Feature/vasundharam exchange rate provider

[Vasundhara369]

Exchange Rate Updater

Application that fetches exchange rates from Czech National Bank (CNB) for specified currencies.

Separation of Concerns

The codebase follows a clear layered architecture:

1. Models (Currency, ExchangeRate) - Domain entities with validation
2. Services - Business logic
   • ExchangeRateProvider - Main service that coordinates exchange rate retrieval
   • CnbExchangeRateService - HTTP client for CNB API communication
   • CnbResponseParser - XML parsing logic
3. Configuration - Dependency injection setup and configuration options
4. Constants - Centralized magic strings and formats

Key Design Principles Used

Single Responsibility Principle: Each class has one clear purpose:

• CnbExchangeRateService - HTTP communication only
• CnbResponseParser - XML parsing only
• ExchangeRateProvider - Business logic only

Dependency Injection: All dependencies injected via constructors

Interface-based Design: Interfaces (ICnbExchangeRateService, ICnbResponseParser) allow for swapping without changing business logic.

Reliability & Resilience

• Retry Policy: 3 retries with exponential backoff for network failures
• Circuit Breaker: Opens after 5 consecutive failures for 30 seconds to prevent hammering the CNB API
• Error Handling: All exceptions caught, logged, and wrapped in CnbApiException
• Timeout Protection: Configurable HTTP timeout (default 30 seconds)
• Date Validation: Validates that response date matches requested date, logs warnings on mismatch

Future Improvements

1. Caching: In-memory cache with date-based expiration
2. Metrics: Application performance monitoring and metrics collection
3. Health Checks: Health check endpoint for service monitoring
4. Integration Tests: Tests against real CNB API (not just mocks)
5. REST API: Expose as ASP.NET Core Web API for external consumption
6. Rate Limiting: If making many calls, throttle requests to CNB API
7. Database Storage: Store historical rates for tracking over time

Notes

• CNB rates are quoted against CZK (base currency)
• Some currencies have amounts > 1 (e.g., JPY is per 100 units) - rates are normalized to "CZK per 1 unit"
• Base currency (CZK) is automatically skipped
• Currencies not provided by CNB are silently ignored
• Application uses Czech culture (cs-CZ) for parsing decimal values (uses comma as decimal separator)

[wiz-mewssystems]

Wiz Scan Summary

Scanner	Findings
Vulnerabilities	-
Sensitive Data	-
Secrets	-
IaC Misconfigurations	-
SAST Findings	2
Total	2

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