Implement EUR support, fallback exchange-rate provider, caching, and currency usage tracking

[olmelikov]

Summary

This PR implements the requested currency enhancements for the Smartphone Catalog API.

Implemented

• Added EUR support

  • GET /api/catalog/EUR
  • GET /api/exchangeRate/EUR

• Added a second exchange-rate provider as fallback

  • Primary provider: NBU
  • Fallback provider: Open ER API

• Added config-driven provider selection via config/currency.php

• Added exchange-rate caching

  • 10-minute TTL
  • automatic fresh fetch on a new calendar day

• Added catalog currency usage tracking

  • every catalog request dispatches a queued job
  • job stores currency and request timestamp in the database

• Added unit and feature tests

  • conversion logic
  • fallback provider behavior
  • cache behavior
  • EUR endpoints
  • usage tracking flow

Architecture notes

The solution uses a modular DDD-style structure for the Currency module.

Patterns used

• Strategy — interchangeable exchange-rate providers via ExchangeRateProviderInterface
• Decorator — CachedExchangeRateProvider and FailoverExchangeRateProvider
• Dependency Injection — application layer depends on abstractions
• Config-driven composition — providers are resolved from config/currency.php

Design decisions

• exchange-rate retrieval is isolated from catalog retrieval
• fallback and caching are separated from concrete provider implementations
• catalog currency tracking is handled asynchronously via queue

Test Plan

Automated

Run:

php artisan test