/**
 * 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();
    // SSE subscriptions register per-event-type listeners (30+ types × N clients).
    // Listeners are properly cleaned up on disconnect, so disable the warning.
    this.emitter.setMaxListeners(0);
  }

  /**
   * 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);
  }
}