import 'dart:collection';

import 'package:flutter/services.dart';
import 'package:shared_preferences/shared_preferences.dart';

import '../modelos/pista_local.dart';

/// SharedPreferences key for the persisted local-music root tree URI
/// (Design "Data Flow"). Read/written exclusively by
/// [FuenteMusicaLocalAutoImpl].
const _keyUriCarpetaLocal = 'musica_local_uri';

/// Dart-side re-validation of a native-reported MIME type (Design
/// "Interfaces / Contracts" — native already filters to `audio/*`; this is
/// defense-in-depth, not the only gate). Requires a non-blank `audio/*`
/// [mime] AND a non-blank [nombre] — a blank filename is never a valid
/// audio entry regardless of MIME.
bool esArchivoAudio(String? mime, String? nombre) {
  final mimeRecortado = mime?.trim();
  final nombreRecortado = nombre?.trim();
  if (mimeRecortado == null || mimeRecortado.isEmpty) return false;
  if (nombreRecortado == null || nombreRecortado.isEmpty) return false;
  return mimeRecortado.toLowerCase().startsWith('audio/');
}

/// Pure-Dart, SAF-URI-parsing derivation of a human-readable folder name
/// (Design ADR-4) — NO native round-trip. SAF tree URIs are
/// `content://<authority>/tree/<encoded-documentId>`; `Uri.pathSegments`
/// already percent-decodes each segment, so the segment right after `tree`
/// is the decoded documentId (e.g. `primary:Music/MyFolder`,
/// `1A2B-3C4D:Music`). The trailing readable part of that documentId is
/// extracted: everything after the last `/` when present, else everything
/// after the last `:`, trimmed. An unparseable [treeUri], a missing/empty
/// `tree` segment, or an empty-after-trim result all fall back to
/// [nombreGenerico] — this function NEVER returns the raw `content://` URI
/// and NEVER returns an empty string.
///
/// [nombreGenerico] is the caller-supplied fallback text (Design ADR-4/ADR-5
/// — genuine phone UI, localized via `AppLocalizations.localMusicFolderGenericName`
/// at the call site in `pantalla_ajustes.dart`). Taking it as a plain
/// `String` parameter — rather than a `BuildContext`/`AppLocalizations`
/// dependency — keeps this function pure and unit-testable without a
/// widget tree, mirroring `pantalla_reproductor.dart`'s
/// `_formatearDuracion(AppLocalizations l10n, ...)` precedent, minus the
/// Flutter-generated-class coupling.
String nombreCarpetaDesdeUri(String treeUri, {required String nombreGenerico}) {
  final uri = Uri.tryParse(treeUri);
  if (uri == null) return nombreGenerico;

  final segmentos = uri.pathSegments;
  final indiceTree = segmentos.indexOf('tree');
  if (indiceTree == -1 || indiceTree + 1 >= segmentos.length) {
    return nombreGenerico;
  }
  final documentId = segmentos[indiceTree + 1];
  if (documentId.isEmpty) return nombreGenerico;

  final String segmento;
  final ultimaBarra = documentId.lastIndexOf('/');
  if (ultimaBarra >= 0) {
    segmento = documentId.substring(ultimaBarra + 1);
  } else {
    final ultimosDosPuntos = documentId.lastIndexOf(':');
    segmento =
        ultimosDosPuntos >= 0
            ? documentId.substring(ultimosDosPuntos + 1)
            : documentId;
  }

  final recortado = segmento.trim();
  return recortado.isEmpty ? nombreGenerico : recortado;
}

/// Browse-source abstraction for the local-music branch of the Android Auto
/// tree (Design "Interfaces / Contracts"), mirroring [FuenteEmisorasAuto]'s
/// (`navegacion_auto.dart`) cold-start-safe, never-throws contract. Kept as
/// a separate interface from [FuenteEmisorasAuto] — local music is its own
/// browse domain, not a station source.
abstract class FuenteMusicaLocalAuto {
  /// Whether a local-music root folder is picked AND its permission is
  /// still valid. Never throws — a revoked/never-granted permission
  /// degrades to `false` (Spec "Permission revoked or never granted").
  Future<bool> hayCarpetaConfigurada();

  /// Immediate children of [documentId] (`''` = the tree root itself), one
  /// SAF level deep (Design "Lazy per-folder enumeration, never an eager
  /// tree dump"). Never throws — any failure degrades to `[]` (Spec
  /// "Permission revoked or never granted", "Browse requested before app
  /// state is loaded").
  Future<List<NodoLocal>> hijos(String documentId);

  /// Resolves a leaf [documentId] to its playable `content://` URI, or
  /// `null` if it cannot be resolved (stale id, revoked permission). Never
  /// throws.
  Future<String?> uriContenidoDePista(String documentId);

  /// Batched embedded-metadata resolution (Design "Interfaces / Contracts",
  /// Phase 2) for [documentIds] — one map entry per requested id that was
  /// resolvable. Never throws: an empty [documentIds], a missing root
  /// folder, or any channel failure degrades to `{}`. A native row with a
  /// null/missing field yields a [MetadatosPista] with that field `null`,
  /// never a crash or a dropped entry.
  Future<Map<String, MetadatosPista>> metadatosDe(List<String> documentIds);
}

/// In-memory, session-scoped LRU cache of resolved [MetadatosPista] (Design
/// ADR-2): a flat `LinkedHashMap`, bounded to [_capacidad] entries,
/// LRU-by-ACCESS (not just insertion) — [obtener] on a hit re-inserts the
/// entry to refresh its recency, so a hot re-visited entry survives even
/// under eviction pressure. Deliberately NOT folder-scoped: paging a large
/// folder must not evict an earlier page's cached metadata (Design ADR-2's
/// rationale — 256 ≈ 5 pages of 50). In-memory only; dies with the process,
/// so there is no persistence-staleness concern.
class CacheMetadatosSesion {
  static const _capacidad = 256;

  final LinkedHashMap<String, MetadatosPista> _entradas =
      LinkedHashMap<String, MetadatosPista>();

  /// Returns the cached [MetadatosPista] for [documentId], or `null` on a
  /// miss. A hit refreshes [documentId]'s recency (moves it to the
  /// most-recently-used end) so it survives longer under LRU eviction.
  MetadatosPista? obtener(String documentId) {
    final valor = _entradas.remove(documentId);
    if (valor == null) return null;
    _entradas[documentId] = valor;
    return valor;
  }

  /// Stores [metadatos] under [documentId], refreshing its recency.
  /// Evicts the least-recently-used entry (the current first key) when
  /// insertion would exceed [_capacidad].
  void guardar(String documentId, MetadatosPista metadatos) {
    _entradas.remove(documentId);
    _entradas[documentId] = metadatos;
    if (_entradas.length > _capacidad) {
      _entradas.remove(_entradas.keys.first);
    }
  }
}

/// Channel-backed [FuenteMusicaLocalAuto] implementation (Design "Hand-rolled
/// SAF channel, not `shared_storage`"): calls the existing
/// `pluriwave/file_actions` `MethodChannel`'s native SAF methods
/// (`MainActivity.kt`, static-review-only) and the picker/persistence side
/// used by the phone settings UI. Every channel call is wrapped in
/// try/catch so a revoked permission, a missing native method (older APK on
/// a mismatched build) or any other native-side failure degrades to an
/// empty/absent result instead of throwing — mirrors
/// `FuenteEmisorasAutoLocal`'s cold-start-safe shape
/// (`navegacion_auto.dart:421-471`).
class FuenteMusicaLocalAutoImpl implements FuenteMusicaLocalAuto {
  FuenteMusicaLocalAutoImpl({SharedPreferences? prefs}) : _prefs = prefs;

  static const MethodChannel _canal = MethodChannel('pluriwave/file_actions');

  final SharedPreferences? _prefs;

  /// Injected startup instance (S3-R4 convention, mirrors
  /// `ServicioEcualizador`'s DI pattern, `servicio_ecualizador.dart:37,54,57`
  /// — `getInstance()` is only a fallback for call sites that don't inject
  /// one, e.g. tests or a lazily-constructed settings-only instance).
  Future<SharedPreferences> _resolverPrefs() async =>
      _prefs ?? SharedPreferences.getInstance();

  Future<String?> _uriPersistida() async {
    final prefs = await _resolverPrefs();
    return prefs.getString(_keyUriCarpetaLocal);
  }

  /// Persists [treeUri] as the local-music root (Design "Data Flow" —
  /// settings write side). Exposed separately from [elegirCarpeta] so a
  /// caller that already has a URI (e.g. a future restore/import flow)
  /// doesn't need to re-invoke the native picker.
  Future<void> guardarCarpeta(String treeUri) async {
    final prefs = await _resolverPrefs();
    await prefs.setString(_keyUriCarpetaLocal, treeUri);
  }

  /// The currently persisted root URI, or `null` if none was ever picked.
  /// Used by the settings UI to render the "current folder" state.
  Future<String?> carpetaActual() => _uriPersistida();

  /// Launches the native SAF folder picker (`pickMusicFolder`) and persists
  /// the result on success (Spec "User picks a local music root folder").
  /// Returns the picked tree URI, or `null` if the user cancelled or the
  /// native call failed — never throws.
  Future<String?> elegirCarpeta() async {
    try {
      final uri = await _canal.invokeMethod<String>('pickMusicFolder');
      if (uri == null || uri.isEmpty) return null;
      await guardarCarpeta(uri);
      return uri;
    } catch (_) {
      return null;
    }
  }

  @override
  Future<bool> hayCarpetaConfigurada() async {
    try {
      final uri = await _uriPersistida();
      if (uri == null || uri.isEmpty) return false;
      final valido = await _canal.invokeMethod<bool>('hasPersistedPermission', {
        'treeUri': uri,
      });
      return valido ?? false;
    } catch (_) {
      // Cold-start / revoked-permission safety (Spec "Permission revoked or
      // never granted"): never throw, degrade to "not configured".
      return false;
    }
  }

  @override
  Future<List<NodoLocal>> hijos(String documentId) async {
    try {
      final uri = await _uriPersistida();
      if (uri == null || uri.isEmpty) return const [];
      final crudos = await _canal.invokeMethod<List<Object?>>(
        'listAudioChildren',
        {'treeUri': uri, 'parentDocumentId': documentId},
      );
      if (crudos == null) return const [];
      return crudos
          .whereType<Map<Object?, Object?>>()
          .map(_nodoDesdeMapa)
          .whereType<NodoLocal>()
          .toList();
    } catch (_) {
      // Cold-start / revoked-permission safety (Spec "Permission revoked or
      // never granted", "Browse requested before app state is loaded").
      return const [];
    }
  }

  @override
  Future<String?> uriContenidoDePista(String documentId) async {
    try {
      final uri = await _uriPersistida();
      if (uri == null || uri.isEmpty) return null;
      return await _canal.invokeMethod<String>('resolvePlayableUri', {
        'treeUri': uri,
        'documentId': documentId,
      });
    } catch (_) {
      return null;
    }
  }

  @override
  Future<Map<String, MetadatosPista>> metadatosDe(
    List<String> documentIds,
  ) async {
    if (documentIds.isEmpty) return const {};
    try {
      final uri = await _uriPersistida();
      if (uri == null || uri.isEmpty) return const {};
      final crudos = await _canal.invokeMethod<List<Object?>>(
        'readAudioMetadataBatch',
        {'treeUri': uri, 'documentIds': documentIds},
      );
      if (crudos == null) return const {};
      final resultado = <String, MetadatosPista>{};
      for (final fila in crudos.whereType<Map<Object?, Object?>>()) {
        final documentId = fila['documentId'] as String?;
        if (documentId == null || documentId.isEmpty) continue;
        resultado[documentId] = MetadatosPista(
          titulo: fila['titulo'] as String?,
          artista: fila['artista'] as String?,
          artUri: fila['artUri'] as String?,
          bitrate: (fila['bitrate'] as num?)?.toInt(),
          sampleRate: (fila['sampleRate'] as num?)?.toInt(),
        );
      }
      return resultado;
    } catch (_) {
      // Cold-start / revoked-permission / channel-error safety (Design
      // "Interfaces / Contracts" — metadatosDe never throws).
      return const {};
    }
  }

  /// Maps a raw `listAudioChildren` row to a [NodoLocal], re-validating
  /// audio files via [esArchivoAudio] (Design "Interfaces / Contracts" —
  /// defense-in-depth on top of the native `audio/*` filter). Returns `null`
  /// for a malformed row (missing id/name) or a file whose MIME fails
  /// re-validation, so [hijos] can silently drop it instead of surfacing a
  /// broken entry.
  NodoLocal? _nodoDesdeMapa(Map<Object?, Object?> mapa) {
    final documentId = mapa['documentId'] as String?;
    final nombre = mapa['nombre'] as String?;
    final esDirectorio = mapa['esDirectorio'] as bool? ?? false;
    if (documentId == null || documentId.isEmpty) return null;
    if (nombre == null) return null;
    if (!esDirectorio) {
      final mime = mapa['mime'] as String?;
      if (!esArchivoAudio(mime, nombre)) return null;
    }
    return NodoLocal(
      documentId: documentId,
      nombre: nombre,
      esDirectorio: esDirectorio,
    );
  }
}