Services (the brain)

Path: hono-backend/src/services/

If routes are waiters, services are chefs. All important rules live here.

Baby rules

Services never read HTTP headers directly — pass userId and DTOs from routes.
Services may call other services and models.
Throw meaningful errors; routes map them to status codes.
Unit tests target services (src/__tests__/).

File	Job
`practice-pyq-learner.service.ts`	Student sessions
`practice-pyq-questions.service.ts`	Question fetching
`practice-pyq-taxonomy.service.ts`	Catalog tree
`practice-pyq-srs-scheduler.ts`	SRS intervals
`practice-pyq-ce-asrs-scheduler.ts`	Alternate scheduler variant
`practice-pyq-week-review.service.ts`	Weekly review bundles
`practice-pyq-grade.ts`	Grading logic
`practice-review-summary.service.ts`	Summaries after practice

File	Job
`current-affairs.service.ts`	Core CA operations
`current-affairs-ancillary.service.ts`	Supporting CA workflows
`current-affairs-bookmark.service.ts`	Bookmarks
`current-affairs-revision.service.ts`	Revision queues
`current-affairs-bookmark-news-revision.service.ts`	News revision
`current-affairs-bookmark-news-revision.scheduler.ts`	Schedule news revisions

File	Job
`continue-learning.service.ts`	Resume pointers
`marketing-deal-coupon.service.ts`	Coupon validation

Notifications — services/notifications/*
Study stats — services/user-study-stats/*
Current affairs search — services/current-affairs-search/*
- text-search-backend.ts — regex vs Atlas Search selector + window-days helper
- vector-search-backend.ts — in-app vs Atlas Vector Search selector + embedding model/version
- Documented inside Current affairs
Rate limit — services/rate-limit/* — policy engine, fixed/sliding/token-bucket algorithms, memory / mongo stores, in-process config cache. Used by rate-limit.middleware.ts. Full design in API rate limiting.