Design a hotel reservation system

Design an online hotel reservation system. The system should allow customers to search for hotels, view available room types, create a reservation, and complete checkout through a third-party asynchronous payment provider. Focus especially on these deep dives: 1. **Availability search:** Given a hotel, check-in date, check-out date, party size, and quantity of rooms, return only room types that are available for every night in the requested date range. 2. **Checkout and payment timeouts:** During checkout, distinguish between these two cases and handle each correctly: - The user never actually paid, and the checkout session timed out. - The user did pay, but the third-party payment provider's asynchronous response arrived later than the timeout configured by your system. Discuss functional requirements, APIs, data models, consistency guarantees, concurrency control, timeout handling, and scalability.