import 'dart:async';
import 'dart:ui' show Locale;

import 'package:audio_service/audio_service.dart';
import 'package:flutter/foundation.dart' show debugPrint, visibleForTesting;
import 'package:just_audio/just_audio.dart';

import '../l10n/display_names.dart';
import '../l10n/gen/app_localizations.dart';
import '../modelos/emisora.dart';
import '../modelos/pista_local.dart';
import '../modelos/preset_ecualizador.dart';
import 'cola_local.dart';
import 'controlador_reconexion.dart';
import 'musica_local_auto.dart';
import 'navegacion_auto.dart';
import 'servicio_audio_session.dart';

/// Estado de reproducción expuesto al UI.
enum EstadoReproduccion {
  detenido,
  cargando,
  reproduciendo,
  pausado,

  /// Transient network stall: the handler is retrying with backoff (S7-R2).
  /// UI surfaces it as a loading indicator, never as an error dialog (S7-R3).
  reconectando,
  error,
}

// ─────────────────────────────────────────────────────────────────────────────
// Handler global — inicializado en main.dart con AudioService.init
// ─────────────────────────────────────────────────────────────────────────────
PluriWaveAudioHandler? _handlerGlobal;

void registrarHandler(PluriWaveAudioHandler handler) {
  _handlerGlobal = handler;
}

// ─────────────────────────────────────────────────────────────────────────────
// Android Auto browse source — registered from main.dart, mirrors
// registrarHandler above (Design "getChildren data source registration").
// ─────────────────────────────────────────────────────────────────────────────
FuenteEmisorasAuto? _fuenteNavegacionGlobal;

void registrarFuenteNavegacion(FuenteEmisorasAuto fuente) {
  _fuenteNavegacionGlobal = fuente;
}

/// Local-music browse source — registered from main.dart, mirrors
/// [registrarFuenteNavegacion] above (Design "getChildren data source
/// registration"). `null` until registered (headless cold bind before
/// main.dart's registration line runs) — every consumer below treats a
/// `null` fuente as "not configured" rather than throwing.
FuenteMusicaLocalAuto? _fuenteMusicaLocalGlobal;

void registrarFuenteMusicaLocal(FuenteMusicaLocalAuto fuente) {
  _fuenteMusicaLocalGlobal = fuente;
}

/// User-saved EQ presets browse source — registered from main.dart, mirrors
/// the two registrations above.
///
/// On-device feedback: the car's `Ecualizador` folder only ever listed the
/// six FACTORY presets, so a driver who had carefully saved their own could
/// not reach it from the car at all — the one place a preset picker is most
/// useful. The handler owns no persistence, so the list arrives through this
/// seam exactly like stations and local music do.
///
/// A function rather than the service object: the folder needs a fresh read
/// on every browse (a preset saved on the phone must appear in the car
/// without an app restart), and this keeps `servicio_audio.dart` from
/// importing the persistence layer. `null` until registered (headless cold
/// bind) — consumers fall back to factory presets only, never throw.
Future<List<PresetEcualizador>> Function()? _fuentePresetsPersonalizadosGlobal;

void registrarFuentePresetsPersonalizados(
  Future<List<PresetEcualizador>> Function() fuente,
) {
  _fuentePresetsPersonalizadosGlobal = fuente;
}

/// Reads the registered custom-preset source, tolerating both "never
/// registered" and "the read blew up" as the same empty result: a
/// diagnostics-grade failure must degrade the folder to its factory presets,
/// never make browsing fail.
Future<List<PresetEcualizador>> _leerPresetsPersonalizados() async {
  final fuente = _fuentePresetsPersonalizadosGlobal;
  if (fuente == null) return const [];
  try {
    return await fuente();
  } catch (_) {
    return const [];
  }
}

/// The full ordered preset universe the car's `Ecualizador` folder offers:
/// the six factory presets first, then [personalizados] in save order.
///
/// A custom preset whose `nombre` matches a factory preset is DROPPED, not
/// appended. Identity here is the raw name — [ConstructorArbolAuto.idPresetEq]
/// builds `eq_preset:<nombre>` from it and
/// [ConstructorArbolAuto.resolverPresetEq] resolves by first name match — so
/// two entries sharing a name would produce one media id that can only ever
/// reach the first of them. Rendering an item that silently applies a
/// different preset than the one whose name it shows is worse than not
/// rendering it, and the factory entry is the one the id is guaranteed to
/// resolve to.
///
/// Single source of truth on purpose: [itemsEcualizadorAuto] builds the items
/// from this list and the tap dispatch resolves against this same list, so
/// the folder can never show an item that resolution then refuses.
List<PresetEcualizador> presetsEcualizadorAuto({
  required List<PresetEcualizador> personalizados,
  List<PresetEcualizador>? deFabrica,
}) {
  final fabrica = deFabrica ?? PresetEcualizador.presets;
  final nombresFabrica = fabrica.map((p) => p.nombre).toSet();
  return [
    ...fabrica,
    ...personalizados.where((p) => !nombresFabrica.contains(p.nombre)),
  ];
}

/// Teardown hook for whatever `main.dart` wired around the handler and must
/// be undone when the handler itself dies — today only the
/// `AudioService.asyncError` subscription (`observarErroresAudio`). Registered
/// from `main.dart`, mirroring [registrarHandler] and the two browse-source
/// registrations above; run exactly once from
/// [PluriWaveAudioHandler.onTaskRemoved].
///
/// The direction of the dependency matters: the bootstrap layer injects its
/// cleanup INTO the service layer, so `servicio_audio.dart` never has to
/// import `arranque_audio.dart` (nor the plugin's static error stream) just to
/// be able to close it.
Future<void> Function()? _limpiezaArranqueGlobal;

void registrarLimpiezaArranque(Future<void> Function() limpieza) {
  _limpiezaArranqueGlobal = limpieza;
}

/// Builds the phone-initiated "play a station" `MediaItem` (item 3, Android
/// Auto fallback artwork): reuses [artUriPara] (`navegacion_auto.dart`) so a
/// station with no usable favicon gets the SAME on-brand rotating fallback
/// the browse tree and the car-tap path already show, instead of a blank
/// tile on the car/lockscreen/notification. Pure — no [PluriWaveAudioHandler]
/// dependency — so it is unit-testable without instantiating the handler.
MediaItem mediaItemParaEmisora(
  Emisora emisora, {
  required AppLocalizations l10n,
}) {
  return MediaItem(
    id: emisora.url,
    title: localizedStationName(l10n, emisora.nombre),
    artist: emisora.pais ?? '',
    album: 'PluriWave',
    artUri: Uri.parse(artUriPara(emisora)),
    extras: {'uuid': emisora.uuid},
  );
}

/// Reconstructs the phone-side [Emisora] from the handler's current
/// [MediaItem] (item 3): gates `favicon` through [faviconUsable]
/// (`navegacion_auto.dart`) so a car/car-tap "now playing" item's on-brand
/// FALLBACK `artUri` (an `android.resource://` drawable, never a real
/// favicon) is never misread as a genuine station favicon — the phone UI's
/// `CachedNetworkImage` widgets gate only on `favicon != null && isNotEmpty`
/// (not on `faviconUsable`'s scheme check), so without this guard they would
/// attempt a doomed network fetch of the fallback's non-http URI before
/// falling back to [PluriStationArtFallback] themselves. A genuine http(s)
/// favicon still round-trips exactly as before. Pure — no handler
/// dependency — unit-testable directly.
Emisora emisoraDesdeMediaItem(MediaItem mediaItem) {
  final uuid = mediaItem.extras?['uuid'] as String? ?? mediaItem.id;
  final artUriTexto = mediaItem.artUri?.toString();
  return Emisora(
    uuid: uuid,
    nombre: mediaItem.title,
    url: mediaItem.id,
    pais: (mediaItem.artist?.isNotEmpty ?? false) ? mediaItem.artist : null,
    favicon: faviconUsable(artUriTexto) ? artUriTexto : null,
  );
}

/// Maps a `just_audio` [ProcessingState] to the `audio_service`
/// [AudioProcessingState] pushed into `playbackState`. Identical to the
/// previous private `_mapProcState` in every case EXCEPT one:
/// [ProcessingState.idle] maps to [AudioProcessingState.loading] while
/// [cambiandoFuente] is `true`.
///
/// Why that single exception exists — this is the media-notification
/// regression, not a cosmetic tweak:
///
/// `audio_service`'s `_observePlaybackState` (`audio_service.dart:1131-1136`)
/// calls `AudioService._stop()` — which reaches `stopService()` and cancels
/// the notification through `deactivateMediaSession()` — on ANY transition
/// into `idle` from a non-idle state. The notification is posted at exactly
/// one place, `internalStartForeground()`, reachable only from the
/// `!wasPlaying && playing` edge, and its FIRST statement is
/// `ContextCompat.startForegroundService(...)`, which throws
/// `ForegroundServiceStartNotAllowedException` on API 31+ whenever the
/// process is not in a foreground state.
///
/// Every station change walked straight into that: `_cambiarFuente` pushes
/// `loading`, then `_recrearPlayer` disposes the old [AudioPlayer] and builds
/// a FRESH one, and a fresh player's first `playerStateStream` event is
/// always `idle`. Forwarded verbatim, that is a `loading -> idle` transition,
/// so the foreground service was torn down mid-source-change and the app then
/// depended on the following `playing: true` edge to restart it. With the
/// screen off, on the lock screen, or on an Android Auto / Bluetooth-initiated
/// start, that restart is exactly the case the platform refuses — audio keeps
/// playing, the notification never comes back. Self-inflicted, on every API
/// level, no plugin patch needed: just stop emitting the transient `idle`.
///
/// A genuine user stop is unaffected: `stop()` clears the flag BEFORE
/// `_player.stop()`, so its `idle` still reaches `playbackState` as a real
/// `idle` and still tears the service down. Pure — no handler dependency — so
/// the full [ProcessingState] x [cambiandoFuente] matrix is unit-testable
/// directly.
AudioProcessingState mapearEstadoProceso(
  ProcessingState proc, {
  required bool cambiandoFuente,
}) {
  if (cambiandoFuente && proc == ProcessingState.idle) {
    return AudioProcessingState.loading;
  }
  return switch (proc) {
    ProcessingState.idle => AudioProcessingState.idle,
    ProcessingState.loading => AudioProcessingState.loading,
    ProcessingState.buffering => AudioProcessingState.buffering,
    ProcessingState.ready => AudioProcessingState.ready,
    ProcessingState.completed => AudioProcessingState.completed,
  };
}

/// Custom-action names for the equalizer's `PlaybackStateCompat` custom
/// actions on the now-playing screen (Design "EQ custom actions", item 4).
/// Public consts so tests and this file's own `customAction` dispatch share
/// the exact same literals; distinct from every browse-tree media-id prefix
/// in `navegacion_auto.dart` (they live in a completely different
/// `MediaControl`/`customAction` namespace, never compared against a
/// media id).
const accionEqToggle = 'eq_toggle';

/// Advances to the NEXT factory preset after [actual] in [presets] order
/// (Design "EQ custom actions — cycling presets", item 4): wraps around
/// after the last one. When [actual] is not found in [presets] (e.g. a
/// user-tweaked "Personalizado" preset from `EstadoEcualizador.cambiarBanda`),
/// starts from the FIRST preset rather than throwing — cycling from an
/// unknown state always lands somewhere sane. Pure, no I/O.
///
/// [presets] defaults to [PresetEcualizador.presets] — not a literal default
/// value, since that field is `static final` (not `const`) and Dart default
/// parameter values must be compile-time constants.
PresetEcualizador presetSiguiente(
  PresetEcualizador actual, {
  List<PresetEcualizador>? presets,
}) {
  final lista = presets ?? PresetEcualizador.presets;
  final indice = lista.indexWhere((p) => p == actual);
  if (indice == -1) return lista.first;
  return lista[(indice + 1) % lista.length];
}

/// Localizes a preset's raw `nombre` for the equalizer custom action's
/// label (Design "EQ custom actions", item 4) — mirrors
/// `ecualizador_widget.dart`'s private `_nombrePreset` mapping (duplicated
/// rather than shared: that file is UI-widget layer, this one is the
/// service/handler layer, and the mapping is a single small switch, not
/// worth a cross-layer import for). An unrecognized name (e.g. a future
/// user-named custom preset) falls through to the raw name verbatim.
String nombrePresetVisible(AppLocalizations l10n, String nombre) {
  return switch (nombre) {
    'Flat' => l10n.equalizerPresetFlat,
    'Rock' => l10n.equalizerPresetRock,
    'Pop' => l10n.equalizerPresetPop,
    'Bass Boost' => l10n.equalizerPresetBassBoost,
    'Jazz' => l10n.equalizerPresetJazz,
    'Voz' => l10n.equalizerPresetVoice,
    'Personalizado' => l10n.equalizerPresetCustom,
    _ => nombre,
  };
}

/// Builds the equalizer's custom-action `MediaControl`s for the now-playing
/// screen (decision `auto/ecualizador-diseno`) — exactly 1: an on/off
/// toggle. The previous design paired this with a SECOND action that cycled
/// through the six factory presets; that action is REMOVED. On-device
/// feedback: many head units render custom actions icon-first, so two
/// static, non-parametrized glyphs sitting side by side looked identical/
/// dead even though the toggle's own icon DID change and the cycle action
/// DID work — a monochrome icon simply cannot legibly encode "which of six
/// presets" the way a browsable list's text rows can. Preset selection now
/// lives in the "Ecualizador" browsable folder instead (see
/// [itemsEcualizadorAuto]), which also frees this scarce custom-action
/// slot. Do NOT re-add a preset-cycling custom action; extend the folder
/// instead.
/// Empty when [disponible] is false (gate on EQ availability, mirrors the
/// existing `debeReaplicarEcualizador`/`_eqDisponible` gate) — a device
/// without the native Equalizer effect gets no EQ actions at all, not
/// broken ones.
///
/// On-device feedback follow-up: this action used to reuse the SAME
/// `ic_stat_pluriwave` drawable as everything else and was visually
/// indistinguishable on a car head unit, which foregrounds the icon over
/// the label. It now gets its own dedicated drawables
/// (`ic_auto_eq_on`/`ic_auto_eq_off`), and the icon itself reflects
/// [activo] (not just its label) so on/off is legible at a glance. Pure, no
/// handler dependency.
List<MediaControl> controlesEcualizadorPersonalizados({
  required bool disponible,
  required bool activo,
  required AppLocalizations l10n,
}) {
  if (!disponible) return const [];
  return [
    MediaControl.custom(
      androidIcon:
          activo ? 'drawable/ic_auto_eq_on' : 'drawable/ic_auto_eq_off',
      label:
          activo
              ? l10n.eqCustomActionDisableLabel
              : l10n.eqCustomActionEnableLabel,
      name: accionEqToggle,
    ),
  ];
}

/// The handler's full transport `controls` list for a `playbackState` push.
///
/// Top-level and public so tests exercise THIS function rather than a copy of
/// its shape. `servicio_audio_controles_notificacion_test.dart` used to
/// re-declare the list inline, which meant it stayed green while asserting a
/// shape `lib/` no longer produced — a guard that cannot see the thing it
/// guards. `PluriWaveAudioHandler` itself cannot be instantiated in a unit
/// test (a real `just_audio.AudioPlayer` needs platform MethodChannels), so
/// pulling the pure part out is the only way to test the real thing.
///
/// ORDER MATTERS, and only for the car.
///
/// On Android 13+ `createCustomAction` (AudioService.java:466-469) turns
/// [MediaControl.stop] into a `CUSTOM_ACTION_STOP` custom action too. So on a
/// modern phone the car receives TWO custom actions, in list order, and a head
/// unit that exposes a single custom-action slot shows only the first and
/// buries the rest in an overflow menu — which is why the equalizer toggle
/// stayed invisible on the playback screen even once it was back in this list
/// (reported on v1.2.14+136, which does contain it).
///
/// The equalizer therefore goes BEFORE `stop`, and wins that slot on purpose:
/// the car already has its own path to stop playback and Auto's template
/// renders play/pause itself, while the equalizer is reachable no other way
/// from this screen.
///
/// The phone notification is untouched by that ordering, on every API level.
/// `setState` (AudioService.java:513-521) splits this list by whether a
/// control carries a `customAction`: on 13+ `stop` goes to `customActions`
/// (never the notification) and the equalizer was never in `nativeActions`
/// anyway; below 13 the equalizer is the only custom action and `stop` stays
/// native. Either way `nativeActions` comes out as
/// `[prev?, play/pause, stop, next?]`, and `androidCompactActionIndices`
/// (`[colaActiva ? 1 : 0]`) still lands on play/pause.
List<MediaControl> construirControlesTransporte({
  required bool colaActiva,
  required bool playing,
  required bool eqDisponible,
  required bool eqActivo,
  required AppLocalizations l10n,
}) => [
  if (colaActiva) MediaControl.skipToPrevious,
  if (playing) MediaControl.pause else MediaControl.play,
  ...controlesEcualizadorPersonalizados(
    disponible: eqDisponible,
    activo: eqActivo,
    l10n: l10n,
  ),
  MediaControl.stop,
  if (colaActiva) MediaControl.skipToNext,
];

/// Content-style extras for the Ecualizador folder's items (decision
/// `auto/ecualizador-diseno`), mirrors `ConstructorArbolAuto
/// ._contentStyleLista` in `navegacion_auto.dart` — duplicated rather than
/// exposed publicly (see [nombrePresetVisible]'s doc for why small pieces
/// are deliberately duplicated across this handler/service layer and the
/// pure browse-tree builder layer rather than cross-layer-shared). List
/// style, not grid: these items are short text options with no artwork of
/// their own, unlike a station or local-track tile.
const _contentStyleListaEq = {
  'android.media.browse.CONTENT_STYLE_BROWSABLE_HINT': 1,
  'android.media.browse.CONTENT_STYLE_PLAYABLE_HINT': 1,
};

/// Marks the active Ecualizador-folder item by prefixing [titulo] with a
/// checkmark glyph (decision `auto/ecualizador-diseno`, spec "the active
/// preset must be visibly marked").
///
/// A `MediaItem.extras` completion-status flag (`androidx.media.utils.
/// MediaConstants.DESCRIPTION_EXTRAS_KEY_COMPLETION_STATUS`) was considered
/// and REJECTED as the marking mechanism: this project's `audio_service`
/// version (0.18.18) has no Dart wrapper for it — only `AndroidContentStyle`
/// 's list/grid hints are exposed — and the raw platform key itself is
/// designed for playback-COMPLETION tracking (e.g. "this podcast episode
/// was already listened to"), not item SELECTION; repurposing it here could
/// render as "already played" on some head units, which would be actively
/// misleading for a preset picker, and there is no way to verify its actual
/// rendering on a real head unit from this environment. A plain-text
/// marker renders identically and unambiguously on every head unit, which
/// an unverifiable, semantically-mismatched extras key cannot guarantee.
String _marcarActivoEq(String titulo, {required bool activo}) =>
    activo ? '✓ $titulo' : titulo;

/// Builds the "Ecualizador" folder's children for the Android Auto browse
/// tree (decision `auto/ecualizador-diseno`): "Desactivar" FIRST, then the
/// six factory presets in [PresetEcualizador.presets] order, each localized
/// via [nombrePresetVisible] — the SAME helper the toggle's custom-action
/// label already uses, so a preset's name reads identically whether the
/// driver sees it in the now-playing screen's tooltip or in this folder.
/// All items are playable: tapping one is dispatched through
/// `playFromMediaId` -> `seleccionarPresetEqPorMediaId` (`navegacion_auto.
/// dart`), the same seam every other browse-tree leaf already uses; this
/// folder has no sub-browsing. Exactly one item is marked active via
/// [_marcarActivoEq]: "Desactivar" when [activo] is `false`, otherwise
/// whichever preset equals [presetActual] — never both at once, and never
/// zero once this function is reached (an unresolvable [presetActual] with
/// [activo] `true` simply marks nothing, which cannot happen in practice
/// since [presetActual] always originates from [PresetEcualizador.presets]
/// or a "Personalizado" tweak that would just leave every item unmarked
/// rather than mis-marking one).
///
/// [presetsPersonalizados] are the user's own saved presets, appended after
/// the factory six by [presetsEcualizadorAuto] (which also settles name
/// collisions). They render through the same [nombrePresetVisible] call as
/// everything else: that helper passes an unrecognized name through
/// verbatim, which is exactly right for a name the user typed themselves.
List<MediaItem> itemsEcualizadorAuto({
  required bool activo,
  required PresetEcualizador presetActual,
  required AppLocalizations l10n,
  List<PresetEcualizador> presetsPersonalizados = const [],
}) {
  final constructor = ConstructorArbolAuto();
  final items = <MediaItem>[
    MediaItem(
      id: ConstructorArbolAuto.idDesactivarEq,
      title: _marcarActivoEq(l10n.autoEqDisableOption, activo: !activo),
      playable: true,
      extras: _contentStyleListaEq,
    ),
  ];
  for (final preset in presetsEcualizadorAuto(
    personalizados: presetsPersonalizados,
  )) {
    items.add(
      MediaItem(
        id: constructor.idPresetEq(preset.nombre),
        title: _marcarActivoEq(
          nombrePresetVisible(l10n, preset.nombre),
          activo: activo && preset == presetActual,
        ),
        playable: true,
        extras: _contentStyleListaEq,
      ),
    );
  }
  return items;
}

/// Wrapper de alto nivel para el UI.
class ServicioAudio {
  PluriWaveAudioHandler get _handler {
    assert(
      _handlerGlobal != null,
      'registrarHandler() no fue llamado en main.dart',
    );
    return _handlerGlobal!;
  }

  Emisora? get emisoraActual => _handler.emisoraActual;

  void configurarLocalizaciones(AppLocalizations l10n) {
    _handler.configurarLocalizaciones(l10n);
  }

  Stream<EstadoReproduccion> get estadoStream =>
      _handler.playbackState.map((s) {
        if (s.processingState == AudioProcessingState.error) {
          return EstadoReproduccion.error;
        }
        if (_handler.reconectando) return EstadoReproduccion.reconectando;
        if (s.processingState == AudioProcessingState.loading ||
            s.processingState == AudioProcessingState.buffering) {
          return EstadoReproduccion.cargando;
        }
        if (s.playing) return EstadoReproduccion.reproduciendo;
        if (s.processingState == AudioProcessingState.idle) {
          return EstadoReproduccion.detenido;
        }
        return EstadoReproduccion.pausado;
      });

  Future<void> reproducir(Emisora emisora) async {
    final item = mediaItemParaEmisora(
      emisora,
      l10n: lookupAppLocalizations(const Locale('es')),
    );
    await _handler.playMediaItem(item);
  }

  Future<void> pausar() => _handler.pause();
  Future<void> reanudar() => _handler.play();

  Future<void> togglePlay() async {
    if (_handler.playbackState.value.playing) {
      await pausar();
    } else {
      await reanudar();
    }
  }

  Future<void> detener() => _handler.stop();
  Future<void> setVolumen(double vol) => _handler.setVolumen(vol);
  double get volumen => _handler.volumen;
  bool get estaSonando => _handler.playbackState.value.playing;
  Stream<int?> get androidAudioSessionIdStream async* {
    yield _handler.androidAudioSessionId;
    yield* _handler.androidAudioSessionIdStream;
  }

  Future<void> dispose() async {}

  // ── Ecualizador ───────────────────────────────────────────────────────────
  AndroidEqualizer? get ecualizador => _handler.ecualizador;
  bool get ecualizadorDisponible => _handler.ecualizadorDisponible;
  PresetEcualizador get presetActual => _handler.presetActual;

  Future<void> aplicarPreset(PresetEcualizador preset) =>
      _handler.aplicarPreset(preset);
  Future<void> setEcualizadorActivo(bool activo) =>
      _handler.setEcualizadorActivo(activo);

  Future<void> setBanda(int index, double db) => _handler.setBanda(index, db);
}

// ─────────────────────────────────────────────────────────────────────────────
// AudioHandler
// ─────────────────────────────────────────────────────────────────────────────
class PluriWaveAudioHandler extends BaseAudioHandler
    with SeekHandler
    implements ObjetivoAudioInterrumpible {
  static const _timeoutCambioFuente = Duration(seconds: 12);
  static const _timeoutCierrePlayer = Duration(seconds: 3);
  static const _factorAtenuacion = 0.3;

  // ── Live-stream buffer (Design 7.1, S7-R1) ────────────────────────────────
  // Forward jitter cushion for live radio: there is no rewind history, so the
  // buffer only absorbs short drops (up to roughly what was buffered when the
  // drop hit); on reconnect we rejoin the live edge.
  static const bufferMinimo = Duration(seconds: 15);
  static const bufferMaximo = Duration(seconds: 50);
  static const bufferParaIniciar = Duration(milliseconds: 2500);
  static const bufferTrasRebuffer = Duration(seconds: 5);

  /// Buffer configuration applied at [AudioPlayer] construction. Exposed so
  /// tests can assert the values without touching platform channels (S7-R1).
  static const configuracionCargaAndroid = AudioLoadConfiguration(
    androidLoadControl: AndroidLoadControl(
      minBufferDuration: bufferMinimo,
      maxBufferDuration: bufferMaximo,
      bufferForPlaybackDuration: bufferParaIniciar,
      bufferForPlaybackAfterRebufferDuration: bufferTrasRebuffer,
      prioritizeTimeOverSizeThresholds: true,
    ),
  );

  AndroidEqualizer _eq = AndroidEqualizer();
  late AudioPlayer _player = _crearPlayer();
  StreamSubscription<PlayerState>? _estadoPlayerSub;
  StreamSubscription<Duration>? _bufferedSub;
  StreamSubscription<Duration?>? _duracionSub;
  StreamSubscription<PlaybackEvent>? _eventosSub;
  StreamSubscription<int?>? _androidAudioSessionIdSub;
  final _androidAudioSessionIdController = StreamController<int?>.broadcast();
  int? _androidAudioSessionId;

  /// Last session id processed for EQ re-apply purposes (Design "Change-guard
  /// field separate from broadcast field"). Kept apart from
  /// [_androidAudioSessionId] so external broadcast semantics on
  /// [androidAudioSessionIdStream] stay untouched by the EQ re-apply guard.
  int? _ultimaSessionIdEq;
  Future<void> _colaCambioFuente = Future<void>.value();
  int _revisionFuente = 0;

  /// `true` only for the window inside [_cambiarFuente] where the OLD player
  /// has been disposed and the FRESH one has not loaded its URL yet — the
  /// window in which `playerStateStream` unavoidably emits a transient
  /// `idle` that is NOT a stop. [mapearEstadoProceso] masks that one `idle`
  /// as `loading` so `audio_service` does not tear the foreground service
  /// (and with it the media notification) down mid-source-change; see that
  /// function's doc for the full mechanism.
  ///
  /// A value stuck at `true` is the ONLY risk this flag introduces: a real
  /// user stop would then be masked away from `idle` and the service would
  /// never stop, leaving an unkillable notification. It is therefore cleared
  /// by a `finally` in [_cambiarFuente] (which covers normal completion,
  /// both revision-mismatch `return`s, every `rethrow`, and any non-`Exception`
  /// `Error` that no catch clause matches), AND eagerly at the top of every
  /// catch clause, AND at the start of [stop] and [_gestionarErrorReproduccion]
  /// — i.e. before every single `_player.stop()` call in this class.
  bool _cambiandoFuente = false;

  /// Active local-music queue (Design "single load-bearing invariant"):
  /// `null` means "not local-queue playback" — the ONLY gate the
  /// auto-advance/skip/isolation logic reads. Radio never sets this field.
  ColaLocal? _colaLocal;

  /// Re-entry latch (Design ADR-3): armed synchronously the instant an
  /// auto-advance is triggered, cleared when the next track reaches
  /// `playing && ready`, or on deactivate/stop/external play. Guards
  /// against a double-advance from repeated `completed` emissions during
  /// the async URI-resolve gap.
  bool _avanzandoCola = false;

  Emisora? emisoraActual;
  double _volumen = 1.0;
  double get volumen => _volumen;
  AppLocalizations? _l10n;

  /// Intent-to-play flag (Designs 3.1/7.2): reflects the LAST explicit
  /// intent (play/pause/stop, including audio-session interruptions, which
  /// pause through [pausar]). The S7 reconnect state machine reads it to
  /// distinguish a network stall from an intentional pause.
  bool _intencionReproducir = false;

  /// Ducked state requested by the audio session (transient focus loss).
  bool _atenuado = false;

  /// Reconnect-on-stall state machine (Design 7.2, S7-R2).
  final ControladorReconexion _reconexion = ControladorReconexion();

  /// True while the handler is inside the reconnect window. [ServicioAudio]
  /// maps it to [EstadoReproduccion.reconectando] so the UI shows a loading
  /// indicator instead of an error during retries (S7-R3).
  bool _reconectando = false;
  bool get reconectando => _reconectando;

  AndroidEqualizer? get ecualizador => _eq;
  bool _eqDisponible = false;
  bool get ecualizadorDisponible => _eqDisponible;
  bool _ecualizadorActivo = true;
  bool get ecualizadorActivo => _ecualizadorActivo;

  PresetEcualizador _presetActual = PresetEcualizador.flat;
  PresetEcualizador get presetActual => _presetActual;
  int? get androidAudioSessionId => _androidAudioSessionId;
  Stream<int?> get androidAudioSessionIdStream =>
      _androidAudioSessionIdController.stream;

  PluriWaveAudioHandler() {
    _conectarStreamsPlayer();
  }

  AppLocalizations get _textos {
    final actual = _l10n;
    if (actual != null) return actual;
    return lookupAppLocalizations(const Locale('es'));
  }

  void configurarLocalizaciones(AppLocalizations l10n) {
    _l10n = l10n;
  }

  AudioPlayer _crearPlayer() {
    return AudioPlayer(
      audioPipeline: AudioPipeline(androidAudioEffects: [_eq]),
      audioLoadConfiguration: configuracionCargaAndroid,
    );
  }

  void _conectarStreamsPlayer() {
    _estadoPlayerSub = _player.playerStateStream.listen((state) {
      final playing = state.playing;
      final proc = state.processingState;
      // First line of the listener (Design ADR-3, Phase 3 task 3.3):
      // double-gated on `completed` + an active local queue, so this is a
      // no-op for radio (which never emits `completed`) and for
      // single-track local playback (which never sets `_colaLocal`).
      _manejarFinPista(proc);
      if (playing && proc == ProcessingState.ready) {
        // Successful (re)connection: reset the backoff so the next stall
        // starts over, and leave the reconnect window (S7-R7).
        _reconexion.restablecer();
        _reconectando = false;
        // Local queue (Design ADR-3): the next queued track reached a
        // stable playing state — clear the re-entry latch so a LATER
        // completion can advance again. A no-op for radio, which never
        // sets `_avanzandoCola`.
        _avanzandoCola = false;
      }
      // Local queue transport (Design "Transport wiring"): skip controls
      // are only offered while a queue is active — when `_colaLocal` is
      // `null` this list/set/index is byte-identical to the pre-change
      // radio behavior (regression guard).
      final colaActiva = _colaLocal != null;
      playbackState.add(
        playbackState.value.copyWith(
          controls: _controlesTransporte(
            colaActiva: colaActiva,
            playing: playing,
          ),
          // Android for Cars, "Enable playback control": «Android Auto and
          // AAOS display playback controls based on the actions that are
          // enabled in the PlaybackStateCompat object. By default, your app
          // must support the following actions: ACTION_PLAY, ACTION_PAUSE,
          // ACTION_STOP, ACTION_PLAY_FROM_MEDIA_ID, ACTION_PLAY_FROM_SEARCH.»
          //
          // This set had carried only `seek` + `stop` since the very first
          // commit, so the required transport actions were never advertised.
          // The car got away with it for a long time — but Android Auto is a
          // separate app that updates itself, so a tolerance it used to have
          // can disappear without a single line changing on our side. That
          // matches the report exactly: "it used to work, and in the latest
          // versions it doesn't", with no audio commit in between that could
          // explain it.
          //
          // The phone notification never depended on any of this: it builds
          // its play/pause button from `controls`, which is why the symptom
          // is car-only.
          systemActions: {
            MediaAction.play,
            MediaAction.pause,
            MediaAction.playPause,
            MediaAction.stop,
            MediaAction.playFromMediaId,
            MediaAction.playFromSearch,
            MediaAction.seek,
            // Previous/next are advertised ALWAYS now, not only for a local
            // queue. Android Auto reserves those two slots and only hands the
            // space to custom actions when the app declares no support, so
            // this is what puts prev/next on the car's transport row -- and
            // `skipToNext`/`skipToPrevious` fall back to station-to-station
            // skipping when there is no queue, so neither button is inert.
            MediaAction.skipToPrevious,
            MediaAction.skipToNext,
          },
          androidCompactActionIndices: [colaActiva ? 1 : 0],
          processingState: mapearEstadoProceso(
            proc,
            cambiandoFuente: _cambiandoFuente,
          ),
          playing: playing,
          // Reported: in Android Auto the progress bar and the time labels of
          // a local track never move. `updatePosition` was NEVER set anywhere
          // in this file, so it stayed at its `Duration.zero` default while
          // `copyWith` refreshed `updateTime` to now on every push
          // (audio_service.dart:411-413, :256). A client extrapolates
          // `updatePosition + (now - updateTime) * speed`, so it was told
          // "position 0, as of right now" over and over — a bar pinned at the
          // start. The phone UI never noticed because it reads
          // `_player.positionStream` directly.
          updatePosition: _player.position,
          bufferedPosition: _player.bufferedPosition,
          speed: _player.speed,
        ),
      );
      _trazarEstadoPublicado();
    });

    _bufferedSub = _player.bufferedPositionStream.listen((pos) {
      playbackState.add(
        playbackState.value.copyWith(
          bufferedPosition: pos,
          // Must ride along: `copyWith` stamps a fresh `updateTime` but keeps
          // the old `updatePosition`, so a push without it actively tells the
          // client the PREVIOUS position is current NOW — freezing the bar
          // between player-state events. This stream ticks ~2/s, which is
          // what keeps the car's bar smooth.
          updatePosition: _player.position,
        ),
      );
    });

    // Duration arrives asynchronously once the source is parsed, and Android
    // Auto draws no progress bar for a MediaItem without one. Radio streams
    // report null (correct: live audio has no length) and are left alone.
    _duracionSub = _player.durationStream.listen((duracion) {
      final actual = mediaItem.value;
      if (duracion == null || actual == null) return;
      if (actual.duration == duracion) return;
      mediaItem.add(actual.copyWith(duration: duracion));
    });

    _eventosSub = _player.playbackEventStream.listen(
      (_) {},
      onError: (Object error, StackTrace stackTrace) {
        _gestionarErrorReproduccion(error);
      },
    );

    _androidAudioSessionIdSub = _player.androidAudioSessionIdStream.listen((
      sessionId,
    ) {
      _androidAudioSessionId = sessionId;
      if (!_androidAudioSessionIdController.isClosed) {
        _androidAudioSessionIdController.add(sessionId);
      }
      if (debeReaplicarEcualizador(
        sessionId: sessionId,
        ultimaSessionIdEq: _ultimaSessionIdEq,
        eqDisponible: _eqDisponible,
      )) {
        _ultimaSessionIdEq = sessionId;
        unawaited(_activarEcualizador());
      }
    });
  }

  String? _ultimaTrazaEstado;

  /// Logs the state actually handed to `AudioService.setState`, once per real
  /// change (this fires on every player event, so unconditional logging would
  /// bury the signal).
  ///
  /// Exists for one open question that static reading could not settle: the
  /// Android Auto playback screen shows PLAY while a station is audibly
  /// playing. The car does NOT take that icon from `controls` — it takes it
  /// from `PlaybackStateCompat.getState()` (AudioService.java:601-611), where
  /// `ready` + `playing` is the only combination that yields `STATE_PLAYING`;
  /// `idle` gives `STATE_NONE`, which is what a freshly created session
  /// carries (:319) and what a car would render as a play button. Every
  /// `playbackState.add` in this file was audited and none publishes
  /// `playing: false` while audio runs, so the failing input is unknown and
  /// any fix would be guesswork.
  ///
  /// `eqDisponible` rides along because the equalizer custom action is gated
  /// on it and the flag is otherwise unobservable — one car session answers
  /// both questions at once:
  ///
  ///   adb logcat | grep PluriWave
  ///
  /// It uses [debugPrint] and NOT `dart:developer`'s `log`, and that is not a
  /// style choice. `log()` writes to the VM service, which a RELEASE build
  /// does not have — so this trace, and every error line in this file, was
  /// invisible in the only build that ever runs in a car. Weeks of "no
  /// evidence" were this, not a quiet app. Do not convert these back.
  void _trazarEstadoPublicado() {
    final s = playbackState.value;
    final traza =
        'proc=${s.processingState.name} playing=${s.playing} '
        'eqDisponible=$_eqDisponible eqActivo=$_ecualizadorActivo '
        'custom=${s.controls.where((c) => c.customAction != null).length} '
        'controles=${s.controls.length}';
    if (traza == _ultimaTrazaEstado) return;
    _ultimaTrazaEstado = traza;
    debugPrint('[PluriWave][ServicioAudio] estado $traza');
  }

  /// Binds [construirControlesTransporte] — which holds the whole contract,
  /// including why the equalizer must precede `stop` — to this handler's live
  /// equalizer state.
  List<MediaControl> _controlesTransporte({
    required bool colaActiva,
    required bool playing,
  }) => construirControlesTransporte(
    colaActiva: colaActiva,
    playing: playing,
    eqDisponible: _eqDisponible,
    eqActivo: _ecualizadorActivo,
    l10n: _textos,
  );

  /// Re-pushes `playbackState` with a freshly built controls list (item 4):
  /// called whenever EQ availability/enabled state changes outside a
  /// player-state transition (a custom-action tap, or a phone-side toggle),
  /// so the equalizer action's icon and label stay in sync on the car's
  /// now-playing screen without waiting for an unrelated player event.
  /// Idempotent and cheap (no native calls) — safe to call from any EQ
  /// state-changing path.
  void _actualizarControlesEq() {
    playbackState.add(
      playbackState.value.copyWith(
        controls: _controlesTransporte(
          colaActiva: _colaLocal != null,
          playing: playbackState.value.playing,
        ),
      ),
    );
  }

  /// Gestiona cualquier error de reproducción de ExoPlayer.
  ///
  /// Network-class failures while the user still intends to play enter the
  /// reconnect state machine (S7-R2) instead of surfacing a terminal error;
  /// only retry exhaustion (or non-network errors) falls through to the
  /// existing error path, so the user sees a single error — no spam per retry.
  void _gestionarErrorReproduccion(Object error) {
    // Terminal-error path also ends in `_player.stop()` below, and it is
    // reachable from `_eventosSub`'s `onError` WHILE a source change is still
    // in flight. Dropping the mask here keeps the invariant total: the flag
    // is `false` before every `_player.stop()` call in this class.
    _cambiandoFuente = false;
    if (_intentarReconexion(error)) return;

    String mensaje;
    String codigoLog;

    if (error is PlayerException) {
      codigoLog = 'PlayerException(code=${error.code}): ${error.message}';
      mensaje = _mensajeAmigable(error);
    } else if (error is TimeoutException) {
      codigoLog = 'TimeoutException: $error';
      mensaje = _textos.audioErrorTimeout;
    } else {
      codigoLog = 'Error desconocido: $error';
      mensaje = _textos.audioErrorGeneric;
    }

    debugPrint('[PluriWave][ServicioAudio] Error reproducción: $codigoLog');

    _detenerReconexion();
    playbackState.add(
      playbackState.value.copyWith(
        processingState: AudioProcessingState.error,
        playing: false,
        errorMessage: mensaje,
      ),
    );
    emisoraActual = null;
    mediaItem.add(null);

    _player.stop().catchError((_) {});
  }

  /// Network-class failures: ExoPlayer 2xxx source errors (no internet, bad
  /// URL/host, timeout) and our own source-change timeout guard.
  bool _esErrorDeRed(Object error) =>
      (error is PlayerException && error.code >= 2000 && error.code < 3000) ||
      error is TimeoutException;

  /// Attempts to enter (or stay in) the reconnect window. Returns true when a
  /// retry was scheduled and the terminal error path must be skipped.
  bool _intentarReconexion(Object error) {
    if (!_esErrorDeRed(error)) return false;
    final item = mediaItem.value;
    if (item == null) return false;

    final decision = _reconexion.registrarFallo(
      intencionReproducir: _intencionReproducir,
      alReintentar: () => _reintentarFuente(item),
    );
    if (decision != DecisionReconexion.reintentar) {
      // ignorar (user pause/stop or interruption) keeps the player quiet;
      // agotado falls through to the single terminal error (S7-R2-C).
      if (decision == DecisionReconexion.ignorar) {
        _reconectando = false;
      }
      return decision == DecisionReconexion.ignorar;
    }

    _reconectando = true;
    debugPrint(
      '[PluriWave][ServicioAudio] Stall de red, reintento ${_reconexion.intentos}/'
      '${_reconexion.maxReintentos} en '
      '${_reconexion.retrasoParaIntento(_reconexion.intentos).inSeconds}s',
    );
    playbackState.add(
      playbackState.value.copyWith(
        processingState: AudioProcessingState.buffering,
        playing: false,
        errorMessage: null,
      ),
    );
    return true;
  }

  /// Re-issues the live source through the revision-guarded source-change
  /// queue, so a user source switch or stop during the retry cancels it.
  void _reintentarFuente(MediaItem item) {
    if (!_intencionReproducir) {
      _detenerReconexion();
      return;
    }
    final revision = ++_revisionFuente;
    _colaCambioFuente = _colaCambioFuente
        .catchError((_) {})
        .then((_) => _cambiarFuente(item, revision))
        // Failures already routed through _gestionarErrorReproduccion, which
        // schedules the next backoff retry or surfaces the terminal error.
        .catchError((_) {});
  }

  void _detenerReconexion() {
    _reconexion.cancelar();
    _reconectando = false;
  }

  /// Traduce códigos de error de ExoPlayer a mensajes para el usuario.
  String _mensajeAmigable(PlayerException e) {
    final code = e.code;

    if (code >= 2000 && code < 3000) {
      if (code == 2001) return _textos.audioErrorNoInternet;
      if (code == 2002) return _textos.audioErrorInvalidUrl;
      if (code == 2003) return _textos.audioErrorNotFound;
      if (code == 2004) return _textos.audioErrorTimeout;
      return _textos.audioErrorCannotConnect;
    }

    if (code >= 3000 && code < 4000) {
      return _textos.audioErrorUnsupportedFormat;
    }

    if (code >= 4000 && code < 5000) {
      return _textos.audioErrorDecode;
    }

    final msg = e.message ?? '';
    if (msg.contains('Cleartext') || msg.contains('cleartext')) {
      return _textos.audioErrorCleartext;
    }
    if (msg.contains('CERTIFICATE') || msg.contains('HandshakeException')) {
      return _textos.audioErrorSsl;
    }

    return _textos.audioErrorCannotPlay;
  }

  /// Public entry point for EVERY external play (phone `reproducir`, car
  /// `emisora:`/`grupo:`/`pista:` non-path). ALWAYS clears the
  /// local queue FIRST (Design ADR-2, the single load-bearing invariant:
  /// "external play = leave queue mode") so a stale auto-advance can never
  /// fire after an external source switch, then delegates to the private
  /// [_encolarCambioFuente] — the SAME source-change path queue playback
  /// uses via [_reproducirEntradaCola].
  @override
  Future<void> playMediaItem(MediaItem mediaItem) async {
    _colaLocal = null;
    _avanzandoCola = false;
    return _encolarCambioFuente(mediaItem);
  }

  /// The revision-guarded source-change queue (Design ADR-1/ADR-2), shared
  /// by public [playMediaItem] (which clears `_colaLocal` first) and
  /// [_reproducirEntradaCola] (queue play, which does NOT clear it) — the
  /// body is exactly [playMediaItem]'s previous implementation, unchanged.
  Future<void> _encolarCambioFuente(MediaItem mediaItem) async {
    _intencionReproducir = true;
    // Fresh user play/source switch: restart the backoff from scratch and
    // leave any previous reconnect window (S7-R2).
    _reconexion.restablecer();
    _reconectando = false;
    final revision = ++_revisionFuente;
    _colaCambioFuente = _colaCambioFuente
        .catchError((_) {})
        .then((_) => _cambiarFuente(mediaItem, revision));
    return _colaCambioFuente;
  }

  /// Plays a single local-queue track WITHOUT clearing `_colaLocal` (Design
  /// ADR-2's "queue play" transition) — the ONLY other caller of
  /// [_encolarCambioFuente] besides public [playMediaItem]. Callers are
  /// responsible for setting/keeping `_colaLocal` themselves before calling
  /// this (queue start, auto-advance, skip) — this method itself never
  /// touches the field on the happy path.
  ///
  /// [colaEsperada], when provided, is the mid-await race guard (Design
  /// ADR-3's advance flow): after resolving [nodo]'s content URI (the
  /// async gap where a user action could replace `_colaLocal`), playback
  /// only proceeds when `_colaLocal` is still IDENTICAL to [colaEsperada].
  /// Skip/queue-start callers omit it (no prior async gap to guard).
  Future<void> _reproducirEntradaCola(
    NodoLocal nodo, {
    ColaLocal? colaEsperada,
  }) async {
    final fuente = _fuenteMusicaLocalGlobal;
    if (fuente == null) {
      if (colaEsperada != null) _avanzandoCola = false;
      return;
    }
    final item = await construirMediaItemColaLocal(nodo, fuente: fuente);
    if (colaEsperada != null && !avanceEsValido(_colaLocal, colaEsperada)) {
      // Stale: a user action (external play, stop, another skip) replaced
      // `_colaLocal` during the await — abort this advance without
      // touching whatever the newer action already set.
      return;
    }
    if (item == null) {
      // The local track's content URI could not be resolved (revoked
      // permission, moved/deleted file). Only an in-flight advance owns
      // the latch here (a direct skip/queue-start never armed it) — end
      // the queue cleanly instead of leaving `_avanzandoCola` stuck.
      if (colaEsperada != null) {
        _avanzandoCola = false;
        _desactivarCola();
        unawaited(stop());
      }
      return;
    }
    await _encolarCambioFuente(item);
  }

  /// Clears the local queue (Design ADR-2/ADR-4): shared by [stop], the
  /// end-of-queue path, and a resolve failure mid-advance.
  void _desactivarCola() {
    _colaLocal = null;
    _avanzandoCola = false;
  }

  /// Sets up a fresh local-music queue and plays its first track (Design
  /// "Data Flow" — the `iniciarCola` seam [playFromMediaId] passes to
  /// [reproducirCarpetaLocal]).
  Future<void> _iniciarColaLocal(List<NodoLocal> pistas) async {
    final cola = ColaLocal(pistas: pistas);
    _colaLocal = cola;
    await _reproducirEntradaCola(cola.actual);
  }

  /// First line of the `playerStateStream` listener (Design ADR-3, Phase 3
  /// task 3.3): pure-decision-driven queue-advance handling. A no-op for
  /// radio (never emits `completed`) and single-track local playback
  /// (never sets `_colaLocal`) — see [decidirAvanceCola]'s doc comment for
  /// the full gating contract.
  void _manejarFinPista(ProcessingState proc) {
    final decision = decidirAvanceCola(
      colaLocal: _colaLocal,
      avanzandoCola: _avanzandoCola,
      trackCompletado: proc == ProcessingState.completed,
    );
    switch (decision) {
      case DecisionAvanceCola.ninguna:
        return;
      case DecisionAvanceCola.desactivar:
        _desactivarCola();
        unawaited(stop());
        return;
      case DecisionAvanceCola.avanzar:
        final siguiente = _colaLocal!.conSiguiente();
        if (siguiente == null) {
          // Structurally unreachable — decidirAvanceCola already proved
          // conSiguiente() != null for `avanzar` — guarded defensively.
          _desactivarCola();
          unawaited(stop());
          return;
        }
        // Set the re-entry latch synchronously, before any await, so a
        // second rapid `completed` emission is caught by
        // decidirAvanceCola's `avanzandoCola == true` gate (Design
        // ADR-3).
        _avanzandoCola = true;
        _colaLocal = siguiente;
        unawaited(
          _reproducirEntradaCola(siguiente.actual, colaEsperada: siguiente),
        );
    }
  }

  Future<void> _cambiarFuente(MediaItem mediaItem, int revision) async {
    this.mediaItem.add(mediaItem);
    emisoraActual = _emisoraDesdeMediaItem(mediaItem);
    playbackState.add(
      playbackState.value.copyWith(
        processingState: AudioProcessingState.loading,
        playing: false,
        errorMessage: null,
      ),
    );
    // Opens the masking window BEFORE `_recrearPlayer`, which is what
    // disposes the old player and constructs the fresh one whose first
    // `playerStateStream` event is the transient `idle` we must not forward
    // (see [mapearEstadoProceso]).
    _cambiandoFuente = true;
    try {
      await _recrearPlayer();
      if (revision != _revisionFuente) return;

      await _player.setUrl(mediaItem.id).timeout(_timeoutCambioFuente);
      // Source swap complete: the fresh player's transient `idle` is behind
      // us, so stop masking immediately — before anything below can await —
      // and let a real `idle` through again from here on.
      _cambiandoFuente = false;
      if (revision != _revisionFuente) return;

      _iniciarPlaySinBloquear(mediaItem, revision);
      unawaited(_activarEcualizador());
    } on PlayerException catch (e) {
      // Cleared BEFORE `_gestionarErrorReproduccion`, not just by the
      // `finally`: that method calls `_player.stop()` without awaiting it, so
      // the resulting `idle` could otherwise land while the mask was still
      // up and be rewritten to `loading`. Same reason in the two clauses
      // below.
      _cambiandoFuente = false;
      if (revision == _revisionFuente) {
        _gestionarErrorReproduccion(e);
        // Reconnect engaged: complete normally so callers do not surface a
        // snackbar/dialog while the handler keeps retrying (S7-R3).
        if (_reconectando) return;
      }
      throw Exception(_mensajeAmigable(e));
    } on TimeoutException catch (e) {
      _cambiandoFuente = false;
      // A real network drop usually surfaces as our 12s source timeout:
      // route it through the reconnect machine instead of a terminal error.
      if (revision == _revisionFuente) {
        _gestionarErrorReproduccion(e);
        if (_reconectando) return;
      }
      rethrow;
    } on Exception catch (e, stackTrace) {
      _cambiandoFuente = false;
      debugPrint(
        '[PluriWave][ServicioAudio] Error inesperado en playMediaItem: $e',
      );
      if (revision == _revisionFuente) {
        playbackState.add(
          playbackState.value.copyWith(
            processingState: AudioProcessingState.error,
            playing: false,
            errorMessage: _textos.audioErrorUnexpectedPlayback,
          ),
        );
        emisoraActual = null;
        this.mediaItem.add(null);
      }
      rethrow;
    } finally {
      // Leak-proof backstop. Dart runs `finally` on EVERY exit from the
      // block above: normal completion, both `revision != _revisionFuente`
      // early returns, every `throw`/`rethrow` out of a catch clause, and —
      // crucially — any `Error` (as opposed to `Exception`) that none of the
      // three clauses catches. The flag must never depend on a single
      // hand-audited exit path, because a `_cambiandoFuente` stuck at `true`
      // would mask a REAL stop's `idle` and leave the notification unkillable.
      _cambiandoFuente = false;
    }
  }

  Future<void> _recrearPlayer() async {
    await _estadoPlayerSub?.cancel();
    await _bufferedSub?.cancel();
    await _duracionSub?.cancel();
    await _eventosSub?.cancel();
    await _androidAudioSessionIdSub?.cancel();

    final anterior = _player;
    try {
      await anterior.stop().timeout(_timeoutCierrePlayer);
    } catch (_) {}
    try {
      await anterior.dispose().timeout(_timeoutCierrePlayer);
    } catch (_) {}

    _eq = AndroidEqualizer();
    _eqDisponible = false;
    _androidAudioSessionId = null;
    _ultimaSessionIdEq = null;
    _player = _crearPlayer();
    await _player.setVolume(_volumenEfectivo);
    _conectarStreamsPlayer();
  }

  void _iniciarPlaySinBloquear(MediaItem mediaItem, int revision) {
    unawaited(
      _player.play().catchError((Object error, StackTrace stackTrace) {
        debugPrint(
          '[PluriWave][ServicioAudio] Error al iniciar ${mediaItem.title}: $error',
        );
        if (revision == _revisionFuente) {
          _gestionarErrorReproduccion(error);
        }
      }),
    );
  }

  Future<void> _activarEcualizador() async {
    try {
      final params = await _eq.parameters;
      _eqDisponible = params.bands.isNotEmpty;
      if (_eqDisponible) {
        await _eq.setEnabled(_ecualizadorActivo);
        await aplicarPreset(_presetActual);
      }
    } catch (_) {
      _eqDisponible = false;
    }
    // Item 4: an availability flip (e.g. a station switch that lands on a
    // device without the native Equalizer effect) must show/hide the EQ
    // custom actions immediately, not wait for a coincidental later
    // player-state event.
    _actualizarControlesEq();
  }

  /// Pure re-apply decision for a native session-id emission. No side effects.
  ///
  /// Returns `true` when the native audio session id genuinely rotated
  /// mid-playback (audio-focus ducking by another app) and the equalizer is
  /// currently attached, meaning the caller should re-attach the EQ and
  /// re-push the current preset's gains via [_activarEcualizador].
  @visibleForTesting
  static bool debeReaplicarEcualizador({
    required int? sessionId,
    required int? ultimaSessionIdEq,
    required bool eqDisponible,
  }) => sessionId != null && sessionId != ultimaSessionIdEq && eqDisponible;

  /// Aplica un preset al ecualizador nativo Android.
  Future<void> aplicarPreset(PresetEcualizador preset) async {
    _presetActual = preset;
    if (_eqDisponible) {
      try {
        await _eq.setEnabled(_ecualizadorActivo);
        if (_ecualizadorActivo) {
          final params = await _eq.parameters;
          for (
            int i = 0;
            i < params.bands.length && i < preset.bandas.length;
            i++
          ) {
            await params.bands[i].setGain(
              _mapearGananciaNativa(
                preset.bandas[i],
                minDecibels: params.minDecibels,
                maxDecibels: params.maxDecibels,
              ),
            );
          }
        }
      } catch (_) {}
    }
    // Item 4: keeps the EQ custom action's preset-cycle label in sync
    // regardless of WHO changed the preset (a car customAction tap or the
    // phone settings screen via EstadoEcualizador) — single chokepoint.
    _actualizarControlesEq();
  }

  /// Ajusta una banda individual.
  Future<void> setBanda(int index, double db) async {
    final bandas = List<double>.from(_presetActual.bandas);
    if (index >= 0 && index < bandas.length) {
      bandas[index] = db;
      _presetActual = _presetActual.copyWithBandas(bandas);
    }
    if (!_eqDisponible || !_ecualizadorActivo) return;
    try {
      final params = await _eq.parameters;
      if (index < params.bands.length) {
        await params.bands[index].setGain(
          _mapearGananciaNativa(
            db,
            minDecibels: params.minDecibels,
            maxDecibels: params.maxDecibels,
          ),
        );
      }
    } catch (_) {}
  }

  double _mapearGananciaNativa(
    double db, {
    required double minDecibels,
    required double maxDecibels,
  }) {
    final normalizado = ((db.clamp(-12.0, 12.0) + 12.0) / 24.0).clamp(0.0, 1.0);
    return minDecibels + (normalizado * (maxDecibels - minDecibels));
  }

  Future<void> setEcualizadorActivo(bool activo) async {
    _ecualizadorActivo = activo;
    if (_eqDisponible) {
      try {
        await _eq.setEnabled(activo);
        if (activo) {
          await aplicarPreset(_presetActual);
        }
      } catch (_) {}
    }
    // Item 4: keeps the EQ custom action's on/off label in sync regardless
    // of WHO toggled it (a car customAction tap or the phone settings
    // screen via EstadoEcualizador).
    _actualizarControlesEq();
  }

  Future<void> setVolumen(double vol) async {
    _volumen = vol.clamp(0.0, 1.0);
    await _player.setVolume(_volumenEfectivo);
  }

  double get _volumenEfectivo =>
      _atenuado ? _volumen * _factorAtenuacion : _volumen;

  // ── ObjetivoAudioInterrumpible (audio-session seam, S3-R1) ───────────────

  @override
  bool get intencionReproducir => _intencionReproducir;

  @override
  bool get estaReproduciendo => playbackState.value.playing;

  @override
  Future<void> pausar() => pause();

  @override
  Future<void> reanudar() => play();

  @override
  Future<void> setAtenuado(bool atenuado) async {
    if (_atenuado == atenuado) return;
    _atenuado = atenuado;
    await _player.setVolume(_volumenEfectivo);
  }

  /// Fix "EQ Re-Apply After Audio-Focus Interruption": thin delegate to the
  /// existing [_activarEcualizador] (already does the correct idempotent
  /// `setEnabled` + re-push-gains work, already re-asserts the CURRENT
  /// [_ecualizadorActivo] rather than forcing it on). Called by
  /// [ServicioAudioSession] on resume-from-pause and on un-duck — see that
  /// interface member's doc for why the existing session-id-change trigger
  /// misses this case.
  @override
  Future<void> reaplicarEcualizador() => _activarEcualizador();

  @override
  Future<void> play() {
    _intencionReproducir = true;
    return _player.play();
  }

  @override
  Future<void> pause() {
    // User (or audio-session interruption) pause: disarm any pending retry —
    // a stall must never fight an intentional pause (S7-R2-B, S7-R6).
    _intencionReproducir = false;
    _detenerReconexion();
    return _player.pause();
  }

  @override
  Future<void> stop() async {
    // User stop (including the sleep-timer fade-out stop): cancel reconnect
    // so retries never restart playback after a stop (S7-R6).
    _intencionReproducir = false;
    _detenerReconexion();
    // Local queue (Design ADR-2): clears alongside the reconnect-cancel
    // logic above — `onTaskRemoved` (which calls stop()) inherits this for
    // free (Phase 3 task 3.5).
    _desactivarCola();
    // Genuine user stop: drop the source-change mask BEFORE `_player.stop()`,
    // so its `idle` reaches `playbackState` as a REAL `idle` and
    // `audio_service` tears the foreground service down as it always has.
    // `stop()` never pushes `idle` itself — `BaseAudioHandler.stop()` is
    // empty and the teardown is driven entirely by the player's emission —
    // so a stop landing while a station change is still in flight would
    // otherwise be masked to `loading` and the notification would become
    // unkillable. Paired with `_revisionFuente++` below, which invalidates
    // that in-flight change; its `finally` only re-clears the flag, and
    // nothing re-arms it (the single `= true` assignment already ran).
    _cambiandoFuente = false;
    _revisionFuente++;
    await _player.stop();
    // Publish `idle` OURSELVES rather than trusting the player to emit it.
    // `just_audio`'s `playerStateStream` is `.distinct()` over a value-equal
    // `PlayerState`, so a stop landing on an already-idle player (a station
    // change stopped before its native init finished pushing `loading`)
    // emits NOTHING. Combined with the source-change mask above — which
    // WRITES `loading` into `playbackState` rather than filtering at read
    // time — that would leave the state stuck at `loading` forever:
    // `audio_service` only tears the service down on a non-idle -> idle
    // transition (`audio_service.dart:1131-1136`), so the notification would
    // survive as an unkillable "cargando" with a dead Stop button. Strictly
    // worse than the bug this branch fixes. Additive and idempotent: when
    // the player DOES emit its own `idle`, this simply lands first and the
    // duplicate is a no-op transition.
    playbackState.add(
      playbackState.value.copyWith(
        processingState: AudioProcessingState.idle,
        playing: false,
        errorMessage: null,
      ),
    );
    emisoraActual = null;
    mediaItem.add(null);
    await super.stop();
  }

  @override
  Future<void> seek(Duration position) => _player.seek(position);

  /// Moves to the next queued track (Design ADR-3/ADR-4, Phase 3 task
  /// 3.6). Past the last track, clears the queue and stops — mirroring
  /// auto-advance's end-of-queue behavior (no wraparound).
  ///
  /// With NO local queue this now moves to the next STATION instead of doing
  /// nothing: the car's transport row offers previous/next for radio too,
  /// and a button that is present but inert is worse than no button.
  @override
  Future<void> skipToNext() async {
    final cola = _colaLocal;
    if (cola == null) {
      await _saltarEmisora(haciaAtras: false);
      return;
    }
    final siguiente = cola.conSiguiente();
    if (siguiente == null) {
      _desactivarCola();
      await stop();
      return;
    }
    _colaLocal = siguiente;
    await _reproducirEntradaCola(siguiente.actual);
  }

  /// Moves to the previous queued track (Design ADR-4, Phase 3 task 3.6).
  /// Clamps at the first track (restarts it) instead of wrapping to the last
  /// one. With no local queue, moves to the previous STATION — see
  /// [skipToNext].
  @override
  Future<void> skipToPrevious() async {
    final cola = _colaLocal;
    if (cola == null) {
      await _saltarEmisora(haciaAtras: true);
      return;
    }
    final anterior = cola.conAnterior();
    _colaLocal = anterior;
    await _reproducirEntradaCola(anterior.actual);
  }

  /// Station-to-station skipping for the car's transport row.
  ///
  /// The list to walk is resolved by [listaParaSaltoEmisora]: the narrowest
  /// list the current station actually belongs to, favourites first. Anything
  /// unresolvable — no source, no current station, a station that is in no
  /// list, a single-entry list — leaves playback untouched. Never throws;
  /// this runs from a hardware/steering-wheel button and an exception here
  /// would surface as the app going silent mid-drive.
  Future<void> _saltarEmisora({required bool haciaAtras}) async {
    try {
      final fuente = _fuenteNavegacionGlobal;
      final actual = emisoraActual;
      if (fuente == null || actual == null) return;
      final lista = listaParaSaltoEmisora(
        actual: actual,
        favoritos: await fuente.favoritos(),
        misEmisoras: await fuente.misEmisoras(),
        todas: await fuente.todas(),
      );
      final destino = emisoraVecina(actual, lista, haciaAtras: haciaAtras);
      if (destino == null) return;
      await playMediaItem(mediaItemParaEmisora(destino, l10n: _textos));
    } catch (e) {
      debugPrint('[PluriWave][ServicioAudio] Error saltando de emisora: $e');
    }
  }

  /// Dispatches the equalizer's only custom action (decision
  /// `auto/ecualizador-diseno`): `accionEqToggle` flips on/off, delegating
  /// to the existing [setEcualizadorActivo] — the SAME entry point the
  /// phone settings screen uses via `EstadoEcualizador` — so a car tap and a
  /// phone tap have identical effects and both refresh the action's label
  /// via `_actualizarControlesEq()` (already wired into that method). The
  /// preset-cycling action that used to live here is REMOVED — preset
  /// selection now goes through the "Ecualizador" browsable folder (see
  /// `seleccionarPresetEqPorMediaId` in `navegacion_auto.dart`, dispatched
  /// from [playFromMediaId] below). Any other [name] is a no-op — never
  /// throws.
  @override
  Future<dynamic> customAction(
    String name, [
    Map<String, dynamic>? extras,
  ]) async {
    switch (name) {
      case accionEqToggle:
        await setEcualizadorActivo(!_ecualizadorActivo);
    }
  }

  @override
  Future<void> onTaskRemoved() async {
    await stop();
    await _estadoPlayerSub?.cancel();
    await _bufferedSub?.cancel();
    await _duracionSub?.cancel();
    await _eventosSub?.cancel();
    await _androidAudioSessionIdSub?.cancel();
    await _player.dispose();
    await _androidAudioSessionIdController.close();
    // Handler teardown: release the bootstrap-owned `AudioService.asyncError`
    // subscription too, so it cannot outlive the handler it was instrumenting.
    // Never throws out of teardown — a failing cleanup hook must not prevent
    // the rest of `onTaskRemoved` from having completed above.
    try {
      await _limpiezaArranqueGlobal?.call();
    } catch (_) {}
  }

  Emisora _emisoraDesdeMediaItem(MediaItem mediaItem) {
    // Item 3: delegates to the top-level, unit-testable function so the
    // `faviconUsable` guard (never reflect the on-brand fallback artUri
    // back as a real favicon) is covered without instantiating the handler.
    return emisoraDesdeMediaItem(mediaItem);
  }

  // ── Android Auto browsing (thin delegation to navegacion_auto.dart's
  // already-tested pure logic — Design "getChildren data source") ─────────

  /// One-shot device-query channel (feature auto-custom-eq): the SAME
  /// method channel `ServicioDispositivoAudioReal` talks to, but method
  /// calls only — opening a second EventChannel subscription here would
  /// steal the phone-side service's Dart stream handler.
  @override
  Future<List<MediaItem>> getChildren(
    String parentMediaId, [
    Map<String, dynamic>? options,
  ]) async {
    try {
      final constructor = ConstructorArbolAuto();
      final fuenteLocal = _fuenteMusicaLocalGlobal;
      if (parentMediaId == AudioService.browsableRootId) {
        final incluirMusicaLocal =
            fuenteLocal != null && await fuenteLocal.hayCarpetaConfigurada();
        return constructor.raiz(incluirMusicaLocal: incluirMusicaLocal);
      }
      final musicaLocal = await hijosMusicaLocal(
        parentMediaId,
        fuente: fuenteLocal,
      );
      if (musicaLocal != null) return musicaLocal;
      // Ecualizador folder (decision `auto/ecualizador-diseno`): needs no
      // external data source, unlike every branch below it -- checked
      // before the `_fuenteNavegacionGlobal` gate, mirroring how the
      // local-music branch above is also resolved before that gate.
      // The Ecualizador folder is no longer offered by `raiz()` (owner
      // decision: the car keeps only the on/off toggle on the playback
      // screen). This branch stays as a TRANSITIONAL courtesy: Android Auto
      // caches browse trees on the head unit, so a stale "Ecualizador" entry
      // can survive the update for a session or two. Answering it keeps that
      // leftover working instead of opening an empty dead folder. Delete
      // once no head unit can still be holding the old tree.
      if (parentMediaId == ConstructorArbolAuto.idEcualizador) {
        return itemsEcualizadorAuto(
          activo: _ecualizadorActivo,
          presetActual: _presetActual,
          l10n: _textos,
          // Read per browse, not cached: a preset saved on the phone must
          // show up in the car on the next open, with no app restart.
          presetsPersonalizados: await _leerPresetsPersonalizados(),
        );
      }
      final fuente = _fuenteNavegacionGlobal;
      if (fuente == null) return const [];
      if (parentMediaId == ConstructorArbolAuto.idFavoritos) {
        return constructor.carpetasFavoritos(
          grupos: await fuente.grupos(),
          favoritos: await fuente.favoritos(),
        );
      }
      if (constructor.esCarpetaGrupo(parentMediaId)) {
        return constructor.hijosGrupo(
          parentMediaId,
          favoritos: await fuente.favoritos(),
        );
      }
      final emisoras = await _listaParaCarpeta(fuente, parentMediaId);
      return constructor.hijos(parentMediaId, emisoras: emisoras);
    } catch (_) {
      // Spec "Browse requested before app state is loaded": never throw out
      // of a browse call, even on an unexpected failure.
      return const [];
    }
  }

  @override
  Future<MediaItem?> getMediaItem(String mediaId) async {
    try {
      final fuente = _fuenteNavegacionGlobal;
      if (fuente == null) return null;
      final universo = await _universoCompleto(fuente);
      final constructor = ConstructorArbolAuto();
      final emisora = constructor.resolver(mediaId, universo);
      return emisora == null ? null : constructor.itemEmisora(emisora);
    } catch (_) {
      return null;
    }
  }

  /// Voice search from the car ("pon Radio Clásica").
  ///
  /// `ACTION_PLAY_FROM_SEARCH` is one of the actions Android for Cars
  /// documents as required, and it is now advertised in `systemActions` — so
  /// it has to actually do something. Advertising it unimplemented would be
  /// worse than omitting it: the assistant would accept the command and
  /// nothing would play, with no error to explain it.
  ///
  /// Favourites first, then my stations, then the full list, so a station the
  /// driver already cares about wins a name tie. Never throws and never plays
  /// something arbitrary on a miss — see [emisoraParaBusqueda].
  @override
  Future<void> playFromSearch(
    String query, [
    Map<String, dynamic>? extras,
  ]) async {
    try {
      final fuente = _fuenteNavegacionGlobal;
      if (fuente == null) return;
      final candidatas = <Emisora>[
        ...await fuente.favoritos(),
        ...await fuente.misEmisoras(),
        ...await fuente.todas(),
      ];
      final emisora = emisoraParaBusqueda(query, candidatas);
      if (emisora == null) return;
      await playMediaItem(mediaItemParaEmisora(emisora, l10n: _textos));
    } catch (e) {
      debugPrint(
        '[PluriWave][ServicioAudio] Error en playFromSearch($query): $e',
      );
    }
  }

  @override
  Future<void> playFromMediaId(
    String mediaId, [
    Map<String, dynamic>? extras,
  ]) async {
    try {
      // Local-track playback (Design "Local Track Playback Reuses Existing
      // Pipeline", Spec "User selects a local track"): FIRST branch,
      // unconditional `return` — a `pista:` id never falls through to the
      // station routing below.
      if (esPistaMediaId(mediaId)) {
        final fuenteLocal = _fuenteMusicaLocalGlobal;
        if (fuenteLocal == null) return;
        await reproducirPistaLocal(
          mediaId,
          fuente: fuenteLocal,
          reproducir: playMediaItem,
        );
        return;
      }
      // Folder-play actions (Design ADR-5, Phase 3 task 4.3): SECOND
      // branch, after `pista:`, before the station fallthrough — mirrors the
      // branch above's unconditional-return shape so neither new action id
      // can fall through to station routing.
      final constructorArbol = ConstructorArbolAuto();
      final esAccionCarpeta =
          constructorArbol.esCarpetaLocalReproducirMediaId(mediaId) ||
          constructorArbol.esCarpetaLocalAleatorioMediaId(mediaId);
      if (esAccionCarpeta) {
        final fuenteLocal = _fuenteMusicaLocalGlobal;
        if (fuenteLocal == null) return;
        await reproducirCarpetaLocal(
          mediaId,
          aleatorio: constructorArbol.esCarpetaLocalAleatorioMediaId(mediaId),
          fuente: fuenteLocal,
          iniciarCola: _iniciarColaLocal,
        );
        return;
      }
      // Equalizer preset selection (decision `auto/ecualizador-diseno`):
      // THIRD branch, same unconditional-return shape as the two above --
      // an `eq_preset:` id never falls through to station routing.
      if (constructorArbol.esPresetEqMediaId(mediaId)) {
        await seleccionarPresetEqPorMediaId(
          mediaId,
          activo: _ecualizadorActivo,
          aplicarPreset: aplicarPreset,
          activarEcualizador: setEcualizadorActivo,
          // The SAME list `itemsEcualizadorAuto` rendered from, so a tapped
          // custom preset resolves instead of silently doing nothing.
          presets: presetsEcualizadorAuto(
            personalizados: await _leerPresetsPersonalizados(),
          ),
        );
        return;
      }
      final fuente = _fuenteNavegacionGlobal;
      if (fuente == null) return;
      await reproducirPorMediaId(
        mediaId,
        fuente: fuente,
        reproducir: playMediaItem,
      );
    } catch (e) {
      // Spec "Unknown or stale media id": never propagate from the handler.
      debugPrint(
        '[PluriWave][ServicioAudio] Error en playFromMediaId($mediaId): $e',
      );
    }
  }

  Future<List<Emisora>> _listaParaCarpeta(
    FuenteEmisorasAuto fuente,
    String parentId,
  ) => switch (parentId) {
    ConstructorArbolAuto.idMisEmisoras => fuente.misEmisoras(),
    ConstructorArbolAuto.idTodas => fuente.todas(),
    _ => Future.value(const []),
  };

  Future<List<Emisora>> _universoCompleto(FuenteEmisorasAuto fuente) async {
    final listas = await Future.wait([
      fuente.favoritos(),
      fuente.misEmisoras(),
      fuente.todas(),
    ]);
    return listas.expand((lista) => lista).toList();
  }
}