mobile-music/lib/state/remote_providers.dart

import 'dart:async';
import 'dart:io' show Platform;

import 'package:flutter/foundation.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';

import '../playback/playback_engine.dart';
import '../remote/discovery.dart';
import '../remote/host_server.dart';
import '../remote/messages.dart';
import '../remote/remote_playback.dart';
import '../remote/remote_session.dart';
import 'providers.dart';

/// Snapshot of cross-device control state for the UI (updates-features.md #3).
class RemoteControlState {
  const RemoteControlState({
    this.supported = false,
    this.advertising = false,
    this.browsing = false,
    this.devices = const [],
    this.attachedDevice,
    this.status = RemoteConnStatus.disconnected,
    this.remoteState,
  });

  /// Whether this platform can host/discover at all (mobile, macOS, Linux).
  final bool supported;

  /// This device is published as a controllable player.
  final bool advertising;

  /// A discovery browse is running (device sheet open).
  final bool browsing;

  /// Same-server players found on the LAN.
  final List<DiscoveredDevice> devices;

  /// The device we're controlling as a remote, or null when playing locally.
  final DiscoveredDevice? attachedDevice;

  /// Connection status of the active remote session.
  final RemoteConnStatus status;

  /// The controlled device's mirrored playback state (null until the first
  /// snapshot arrives). The facade renders this in place of the local engine.
  final PlaybackState? remoteState;

  /// True once we've committed to controlling a remote device (connecting or
  /// connected). The facade routes commands to the remote while this holds.
  bool get isAttached =>
      attachedDevice != null &&
      (status == RemoteConnStatus.connecting ||
          status == RemoteConnStatus.connected);

  RemoteControlState copyWith({
    bool? supported,
    bool? advertising,
    bool? browsing,
    List<DiscoveredDevice>? devices,
    DiscoveredDevice? attachedDevice,
    RemoteConnStatus? status,
    PlaybackState? remoteState,
    bool clearAttached = false,
    bool clearRemoteState = false,
  }) =>
      RemoteControlState(
        supported: supported ?? this.supported,
        advertising: advertising ?? this.advertising,
        browsing: browsing ?? this.browsing,
        devices: devices ?? this.devices,
        attachedDevice:
            clearAttached ? null : (attachedDevice ?? this.attachedDevice),
        status: status ?? this.status,
        remoteState:
            clearRemoteState ? null : (remoteState ?? this.remoteState),
      );
}

/// Owns both halves of cross-device control:
///  * **Host** — while online, runs a [RemoteHost] and advertises it over mDNS
///    so other devices can control this one.
///  * **Remote** — [attach]/[detach] to control another device, mirroring its
///    playback into [RemoteControlState.remoteState] (with smooth position
///    interpolation between the host's ~1 Hz snapshots).
///
/// The facade providers (`activePlaybackProvider` / `playbackCommandsProvider`
/// in providers.dart) read this to decide whether the UI drives the local
/// engine or the attached remote.
class RemoteControlController extends StateNotifier<RemoteControlState> {
  RemoteControlController(this._ref)
      : super(RemoteControlState(supported: _supported())) {
    if (state.supported) {
      _ref.listen<ConnectionState>(
        connectionProvider,
        (_, next) => _onConnection(next),
        fireImmediately: true,
      );
    }
  }

  final Ref _ref;
  final RemoteDiscovery _discovery = RemoteDiscovery();

  RemoteHost? _host;
  RemoteSession? _session;
  RemotePlaybackProxy? _proxy;
  StreamSubscription<StateSnapshot>? _snapSub;
  StreamSubscription<RemoteConnStatus>? _statusSub;
  StreamSubscription<List<DiscoveredDevice>>? _devSub;
  Timer? _interpolate;

  /// The command sink while attached, consumed by `playbackCommandsProvider`.
  PlaybackCommands? get remoteCommands => _proxy;

  static bool _supported() =>
      !kIsWeb &&
      (Platform.isAndroid ||
          Platform.isIOS ||
          Platform.isMacOS ||
          Platform.isLinux);

  /// Mutate state only while still mounted. Async hosting/session callbacks can
  /// resolve after the provider is disposed (e.g. app teardown); touching
  /// `state` then throws, so every write funnels through here.
  void _update(RemoteControlState Function(RemoteControlState) f) {
    if (!mounted) return;
    state = f(state);
  }

  // ---- Hosting ----------------------------------------------------------

  Future<void> _onConnection(ConnectionState conn) async {
    if (conn.isOnline) {
      await _startHosting(conn);
    } else {
      await detach();
      await _stopHosting();
    }
  }

  Future<void> _startHosting(ConnectionState conn) async {
    if (_host != null) return; // already hosting
    final creds = conn.credentials;
    if (creds == null) return;
    final host = RemoteHost(
      controller: _ref.read(playbackProvider.notifier),
      serverKey: creds.id,
      password: creds.password,
      deviceName: _deviceName(),
    );
    try {
      final port = await host.start();
      _host = host;
      await _discovery.advertise(
        deviceName: _deviceName(),
        port: port,
        serverKey: creds.id,
      );
      _update((s) => s.copyWith(advertising: true));
    } catch (_) {
      await host.stop();
      _host = null;
    }
  }

  Future<void> _stopHosting() async {
    await _discovery.stopAdvertising();
    final host = _host;
    _host = null;
    if (host != null) await host.stop();
    _update((s) => s.copyWith(advertising: false));
  }

  // ---- Browsing (device sheet) ------------------------------------------

  Future<void> startBrowsing() async {
    if (!state.supported) return;
    final key = _ref.read(serverKeyProvider);
    if (key == null) return;
    _devSub ??= _discovery.devices.listen(
      (list) => _update((s) => s.copyWith(devices: list)),
    );
    await _discovery.startBrowsing(key);
    _update((s) => s.copyWith(browsing: true, devices: _discovery.current));
  }

  Future<void> stopBrowsing() async {
    await _discovery.stopBrowsing();
    _update((s) => s.copyWith(browsing: false, devices: const []));
  }

  // ---- Attach / detach as a remote --------------------------------------

  Future<void> attach(DiscoveredDevice device) async {
    await detach();
    final creds = _ref.read(connectionProvider).credentials;
    if (creds == null) return;

    final session = RemoteSession(
      device: device,
      serverKey: creds.id,
      password: creds.password,
      deviceName: _deviceName(),
    );
    _session = session;
    _proxy = RemotePlaybackProxy(session);
    _update((s) => s.copyWith(
          attachedDevice: device,
          status: RemoteConnStatus.connecting,
          clearRemoteState: true,
        ));

    _statusSub = session.status.listen((st) {
      _update((s) => s.copyWith(status: st));
      // Only a terminal status drops us back to local playback. Transient
      // drops (phone locked, Wi-Fi blip) are healed inside the session, which
      // retries and re-emits `connecting` — we stay attached (bug-fixes #5).
      // `denied` is a hard rejection; `error` here only means a device that
      // never answered the initial dial.
      if (st == RemoteConnStatus.denied || st == RemoteConnStatus.error) {
        // Defer so we're not tearing the session down inside its own callback.
        scheduleMicrotask(detach);
      }
    });
    _snapSub = session.snapshots.listen((snap) {
      _update((s) => s.copyWith(remoteState: playbackStateFromSnapshot(snap)));
    });

    _startInterpolation();
    await session.connect();
  }

  /// Re-establish a dropped remote session immediately when the app returns to
  /// the foreground. A controller is suspended while the phone is locked, so
  /// its socket to the host is usually dead on resume; without this nudge the
  /// user would wait out the reconnect backoff before control is restored
  /// (bug-fixes #5). No-op when playing locally.
  void onResume() => _session?.reconnectNow();

  Future<void> detach() async {
    await _snapSub?.cancel();
    _snapSub = null;
    await _statusSub?.cancel();
    _statusSub = null;
    _interpolate?.cancel();
    _interpolate = null;
    final session = _session;
    _session = null;
    _proxy = null;
    if (session != null) await session.close();
    if (!mounted) return;
    if (state.attachedDevice != null || state.remoteState != null) {
      state = state.copyWith(
        clearAttached: true,
        clearRemoteState: true,
        status: RemoteConnStatus.disconnected,
      );
    }
  }

  /// Advance the mirrored position between snapshots so the progress bar moves
  /// smoothly instead of stepping once per snapshot. Each authoritative
  /// snapshot resets the baseline (see the `_snapSub` listener).
  void _startInterpolation() {
    _interpolate ??= Timer.periodic(const Duration(milliseconds: 500), (_) {
      if (!mounted) return;
      final rs = state.remoteState;
      if (rs == null || !rs.playing) return;
      final next = rs.position + const Duration(milliseconds: 500);
      final dur = rs.effectiveDuration;
      final capped = (dur > Duration.zero && next > dur) ? dur : next;
      state = state.copyWith(remoteState: rs.copyWith(position: capped));
    });
  }

  String _deviceName() {
    if (Platform.isIOS) return 'iOS device';
    if (Platform.isAndroid) return 'Android device';
    if (Platform.isMacOS) return 'Mac';
    if (Platform.isLinux) return 'Linux';
    return 'Timbre';
  }

  @override
  void dispose() {
    // Tear down resources directly (not via detach/_stopHosting, which write
    // `state`) — those async paths would resolve after the notifier is
    // unmounted and throw.
    unawaited(_devSub?.cancel());
    unawaited(_snapSub?.cancel());
    unawaited(_statusSub?.cancel());
    _interpolate?.cancel();
    final session = _session;
    _session = null;
    _proxy = null;
    if (session != null) unawaited(session.close());
    final host = _host;
    _host = null;
    if (host != null) unawaited(host.stop());
    unawaited(_discovery.dispose());
    super.dispose();
  }
}

final remoteControlProvider =
    StateNotifierProvider<RemoteControlController, RemoteControlState>(
  (ref) => RemoteControlController(ref),
);