Feature/repository layer

[soraiayugulis]

Summary

Implements the repository layer with interfaces in the application layer and thread-safe in-memory implementations in the infrastructure layer, following hexagonal architecture.

Changes

Interfaces (application/repository)

• CardRepository — save, findById, findByNumber, update, delete
• MerchantRepository — save, findById, update
• TransactionRepository — save, findById, findByCardId

Implementations (infrastructure/repository)

• InMemoryCardRepository — ConcurrentHashMap-backed, supports lookup by id and card number
• InMemoryMerchantRepository — ConcurrentHashMap-backed
• InMemoryTransactionRepository — ConcurrentHashMap-backed with:
  • Chronological ordering by createdAt
  • 90-day retention filter (excludes transactions older than 90 days)

Tests

• 76 unit tests — all passing
• Covers: CRUD operations, lookup by different keys, updates, deletes, empty results, chronological ordering

Architecture

• Interfaces in application layer (domain-agnostic contracts)
• Implementations in infrastructure layer
• Thread-safe via ConcurrentHashMap
• Ready for future swap to database-backed implementations