import 'dart:async';

import 'package:connectivity_plus/connectivity_plus.dart';
import 'package:flutter/foundation.dart' show kIsWeb;

/// Observes network reachability and exposes online/offline transitions.
class ConnectivityService {
  ConnectivityService({Connectivity? connectivity})
    : _connectivity = connectivity ?? Connectivity();

  final Connectivity _connectivity;
  final StreamController<bool> _onlineController =
      StreamController<bool>.broadcast();

  StreamSubscription<List<ConnectivityResult>>? _subscription;
  bool _isOnline = true;

  Stream<bool> get onlineChanges => _onlineController.stream;

  bool get isOnline => _isOnline;

  Future<void> initialize() async {
    if (kIsWeb) {
      _isOnline = true;
      _onlineController.add(true);
      return;
    }

    final List<ConnectivityResult> results = await _connectivity
        .checkConnectivity();
    _emitOnline(_resultsOnline(results));

    _subscription = _connectivity.onConnectivityChanged.listen(
      (List<ConnectivityResult> results) => _emitOnline(_resultsOnline(results)),
    );
  }

  void dispose() {
    _subscription?.cancel();
    _onlineController.close();
  }

  bool _resultsOnline(List<ConnectivityResult> results) {
    if (results.isEmpty) {
      return false;
    }
    return results.any(
      (ConnectivityResult r) =>
          r == ConnectivityResult.mobile ||
          r == ConnectivityResult.wifi ||
          r == ConnectivityResult.ethernet ||
          r == ConnectivityResult.vpn,
    );
  }

  void _emitOnline(bool online) {
    if (_isOnline == online) {
      return;
    }
    _isOnline = online;
    _onlineController.add(online);
  }
}