import 'dart:async';

/// Outcome of a playback failure reported to [ControladorReconexion].
enum DecisionReconexion {
  /// A retry was scheduled after the backoff delay.
  reintentar,

  /// All retries were consumed — surface the terminal error to the user.
  agotado,

  /// Playback was not intended (user pause/stop or interruption) — no retry.
  ignorar,
}

/// Reconnect decision and bounded exponential backoff logic (Design 7.2,
/// S7-R2/S7-R7), extracted from `PluriWaveAudioHandler` so it is unit-testable
/// without platform channels. The timer factory is injectable for tests.
///
/// Defaults: 5 retries with delays 1s, 2s, 4s, 8s, 16s (capped at 30s).
/// Combined with the 12s source-change timeout per attempt this keeps the
/// total reconnect window inside the ~60-90s budget from the design.
class ControladorReconexion {
  ControladorReconexion({
    this.maxReintentos = 5,
    this.retrasoBase = const Duration(seconds: 1),
    this.retrasoMaximo = const Duration(seconds: 30),
    Timer Function(Duration, void Function())? crearTemporizador,
  }) : _crearTemporizador = crearTemporizador ?? _temporizadorReal;

  static Timer _temporizadorReal(Duration duracion, void Function() callback) =>
      Timer(duracion, callback);

  final int maxReintentos;
  final Duration retrasoBase;
  final Duration retrasoMaximo;
  final Timer Function(Duration, void Function()) _crearTemporizador;

  int _intentos = 0;
  Timer? _temporizador;

  /// Retries consumed since the last [restablecer].
  int get intentos => _intentos;

  /// True while a retry is scheduled and has not fired or been cancelled.
  bool get reintentoPendiente => _temporizador?.isActive ?? false;

  /// Backoff delay for the 1-based retry [intento]:
  /// `retrasoBase * 2^(intento-1)`, capped at [retrasoMaximo].
  Duration retrasoParaIntento(int intento) {
    assert(intento >= 1, 'los intentos se cuentan desde 1');
    final exponente = (intento - 1).clamp(0, 30);
    final ms = retrasoBase.inMilliseconds * (1 << exponente);
    if (ms >= retrasoMaximo.inMilliseconds) return retrasoMaximo;
    return Duration(milliseconds: ms);
  }

  /// Reports a stall / network failure. Schedules [alReintentar] after the
  /// backoff delay only when the user still intends to play and retries
  /// remain; otherwise returns [DecisionReconexion.ignorar] or
  /// [DecisionReconexion.agotado] without scheduling anything.
  DecisionReconexion registrarFallo({
    required bool intencionReproducir,
    required void Function() alReintentar,
  }) {
    if (!intencionReproducir) {
      cancelar();
      return DecisionReconexion.ignorar;
    }
    if (_intentos >= maxReintentos) {
      cancelar();
      return DecisionReconexion.agotado;
    }
    _intentos++;
    _temporizador?.cancel();
    _temporizador = _crearTemporizador(
      retrasoParaIntento(_intentos),
      alReintentar,
    );
    return DecisionReconexion.reintentar;
  }

  /// Successful playback (or a fresh user play): reset the retry counter and
  /// drop any pending retry, so the next stall starts the backoff over.
  void restablecer() {
    _intentos = 0;
    cancelar();
  }

  /// Cancels any pending retry without resetting the counter (user stop or
  /// pause during the backoff window).
  void cancelar() {
    _temporizador?.cancel();
    _temporizador = null;
  }
}