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Account Service Refactor

Welcome to the Account Service Refactor guide! This page explains how we transformed our account service for clarity, maintainability, and extensibility. Whether you're a new contributor or a seasoned team member, you'll find actionable insights and a clear roadmap here.

⚠️ Problem Statement

Why Refactor?

The original AccountService had significant code duplication and branching in the Deposit and Withdraw methods. Both methods followed nearly identical patterns, making the codebase hard to maintain and extend.

Issues included:

  • Repeated logic for repository access, validation, and persistence
  • Complex, nested branching for currency conversion and transaction handling
  • Mixed responsibilities (validation, conversion, persistence, logging)
  • Difficult to test and reason about

🛠️ Refactoring Solution: Chain of Responsibility Pattern

The Big Idea

We adopted the Chain of Responsibility pattern, breaking the process into focused, testable handlers. Each handler does one thing well and passes control to the next.

Key changes:

  • Each operation (deposit, withdraw, transfer) is now a chain of handlers
  • Handlers are responsible for a single concern (validation, money creation, conversion, domain operation, persistence)
  • The service method simply builds and invokes the chain

🏗️ Architecture

  • OperationHandler Interface: Contract for all handlers
  • OperationRequest/Response: Data structures for passing information
  • Specialized Handlers: Each with a single responsibility
  • ChainBuilder: Constructs the complete operation chain

🧩 Handler Chain Structure

// Deposit: ValidationHandler → MoneyCreationHandler → CurrencyConversionHandler → DomainOperationHandler → DepositPersistenceHandler
// Withdraw: ... → WithdrawPersistenceHandler

📝 Migration Note

  • The legacy PersistenceHandler is removed
  • All persistence is now event-driven and operation-specific
  • Transaction creation is DRY and unified

🧪 Example Usage

// Deposit example
tx, convInfo, err := accountService.Deposit(userID, accountID, 100.0, currency.Code("EUR"))
// Withdraw example
tx, convInfo, err := accountService.Withdraw(userID, accountID, 50.0, currency.Code("USD"))

✨ Adding New Handlers

To add a new handler (e.g., for audit logging):

// AuditHandler logs all operations for audit purposes
type AuditHandler struct {
    BaseHandler
    logger *slog.Logger
}

func (h *AuditHandler) Handle(ctx context.Context, req *OperationRequest) (*OperationResponse, error) {
    h.logger.Info("Operation executed",
        "userID", req.UserID,
        "accountID", req.AccountID,
        "operation", req.Operation,
        "amount", req.Amount,
        "currency", req.CurrencyCode)
    return h.Next(ctx, req)
}

🔮 Looking Forward

This refactor sets the stage for even more powerful features and easier onboarding. If you have ideas for further improvements, or want to contribute a new handler, jump in!

Happy coding! 🎉