import 'dart:convert';

import '../modelos/emisora.dart';
import '../modelos/grupo_favoritos.dart';
import '../modelos/preset_ecualizador.dart';

/// Owns the backup (export/import) JSON serialization (S4-R4).
///
/// v3 extends v2 with `presetsPorDispositivo`, `presetsMatriz`, and
/// `eqMultiDeviceEnabled`. v4 extends v3 with `ecualizadorActivo` (the
/// equalizer's global ON/OFF toggle). When the version-N extension
/// parameters are all omitted the export stays at the lower version for
/// backward compat with older app builds. State APPLICATION (writing
/// favorites, EQ, alarms back into the app) stays in
/// `EstadoRadio.importarConfig` — this service only owns serialization,
/// parsing and the envelope shape.
class ServicioExportImport {
  const ServicioExportImport();

  /// Current backup schema version (v4 — equalizer on/off toggle).
  static const int versionActual = 4;

  /// v3 version constant (multi-device EQ) kept for clarity.
  static const int versionV3 = 3;

  /// Legacy v2 version constant kept for clarity.
  static const int versionV2 = 2;

  /// Builds the export envelope.
  ///
  /// When [presetsPorDispositivo] or [presetsMatriz] or
  /// [eqMultiDeviceEnabled] are provided (non-null), at least [versionV3] (3)
  /// is written. When [ecualizadorActivo] is ALSO provided (non-null),
  /// [versionActual] (4) is written. Omitting all of them behaves identically
  /// to the original v2 format (version key stays 2) so old backups keep
  /// round-tripping without version bumps.
  ///
  /// The `alarmas` block is the RAW JSON map persisted by ServicioAlarmas
  /// and passes through untouched (no re-parsing here).
  Map<String, dynamic> construirExportacion({
    required List<GrupoFavoritos> gruposFavoritos,
    required List<Emisora> favoritos,
    required List<Emisora> emisorasCustom,
    required PresetEcualizador presetPrincipal,
    required Map<String, PresetEcualizador> presetsPorEmisora,
    required Map<String, dynamic>? alarmas,
    required String? emisoraPreferidaUuid,
    required String ordenListas,
    required List<int> timerSuenoPresetsSegundos,
    DateTime? exportadoEn,
    // v3 extensions — omitting these produces a v2-compatible export.
    Map<String, PresetEcualizador>? presetsPorDispositivo,
    Map<String, PresetEcualizador>? presetsMatriz,
    bool? eqMultiDeviceEnabled,
    // v4 extension — the equalizer's global ON/OFF toggle. Omitting it
    // produces a v3 (or v2)-compatible export.
    bool? ecualizadorActivo,
  }) {
    final tieneExtensionesV3 =
        presetsPorDispositivo != null ||
        presetsMatriz != null ||
        eqMultiDeviceEnabled != null;
    final tieneExtensionV4 = ecualizadorActivo != null;

    final int version;
    if (tieneExtensionV4) {
      version = versionActual;
    } else if (tieneExtensionesV3) {
      version = versionV3;
    } else {
      version = versionV2;
    }

    final envelope = <String, dynamic>{
      'version': version,
      'exportedAt': (exportadoEn ?? DateTime.now()).toIso8601String(),
      // Favorites + groups (preserves grupo_id assignments per station).
      // The protected "sin asignar" group is implicit and never exported.
      'gruposFavoritos':
          gruposFavoritos
              .where((g) => !g.esSinAsignar)
              .map((g) => g.toMap())
              .toList(),
      'favoritos': favoritos.map((e) => e.toMap()).toList(),
      // Custom stations.
      'emisorasCustom': emisorasCustom.map((e) => e.toMap()).toList(),
      // Equalizer (base fields — present in all versions).
      'presetPrincipalEcualizador': presetPrincipal.toJson(),
      'presetsEcualizador': presetsPorEmisora.map(
        (uuid, preset) => MapEntry(uuid, preset.toJson()),
      ),
      // Full alarm block (alarms + vacations + exceptions) — raw passthrough.
      'alarmas': alarmas,
      // User preferences.
      'emisoraPreferidaUuid': emisoraPreferidaUuid,
      'ordenListas': ordenListas,
      'timerSuenoPresetsSegundos': timerSuenoPresetsSegundos,
    };

    // v3 extensions: only written when explicitly provided.
    if (tieneExtensionesV3) {
      envelope['presetsPorDispositivo'] = (presetsPorDispositivo ?? {}).map(
        (deviceId, preset) => MapEntry(deviceId, preset.toJson()),
      );
      envelope['presetsMatriz'] = (presetsMatriz ?? {}).map(
        (clave, preset) => MapEntry(clave, preset.toJson()),
      );
      envelope['eqMultiDeviceEnabled'] = eqMultiDeviceEnabled ?? false;
    }

    // v4 extension: only written when explicitly provided.
    if (tieneExtensionV4) {
      envelope['ecualizadorActivo'] = ecualizadorActivo;
    }

    return envelope;
  }

  /// Serializes an export envelope to pretty-printed JSON (same formatting
  /// the legacy export shared as a file).
  String exportar(Map<String, dynamic> config) =>
      const JsonEncoder.withIndent('  ').convert(config);

  /// Parses a backup JSON string. Returns `null` on malformed input or when
  /// the document is not a JSON object — graceful, never throws (S4-R4).
  Map<String, dynamic>? importar(String raw) {
    try {
      final decoded = jsonDecode(raw);
      if (decoded is! Map) return null;
      return Map<String, dynamic>.from(decoded);
    } on FormatException {
      return null;
    }
  }
}