import 'dart:convert';
import 'dart:io';
import 'dart:isolate';

import 'package:archive/archive_io.dart';
import 'package:path/path.dart' as p;
import 'package:path_provider/path_provider.dart';
import 'package:spotiflac_android/constants/app_info.dart';
import 'package:spotiflac_android/utils/logger.dart';

typedef BackupHistoryPageLoader =
    Future<List<Map<String, dynamic>>> Function(int limit, int offset);

/// Parsed contents of a backup file. ZIP backups keep large history and cover
/// payloads on disk until restore consumes them.
class BackupBundle {
  final int formatVersion;
  final String appVersion;
  final DateTime? createdAt;
  final Map<String, dynamic>? settings;
  final List<Map<String, dynamic>> history;
  final Map<String, dynamic> collections;
  final Map<String, dynamic> playlistCovers;
  final Map<String, dynamic> extensions;
  final bool hasHistory;
  final String? _historyNdjsonPath;
  final int? _historyCount;
  final String? _temporaryDirectoryPath;

  const BackupBundle({
    required this.formatVersion,
    required this.appVersion,
    required this.createdAt,
    required this.settings,
    required this.history,
    required this.collections,
    required this.playlistCovers,
    required this.extensions,
    this.hasHistory = true,
    String? historyNdjsonPath,
    int? historyCount,
    String? temporaryDirectoryPath,
  }) : _historyNdjsonPath = historyNdjsonPath,
       _historyCount = historyCount,
       _temporaryDirectoryPath = temporaryDirectoryPath;

  bool get hasSettings => settings != null && settings!.isNotEmpty;
  bool get hasCollections => collections.isNotEmpty;
  int get historyCount => _historyCount ?? history.length;

  Stream<Map<String, dynamic>> streamHistory() async* {
    if (_historyNdjsonPath == null) {
      yield* Stream.fromIterable(history);
      return;
    }
    await for (final line in File(
      _historyNdjsonPath,
    ).openRead().transform(utf8.decoder).transform(const LineSplitter())) {
      if (line.trim().isEmpty) continue;
      final decoded = jsonDecode(line);
      if (decoded is Map) yield Map<String, dynamic>.from(decoded);
    }
  }

  Future<void> cleanup() async {
    final path = _temporaryDirectoryPath;
    if (path == null || path.isEmpty) return;
    try {
      final directory = Directory(path);
      if (await directory.exists()) await directory.delete(recursive: true);
    } catch (_) {}
  }

  int _collectionListCount(String key) {
    final value = collections[key];
    return value is List ? value.length : 0;
  }

  int get likedCount => _collectionListCount('loved');
  int get wishlistCount => _collectionListCount('wishlist');
  int get playlistCount => _collectionListCount('playlists');
  int get favoriteArtistCount => _collectionListCount('favoriteArtists');

  int get extensionCount {
    final items = extensions['items'];
    return items is List ? items.length : 0;
  }

  bool get hasExtensions => extensionCount > 0;
  bool get isEmpty =>
      !hasSettings &&
      historyCount == 0 &&
      likedCount == 0 &&
      wishlistCount == 0 &&
      playlistCount == 0 &&
      favoriteArtistCount == 0 &&
      extensionCount == 0;
}

class BackupService {
  static final _log = AppLogger('BackupService');

  static const String magic = 'spotiflac-backup';
  // V3 permits omitted categories. Older readers reject it instead of treating
  // an omitted history as an empty history and clearing existing downloads.
  static const int formatVersion = 3;
  static const String fileExtension = 'sflb';
  static const int _historyPageSize = 500;
  static const int _maxMetadataBytes = 8 << 20;
  static const int _maxHistoryBytes = 512 << 20;
  static const int _maxCoverBytes = 20 << 20;
  static const int _maxAllCoversBytes = 256 << 20;

  static String encode(Map<String, dynamic> envelope) =>
      const JsonEncoder.withIndent('  ').convert(envelope);

  /// Legacy JSON envelope retained so backups from earlier releases and unit
  /// tests remain readable. New backups are written by [writeBackupArchive].
  static Map<String, dynamic> buildEnvelope({
    required Map<String, dynamic>? settings,
    required List<Map<String, dynamic>> history,
    required Map<String, dynamic> collections,
    required Map<String, dynamic> playlistCovers,
    required Map<String, dynamic> extensions,
  }) {
    return {
      'magic': magic,
      'format_version': 1,
      'app': 'SpotiFLAC Mobile',
      'app_version': AppInfo.displayVersion,
      'created_at': DateTime.now().toIso8601String(),
      'data': {
        'settings': settings,
        'history': history,
        'collections': collections,
        'playlist_covers': playlistCovers,
        'extensions': extensions,
      },
    };
  }

  static Future<File> writeBackupArchive({
    required Map<String, dynamic>? settings,
    required BackupHistoryPageLoader loadHistoryPage,
    required Map<String, dynamic> collections,
    required Map<String, Map<String, String>> playlistCoverFiles,
    required Map<String, dynamic> extensions,
    Directory? outputDirectory,
    Directory? temporaryDirectory,
    bool includeHistory = true,
  }) async {
    final output = await _newBackupFile(outputDirectory);
    final tempRoot = temporaryDirectory ?? await getTemporaryDirectory();
    final staging = await Directory(
      p.join(
        tempRoot.path,
        'spotiflac_backup_${DateTime.now().microsecondsSinceEpoch}',
      ),
    ).create(recursive: true);
    final historyFile = File(p.join(staging.path, 'history.ndjson'));
    final metadataFile = File(p.join(staging.path, 'metadata.json'));
    final partFile = File('${output.path}.part');

    try {
      var historyCount = 0;
      var offset = 0;
      final historySink = historyFile.openWrite();
      try {
        while (includeHistory) {
          final page = await loadHistoryPage(_historyPageSize, offset);
          for (final item in page) {
            historySink.writeln(jsonEncode(item));
          }
          await historySink.flush();
          historyCount += page.length;
          offset += page.length;
          if (page.length < _historyPageSize) break;
        }
        await historySink.flush();
      } finally {
        await historySink.close();
      }

      final coverManifest = <String, Map<String, String>>{};
      var coverIndex = 0;
      for (final entry in playlistCoverFiles.entries) {
        final sourcePath = entry.value['path'] ?? '';
        final source = File(sourcePath);
        if (sourcePath.isEmpty || !await source.exists()) continue;
        var ext = (entry.value['ext'] ?? p.extension(sourcePath)).toLowerCase();
        if (!RegExp(r'^\.[a-z0-9]{1,8}$').hasMatch(ext)) ext = '.jpg';
        final archiveName = 'covers/cover_${coverIndex++}$ext';
        coverManifest[entry.key] = {'ext': ext, 'file': archiveName};
      }

      final metadata = {
        'magic': magic,
        'format_version': formatVersion,
        'app': 'SpotiFLAC Mobile',
        'app_version': AppInfo.displayVersion,
        'created_at': DateTime.now().toIso8601String(),
        'history_count': historyCount,
        'data': {
          'settings': ?settings,
          if (collections.isNotEmpty) 'collections': collections,
          if (coverManifest.isNotEmpty) 'playlist_covers': coverManifest,
          if (extensions.isNotEmpty) 'extensions': extensions,
        },
      };
      await metadataFile.writeAsString(jsonEncode(metadata), flush: true);

      if (await partFile.exists()) await partFile.delete();
      final archiveFiles = <({String path, String name, bool store})>[
        (path: metadataFile.path, name: 'metadata.json', store: false),
        if (includeHistory)
          (path: historyFile.path, name: 'history.ndjson', store: false),
      ];
      for (final entry in coverManifest.entries) {
        final sourcePath = playlistCoverFiles[entry.key]?['path'];
        if (sourcePath == null) continue;
        archiveFiles.add((
          path: sourcePath,
          name: entry.value['file']!,
          store: true,
        ));
      }
      await _encodeArchiveInBackground(partFile.path, archiveFiles);
      if (await output.exists()) await output.delete();
      await partFile.rename(output.path);
      _log.i('Streaming backup written to ${output.path}');
      return output;
    } finally {
      try {
        if (await staging.exists()) await staging.delete(recursive: true);
      } catch (_) {}
      try {
        if (await partFile.exists()) await partFile.delete();
      } catch (_) {}
    }
  }

  // archive's file-backed encoder still performs compression and writes
  // synchronously. Pass only paths to the worker; database/plugin callbacks
  // and the paged history loader stay on their owning isolate.
  static Future<void> _encodeArchiveInBackground(
    String outputPath,
    List<({String path, String name, bool store})> files,
  ) => Isolate.run(() async {
    final encoder = ZipFileEncoder()..create(outputPath);
    try {
      for (final file in files) {
        await encoder.addFile(
          File(file.path),
          file.name,
          file.store ? ZipFileEncoder.store : null,
        );
      }
    } finally {
      await encoder.close();
    }
  });

  static Future<File> _newBackupFile([Directory? outputDirectory]) async {
    final dir = outputDirectory ?? await getApplicationDocumentsDirectory();
    final backupsDir =
        outputDirectory ?? Directory(p.join(dir.path, 'backups'));
    await backupsDir.create(recursive: true);
    final now = DateTime.now();
    String two(int value) => value.toString().padLeft(2, '0');
    final stamp =
        '${now.year}${two(now.month)}${two(now.day)}_'
        '${two(now.hour)}${two(now.minute)}${two(now.second)}';
    return File(
      p.join(backupsDir.path, 'spotiflac_mobile_backup_$stamp.$fileExtension'),
    );
  }

  /// Legacy JSON writer retained for compatibility with callers outside the
  /// settings UI. It no longer defines the default backup format.
  static Future<File> writeBackupFile(Map<String, dynamic> envelope) async {
    final output = await _newBackupFile();
    await output.writeAsString(encode(envelope), flush: true);
    return output;
  }

  static Future<BackupBundle?> parseFile(
    String path, {
    Directory? temporaryDirectory,
  }) async {
    final tempRoot = temporaryDirectory ?? await getTemporaryDirectory();
    final bundle = await _parseFileInBackground(path, tempRoot.path);
    if (bundle == null) {
      _log.w('Backup file could not be read: invalid or unsupported contents');
    }
    return bundle;
  }

  static Future<BackupBundle?> _parseFileInBackground(
    String path,
    String temporaryPath,
  ) => Isolate.run(() => _parseFile(path, temporaryPath));

  static Future<BackupBundle?> _parseFile(
    String path,
    String temporaryPath,
  ) async {
    final file = File(path);
    final header = await file
        .openRead(0, 4)
        .fold<List<int>>(<int>[], (bytes, chunk) => bytes..addAll(chunk));
    final isZip =
        header.length == 4 &&
        header[0] == 0x50 &&
        header[1] == 0x4b &&
        header[2] == 0x03 &&
        header[3] == 0x04;
    return isZip
        ? _parseArchive(file, temporaryDirectory: Directory(temporaryPath))
        : parse(await file.readAsString());
  }

  static Future<BackupBundle?> _parseArchive(
    File file, {
    required Directory temporaryDirectory,
  }) async {
    InputFileStream? input;
    Archive? archive;
    Directory? extractionDir;
    try {
      input = InputFileStream(file.path);
      archive = ZipDecoder().decodeStream(input);
      final metadataEntry = archive.find('metadata.json');
      final historyEntry = archive.find('history.ndjson');
      if (metadataEntry == null ||
          metadataEntry.size > _maxMetadataBytes ||
          (historyEntry != null && historyEntry.size > _maxHistoryBytes)) {
        return null;
      }
      final rootRaw = jsonDecode(utf8.decode(metadataEntry.content));
      if (rootRaw is! Map) return null;
      final root = Map<String, dynamic>.from(rootRaw);
      final version = root['format_version'];
      if (root['magic'] != magic ||
          (version != 2 && version != formatVersion)) {
        return null;
      }
      if (version == 2 && historyEntry == null) {
        return null;
      }
      final dataRaw = root['data'];
      if (dataRaw is! Map) return null;
      final data = Map<String, dynamic>.from(dataRaw);

      extractionDir = await Directory(
        p.join(
          temporaryDirectory.path,
          'spotiflac_restore_${DateTime.now().microsecondsSinceEpoch}',
        ),
      ).create(recursive: true);
      String? historyPath;
      if (historyEntry != null) {
        historyPath = p.join(extractionDir.path, 'history.ndjson');
        final historyOutput = OutputFileStream(historyPath);
        historyEntry.writeContent(historyOutput);
        historyOutput.closeSync();
      }

      final restoredCovers = <String, dynamic>{};
      final coverManifest = data['playlist_covers'];
      if (coverManifest is Map) {
        var index = 0;
        var extractedCoverBytes = 0;
        for (final manifestEntry in coverManifest.entries) {
          if (manifestEntry.value is! Map) continue;
          final cover = Map<String, dynamic>.from(manifestEntry.value as Map);
          final archiveName = cover['file']?.toString() ?? '';
          if (!archiveName.startsWith('covers/') ||
              archiveName.contains('..')) {
            continue;
          }
          final archiveEntry = archive.find(archiveName);
          if (archiveEntry == null || archiveEntry.size > _maxCoverBytes) {
            continue;
          }
          if (extractedCoverBytes + archiveEntry.size > _maxAllCoversBytes) {
            break;
          }
          var ext = cover['ext']?.toString() ?? '.jpg';
          if (!RegExp(r'^\.[a-z0-9]{1,8}$').hasMatch(ext)) ext = '.jpg';
          final coverPath = p.join(extractionDir.path, 'cover_${index++}$ext');
          final output = OutputFileStream(coverPath);
          archiveEntry.writeContent(output);
          output.closeSync();
          extractedCoverBytes += archiveEntry.size;
          restoredCovers[manifestEntry.key.toString()] = {
            'ext': ext,
            'path': coverPath,
          };
        }
      }

      return BackupBundle(
        formatVersion: version as int,
        appVersion: root['app_version'] as String? ?? '',
        createdAt: DateTime.tryParse(root['created_at'] as String? ?? ''),
        settings: _mapOrNull(data['settings']),
        history: const [],
        hasHistory: historyEntry != null,
        historyNdjsonPath: historyPath,
        historyCount: (root['history_count'] as num?)?.toInt() ?? 0,
        collections: _mapOrEmpty(data['collections']),
        playlistCovers: restoredCovers,
        extensions: _mapOrEmpty(data['extensions']),
        temporaryDirectoryPath: extractionDir.path,
      );
    } catch (e) {
      _log.w('Backup archive parse failed: $e');
      if (extractionDir != null) {
        try {
          await extractionDir.delete(recursive: true);
        } catch (_) {}
      }
      return null;
    } finally {
      if (input != null) await input.close();
    }
  }

  static BackupBundle? parse(String content) {
    dynamic decoded;
    try {
      decoded = jsonDecode(content);
    } catch (e) {
      _log.w('Backup parse failed: not valid JSON ($e)');
      return null;
    }
    if (decoded is! Map) return null;
    final root = Map<String, dynamic>.from(decoded);
    if (root['magic'] != magic || root['data'] is! Map) return null;
    final data = Map<String, dynamic>.from(root['data'] as Map);
    final history = <Map<String, dynamic>>[];
    if (data['history'] is List) {
      for (final item in data['history'] as List) {
        if (item is Map) history.add(Map<String, dynamic>.from(item));
      }
    }
    return BackupBundle(
      formatVersion: (root['format_version'] as num?)?.toInt() ?? 1,
      appVersion: root['app_version'] as String? ?? '',
      createdAt: DateTime.tryParse(root['created_at'] as String? ?? ''),
      settings: _mapOrNull(data['settings']),
      history: history,
      hasHistory: data['history'] is List,
      collections: _mapOrEmpty(data['collections']),
      playlistCovers: _mapOrEmpty(data['playlist_covers']),
      extensions: _mapOrEmpty(data['extensions']),
    );
  }

  static Map<String, dynamic>? _mapOrNull(dynamic value) =>
      value is Map ? Map<String, dynamic>.from(value) : null;

  static Map<String, dynamic> _mapOrEmpty(dynamic value) =>
      value is Map ? Map<String, dynamic>.from(value) : <String, dynamic>{};
}