# All files / src/events bus.ts

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     /**
     * Event Emitter Bus - Adapter Implementation
     *
     * In-process EventBus implementation using Node.js EventEmitter.
     * This is the ADAPTER for the EventBus PORT.
     *
     * Can be swapped for RabbitMQ, Kafka, WebSocket, etc. later
     * without changing consumers.
     */

    import { EventEmitter } from 'node:events';
    import type { DomainEvent, EventBus } from './types.js';

    /**
     * EventEmitter-based implementation of the EventBus interface.
     *
     * Wraps Node.js EventEmitter to provide type-safe event handling
     * that conforms to the EventBus port interface.
     */
    export class EventEmitterBus implements EventBus {
      private emitter: EventEmitter;

      constructor() {
        this.emitter = new EventEmitter();
        // Allow more listeners for complex systems
        this.emitter.setMaxListeners(100);
      }

      /**
       * Emit an event to all subscribed handlers.
       * The event's type property determines which handlers receive it.
       */
      emit<T extends DomainEvent>(event: T): void {
        this.emitter.emit(event.type, event);
      }

      /**
       * Subscribe to events of a specific type.
       */
      on<T extends DomainEvent>(
        eventType: T['type'],
        handler: (event: T) => void
      ): void {
        this.emitter.on(eventType, handler);
      }

      /**
       * Unsubscribe from events of a specific type.
       */
      off<T extends DomainEvent>(
        eventType: T['type'],
        handler: (event: T) => void
      ): void {
        this.emitter.off(eventType, handler);
      }

      /**
       * Subscribe to a single occurrence of an event type.
       * Handler is automatically removed after first invocation.
       */
      once<T extends DomainEvent>(
        eventType: T['type'],
        handler: (event: T) => void
      ): void {
        this.emitter.once(eventType, handler);
      }
    }