// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

part of dds;

class _StreamManager {
  _StreamManager(this.dds);

  /// Send `streamNotify` notifications to clients subscribed to `streamId`.
  ///
  /// If `data` is of type `Uint8List`, the notification is assumed to be a
  /// binary event and is forwarded directly over the subscriber's websocket.
  /// Otherwise, the event is sent via the JSON RPC client.
  ///
  /// If `excludedClient` is provided, the notification will be sent to all
  /// clients subscribed to `streamId` except for `excludedClient`.
  void streamNotify(
    String streamId,
    data, {
    _DartDevelopmentServiceClient excludedClient,
  }) {
    if (streamListeners.containsKey(streamId)) {
      final listeners = streamListeners[streamId];
      final isBinaryData = data is Uint8List;
      for (final listener in listeners) {
        if (listener == excludedClient) {
          continue;
        }
        if (isBinaryData) {
          listener.ws.sink.add(data);
        } else {
          listener.sendNotification('streamNotify', data);
        }
      }
    }
  }

  void sendServiceRegisteredEvent(
    _DartDevelopmentServiceClient client,
    String service,
    String alias,
  ) {
    final namespace = dds._getNamespace(client);
    streamNotify(
      kServiceStream,
      {
        'streamId': kServiceStream,
        'event': {
          'type': 'Event',
          'kind': 'ServiceRegistered',
          'timestamp': DateTime.now().millisecondsSinceEpoch,
          'service': service,
          'method': namespace + '.' + service,
          'alias': alias,
        },
      },
      excludedClient: client,
    );
  }

  void _sendServiceUnregisteredEvents(
    _DartDevelopmentServiceClient client,
  ) {
    final namespace = dds._getNamespace(client);
    for (final service in client.services.keys) {
      streamNotify(
        kServiceStream,
        {
          'streamId': kServiceStream,
          'event': {
            'type': 'Event',
            'kind': 'ServiceUnregistered',
            'timestamp': DateTime.now().millisecondsSinceEpoch,
            'service': service,
            'method': namespace + '.' + service,
          },
        },
        excludedClient: client,
      );
    }
  }

  /// Start listening for `streamNotify` events from the VM service and forward
  /// them to the clients which have subscribed to the stream.
  Future<void> listen() async {
    // The _IsolateManager requires information from both the Debug and
    // Isolate streams, so they must always be subscribed to by DDS.
    for (final stream in ddsCoreStreams) {
      await streamListen(null, stream);
    }
    dds._vmServiceClient.registerMethod(
      'streamNotify',
      (parameters) {
        final streamId = parameters['streamId'].asString;
        // Forward events from the streams _IsolateManager subscribes to.
        if (isolateManagerStreams.contains(streamId)) {
          dds.isolateManager.handleIsolateEvent(parameters);
        }
        streamNotify(streamId, parameters.value);
      },
    );
  }

  /// Subscribes `client` to a stream.
  ///
  /// If `client` is the first client to listen to `stream`, DDS will send a
  /// `streamListen` request for `stream` to the VM service.
  Future<void> streamListen(
    _DartDevelopmentServiceClient client,
    String stream,
  ) async {
    assert(stream != null && stream.isNotEmpty);
    if (!streamListeners.containsKey(stream)) {
      // This will return an RPC exception if the stream doesn't exist. This
      // will throw and the exception will be forwarded to the client.
      final result = await dds._vmServiceClient.sendRequest('streamListen', {
        'streamId': stream,
      });
      assert(result['type'] == 'Success');
      streamListeners[stream] = <_DartDevelopmentServiceClient>[];
    }
    if (streamListeners[stream].contains(client)) {
      throw kStreamAlreadySubscribedException;
    }
    if (client != null) {
      streamListeners[stream].add(client);
    }
  }

  /// Unsubscribes `client` from a stream.
  ///
  /// If `client` is the last client to unsubscribe from `stream`, DDS will
  /// send a `streamCancel` request for `stream` to the VM service.
  Future<void> streamCancel(
    _DartDevelopmentServiceClient client,
    String stream,
  ) async {
    assert(stream != null && stream.isNotEmpty);
    final listeners = streamListeners[stream];
    if (listeners == null || !listeners.contains(client)) {
      throw kStreamNotSubscribedException;
    }
    listeners.remove(client);
    // Don't cancel streams DDS needs to function.
    if (listeners.isEmpty && !ddsCoreStreams.contains(stream)) {
      streamListeners.remove(stream);
      final result = await dds._vmServiceClient.sendRequest('streamCancel', {
        'streamId': stream,
      });
      assert(result['type'] == 'Success');
    } else {
      streamListeners[stream] = listeners;
    }
  }

  /// Cleanup stream subscriptions for `client` when it has disconnected.
  void clientDisconnect(_DartDevelopmentServiceClient client) {
    for (final streamId in streamListeners.keys.toList()) {
      streamCancel(client, streamId).catchError(
        (_) => null,
        // Ignore 'stream not subscribed' errors.
        test: (e) => e is json_rpc.RpcException,
      );
    }
    // Notify other service clients of service extensions that are being
    // unregistered.
    _sendServiceUnregisteredEvents(client);
  }

  static const kServiceStream = 'Service';

  static final kStreamAlreadySubscribedException =
      _RpcErrorCodes.buildRpcException(
    _RpcErrorCodes.kStreamAlreadySubscribed,
  );

  static final kStreamNotSubscribedException = _RpcErrorCodes.buildRpcException(
    _RpcErrorCodes.kStreamNotSubscribed,
  );

  static const kDebugStream = 'Debug';
  static const kIsolateStream = 'Isolate';

  // Never cancel the Debug or Isolate stream as `_IsolateManager` requires
  // them for isolate state notifications.
  static const isolateManagerStreams = <String>{
    kDebugStream,
    kIsolateStream,
  };

  // The set of streams that DDS requires to function.
  static final ddsCoreStreams = <String>{
    ...isolateManagerStreams,
  };

  final _DartDevelopmentService dds;
  final streamListeners = <String, List<_DartDevelopmentServiceClient>>{};
}