import 'drive_service.dart' show DriveLockFile;

/// Ticket-based mutex using timestamped lock files as the coordination
/// point: create a lock named after our own timestamp, then wait until no
/// *other* lock older than ours remains — reaping ("deleting") any it
/// finds older than [staleAge] along the way, as a backstop against a
/// device that crashed/went offline before releasing its own lock.
///
/// Pure orchestration over injected operations (rather than a concrete
/// Drive dependency) so the state machine is unit-testable without a real
/// network connection.
Future<String> acquireLock({
  required String username,
  required Future<String> Function(String lockName) createLock,
  required Future<List<DriveLockFile>> Function() listLocks,
  required Future<void> Function(String lockId) deleteLock,
  DateTime Function()? nowUtc,
  Future<void> Function(Duration)? delay,
  Duration staleAge = const Duration(minutes: 10),
  Duration pollInterval = const Duration(seconds: 1),
}) async {
  final now = nowUtc ?? () => DateTime.now().toUtc();
  final wait = delay ?? Future.delayed;

  final epochMillis = now().millisecondsSinceEpoch;
  final lockName = '$username-$epochMillis.lock';
  final lockId = await createLock(lockName);

  while (true) {
    final locks = await listLocks();
    final others = locks.where((l) => l.id != lockId);
    final olderOthers =
        others.where((l) => l.createdAtUtc.millisecondsSinceEpoch < epochMillis).toList();

    if (olderOthers.isEmpty) break;

    final current = now();
    for (final stale in olderOthers) {
      if (current.difference(stale.createdAtUtc) > staleAge) {
        await deleteLock(stale.id);
      }
    }

    await wait(pollInterval);
  }

  return lockId;
}