Certification Reminder Service

This is a medium-complexity backend service with a focused responsibility set, making it a well-scoped deliverable. It has hard dependencies on both the Certification Repository and the Push Notification Service, so those components must reach a stable interface contract before integration work begins. Testing requires a realistic dataset of near-expiry certification records and a mock or staging push notification endpoint. Delivery risk is low if the nightly cron infrastructure is established early, but delays in the Push Notification Service will block end-to-end validation.

Deduplication logic (hasReminderBeenSent) must be thoroughly covered in unit tests to prevent double-notification incidents in production.

The service exposes four methods: runDailyExpiryCheck() as the cron entry point, getUpcomingExpirations(thresholdDays) to query the repository, sendExpiryReminder(mentorId, coordinatorId, daysRemaining) to dispatch notifications, and hasReminderBeenSent(mentorId, thresholdDays) for idempotency checks. It depends on certification-repository for data access and push-notification-service for delivery. The deduplication guard must persist reminder dispatch records (likely via appendRenewalHistory or a dedicated reminders table) so that reruns of the cron do not produce duplicate alerts. Threshold evaluation logic should treat the thresholds as inclusive boundaries and handle timezone normalisation carefully to avoid off-by-one day errors in production.