freezer/lib/api/download_manager/service_interface.dart

import 'dart:collection';
import 'dart:isolate';

import 'package:flutter_background_service/flutter_background_service.dart';

typedef ListenerCallback = void Function(Map<String, dynamic>? args);

class ServiceInterface {
  final ReceivePort? receivePort;
  late SendPort sendPort;
  final ServiceInstance? service;

  bool _isListening = false;
  final _listeners = HashMap<String, ListenerCallback>();

  ServiceInterface({this.receivePort, this.service})
      : assert(receivePort != null || service != null);

  void on(String method, ListenerCallback listener) {
    if (service != null) {
      service!.on(method).listen(listener);
    }

    if (!_isListening) {
      _isListening = true;
      receivePort!.listen((message) {
        final method = message['_'];
        _listeners[method]!.call(message);
      });
    }

    _listeners[method] = listener;
  }

  void no(String method) {
    _listeners.remove(method);
  }

  void send(String method, [Map<String, dynamic>? args]) {
    if (service != null) {
      return service!.invoke(method, args);
    }

    sendPort!.send({'_': method, if (args != null) ...args});
  }
}