This one had more layers than I expected going in.
Start by clarifying requirements and constraints, then design a RESTful API with endpoints for checking and consuming access, and finally outline mobile-side patterns for handling limits and displaying the toast. Emphasize idempotency, caching, and graceful degradation.
Pro tip: Demonstrate awareness of race conditions and offline scenarios by proposing idempotency keys and client-side caching with optimistic UI updates. This shows you think beyond the happy path and consider real-world mobile constraints.
Ask questions to understand the scope: Is the limit per user, per model version, or both? What defines a 'free access'? How is time until next access calculated? Are there different tiers (free, paid)? What are the mobile platform constraints (iOS/Android)?
Propose endpoints such as GET /v1/models/{model_version}/access to check remaining accesses and reset time, and POST /v1/models/{model_version}/access to consume an access. Include idempotency keys and proper status codes (e.g., 429 for limit exceeded with Retry-After header).
Outline how the mobile app will handle access checks and limit responses: use a repository pattern to abstract API calls, cache access status locally, and handle 429 responses by showing a toast with wait time and upgrade link. Consider offline scenarios and optimistic UI.
Provide example function signatures for key mobile-side operations, such as checkAccess(modelVersion: String) async throws -> AccessStatus, consumeAccess(modelVersion: String, idempotencyKey: String) async throws -> AccessResult, and showLimitToast(waitTime: TimeInterval, upgradeURL: URL).
Address trade-offs like caching vs. real-time accuracy, handling race conditions with idempotency, and graceful degradation when offline. Mention how to handle time zone differences for reset times and how to ensure the toast is non-intrusive.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.