Melo/lib/library/scan_service.dart

import 'dart:io';

import 'package:audio_metadata_reader/audio_metadata_reader.dart';
import 'package:drift/drift.dart';
import 'package:path/path.dart' as p;
import 'package:path_provider/path_provider.dart';
import 'package:uuid/uuid.dart';

import 'categories.dart';
import 'database.dart';

const _audioExt = {
  '.mp3', '.m4a', '.aac', '.flac', '.wav', '.ogg', '.opus', '.wma', '.aiff',
  '.aif', '.alac',
};
const _uuid = Uuid();

/// Scannt alle [folderPaths] rekursiv nach Audiodateien, liest Tags + Cover
/// und schreibt sie in die DB. Bereits bekannte Dateien behalten ihre UUID
/// (sync-stabil); verschwundene Dateien werden per Tombstone markiert.
/// Gibt die Zahl der gefundenen Songs zurück.
// ponytail: Tag-Parsing läuft synchron im UI-Isolate. Reicht für normale
// Bibliotheken; bei >~mehreren Tausend Dateien in ein Isolate (compute) auslagern.
Future<int> scanFolders(
  MeloDb db,
  List<String> folderPaths, {
  Directory? coverDir,
  void Function(int done, int total)? onProgress,
}) async {
  final existing = {for (final s in await db.allSongs()) s.path: s};
  final covers = coverDir ??
      Directory(p.join((await getApplicationSupportDirectory()).path, 'covers'));
  await covers.create(recursive: true);

  final files = <File>[];
  for (final folder in folderPaths) {
    final dir = Directory(folder);
    if (!dir.existsSync()) continue;
    await for (final entity in dir.list(recursive: true, followLinks: false)) {
      if (entity is File &&
          _audioExt.contains(p.extension(entity.path).toLowerCase())) {
        files.add(entity);
      }
    }
  }

  final now = DateTime.now().millisecondsSinceEpoch;
  final companions = <SongsCompanion>[];
  // Kategorien werden erst nach dem Upsert geschrieben — vorher gibt es die
  // Songzeile noch nicht, auf die sie verweisen.
  final categories = <String, List<String>>{};
  var done = 0;

  if (files.isNotEmpty) onProgress?.call(0, files.length);

  for (final file in files) {
    final prev = existing[file.path];
    final id = prev?.id ?? _uuid.v4();

    AudioMetadata? meta;
    try {
      meta = readMetadata(file, getImage: true);
    } catch (_) {
      // Unlesbare/kaputte Tags: Datei trotzdem mit Dateinamen aufnehmen.
    }

    final rawTitle = meta?.title?.trim();
    final title = (rawTitle != null && rawTitle.isNotEmpty)
        ? rawTitle
        : p.basenameWithoutExtension(file.path);

    var coverPath = prev?.coverPath;
    final pics = meta?.pictures ?? const <Picture>[];
    if (pics.isNotEmpty && coverPath == null) {
      try {
        final f = File(p.join(covers.path, '$id.img'));
        await f.writeAsBytes(pics.first.bytes);
        coverPath = f.path;
      } catch (_) {
        // Kaputtes Cover verzögert nicht den Scan.
      }
    }

    companions.add(SongsCompanion.insert(
      id: id,
      path: file.path,
      title: title,
      artist: Value(meta?.artist),
      album: Value(meta?.album),
      durationMs: Value(meta?.duration?.inMilliseconds),
      coverPath: Value(coverPath),
      dateAddedMs: prev?.dateAddedMs ?? now,
      updatedAtMs: now,
      deleted: const Value(false),
    ));
    if (prev?.categoriesEdited != true) {
      categories[id] = parseCategoryList(meta?.genres ?? const []);
    }
    ++done;
    if (done % 50 == 0 || done == files.length) {
      onProgress?.call(done, files.length);
    }
  }

  await db.upsertSongs(companions);
  for (final entry in categories.entries) {
    await db.setCategories(entry.key, entry.value);
  }
  if (companions.isNotEmpty) {
    await db.markMissing(now);
  }
  return companions.length;
}