Movie ticket booking

enum SeatStatus { FREE, RESERVED, BOOKED }

record SeatState(SeatStatus status, BookingId owner, Instant expiresAt) {}

class Seat {
  private final SeatId id;
  private final AtomicReference<SeatState> state =
      new AtomicReference<>(new SeatState(SeatStatus.FREE, null, null));

  boolean tryReserve(BookingId owner, Instant expiresAt) {
    SeatState free = new SeatState(SeatStatus.FREE, null, null);
    SeatState held = new SeatState(SeatStatus.RESERVED, owner, expiresAt);
    return state.compareAndSet(free, held);
  }

  boolean confirm(BookingId owner) {
    SeatState cur = state.get();
    if (cur.status() != SeatStatus.RESERVED || !Objects.equals(cur.owner(), owner))
      return false;
    SeatState booked = new SeatState(SeatStatus.BOOKED, owner, null);
    return state.compareAndSet(cur, booked);
  }

  boolean release(BookingId owner) {
    SeatState cur = state.get();
    if (cur.status() != SeatStatus.RESERVED || !Objects.equals(cur.owner(), owner))
      return false;
    return state.compareAndSet(cur, new SeatState(SeatStatus.FREE, null, null));
  }
}

class Booking {
  private final BookingId id;
  private final ShowId show;
  private final List<SeatId> seats;
  private final Instant expiresAt;
  private BookingStatus status;
}

class BookingService {
  private final Clock clock;
  Booking reserve(ShowId show, List<SeatId> seats) { /* CAS each seat with owner+TTL */ }
  Booking confirm(BookingId id) { /* payment ok; confirm(owner) per seat; idempotent */ }
  void expireDue(Instant now) { /* RESERVED → FREE when expiresAt passed */ }
}