Building software that ships, works, and doesn't fall apart in production.

Gym tracking apps rarely model how real training actually works — cycling between multiple programs, tracking planned vs. actual sets, and preserving history when a routine changes.

Designed a 3-state Program lifecycle (ACTIVE / AVAILABLE / ARCHIVED) with transactional state transitions, and enforced cross-entity ownership checks (a WorkoutSet can only belong to a WorkoutSession the authenticated user actually owns) at the service layer.

Multi-channel notification systems (email, SMS, push) tend to grow into if/else chains that get harder to extend safely every time a new channel is added.

Implemented the Strategy pattern: each channel is an independent class behind a common interface, selected by a factory — adding a new channel means writing one new class, zero changes to existing code (Open/Closed Principle). Backed by a full Jest test suite covering service logic and channel-selection edge cases.