Feature/rest api

[soraiayugulis]

Summary

Implements all 8 REST API endpoints specified in the design, with request validation, proper HTTP status codes, and MockMvc integration tests.

Changes

DTOs

• CardRegistrationRequest/Response — card creation with 16-digit validation
• BalanceAdditionRequest/Response — category balance management
• TransactionRequest/Response — authorization requests with status/error tracking
• TransactionHistoryResponse — chronological transaction list
• MerchantRegistrationRequest/Response — merchant creation with category
• CardStatusUpdateRequest — activate/deactivate

Controllers

• CardController — 6 endpoints: register, add balance, query balance, transaction history, status update, card details
• TransactionController — POST /transactions with full authorization flow (validates card, merchant, amount, balance, daily limit)
• MerchantController — POST /merchants with name/category validation

Error Handling

• CardNotFoundException → 404
• MerchantNotFoundException → 404
• Bean Validation → 400 for invalid inputs

Tests

• 94 unit tests — all passing
• MockMvc standalone setup for all controllers
• Covers: success paths, validation errors, not-found scenarios

Spec Coverage

Endpoint	Status
POST /cards	✅
POST /cards/{id}/balance	✅
GET /cards/{id}/balance/{category}	✅
POST /transactions	✅
GET /cards/{id}/transactions	✅
POST /merchants	✅
PUT /cards/{id}/status	✅
GET /cards/{id}	✅