Start by clarifying requirements and constraints, then design a data model that efficiently handles grants with expiration and consumption. Implement the system with appropriate data structures and algorithms, and finally write comprehensive end-to-end tests covering edge cases.
Pro tip: Discuss trade-offs between different data structures (e.g., priority queues vs. sorted lists) for managing expirations, and emphasize the importance of idempotency and concurrency in a real-world system.
Ask questions to understand expected scale, concurrency, expiration semantics, and whether consumption should follow FIFO or another policy.
Propose a data model for users, grants (with expiration), and consumption records, considering efficient querying and updates.
Outline algorithms for granting credits, consuming credits (respecting expiration and balance), and querying balance, handling edge cases like insufficient credits.
Design tests that cover granting, consuming, expiration, balance queries, and error scenarios, ensuring the system behaves correctly under various conditions.
Explain choices made, potential bottlenecks, and how the system could scale or handle concurrency, showing awareness of production concerns.
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