def available_cars(request, car_id=None, start=None, end=None):
"""
List all cars or available cars in given range or cars for which avail > 0
(that is, models for which there are available car instances)
"""
service = CarRentalService()
cars = service.getAvailCars(car_id=car_id, start=start, end=end)
serializer = CarSerializer(cars, many=True)
return Response(serializer.data)
