,7 @@ void main() {
   }());
   LicenseRegistry.addLicense(additionalLicenses);
   LiveZulipBinding.ensureInitialized();
+  WidgetsFlutterBinding.ensureInitialized();
+  NotificationService.instance.start();
   runApp(const ZulipApp());
 }

lib/model/store.dart

@@ -12,7 +12,9 @@ import '../api/model/initial_snapshot.dart';
 import '../api/model/model.dart';
 import '../api/route/events.dart';
 import '../api/route/messages.dart';
+import '../api/route/notifications.dart';
 import '../log.dart';
+import '../notifications.dart';
 import 'autocomplete.dart';
 import 'database.dart';
 import 'message_list.dart';
@@ -451,6 +453,7 @@ class LivePerAccountStore extends PerAccountStore {
       initialSnapshot: initialSnapshot,
     );
     store.poll();
+    store.registerNotificationToken();
     return store;
   }
 
@@ -472,4 +475,21 @@ class LivePerAccountStore extends PerAccountStore {
       }
     }
   }
+
+  /// Send this client's notification token to the server, now and if it changes.
+  ///
+  /// TODO(#321) handle iOS/APNs; currently only Android/FCM
+  // TODO(#322) save acked token, to dedupe updating it on the server
+  // TODO(#323) track the registerFcmToken/etc request, warn if not succeeding
+  Future<void> registerNotificationToken() async {
+    // TODO call removeListener on [dispose]
+    NotificationService.instance.token.addListener(_registerNotificationToken);
+    await _registerNotificationToken();
+  }
+
+  Future<void> _registerNotificationToken() async {
+    final token = NotificationService.instance.token.value;
+    if (token == null) return;
+    await registerFcmToken(connection, token: token);
+  }
 }

lib/notifications.dart

@@ -0,0 +1,72 @@
+import 'package:flutter/foundation.dart';
+
+import 'log.dart';
+import 'model/binding.dart';
+
+class NotificationService {
+  static NotificationService get instance => (_instance ??= NotificationService._());
+  static NotificationService? _instance;
+
+  NotificationService._();
+
+  /// Reset the state of the [NotificationService], for testing.
+  ///
+  /// TODO refactor this better, perhaps unify with ZulipBinding
+  @visibleForTesting
+  static void debugReset() {
+    instance.token.dispose();
+    instance.token = ValueNotifier(null);
+  }
+
+  /// The FCM registration token for this install of the app.
+  ///
+  /// This is unique to the (app, device) pair, but not permanent.
+  /// Most often it's the same from one run of the app to the next,
+  /// but it can change either during a run or between them.
+  ///
+  /// See also:
+  ///  * Upstream docs on FCM registration tokens in general:
+  ///    https://firebase.google.com/docs/cloud-messaging/manage-tokens
+  ValueNotifier<String?> token = ValueNotifier(null);
+
+  Future<void> start() async {
+    if (defaultTargetPlatform != TargetPlatform.android) return; // TODO(#321)
+
+    await ZulipBinding.instance.firebaseInitializeApp();
+
+    // TODO(#324) defer notif setup if user not logged into any accounts
+    //   (in order to avoid calling for permissions)
+
+    ZulipBinding.instance.firebaseMessagingOnMessage.listen(_onRemoteMessage);
+
+    // Get the FCM registration token, now and upon changes.  See FCM API docs:
+    //   https://firebase.google.com/docs/cloud-messaging/android/client#sample-register
+    ZulipBinding.instance.firebaseMessaging.onTokenRefresh.listen(_onTokenRefresh);
+    await _getToken();
+  }
+
+  Future<void> _getToken() async {
+    final value = await ZulipBinding.instance.firebaseMessaging.getToken(); // TODO(log) if null
+    assert(debugLog("notif token: $value"));
+    // On a typical launch of the app (other than the first one after install),
+    // this is the only way we learn the token value; onTokenRefresh never fires.
+    token.value = value;
+  }
+
+  void _onTokenRefresh(String value) {
+    assert(debugLog("new notif token: $value"));
+    // On first launch after install, our [FirebaseMessaging.getToken] call
+    // causes this to fire, followed by completing its own future so that
+    // `_getToken` sees the value as well.  So in that case this is redundant.
+    //
+    // Subsequently, though, this can also potentially fire on its own, if for
+    // some reason the FCM system decides to replace the token.  So both paths
+    // need to save the value.
+    token.value = value;
+  }
+
+  void _onRemoteMessage(FirebaseRemoteMessage message) {
+    assert(debugLog("notif message: ${message.data}"));
+    // TODO(#122): parse data; show notification UI
+  }
+}

test/model/store_test.dart

@@ -1,14 +1,20 @@
 import 'dart:async';
 
 import 'package:checks/checks.dart';
+import 'package:http/http.dart' as http;
 import 'package:test/scaffolding.dart';
 import 'package:zulip/model/store.dart';
+import 'package:zulip/notifications.dart';
 
 import '../api/fake_api.dart';
 import '../example_data.dart' as eg;
+import '../stdlib_checks.dart';
+import 'binding.dart';
 import 'test_store.dart';
 
 void main() {
+  TestZulipBinding.ensureInitialized();
+
   final account1 = eg.selfAccount.copyWith(id: 1);
   final account2 = eg.otherAccount.copyWith(id: 2);
 
@@ -100,6 +106,70 @@ void main() {
     check(await globalStore.perAccount(1)).identicalTo(store1);
     check(completers(1)).length.equals(1);
   });
+
+  group('PerAccountStore.registerNotificationToken', () {
+    late LivePerAccountStore store;
+    late FakeApiConnection connection;
+
+    void prepareStore() {
+      store = eg.liveStore();
+      connection = store.connection as FakeApiConnection;
+    }
+
+    void checkLastRequest({required String token}) {
+      check(connection.lastRequest).isA<http.Request>()
+        ..method.equals('POST')
+        ..url.path.equals('/api/v1/users/me/android_gcm_reg_id')
+        ..bodyFields.deepEquals({'token': token});
+    }
+
+    test('token already known', () async {
+      // This tests the case where [NotificationService.start] has already
+      // learned the token before the store is created.
+      // (This is probably the common case.)
+      addTearDown(testBinding.reset);
+      testBinding.firebaseMessagingInitialToken = '012abc';
+      addTearDown(NotificationService.debugReset);
+      await NotificationService.instance.start();
+
+      // On store startup, send the token.
+      prepareStore();
+      connection.prepare(json: {});
+      await store.registerNotificationToken();
+      checkLastRequest(token: '012abc');
+
+      // If the token changes, send it again.
+      testBinding.firebaseMessaging.setToken('456def');
+      connection.prepare(json: {});
+      await null; // Run microtasks.  TODO use FakeAsync for these tests.
+      checkLastRequest(token: '456def');
+    });
+
+    test('token initially unknown', () async {
+      // This tests the case where the store is created while our
+      // request for the token is still pending.
+      addTearDown(testBinding.reset);
+      testBinding.firebaseMessagingInitialToken = '012abc';
+      addTearDown(NotificationService.debugReset);
+      final startFuture = NotificationService.instance.start();
+
+      // On store startup, send nothing (because we have nothing to send).
+      prepareStore();
+      await store.registerNotificationToken();
+      check(connection.lastRequest).isNull();
+
+      // When the token later appears, send it.
+      connection.prepare(json: {});
+      await startFuture;
+      checkLastRequest(token: '012abc');
+
+      // If the token subsequently changes, send it again.
+      testBinding.firebaseMessaging.setToken('456def');
+      connection.prepare(json: {});
+      await null; // Run microtasks.  TODO use FakeAsync for these tests.
+      checkLastRequest(token: '456def');
+    });
+  });
 }
 
 class LoadingTestGlobalStore extends TestGlobalStore {