Design a restaurant reservation service

Design the object model for a restaurant reservation service. Restaurants have tables of different sizes and open hours divided into time slots. Guests search for availability by party size and time, book, change and cancel reservations. A table must never be booked twice for overlapping times.

Requirements

• Functional: search a restaurant's free slots for a date, time and party size; book a slot, which holds a table that fits the party; modify a reservation (time or party size) or cancel it; restaurants configure tables, hours and how long a seating lasts; staff mark guests as seated or no-show.
• Large parties can use combined tables if the restaurant allows it.
• Non-functional: no double booking, even when two guests book the last table at the same moment; search is fast for a day's slots.

Clarifying questions

• Is it one restaurant or a platform with many?
• How long is a seating, and is it fixed or by party size?
• Does the guest choose a table, or does the system assign one?
• Can tables be combined for large parties?
• Are deposits, cancellation fees or waitlists in scope?

What a strong answer covers

• Core classes: Restaurant (tables, opening hours, seating rules), Table (ID, capacity, combinable), TimeSlot, Reservation (guest, party size, start, end, table or tables, status), Guest, and a ReservationService for search, book, modify and cancel, with a TableAssignmentStrategy.
• Availability as interval overlap per table: a reservation occupies [start, start + duration), and a table is free if no confirmed reservation overlaps.
• Choosing the smallest table that fits so large tables stay free for large parties.
• Preventing double booking: lock per table (or per restaurant) during booking, or a database constraint on overlapping intervals; a modification as an atomic swap that keeps the old booking if the new time is not free.
• Reservation states (booked, seated, completed, cancelled, no-show) and their transitions.
• Tests: back-to-back bookings, a party too large for any table, modifying into a taken slot.

Follow-ups

• Add a waitlist that offers freed slots to waiting guests.
• Add deposits for large parties and a no-show fee.
• Let walk-ins take tables without breaking upcoming reservations.