import 'dart:async';
import 'dart:convert';

import 'package:fl_clash/clash/clash.dart';
import 'package:fl_clash/models/models.dart';
import 'package:fl_clash/state.dart';
import 'package:flutter/foundation.dart';
import 'package:flutter/services.dart';

abstract mixin class VpnListener {
  void onDnsChanged(String dns) {}
}

class Vpn {
  static Vpn? _instance;
  late MethodChannel methodChannel;
  FutureOr<String> Function()? handleGetStartForegroundParams;

  Vpn._internal() {
    methodChannel = const MethodChannel("vpn");
    methodChannel.setMethodCallHandler((call) async {
      switch (call.method) {
        case "gc":
          clashCore.requestGc();
        case "getStartForegroundParams":
          if (handleGetStartForegroundParams != null) {
            return await handleGetStartForegroundParams!();
          }
          return "";
        default:
          for (final VpnListener listener in _listeners) {
            switch (call.method) {
              case "dnsChanged":
                final dns = call.arguments as String;
                listener.onDnsChanged(dns);
            }
          }
      }
    });
  }

  factory Vpn() {
    _instance ??= Vpn._internal();
    return _instance!;
  }

  final ObserverList<VpnListener> _listeners = ObserverList<VpnListener>();

  Future<bool?> start(AndroidVpnOptions options) async {
    return await methodChannel.invokeMethod<bool>("start", {
      'data': json.encode(options),
    });
  }

  Future<bool?> stop() async {
    return await methodChannel.invokeMethod<bool>("stop");
  }

  void addListener(VpnListener listener) {
    _listeners.add(listener);
  }

  void removeListener(VpnListener listener) {
    _listeners.remove(listener);
  }
}

Vpn? get vpn => globalState.isService ? Vpn() : null;