notif: Support migration of Android notification channels

android/app/src/main/kotlin/com/zulip/flutter/Notifications.g.kt

@@ -408,6 +408,18 @@ interface AndroidNotificationHostApi {
    * See: https://developer.android.com/reference/androidx/core/app/NotificationManagerCompat#createNotificationChannel(androidx.core.app.NotificationChannelCompat)
    */
   fun createNotificationChannel(channel: NotificationChannel)
+  /**
+   * Corresponds to `androidx.core.app.NotificationManagerCompat.getNotificationChannelsCompat`.
+   *
+   * See: https://developer.android.com/reference/kotlin/androidx/core/app/NotificationManagerCompat#getNotificationChannelsCompat()
+   */
+  fun getNotificationChannels(): List<NotificationChannel>
+  /**
+   * Corresponds to `androidx.core.app.NotificationManagerCompat.deleteNotificationChannel`
+   *
+   * See: https://developer.android.com/reference/kotlin/androidx/core/app/NotificationManagerCompat#deleteNotificationChannel(java.lang.String)
+   */
+  fun deleteNotificationChannel(channelId: String)
   /**
    * Corresponds to `android.app.NotificationManager.notify`,
    * combined with `androidx.core.app.NotificationCompat.Builder`.
@@ -487,6 +499,39 @@ interface AndroidNotificationHostApi {
           channel.setMessageHandler(null)
         }
       }
+      run {
+        val channel = BasicMessageChannel<Any?>(binaryMessenger, "dev.flutter.pigeon.zulip.AndroidNotificationHostApi.getNotificationChannels$separatedMessageChannelSuffix", codec)
+        if (api != null) {
+          channel.setMessageHandler { _, reply ->
+            val wrapped: List<Any?> = try {
+              listOf(api.getNotificationChannels())
+            } catch (exception: Throwable) {
+              wrapError(exception)
+            }
+            reply.reply(wrapped)
+          }
+        } else {
+          channel.setMessageHandler(null)
+        }
+      }
+      run {
+        val channel = BasicMessageChannel<Any?>(binaryMessenger, "dev.flutter.pigeon.zulip.AndroidNotificationHostApi.deleteNotificationChannel$separatedMessageChannelSuffix", codec)
+        if (api != null) {
+          channel.setMessageHandler { message, reply ->
+            val args = message as List<Any?>
+            val channelIdArg = args[0] as String
+            val wrapped: List<Any?> = try {
+              api.deleteNotificationChannel(channelIdArg)
+              listOf(null)
+            } catch (exception: Throwable) {
+              wrapError(exception)
+            }
+            reply.reply(wrapped)
+          }
+        } else {
+          channel.setMessageHandler(null)
+        }
+      }
       run {
         val channel = BasicMessageChannel<Any?>(binaryMessenger, "dev.flutter.pigeon.zulip.AndroidNotificationHostApi.notify$separatedMessageChannelSuffix", codec)
         if (api != null) {

android/app/src/main/kotlin/com/zulip/flutter/ZulipPlugin.kt

@@ -53,6 +53,21 @@ private class AndroidNotificationHost(val context: Context)
         NotificationManagerCompat.from(context).createNotificationChannel(notificationChannel)
     }
 
+    override fun getNotificationChannels(): List<NotificationChannel> {
+        return NotificationManagerCompat.from(context)
+            .notificationChannelsCompat
+            .map { NotificationChannel(
+                id = it.id,
+                importance =  it.importance.toLong(),
+                name = it.name?.toString(),
+                lightsEnabled = it.shouldShowLights()
+            ) }
+    }
+
+    override fun deleteNotificationChannel(channelId: String) {
+        NotificationManagerCompat.from(context).deleteNotificationChannel(channelId)
+    }
+
     @SuppressLint(
         // If permission is missing, `notify` will throw an exception.
         // Which hopefully will propagate to Dart, and then it's up to Dart code to handle it.

lib/host/android_notifications.g.dart

@@ -400,6 +400,61 @@ class AndroidNotificationHostApi {
     }
   }
 
+  /// Corresponds to `androidx.core.app.NotificationManagerCompat.getNotificationChannelsCompat`.
+  ///
+  /// See: https://developer.android.com/reference/kotlin/androidx/core/app/NotificationManagerCompat#getNotificationChannelsCompat()
+  Future<List<NotificationChannel?>> getNotificationChannels() async {
+    final String __pigeon_channelName = 'dev.flutter.pigeon.zulip.AndroidNotificationHostApi.getNotificationChannels$__pigeon_messageChannelSuffix';
+    final BasicMessageChannel<Object?> __pigeon_channel = BasicMessageChannel<Object?>(
+      __pigeon_channelName,
+      pigeonChannelCodec,
+      binaryMessenger: __pigeon_binaryMessenger,
+    );
+    final List<Object?>? __pigeon_replyList =
+        await __pigeon_channel.send(null) as List<Object?>?;
+    if (__pigeon_replyList == null) {
+      throw _createConnectionError(__pigeon_channelName);
+    } else if (__pigeon_replyList.length > 1) {
+      throw PlatformException(
+        code: __pigeon_replyList[0]! as String,
+        message: __pigeon_replyList[1] as String?,
+        details: __pigeon_replyList[2],
+      );
+    } else if (__pigeon_replyList[0] == null) {
+      throw PlatformException(
+        code: 'null-error',
+        message: 'Host platform returned null value for non-null return value.',
+      );
+    } else {
+      return (__pigeon_replyList[0] as List<Object?>?)!.cast<NotificationChannel?>();
+    }
+  }
+
+  /// Corresponds to `androidx.core.app.NotificationManagerCompat.deleteNotificationChannel`
+  ///
+  /// See: https://developer.android.com/reference/kotlin/androidx/core/app/NotificationManagerCompat#deleteNotificationChannel(java.lang.String)
+  Future<void> deleteNotificationChannel(String channelId) async {
+    final String __pigeon_channelName = 'dev.flutter.pigeon.zulip.AndroidNotificationHostApi.deleteNotificationChannel$__pigeon_messageChannelSuffix';
+    final BasicMessageChannel<Object?> __pigeon_channel = BasicMessageChannel<Object?>(
+      __pigeon_channelName,
+      pigeonChannelCodec,
+      binaryMessenger: __pigeon_binaryMessenger,
+    );
+    final List<Object?>? __pigeon_replyList =
+        await __pigeon_channel.send(<Object?>[channelId]) as List<Object?>?;
+    if (__pigeon_replyList == null) {
+      throw _createConnectionError(__pigeon_channelName);
+    } else if (__pigeon_replyList.length > 1) {
+      throw PlatformException(
+        code: __pigeon_replyList[0]! as String,
+        message: __pigeon_replyList[1] as String?,
+        details: __pigeon_replyList[2],
+      );
+    } else {
+      return;
+    }
+  }
+
   /// Corresponds to `android.app.NotificationManager.notify`,
   /// combined with `androidx.core.app.NotificationCompat.Builder`.
   ///

lib/notifications/display.dart

@@ -25,6 +25,10 @@ AndroidNotificationHostApi get _androidHost => ZulipBinding.instance.androidNoti
 
 /// Service for configuring our Android "notification channel".
 class NotificationChannelManager {
+  /// The channel ID we use for our one notification channel, which we use for
+  /// all notifications.
+  // TODO(launch) check this doesn't match zulip-mobile's current or previous
+  //   channel IDs
   @visibleForTesting
   static const kChannelId = 'messages-1';
 
@@ -36,6 +40,8 @@ class NotificationChannelManager {
   static final kVibrationPattern = Int64List.fromList([0, 125, 100, 450]);
 
   /// Create our notification channel, if it doesn't already exist.
+  ///
+  /// Deletes obsolete channels, if present, from old versions of the app.
   //
   // NOTE when changing anything here: the changes will not take effect
   // for existing installs of the app!  That's because we'll have already
@@ -52,11 +58,28 @@ class NotificationChannelManager {
   //    settings for the channel -- like "override Do Not Disturb", or "use
   //    a different sound", or "don't pop on screen" -- their changes get
   //    reset.  So this has to be done sparingly.
-  //
-  //    If we do this, we should also look for any channel with the old
-  //    channel ID and delete it.  See zulip-mobile's `createNotificationChannel`
-  //    in android/app/src/main/java/com/zulipmobile/notifications/NotificationChannelManager.kt .
-  static Future<void> _ensureChannel() async {
+  @visibleForTesting
+  static Future<void> ensureChannel() async {
+    // See if our current-version channel already exists; delete any obsolete
+    // previous channels.
+    var found = false;
+    final channels = await _androidHost.getNotificationChannels();
+    for (final channel in channels) {
+      assert(channel != null); // TODO(#942)
+      if (channel!.id == kChannelId) {
+        found = true;
+      } else {
+        await _androidHost.deleteNotificationChannel(channel.id);
+      }
+    }
+
+    if (found) {
+      // The channel already exists; nothing to do.
+      return;
+    }
+
+    // The channel doesn't exist. Create it.
+
     await _androidHost.createNotificationChannel(NotificationChannel(
       id: kChannelId,
       name: 'Messages', // TODO(i18n)
@@ -81,7 +104,7 @@ class NotificationDisplayManager {
     if (launchDetails?.didNotificationLaunchApp ?? false) {
       _handleNotificationAppLaunch(launchDetails!.notificationResponse);
     }
-    await NotificationChannelManager._ensureChannel();
+    await NotificationChannelManager.ensureChannel();
   }
 
   static void onFcmMessage(FcmMessage data, Map<String, dynamic> dataJson) {

pigeon/notifications.dart

@@ -160,6 +160,16 @@ abstract class AndroidNotificationHostApi {
   /// See: https://developer.android.com/reference/androidx/core/app/NotificationManagerCompat#createNotificationChannel(androidx.core.app.NotificationChannelCompat)
   void createNotificationChannel(NotificationChannel channel);
 
+  /// Corresponds to `androidx.core.app.NotificationManagerCompat.getNotificationChannelsCompat`.
+  ///
+  /// See: https://developer.android.com/reference/kotlin/androidx/core/app/NotificationManagerCompat#getNotificationChannelsCompat()
+  List<NotificationChannel> getNotificationChannels();
+
+  /// Corresponds to `androidx.core.app.NotificationManagerCompat.deleteNotificationChannel`
+  ///
+  /// See: https://developer.android.com/reference/kotlin/androidx/core/app/NotificationManagerCompat#deleteNotificationChannel(java.lang.String)
+  void deleteNotificationChannel(String channelId);
+
   /// Corresponds to `android.app.NotificationManager.notify`,
   /// combined with `androidx.core.app.NotificationCompat.Builder`.
   ///

test/model/binding.dart

@@ -543,6 +543,12 @@ class FakeFlutterLocalNotificationsPlugin extends Fake implements FlutterLocalNo
 }
 
 class FakeAndroidNotificationHostApi implements AndroidNotificationHostApi {
+  /// Lists currently active channels, result is aggregated from calls made to
+  /// [createNotificationChannel] and [deleteNotificationChannel],
+  /// order of creation is preserved.
+  Iterable<NotificationChannel> get activeChannels => _activeChannels.values;
+  final Map<String, NotificationChannel> _activeChannels = {};
+
   /// Consume the log of calls made to [createNotificationChannel].
   ///
   /// This returns a list of the arguments to all calls made
@@ -557,6 +563,29 @@ class FakeAndroidNotificationHostApi implements AndroidNotificationHostApi {
   @override
   Future<void> createNotificationChannel(NotificationChannel channel) async {
     _createdChannels.add(channel);
+    _activeChannels[channel.id] = channel;
+  }
+
+  @override
+  Future<List<NotificationChannel?>> getNotificationChannels() async {
+    return _activeChannels.values.toList(growable: false);
+  }
+
+  /// Consume the log of calls made to [deleteNotificationChannel].
+  ///
+  /// This returns a list of the arguments to all calls made
+  /// to [deleteNotificationChannel] since the last call to this method.
+  List<String> takeDeletedChannels() {
+    final result = _deletedChannels;
+    _deletedChannels = [];
+    return result;
+  }
+  List<String> _deletedChannels = [];
+
+  @override
+  Future<void> deleteNotificationChannel(String channelId) async {
+    _deletedChannels.add(channelId);
+    _activeChannels.remove(channelId);
   }
 
   /// Consume the log of calls made to [notify].

test/notifications/display_test.dart

@@ -131,6 +131,81 @@ void main() {
             NotificationChannelManager.kVibrationPattern)
       ;
     });
+
+    test('channel is not recreated if one with same id already exists', () async {
+      addTearDown(testBinding.reset);
+
+      // Setup initial channel.
+      await testBinding.androidNotificationHost.createNotificationChannel(
+        NotificationChannel(
+          id: NotificationChannelManager.kChannelId,
+          name: 'Messages',
+          importance: NotificationImportance.high,
+          lightsEnabled: true,
+          vibrationPattern: NotificationChannelManager.kVibrationPattern));
+      // Clear the log.
+      check(testBinding.androidNotificationHost.takeCreatedChannels())
+        .length.equals(1);
+
+      // Ensure that no calls were made to the deleteChannel or createChannel
+      // functions.
+      await NotificationChannelManager.ensureChannel();
+      check(testBinding.androidNotificationHost.takeDeletedChannels())
+        .isEmpty();
+      check(testBinding.androidNotificationHost.takeCreatedChannels())
+        .isEmpty();
+      check(testBinding.androidNotificationHost.activeChannels).single
+        ..id.equals(NotificationChannelManager.kChannelId)
+        ..name.equals('Messages')
+        ..importance.equals(NotificationImportance.high)
+        ..lightsEnabled.equals(true)
+        ..vibrationPattern.isNotNull().deepEquals(
+            NotificationChannelManager.kVibrationPattern);
+    });
+
+    test('obsolete channels are removed', () async {
+      addTearDown(testBinding.reset);
+
+      // Setup initial channels.
+      await testBinding.androidNotificationHost.createNotificationChannel(
+        NotificationChannel(
+          id: 'obsolete-1',
+          name: 'Obsolete 1',
+          importance: NotificationImportance.high,
+          lightsEnabled: true,
+          vibrationPattern: NotificationChannelManager.kVibrationPattern));
+      await testBinding.androidNotificationHost.createNotificationChannel(
+        NotificationChannel(
+          id: 'obsolete-2',
+          name: 'Obsolete 2',
+          importance: NotificationImportance.high,
+          lightsEnabled: true,
+          vibrationPattern: NotificationChannelManager.kVibrationPattern));
+      // Clear the log.
+      check(testBinding.androidNotificationHost.takeCreatedChannels())
+        .length.equals(2);
+
+      // Ensure that any channel whose channel-id differs from the desired
+      // channel-id (NotificationChannelManager.kChannelId) is deleted, and a
+      // new one with the desired channel-id is created.
+      await NotificationChannelManager.ensureChannel();
+      check(testBinding.androidNotificationHost.takeDeletedChannels())
+        .deepEquals(['obsolete-1', 'obsolete-2']);
+      check(testBinding.androidNotificationHost.takeCreatedChannels()).single
+        ..id.equals(NotificationChannelManager.kChannelId)
+        ..name.equals('Messages')
+        ..importance.equals(NotificationImportance.high)
+        ..lightsEnabled.equals(true)
+        ..vibrationPattern.isNotNull().deepEquals(
+            NotificationChannelManager.kVibrationPattern);
+      check(testBinding.androidNotificationHost.activeChannels).single
+        ..id.equals(NotificationChannelManager.kChannelId)
+        ..name.equals('Messages')
+        ..importance.equals(NotificationImportance.high)
+        ..lightsEnabled.equals(true)
+        ..vibrationPattern.isNotNull().deepEquals(
+            NotificationChannelManager.kVibrationPattern);
+    });
   });
 
   group('NotificationDisplayManager show', () {