import 'dart:convert';
import 'dart:io';
import 'package:crypto/crypto.dart';
import 'package:flutter/foundation.dart';
import 'package:path_provider/path_provider.dart';
import 'package:path/path.dart' as path;

import '../media/media_item.dart';
import '../utils/app_logger.dart';
import '../utils/formatters.dart';
import 'settings_service.dart';

/// Thrown when the downloads storage layer cannot create or access a directory
/// (permission denied, quota exceeded, SAF permission revoked, etc.).
class DownloadStorageException implements Exception {
  final String message;
  final String path;
  final Object cause;

  DownloadStorageException(this.message, this.path, this.cause);

  @override
  String toString() => 'DownloadStorageException: $message (path: $path, cause: $cause)';
}

class DownloadStorageService {
  static DownloadStorageService? _instance;
  static DownloadStorageService get instance => _instance ??= DownloadStorageService._();
  DownloadStorageService._();

  /// Drop the cached singleton so the next [instance] call returns a fresh
  /// service. Test-only.
  @visibleForTesting
  static void resetForTesting() {
    _instance = null;
  }

  Directory? _baseDownloadsDir;
  String? _artworkDirectoryPath;

  SettingsService? _settingsService;
  String? _customDownloadPath;
  String _customPathType = 'file';

  bool get isUsingSaf => Platform.isAndroid && _customPathType == 'saf' && _customDownloadPath != null;

  String? get safBaseUri => isUsingSaf ? _customDownloadPath : null;

  String? get artworkDirectoryPath => _artworkDirectoryPath;

  Future<void> initialize(SettingsService settingsService) async {
    _settingsService = settingsService;
    _customDownloadPath = settingsService.read(SettingsService.customDownloadPath);
    _customPathType = settingsService.read(SettingsService.customDownloadPathType) ?? 'file';
    _baseDownloadsDir = null;
    _artworkDirectoryPath = null;

    await getArtworkDirectory();
  }

  Future<void> refreshCustomPath() async {
    if (_settingsService != null) {
      _customDownloadPath = _settingsService!.read(SettingsService.customDownloadPath);
      _customPathType = _settingsService!.read(SettingsService.customDownloadPathType) ?? 'file';
      _baseDownloadsDir = null;
      _artworkDirectoryPath = null;
      await getArtworkDirectory();
    }
  }

  /// Get the base app directory for storing data.
  /// Uses ApplicationDocumentsDirectory on mobile, ApplicationSupportDirectory on desktop.
  Future<Directory> _getBaseAppDir() {
    if (Platform.isAndroid || Platform.isIOS) {
      return getApplicationDocumentsDirectory();
    }
    return getApplicationSupportDirectory();
  }

  /// Format episode filename base: S{XX}E{XX} - {Title}
  String _formatEpisodeFileName(MediaItem episode) {
    final season = padNumber(episode.parentIndex ?? 0, 2);
    final ep = padNumber(episode.index ?? 0, 2);
    final episodeName = _sanitizeFileName(episode.title!);
    return 'S${season}E$ep - $episodeName';
  }

  bool isUsingCustomPath() => _customDownloadPath != null;

  Future<String> getCurrentDownloadPathDisplay() async {
    if (_customDownloadPath != null) {
      return _customDownloadPath!;
    }
    final dir = await getDownloadsDirectory();
    return dir.path;
  }

  Future<bool> isDirectoryWritable(Directory dir) async {
    try {
      if (!await dir.exists()) {
        await dir.create(recursive: true);
      }
      // Test write access with a temp file
      final testFile = File(path.join(dir.path, '.write_test_${DateTime.now().millisecondsSinceEpoch}'));
      await testFile.writeAsString('test');
      await testFile.delete();
      return true;
    } catch (e) {
      return false;
    }
  }

  Future<Directory> getDownloadsDirectory() async {
    if (_baseDownloadsDir != null) return _baseDownloadsDir!;

    if (_customDownloadPath != null && _customPathType == 'file') {
      final customDir = Directory(_customDownloadPath!);
      if (await isDirectoryWritable(customDir)) {
        _baseDownloadsDir = customDir;
        return _baseDownloadsDir!;
      }
      // Fall through to default if custom path is not writable
    }

    final baseDir = await _getBaseAppDir();
    _baseDownloadsDir = await _ensureDirectoryExists(Directory(path.join(baseDir.path, 'downloads')));
    return _baseDownloadsDir!;
  }

  /// Get centralized artwork directory for offline artwork caching
  /// This directory stores artwork files with hashed filenames for deduplication
  Future<Directory> getArtworkDirectory() async {
    // If custom download path is set, put artwork alongside downloads
    if (_customDownloadPath != null && _customPathType == 'file') {
      final customDir = Directory(_customDownloadPath!);
      final parent = customDir.parent;
      final artworkDir = Directory(path.join(parent.path, 'artwork'));
      try {
        // Validate writeability for custom artwork path
        if (await isDirectoryWritable(artworkDir)) {
          _artworkDirectoryPath = artworkDir.path;
          return artworkDir;
        }
      } catch (e) {
        // Fall through to default if we can't create artwork dir
      }
    }

    // Default: Get the app base directory directly (not downloads directory)
    final baseDir = await _getBaseAppDir();
    final artworkDir = await _ensureDirectoryExists(Directory(path.join(baseDir.path, 'artwork')));
    // Cache the path for synchronous access
    _artworkDirectoryPath = artworkDir.path;
    return artworkDir;
  }

  /// Get artwork file path from a server-side thumb path (synchronous, requires initialization).
  /// Works for any backend — the thumb path is hashed alongside the serverId,
  /// so Plex `/library/metadata/.../thumb` and Jellyfin
  /// `/Items/.../Images/Primary` paths both round-trip cleanly.
  /// Returns path to cached artwork file using hash of the thumb URL, or null if not initialized.
  /// Example: artwork/a1b2c3d4e5f6.jpg
  String? getArtworkPathSync(String serverId, String thumbPath) {
    if (_artworkDirectoryPath == null) return null;
    final hash = _hashArtworkPath(serverId, thumbPath);
    return path.join(_artworkDirectoryPath!, '$hash.jpg');
  }

  /// Get artwork file path from a server-side thumb path (async version).
  /// Backend-neutral — see [getArtworkPathSync] for details.
  Future<String> getArtworkPathFromThumb(String serverId, String thumbPath) async {
    final artworkDir = await getArtworkDirectory();
    final hash = _hashArtworkPath(serverId, thumbPath);
    return path.join(artworkDir.path, '$hash.jpg');
  }

  Future<bool> artworkExists(String serverId, String thumbPath) async {
    final artworkPath = await getArtworkPathFromThumb(serverId, thumbPath);
    return File(artworkPath).exists();
  }

  /// Hash artwork path for filename using MD5 for stability across app restarts
  String _hashArtworkPath(String serverId, String thumbPath) {
    final combined = '$serverId:$thumbPath';
    return md5.convert(utf8.encode(combined)).toString();
  }

  Future<Directory> getMediaDirectory(String serverId, String ratingKey) async {
    final baseDir = await getDownloadsDirectory();
    return _ensureDirectoryExists(Directory(path.join(baseDir.path, serverId, ratingKey)));
  }

  Future<String> getVideoFilePath(String serverId, String ratingKey, String extension) async {
    final mediaDir = await getMediaDirectory(serverId, ratingKey);
    return path.join(mediaDir.path, 'video.$extension');
  }

  Future<Directory> getSubtitlesDirectory(String serverId, String ratingKey) async {
    final mediaDir = await getMediaDirectory(serverId, ratingKey);
    final subtitlesDir = Directory(path.join(mediaDir.path, 'subtitles'));
    if (!await subtitlesDir.exists()) {
      await subtitlesDir.create(recursive: true);
    }
    return subtitlesDir;
  }

  Future<String> getSubtitlePath(String serverId, String ratingKey, int trackId, String extension) async {
    final subtitlesDir = await getSubtitlesDirectory(serverId, ratingKey);
    return path.join(subtitlesDir.path, '$trackId.$extension');
  }

  /// Sanitize a filename by removing invalid filesystem characters
  String _sanitizeFileName(String name) {
    // Remove invalid filesystem characters: < > : " / \ | ? *
    // Also remove leading/trailing whitespace and dots
    return name
        .replaceAll(RegExp(r'[<>:"/\\|?*]'), '')
        .replaceAll(RegExp(r'^\.+|\.+$'), '')
        .replaceAll('.', '_')
        .trim();
  }

  /// Ensure a directory exists, creating it if necessary.
  /// `Directory.create(recursive: true)` is idempotent — it no-ops if the
  /// directory already exists.
  Future<Directory> _ensureDirectoryExists(Directory dir) async {
    try {
      await dir.create(recursive: true);
      return dir;
    } catch (e, st) {
      appLogger.e('Failed to ensure directory exists: ${dir.path}', error: e, stackTrace: st);
      throw DownloadStorageException('Cannot create directory', dir.path, e);
    }
  }

  /// Format a media title with optional year: "Title (YYYY)" or "Title"
  String _formatTitleWithYear(String title, int? year) {
    final sanitized = _sanitizeFileName(title);
    return year != null ? '$sanitized ($year)' : sanitized;
  }

  String _getMovieFolderName(MediaItem movie) {
    return _formatTitleWithYear(movie.title!, movie.year);
  }

  /// Get the folder name for a TV show: "Show Name (YYYY)"
  /// [showYear]: Pass explicitly for episodes (episode.year may differ from show's year)
  String _getShowFolderName(MediaItem metadata, {int? showYear}) {
    final title = metadata.grandparentTitle ?? metadata.title!;
    final year = showYear ?? metadata.year;
    return _formatTitleWithYear(title, year);
  }

  Future<Directory> getMovieDirectory(MediaItem movie) async {
    final baseDir = await getDownloadsDirectory();
    final movieFolder = _getMovieFolderName(movie);
    return _ensureDirectoryExists(Directory(path.join(baseDir.path, 'Movies', movieFolder)));
  }

  /// Get movie video file path: .../Movie Name (YYYY)/Movie Name (YYYY).{ext}
  Future<String> getMovieVideoPath(MediaItem movie, String extension) async {
    final movieDir = await getMovieDirectory(movie);
    final fileName = _getMovieFolderName(movie);
    return path.join(movieDir.path, '$fileName.$extension');
  }

  /// Get show directory: downloads/TV Shows/{Show Name} ({Year})/
  /// [showYear]: Pass the show's premiere year explicitly (for episodes, the episode's
  /// year may differ from the show's year). If not provided, uses metadata.year.
  Future<Directory> getShowDirectory(MediaItem metadata, {int? showYear}) async {
    final baseDir = await getDownloadsDirectory();
    final showFolder = _getShowFolderName(metadata, showYear: showYear);
    return _ensureDirectoryExists(Directory(path.join(baseDir.path, 'TV Shows', showFolder)));
  }

  /// Get season directory: .../TV Shows/{Show}/Season {XX}/
  /// [showYear]: Pass the show's premiere year (not episode or season year)
  Future<Directory> getSeasonDirectory(MediaItem metadata, {int? showYear}) async {
    final showDir = await getShowDirectory(metadata, showYear: showYear);
    final seasonNum = padNumber(metadata.parentIndex ?? 0, 2);
    return _ensureDirectoryExists(Directory(path.join(showDir.path, 'Season $seasonNum')));
  }

  /// Get base path info for episode files (season directory path and formatted filename).
  /// [showYear]: Pass the show's premiere year (not episode year)
  Future<({String seasonDirPath, String fileName})> _getEpisodeBasePath(MediaItem episode, {int? showYear}) async {
    final seasonDir = await getSeasonDirectory(episode, showYear: showYear);
    final fileName = _formatEpisodeFileName(episode);
    return (seasonDirPath: seasonDir.path, fileName: fileName);
  }

  /// Get episode video file path: .../Season XX/S{XX}E{XX} - {Title}.{ext}
  /// [showYear]: Pass the show's premiere year (not episode year)
  Future<String> getEpisodeVideoPath(MediaItem episode, String extension, {int? showYear}) async {
    final base = await _getEpisodeBasePath(episode, showYear: showYear);
    return path.join(base.seasonDirPath, '${base.fileName}.$extension');
  }

  /// Get episode thumbnail path: .../Season XX/S{XX}E{XX} - {Title}.jpg
  /// [showYear]: Pass the show's premiere year (not episode year)
  Future<String> getEpisodeThumbnailPath(MediaItem episode, {int? showYear}) async {
    final base = await _getEpisodeBasePath(episode, showYear: showYear);
    return path.join(base.seasonDirPath, '${base.fileName}.jpg');
  }

  /// Get subtitles directory for episode: .../Season XX/S{XX}E{XX} - {Title}_subs/
  /// [showYear]: Pass the show's premiere year (not episode year)
  Future<Directory> getEpisodeSubtitlesDirectory(MediaItem episode, {int? showYear}) async {
    final base = await _getEpisodeBasePath(episode, showYear: showYear);
    return _ensureDirectoryExists(Directory(path.join(base.seasonDirPath, '${base.fileName}_subs')));
  }

  /// [showYear]: Pass the show's premiere year (not episode year)
  Future<String> getEpisodeSubtitlePath(MediaItem episode, int trackId, String extension, {int? showYear}) async {
    final subsDir = await getEpisodeSubtitlesDirectory(episode, showYear: showYear);
    return path.join(subsDir.path, '$trackId.$extension');
  }

  Future<Directory> getMovieSubtitlesDirectory(MediaItem movie) async {
    final movieDir = await getMovieDirectory(movie);
    final baseName = _getMovieFolderName(movie);
    return _ensureDirectoryExists(Directory(path.join(movieDir.path, '${baseName}_subs')));
  }

  Future<String> getMovieSubtitlePath(MediaItem movie, int trackId, String extension) async {
    final subsDir = await getMovieSubtitlesDirectory(movie);
    return path.join(subsDir.path, '$trackId.$extension');
  }

  /// Convert an absolute file path to a relative path (for database storage)
  /// This ensures paths remain valid across app reinstalls on iOS where
  /// the container UUID can change.
  /// Returns a path relative to the app's documents directory.
  Future<String> toRelativePath(String absolutePath) async {
    final baseDir = await _getBaseAppDir();

    // Strip the base directory prefix iteratively — background_downloader
    // recovery paths can contain the base dir doubled (e.g.
    // /data/.../app_flutter/data/.../app_flutter/downloads/...).
    var result = absolutePath;
    while (result.startsWith(baseDir.path)) {
      result = result.substring(baseDir.path.length);
      if (result.startsWith('/') || result.startsWith('\\')) {
        result = result.substring(1);
      }
    }
    if (result != absolutePath) return result;

    return absolutePath;
  }

  /// Convert a relative file path to an absolute path (for file operations)
  /// Reconstructs the full path using the current app documents directory.
  Future<String> toAbsolutePath(String relativePath) async {
    if (path.isAbsolute(relativePath)) {
      return relativePath;
    }

    final baseDir = await _getBaseAppDir();
    return path.join(baseDir.path, relativePath);
  }

  /// Convert a potentially absolute path (from old database entries) to absolute
  /// This handles both old absolute paths and new relative paths, including
  /// corrupted paths that contain nested base-dir fragments without a leading slash
  /// (e.g. "data/user/0/.../app_flutter/downloads/...").
  Future<String> ensureAbsolutePath(String storedPath) async {
    appLogger.d('ensureAbsolutePath: input="$storedPath", isAbsolute=${path.isAbsolute(storedPath)}');
    final baseDir = await _getBaseAppDir();
    final normalizedCandidates = <String>[];

    void addCandidate(String candidate) {
      if (candidate.isEmpty) return;
      final normalized = path.normalize(candidate);
      if (!normalizedCandidates.contains(normalized)) {
        normalizedCandidates.add(normalized);
      }
    }

    String trimLeadingSeparators(String value) => value.replaceFirst(RegExp(r'^[\\/]+'), '');

    if (path.isAbsolute(storedPath)) {
      // Keep the original absolute path first (covers valid custom download paths).
      addCandidate(storedPath);

      // Recover from doubled app base path corruption:
      // /data/.../app_flutter/data/.../app_flutter/downloads/...
      final firstBaseIndex = storedPath.indexOf(baseDir.path);
      if (firstBaseIndex != -1) {
        final secondBaseIndex = storedPath.indexOf(baseDir.path, firstBaseIndex + baseDir.path.length);
        if (secondBaseIndex != -1) {
          final tail = trimLeadingSeparators(storedPath.substring(secondBaseIndex + baseDir.path.length));
          addCandidate(path.join(baseDir.path, tail));
        }
      }

      // Recover from paths that contain downloads/ but wrong prefix.
      final downloadsIndex = storedPath.lastIndexOf('downloads/');
      if (downloadsIndex != -1) {
        final relativePart = storedPath.substring(downloadsIndex);
        addCandidate(await toAbsolutePath(relativePart));
      }
    } else {
      // Normal relative path.
      addCandidate(await toAbsolutePath(storedPath));

      // Recover from nested base-dir fragment without leading slash.
      final baseIndex = storedPath.indexOf(baseDir.path);
      if (baseIndex > 0) {
        final tail = trimLeadingSeparators(storedPath.substring(baseIndex + baseDir.path.length));
        addCandidate(path.join(baseDir.path, tail));
      }

      // Recover from nested fragment containing downloads/.
      final downloadsIndex = storedPath.lastIndexOf('downloads/');
      if (downloadsIndex >= 0) {
        addCandidate(await toAbsolutePath(storedPath.substring(downloadsIndex)));
      }
    }

    // Prefer the first candidate that exists on disk.
    for (final candidate in normalizedCandidates) {
      if (await File(candidate).exists()) {
        appLogger.d('ensureAbsolutePath: resolved="$candidate"');
        return candidate;
      }
    }

    // Fall back to the most conservative candidate if none currently exist.
    final fallback = normalizedCandidates.isNotEmpty ? normalizedCandidates.first : await toAbsolutePath(storedPath);
    appLogger.d('ensureAbsolutePath: resolved="$fallback" (fallback)');
    return fallback;
  }

  List<String> getMovieSafPathComponents(MediaItem movie) {
    return ['Movies', _getMovieFolderName(movie)];
  }

  List<String> getEpisodeSafPathComponents(MediaItem episode, {int? showYear}) {
    final showFolder = _getShowFolderName(episode, showYear: showYear);
    final seasonNum = padNumber(episode.parentIndex ?? 0, 2);
    return ['TV Shows', showFolder, 'Season $seasonNum'];
  }

  /// Get SAF path components for a show directory: ['TV Shows', {showFolder}]
  List<String> getShowSafPathComponents(MediaItem metadata, {int? showYear}) {
    return ['TV Shows', _getShowFolderName(metadata, showYear: showYear)];
  }

  /// Get SAF path components for a season directory when called with season metadata:
  /// ['TV Shows', {showFolder}, 'Season XX']. Uses season.index for the season number.
  List<String> getSeasonSafPathComponents(MediaItem season, {int? showYear}) {
    final showFolder = _getShowFolderName(season, showYear: showYear);
    final seasonNum = padNumber(season.index ?? 0, 2);
    return ['TV Shows', showFolder, 'Season $seasonNum'];
  }

  String getMovieSafFileName(MediaItem movie, String extension) {
    return '${_getMovieFolderName(movie)}.$extension';
  }

  String getEpisodeSafFileName(MediaItem episode, String extension) {
    final fileName = _formatEpisodeFileName(episode);
    return '$fileName.$extension';
  }

  /// Get the extension-less episode filename used for SAF lookups.
  String getEpisodeSafBaseName(MediaItem episode) => _formatEpisodeFileName(episode);

  bool isSafUri(String storedPath) {
    return storedPath.startsWith('content://');
  }

  /// Get a readable path for a stored path (handles both SAF URIs and file paths)
  /// For SAF URIs, returns the URI as-is (content:// URIs work with media players)
  /// For file paths, ensures the path is absolute
  Future<String> getReadablePath(String storedPath) async {
    if (isSafUri(storedPath)) {
      return storedPath;
    }
    return await ensureAbsolutePath(storedPath);
  }
}