import 'dart:async';
import 'dart:developer' as developer;

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

/// Minimal playback contract this service needs from the audio handler
/// (Design 3.1). `PluriWaveAudioHandler` implements it; tests use a fake.
abstract class ObjetivoAudioInterrumpible {
  /// Intent-to-play flag (Designs 3.1/7.2): true while the user wants audio
  /// playing. The S7 reconnect logic reads the same flag, so an interruption
  /// pause also disarms reconnection attempts.
  bool get intencionReproducir;

  bool get estaReproduciendo;

  Future<void> pausar();

  Future<void> reanudar();

  /// Temporarily lowers ("ducks") the output volume without pausing.
  Future<void> setAtenuado(bool atenuado);

  /// Re-attaches the equalizer effect and re-pushes the current preset's
  /// gains (fix "EQ Re-Apply After Audio-Focus Interruption"). Called after
  /// resuming from a transient interruption pause and after un-ducking,
  /// because Android's AudioEffect framework can let a higher-priority
  /// client silently disable this app's effect instance while the
  /// underlying player session id never changes — the existing session-id
  /// rotation trigger (`ServicioAudio.debeReaplicarEcualizador`) therefore
  /// never fires for a SHORT interruption (e.g. a nav-app voice prompt).
  /// Idempotent and cheap (a `setEnabled` plus band `setGain` calls); takes
  /// no argument by design — it re-asserts whatever enabled/disabled state
  /// the handler ALREADY holds, so a caller here can never force the
  /// equalizer on. Never restarts or repositions playback.
  Future<void> reaplicarEcualizador();
}

/// Wrapper around `package:audio_session` (S3-R1): configures the session
/// for music playback and translates interruption / becoming-noisy events
/// into pause, duck and auto-resume calls on the audio handler.
class ServicioAudioSession {
  ServicioAudioSession({
    required ObjetivoAudioInterrumpible objetivo,
    Future<AudioSession> Function()? obtenerSesion,
  }) : _objetivo = objetivo,
       _obtenerSesion = obtenerSesion ?? (() => AudioSession.instance);

  final ObjetivoAudioInterrumpible _objetivo;
  final Future<AudioSession> Function() _obtenerSesion;
  StreamSubscription<AudioInterruptionEvent>? _interrupcionesSub;
  StreamSubscription<void>? _ruidoSub;

  /// True when WE paused because of an interruption; only then does an
  /// interruption end with shouldResume restart playback.
  bool _pausadoPorInterrupcion = false;

  Future<void> configurar() async {
    try {
      final sesion = await _obtenerSesion();
      // DUCK, never pause, when another app asks for transient focus.
      //
      // `androidWillPauseWhenDucked: true` makes `audio_session` translate
      // Android's AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK into a full PAUSE. In a
      // car that fires constantly — every navigation instruction, every
      // speed-camera warning, every "OK Google" — and each one used to stop
      // the radio outright instead of dipping the volume for two seconds.
      //
      // Worse than the audio gap: a pause publishes `playing: false`, which
      // `AudioService.setState` turns into `exitPlayingState()` and, with
      // `androidStopForegroundOnPause`, into `stopForeground(...)`. A service
      // that is no longer in the foreground is killable, and when Android
      // took it the app vanished from the Android Auto pane mid-drive and
      // another media app took its slot. Ducking keeps `playing: true`
      // throughout, so the session, the notification and the car pane all
      // survive an interruption — which is also what keeps the equalizer
      // alive across it.
      await sesion.configure(
        const AudioSessionConfiguration.music().copyWith(
          androidWillPauseWhenDucked: false,
        ),
      );
      await _interrupcionesSub?.cancel();
      await _ruidoSub?.cancel();
      _interrupcionesSub = sesion.interruptionEventStream.listen(
        (evento) => unawaited(manejarInterrupcion(evento)),
      );
      _ruidoSub = sesion.becomingNoisyEventStream.listen(
        (_) => unawaited(manejarDesconexionSalida()),
      );
    } catch (e) {
      developer.log(
        '[PluriWave] No se pudo configurar la sesion de audio: $e',
        name: 'ServicioAudioSession',
        level: 900,
      );
    }
  }

  @visibleForTesting
  Future<void> manejarInterrupcion(AudioInterruptionEvent evento) async {
    if (evento.begin) {
      switch (evento.type) {
        case AudioInterruptionType.duck:
          await _objetivo.setAtenuado(true);
        case AudioInterruptionType.pause:
        case AudioInterruptionType.unknown:
          if (_objetivo.estaReproduciendo || _objetivo.intencionReproducir) {
            _pausadoPorInterrupcion = true;
            await _objetivo.pausar();
          }
      }
      return;
    }
    switch (evento.type) {
      case AudioInterruptionType.duck:
        await _objetivo.setAtenuado(false);
        // Un-ducking never rotates the native player session id, so the
        // session-id-change trigger never fires for this case — re-assert
        // here too (belt-and-braces, additive to that trigger).
        await _objetivo.reaplicarEcualizador();
      case AudioInterruptionType.pause:
        // Transient loss ended and the OS says we may resume.
        if (_pausadoPorInterrupcion) {
          _pausadoPorInterrupcion = false;
          await _objetivo.reanudar();
          // Same rationale as the duck branch above: a short transient
          // interruption keeps the SAME player session id.
          await _objetivo.reaplicarEcualizador();
        }
      case AudioInterruptionType.unknown:
        // Permanent focus loss: never auto-resume.
        _pausadoPorInterrupcion = false;
    }
  }

  @visibleForTesting
  Future<void> manejarDesconexionSalida() async {
    // Headphones unplugged: hard pause, never auto-resume afterwards.
    _pausadoPorInterrupcion = false;
    if (_objetivo.estaReproduciendo) {
      await _objetivo.pausar();
    }
  }

  Future<void> dispose() async {
    await _interrupcionesSub?.cancel();
    await _ruidoSub?.cancel();
  }
}