Design a parking lot system. Walk me through your approach.

enum VehicleType { CAR, MOTORCYCLE, TRUCK }
enum SpotSize    { COMPACT, REGULAR, LARGE }

// Inheritance: every vehicle IS-A Vehicle
abstract class Vehicle {
    private final String plate;
    private final VehicleType type;
    Vehicle(String plate, VehicleType type) { this.plate = plate; this.type = type; }
    abstract SpotSize requiredSize();
}
class Car extends Vehicle {
    Car(String plate) { super(plate, VehicleType.CAR); }
    SpotSize requiredSize() { return SpotSize.REGULAR; }
}

class ParkingSpot {
    private final String id;
    private final SpotSize size;
    private Vehicle vehicle;          // null = free
    boolean isFree() { return vehicle == null; }
    synchronized boolean park(Vehicle v) {   // thread-safe claim
        if (vehicle != null || v.requiredSize().ordinal() > size.ordinal()) return false;
        vehicle = v; return true;
    }
}

record ParkingTicket(String id, Vehicle vehicle, ParkingSpot spot, LocalDateTime entry) {}

class ParkingLot {                    // Composition: lot HAS floors HAS spots
    private final List<ParkingFloor> floors = new ArrayList<>();
    private final FeeCalculator feeCalculator = new HourlyFeeCalculator();
    Optional<ParkingTicket> park(Vehicle v) {
        for (ParkingFloor f : floors) {
            Optional<ParkingSpot> spot = f.findFree(v.requiredSize());
            if (spot.isPresent() && spot.get().park(v))
                return Optional.of(new ParkingTicket(UUID.randomUUID().toString(), v, spot.get(), LocalDateTime.now()));
        }
        return Optional.empty();      // lot full
    }
}