import 'dart:convert';

import 'package:shared_preferences/shared_preferences.dart';

import '../modelos/preset_ecualizador.dart';
import 'persistencia_tolerante.dart';

/// Persistence for USER-NAMED custom EQ presets (design ADR-5 hazard box,
/// `eq-custom-presets` spec — "Custom Preset Save").
///
/// Deliberately its OWN file and OWN SharedPreferences key
/// (`eq_custom_presets_v1`), never folded into [ServicioEcualizador]: that
/// file has an empty-`git diff` success criterion for this change, so
/// nothing custom-preset-related may be added there. A custom preset is
/// just a [PresetEcualizador] with a user-supplied `nombre` — the model
/// itself needs no change (`toJson`/`desdeJson` already exist).
class ServicioPresetsPersonalizados {
  ServicioPresetsPersonalizados({SharedPreferences? prefs}) : _prefs = prefs;

  static const _keyPresetsPersonalizados = 'eq_custom_presets_v1';

  final SharedPreferences? _prefs;

  Future<SharedPreferences> _resolverPrefs() async =>
      _prefs ?? SharedPreferences.getInstance();

  /// Returns every saved custom preset, in save order.
  Future<List<PresetEcualizador>> listar() async {
    final prefs = await _resolverPrefs();
    return _leer(prefs);
  }

  /// Saves [preset] under its own name. A preset already saved under the
  /// same name is replaced (last write wins) rather than duplicated.
  Future<void> guardar(PresetEcualizador preset) async {
    final prefs = await _resolverPrefs();
    final actuales =
        _leer(prefs)
          ..removeWhere((p) => p.nombre == preset.nombre)
          ..add(preset);
    await _guardarTodos(prefs, actuales);
  }

  /// Removes the custom preset named [nombre], if present. A safe no-op
  /// when no preset with that name exists.
  Future<void> eliminar(String nombre) async {
    final prefs = await _resolverPrefs();
    final actuales = _leer(prefs)..removeWhere((p) => p.nombre == nombre);
    await _guardarTodos(prefs, actuales);
  }

  /// Reads the persisted list with per-entry tolerance
  /// (persistence-resilience D1/D6, same shared helper `ServicioEcualizador`
  /// uses): an entry that fails to parse is skipped and logged, its
  /// siblings survive. A top-level decode failure degrades to an empty
  /// list (also logged) — custom presets are explicit-only user writes and
  /// trivially re-creatable, so there is no flag/quarantine here, matching
  /// `ServicioEcualizador`'s own documented D6 asymmetry vs. Alarms/Stations.
  List<PresetEcualizador> _leer(SharedPreferences prefs) {
    final raw = prefs.getString(_keyPresetsPersonalizados);
    if (raw == null || raw.isEmpty) return [];
    try {
      final data = jsonDecode(raw) as List<dynamic>;
      final resultado = parseListaTolerante<PresetEcualizador>(
        data,
        (entrada) => PresetEcualizador.desdeJson(entrada),
        subsistema: 'presets_personalizados',
        coleccion: _keyPresetsPersonalizados,
      );
      return resultado.validas;
    } catch (e) {
      registrarSaltoPersistencia(
        subsistema: 'presets_personalizados',
        detalle: _keyPresetsPersonalizados,
        razon: e.toString(),
      );
      return [];
    }
  }

  Future<void> _guardarTodos(
    SharedPreferences prefs,
    List<PresetEcualizador> presets,
  ) async {
    final serializado = presets.map((p) => p.toJson()).toList();
    await prefs.setString(_keyPresetsPersonalizados, jsonEncode(serializado));
  }
}