import 'dart:io';
import 'dart:isolate';
import 'package:spotiflac_android/services/native_cache_maintenance.dart';

/// Trims old cached payloads to a byte budget. Repository metadata, symlinks,
/// and recently written files (possibly active downloads) are left alone.
Future<int> trimCacheToByteBudget(
  Directory directory, {
  required int maxBytes,
  required int targetBytes,
  Duration minimumAge = const Duration(minutes: 1),
  NativeCacheJobRunner? nativeJobRunner,
}) async {
  assert(targetBytes >= 0 && targetBytes <= maxBytes);
  if (maxBytes < 0 ||
      targetBytes < 0 ||
      targetBytes > maxBytes ||
      minimumAge.isNegative) {
    throw ArgumentError('Invalid cache byte budget or minimum age');
  }
  final result = await runNativeCacheMaintenance({
    'operation': 'cache_trim_budget',
    'directory': directory.absolute.path,
    'max_bytes': maxBytes,
    'target_bytes': targetBytes,
    'minimum_age_us': minimumAge.inMicroseconds,
  }, nativeJobRunner: nativeJobRunner);
  if (result != null) return cacheMaintenanceDeletedCount(result);
  final path = directory.path;
  return _trimCacheOnWorker(path, maxBytes, targetBytes, minimumAge);
}

Future<int> _trimCacheOnWorker(
  String path,
  int maximum,
  int target,
  Duration age,
) => Isolate.run(() => _trimCacheInWorker(path, maximum, target, age));

Future<int> _trimCacheInWorker(
  String path,
  int maxBytes,
  int targetBytes,
  Duration minimumAge,
) async {
  final directory = Directory(path);
  if (!await directory.exists()) return 0;
  final files = <(File, FileStat)>[];
  var total = 0;
  await for (final entry in directory.list(
    recursive: true,
    followLinks: false,
  )) {
    if (entry is! File || entry.path.endsWith('.json')) continue;
    final stat = await entry.stat();
    if (stat.type != FileSystemEntityType.file) continue;
    files.add((entry, stat));
    total += stat.size;
  }
  if (total <= maxBytes) return 0;
  files.sort((a, b) => a.$2.modified.compareTo(b.$2.modified));
  final cutoff = DateTime.now().subtract(minimumAge);
  var deleted = 0;
  for (final (file, stat) in files) {
    if (total <= targetBytes) break;
    if (stat.modified.isAfter(cutoff)) continue;
    try {
      await file.delete();
      total -= stat.size;
      deleted++;
    } on FileSystemException {
      // A cache download/eviction may have changed the directory since listing.
    }
  }
  return deleted;
}