The undo mechanic is where I got tripped up.
Start by clarifying functional and non-functional requirements, then design a high-level architecture with separate services for game state, invitations, and leaderboard. Dive into data models and trade-offs for undo and leaderboard consistency, and discuss scaling and real-time updates.
Pro tip: Emphasize idempotency and consistency: undo must be atomic and only allowed before opponent's move, and leaderboard updates should be eventually consistent to avoid contention. Show awareness of Meta's scale by discussing sharding and caching.
Ask about scale (DAU, concurrent games), latency, consistency needs, and whether undo is per-move or per-turn. Confirm leaderboard scope (global, friends, time-based).
Propose microservices: Game Service (state, moves), Invitation Service, Leaderboard Service, and Notification Service. Use WebSockets for real-time updates and a message queue for async events.
Design schemas: Game (id, players, board state, move history, status), Move (game_id, player, from, to, timestamp, undone), Invitation (sender, receiver, status), Leaderboard (user_id, wins, losses, rating). Use Redis for leaderboard sorted sets and a relational DB for game state.
Implement undo as a reversible operation: store move history with a flag; allow undo only if the last move was by the same player and opponent hasn't moved. Use optimistic locking or versioning to prevent race conditions.
Update leaderboard asynchronously via events (e.g., game finished). Use Redis sorted sets for real-time ranking; shard by region or game type. Discuss caching, read replicas, and eventual consistency.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.