// connection_provider.dart — 连接状态机（严格三态，状态由内核事件驱动）
//
// 设计约定：
//   - UI 调用 toggle()，控制器内部读取有效节点 + 认证令牌，调用 ConnectApi
//     并启动 VpnBridge 子进程。
//   - 严禁乐观翻转：VpnPhase.on 必须由 bridge.statusStream 确认后才置。
//   - 状态来源：bridge.statusStream（来自内核回调），非 Timer 模拟。
import 'dart:async';
import 'dart:io';

import 'package:flutter_riverpod/flutter_riverpod.dart';

import '../bridge/vpn_bridge.dart';
import '../bridge/vpn_bridge_provider.dart';
import '../l10n/app_text.dart';
import '../models/node.dart';
import '../services/api_config.dart';
import '../services/connect_api.dart';
import '../services/device_identity.dart';
import 'app_providers.dart';
import 'auth_provider.dart';
import 'nodes_provider.dart';
import 'settings_provider.dart';

// 设备 ID 由 deviceIdentityProvider 提供(secure storage 持久化的稳定 UUID)。
// API base URL 统一用 api_config.dart 的 kApiBaseUrl(单一来源,勿再重复声明)。

// ── 连接阶段枚举 ──────────────────────────────────────────────────

/// 连接阶段。严格三态，与设计稿一致。
enum VpnPhase { off, connecting, on }

// ── 连接状态快照 ──────────────────────────────────────────────────

class ConnectionState {
  const ConnectionState({required this.phase, this.elapsed = Duration.zero, this.error});

  final VpnPhase phase;
  final Duration elapsed;

  /// 连接失败原因(已本地化);null = 无错误。供 UI 提示,不再静默吞掉。
  final String? error;

  ConnectionState copyWith({VpnPhase? phase, Duration? elapsed}) =>
      ConnectionState(phase: phase ?? this.phase, elapsed: elapsed ?? this.elapsed);

  @override
  bool operator ==(Object other) =>
      other is ConnectionState &&
      other.phase == phase &&
      other.elapsed == elapsed &&
      other.error == error;

  @override
  int get hashCode => Object.hash(phase, elapsed, error);
}

// ── 连通看门狗 ─────────────────────────────────────────────────────
//
// 已连接(本地 TUN 已起)≠ 远端节点数据面可用:节点 sing-box 崩了/数据口不通而
// agent 仍在线时,客户端会一直显示「已连接」但流量全失败。看门狗周期性经隧道做
// 连通性探测,连续失败即判当前节点不可用 → 智能选择自动切节点 / 手动选定的只断开提示。

/// 连通探测接缝:true=经隧道能到外网。默认走海外 204 端点;测试可注入假实现。
typedef HealthProber = Future<bool> Function();

const _kWatchdogInterval = Duration(seconds: 15);
const _kHealthFailLimit = 3; // 连续 N 次失败(≈45s)才判定不可用,防抖

/// 默认探测:GET 海外 generate_204(全局 TUN 下走隧道 → 真实检验代理出网)。
/// 任一端点 2xx/204 即视为通;多端点容错,避免单点误判。
Future<bool> defaultHealthProbe() async {
  const urls = [
    'https://www.gstatic.com/generate_204',
    'https://cp.cloudflare.com/generate_204',
  ];
  for (final u in urls) {
    final client = HttpClient()..connectionTimeout = const Duration(seconds: 4);
    try {
      final req = await client.getUrl(Uri.parse(u)).timeout(const Duration(seconds: 5));
      final resp = await req.close().timeout(const Duration(seconds: 5));
      await resp.drain<void>();
      if (resp.statusCode >= 200 && resp.statusCode < 300) return true;
    } catch (_) {
      // 该端点不通,试下一个
    } finally {
      client.close(force: true);
    }
  }
  return false;
}

// ── 状态机 ───────────────────────────────────────────────────────

class ConnectionController extends StateNotifier<ConnectionState> {
  ConnectionController(this._ref, this._bridge, {HealthProber? prober})
      : _prober = prober ?? defaultHealthProbe,
        super(const ConnectionState(phase: VpnPhase.off)) {
    // 订阅桥状态流：状态由内核事件驱动，严禁 UI 乐观翻转。
    _statusSub = _bridge.statusStream.listen(_onKernelStatus);
  }

  final Ref _ref;
  final VpnBridge _bridge;
  final HealthProber _prober;
  StreamSubscription<VpnStatus>? _statusSub;
  Timer? _elapsed;
  Timer? _watchdog;
  int _healthFails = 0;
  bool _probing = false;
  ConnectApi? _api;

  // ── 公有 API ───────────────────────────────────────────────────

  /// 用户点击连接键：按当前状态决定动作，握手中忽略（禁乐观）。
  void toggle() {
    switch (state.phase) {
      case VpnPhase.off:
        _connect();
      case VpnPhase.on:
        _disconnect();
      case VpnPhase.connecting:
        break; // 握手进行中，不响应
    }
  }

  /// 节点切换时触发：已连接则重连。
  void onNodeChanged() {
    if (state.phase == VpnPhase.on || state.phase == VpnPhase.connecting) {
      _disconnect().then((_) => _connect());
    }
  }

  // ── 内部 ─────────────────────────────────────────────────────

  Future<void> _connect() async {
    state = const ConnectionState(phase: VpnPhase.connecting);

    final node = _ref.read(effectiveNodeProvider);
    final zh = _ref.read(localeProvider) == AppLang.zh;

    // 节点未就绪(列表加载中/为空):不连接,提示用户。
    if (node.uuid.isEmpty) {
      if (mounted) {
        state = ConnectionState(
          phase: VpnPhase.off,
          error: zh ? '节点尚未就绪,请稍候重试' : 'Nodes not ready, please retry',
        );
      }
      return;
    }

    try {
      final configJson = await _fetchConfigWithRefresh(node.uuid);
      // bridge.start() 不阻塞至连接建立；on 状态由 statusStream 回调驱动。
      await _bridge.start(configJson);
    } on ConnectApiException catch (e) {
      // 把后端/网络错误冒泡到 UI(原静默回 off,用户不知所以)。
      if (mounted) state = ConnectionState(phase: VpnPhase.off, error: zh ? e.messageZh : e.messageEn);
    } catch (e) {
      if (mounted) {
        state = ConnectionState(
          phase: VpnPhase.off,
          error: zh ? '连接失败,请重试' : 'Connection failed, please retry',
        );
      }
    }
  }

  /// 取配置;access token 过期(401)时用 refresh token 续期后**重试一次**。
  /// 续期失败(refresh 也过期 / 被拒)由 authProvider.refresh() 触发登出 → UI 回登录页。
  Future<String> _fetchConfigWithRefresh(String nodeUuid) async {
    final deviceId = await _ref.read(deviceIdentityProvider).deviceId();
    Future<String> doFetch() {
      final token = _ref.read(authProvider).accessToken ?? '';
      _api?.dispose();
      _api = _ref.read(connectApiFactoryProvider)(token);
      return _api!.fetchConfig(
        nodeId: nodeUuid,
        deviceId: deviceId,
        // smartRoute 偏好 → 国内分流(#5):国内 IP/域名直连,不走隧道。
        splitCN: _ref.read(settingsProvider).smartRoute,
      );
    }

    try {
      return await doFetch();
    } on ConnectApiException catch (e) {
      if (e.statusCode == 401) {
        // token 过期 → 续期后重试一次;续期成功则用新 token 再取。
        final ok = await _ref.read(authProvider.notifier).refresh();
        if (ok) return await doFetch();
      }
      rethrow;
    }
  }

  Future<void> _disconnect() async {
    _stopElapsed();
    try {
      await _bridge.stop();
    } catch (_) {}
    if (mounted) state = const ConnectionState(phase: VpnPhase.off);
  }

  void _onKernelStatus(VpnStatus s) {
    if (!mounted) return;
    switch (s) {
      case VpnStatus.on:
        state = state.copyWith(phase: VpnPhase.on);
        _startElapsed();
        _startWatchdog();
      case VpnStatus.connecting:
        state = state.copyWith(phase: VpnPhase.connecting);
        _stopElapsed();
        _stopWatchdog();
      case VpnStatus.off:
      case VpnStatus.error:
        state = const ConnectionState(phase: VpnPhase.off);
        _stopElapsed();
        _stopWatchdog();
    }
  }

  // ── 连通看门狗 ───────────────────────────────────────────────
  void _startWatchdog() {
    _watchdog?.cancel();
    _healthFails = 0;
    _watchdog = Timer.periodic(_kWatchdogInterval, (_) => _checkHealth());
  }

  void _stopWatchdog() {
    _watchdog?.cancel();
    _watchdog = null;
    _healthFails = 0;
    _probing = false;
  }

  Future<void> _checkHealth() async {
    if (_probing || !mounted || state.phase != VpnPhase.on) return;
    _probing = true;
    final ok = await _prober();
    _probing = false;
    if (!mounted || state.phase != VpnPhase.on) return;
    if (ok) {
      _healthFails = 0;
      return;
    }
    _healthFails++;
    if (_healthFails >= _kHealthFailLimit) {
      _stopWatchdog();
      await _onNodeUnhealthy();
    }
  }

  /// 当前节点连续探测失败:智能选择 → 切到其他最优可用节点重连;手动选定 → 断开并提示。
  Future<void> _onNodeUnhealthy() async {
    final t = _ref.read(appTextProvider);
    final smart = _ref.read(selectedNodeCodeProvider) == kSmartNodeCode;
    final altCode = smart ? _pickAlternativeCode(_ref.read(effectiveNodeProvider).code) : null;
    if (smart && altCode != null) {
      _ref.read(selectedNodeCodeProvider.notifier).state = altCode;
      await _disconnect();
      await _connect();
      // 重连进行中给出「已自动切换」提示(connecting 态显示,连上后随 copyWith 清除)。
      if (mounted && state.phase != VpnPhase.off) {
        state = ConnectionState(phase: state.phase, error: t.nodeUnhealthySwitched);
      }
      return;
    }
    // 手动选定节点(或智能模式无其他可用节点):断开并提示,尊重用户选择、不自动换。
    await _disconnect();
    if (mounted) state = ConnectionState(phase: VpnPhase.off, error: t.nodeUnhealthyError);
  }

  /// 选延迟最优、可用(status up)、非当前节点的 code;无则 null。
  String? _pickAlternativeCode(String excludeCode) {
    final nodes = (_ref.read(nodesProvider).valueOrNull ?? const [])
        .where((n) => !n.isDown && n.uuid.isNotEmpty && n.code != excludeCode)
        .toList();
    if (nodes.isEmpty) return null;
    nodes.sort((a, b) {
      final pa = a.ping > 0 ? a.ping : 1 << 30;
      final pb = b.ping > 0 ? b.ping : 1 << 30;
      return pa.compareTo(pb);
    });
    return nodes.first.code;
  }

  void _startElapsed() {
    _elapsed?.cancel();
    _elapsed = Timer.periodic(const Duration(seconds: 1), (_) {
      if (mounted && state.phase == VpnPhase.on) {
        state = state.copyWith(elapsed: state.elapsed + const Duration(seconds: 1));
      }
    });
  }

  void _stopElapsed() {
    _elapsed?.cancel();
    _elapsed = null;
  }

  @override
  void dispose() {
    _statusSub?.cancel();
    _stopElapsed();
    _stopWatchdog();
    _api?.dispose();
    super.dispose();
  }
}

// ── Provider ──────────────────────────────────────────────────────

final connectionProvider =
    StateNotifierProvider<ConnectionController, ConnectionState>(
  (ref) => ConnectionController(ref, ref.watch(vpnBridgeProvider)),
);

/// 内核实时统计流(上/下行瞬时速率、字节数)。连接页速度行的真实数据源。
final vpnStatsProvider = StreamProvider<VpnStatsEvent>(
  (ref) => ref.watch(vpnBridgeProvider).statsStream,
);

/// 按 authToken 造 ConnectApi 的工厂(支柱 1:接缝即接口)。默认走真控制面;
/// 测试 override 注入 MockClient,即可驱动「连接成功」路径而不打真网络。
typedef ConnectApiFactory = ConnectApi Function(String authToken);

final connectApiFactoryProvider = Provider<ConnectApiFactory>(
  (_) => (authToken) => ConnectApi(baseUrl: kApiBaseUrl, authToken: authToken),
);