minstrel/flutter_client/lib/cache/audio_cache_manager.dart

import 'dart:io';

import 'package:dio/dio.dart';
import 'package:drift/drift.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:path_provider/path_provider.dart';

import '../library/library_providers.dart' show dioProvider;
import 'db.dart';

/// Owns the audio cache directory + drift index.
/// API:
///   - isCached(trackId)
///   - pathFor(trackId)
///   - pin(trackId, source) — downloads + indexes
///   - unpin(trackId)
///   - evict(targetBytes) — tiered LRU
///   - usageBytes()
///   - clearAll()
class AudioCacheManager {
  AudioCacheManager({
    required AppDb db,
    required Future<Dio> Function() dioFactory,
    Future<Directory> Function()? cacheDirFactory,
  })  : _db = db,
        _dioFactory = dioFactory,
        _cacheDirFactory = cacheDirFactory ?? getApplicationCacheDirectory;

  final AppDb _db;
  final Future<Dio> Function() _dioFactory;
  final Future<Directory> Function() _cacheDirFactory;

  Future<String> _tracksDir() async {
    final base = await _cacheDirFactory();
    final d = Directory('${base.path}/audio_cache');
    if (!await d.exists()) await d.create(recursive: true);
    return d.path;
  }

  /// True if the trackId has a complete file on disk.
  Future<bool> isCached(String trackId) async {
    final row = await (_db.select(_db.audioCacheIndex)
          ..where((t) => t.trackId.equals(trackId)))
        .getSingleOrNull();
    if (row == null) return false;
    return File(row.path).existsSync();
  }

  /// Returns the local file path if cached, else null.
  Future<String?> pathFor(String trackId) async {
    final row = await (_db.select(_db.audioCacheIndex)
          ..where((t) => t.trackId.equals(trackId)))
        .getSingleOrNull();
    if (row == null) return null;
    return File(row.path).existsSync() ? row.path : null;
  }

  /// Downloads the track's stream to disk and indexes it. Idempotent —
  /// returns the existing path if already cached.
  Future<String?> pin(String trackId, {required CacheSource source}) async {
    final existing = await pathFor(trackId);
    if (existing != null) return existing;

    final dir = await _tracksDir();
    final path = '$dir/$trackId.mp3';
    final dio = await _dioFactory();
    try {
      await dio.download('/api/tracks/$trackId/stream', path);
    } catch (_) {
      final f = File(path);
      if (f.existsSync()) await f.delete();
      return null;
    }
    final size = await File(path).length();
    await _db.into(_db.audioCacheIndex).insertOnConflictUpdate(
          AudioCacheIndexCompanion.insert(
            trackId: trackId,
            path: path,
            sizeBytes: size,
            source: source,
          ),
        );
    return path;
  }

  /// Removes a track from the index AND deletes the file.
  Future<void> unpin(String trackId) async {
    final row = await (_db.select(_db.audioCacheIndex)
          ..where((t) => t.trackId.equals(trackId)))
        .getSingleOrNull();
    if (row == null) return;
    final f = File(row.path);
    if (f.existsSync()) await f.delete();
    await (_db.delete(_db.audioCacheIndex)
          ..where((t) => t.trackId.equals(trackId)))
        .go();
  }

  /// Total bytes used by the cache. Walks the cache directory directly
  /// instead of summing the index, because the streaming-as-you-play
  /// path (audio_handler's LockCachingAudioSource) writes files
  /// without registering an index row. The index sum would always
  /// understate (often to zero) for users who only stream.
  Future<int> usageBytes() async {
    final dir = Directory(await _tracksDir());
    if (!await dir.exists()) return 0;
    var total = 0;
    await for (final entity in dir.list(followLinks: false)) {
      if (entity is File) {
        try {
          total += await entity.length();
        } catch (_) {
          // Race against concurrent writes / deletes — just skip.
        }
      }
    }
    return total;
  }

  /// Evicts files until usage ≤ targetBytes. Eviction order:
  /// incidental → autoPrefetch → autoPlaylist → autoLiked.
  /// `manual` never evicts via this path; only clearAll() removes them.
  Future<void> evict({required int targetBytes}) async {
    final used = await usageBytes();
    if (used <= targetBytes) return;
    final order = [
      CacheSource.incidental,
      CacheSource.autoPrefetch,
      CacheSource.autoPlaylist,
      CacheSource.autoLiked,
    ];
    int remaining = used - targetBytes;
    for (final src in order) {
      if (remaining <= 0) break;
      final rows = await (_db.select(_db.audioCacheIndex)
            ..where((t) => t.source.equalsValue(src))
            ..orderBy([(t) => OrderingTerm.asc(t.cachedAt)]))
          .get();
      for (final row in rows) {
        if (remaining <= 0) break;
        final f = File(row.path);
        if (f.existsSync()) await f.delete();
        await (_db.delete(_db.audioCacheIndex)
              ..where((t) => t.trackId.equals(row.trackId)))
            .go();
        remaining -= row.sizeBytes;
      }
    }
  }

  /// Clears EVERY row + EVERY file. Wired to the operator's "Clear cache"
  /// button — `manual` source rows are removed here but only here.
  Future<void> clearAll() async {
    final dir = await _tracksDir();
    final d = Directory(dir);
    if (d.existsSync()) {
      for (final entity in d.listSync()) {
        if (entity is File) await entity.delete();
      }
    }
    await _db.delete(_db.audioCacheIndex).go();
  }
}

/// AppDb singleton. One per app run; ref.onDispose closes it.
final appDbProvider = Provider<AppDb>((ref) {
  final db = AppDb();
  ref.onDispose(db.close);
  return db;
});

final audioCacheManagerProvider = Provider<AudioCacheManager>((ref) {
  final db = ref.watch(appDbProvider);
  return AudioCacheManager(
    db: db,
    dioFactory: () async => ref.read(dioProvider.future),
  );
});