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⚡ Event-Driven Transfer Flow (Current Architecture)

🏁 Overview

The current transfer process is a fully event-driven, linear workflow. Each business step is handled by a dedicated, single-responsibility handler with defensive validation. This design ensures modularity, testability, and a clear, robust separation of concerns, preventing unintended side effects like accidental payment initiation.

🖼️ Event Flow Diagram

flowchart TD
    subgraph "Refactored Transfer Event Flow"
        A[API Request] --> B(Transfer.Requested);
        B --> C[Validation Handler];
        C --> D(Transfer.Validated);
        D --> E[Initial HandleProcessed Handler];
        E --> F(CurrencyConversion.Requested);
        F --> G[Conversion Handler];
        G --> H(Transfer.CurrencyConverted);
        H --> I[Business Validation Handler];
        I --> J(Transfer.Completed);
        I -->|On Failure| K(Transfer.Failed);
        J --> L[Final HandleProcessed Handler];
        L --> M(Transfer.Completed);
        L -->|On Failure| K;
    end

🧩 Event Handler Responsibilities

1. Validation Handler

  • Consumes: Transfer.Requested
  • Responsibility: Performs basic structural validation on the request (e.g., non-nil UUIDs, positive amount). Malformed events are logged and discarded.
  • Emits: Transfer.Validated on success.

2. Initial HandleProcessed Handler

  • Consumes: Transfer.Validated
  • Responsibility: Creates the initial outgoing transaction (tx_out) with a pending status. This provides a durable record of the request early.
  • Emits: CurrencyConversion.Requested to trigger currency conversion (if needed).

3. Conversion Handler (Generic)

  • Consumes: CurrencyConversion.Requested
  • Responsibility: Performs currency conversion.
  • Emits: Transfer.CurrencyConverted (a context-specific event).

4. Business Validation Handler

  • Consumes: Transfer.CurrencyConverted
  • Responsibility: Performs all business-level validation against the current state of the system (e.g., sufficient funds in the source account).
  • Emits:
  • Transfer.Completed on success.
  • Transfer.Failed on business rule failure (e.g., insufficient funds).

5. Final HandleProcessed Handler

  • Consumes: Transfer.Completed
  • Responsibility: Atomically performs the final state changes:
  • Creates the incoming transaction (tx_in) for the receiver with a completed status.
  • Updates the outgoing transaction (tx_out) to completed.
  • Updates the balances of both the source and destination accounts.
  • Emits:
  • Transfer.Completed on success.
  • Transfer.Failed if the atomic database operation fails.