NestJS Events EmitEventAndSubscribeResult

import { EventEmitter2 } from '@nestjs/event-emitter';

import { ulid } from 'ulid';
import { Logger } from '@nestjs/common';

export interface EventFlow {
  id: string;
  event: string;
  timestamp?: string;
}


export function SubscribeEventResult<T>(
  eventInstance: EventEmitter2,
  eventFlow: EventFlow,
): Promise<T> {
  return new Promise((resolve) => {
    const event = `RESULT/${eventFlow.event}/${eventFlow.id}`;

    const listener = eventInstance.once(event, (result) => {
      listener.off(event, this);
      eventInstance.removeAllListeners(event);
      resolve(result);
    });
  });
}

export const EmitEventAndSubscribeResult = <T>(
  eventInstance: EventEmitter2,
  event: any,
  ...values: any[]
): Promise<T> => {
  return new Promise((resolve) => {
    const eventId = ulid();

    const eventParam = {
      event,
      id: eventId,
    };
    const eventResult = `RESULT/${eventParam.event}/${eventParam.id}`;
    let expired = false;
    const listener = eventInstance.once(eventResult, (result) => {
      eventInstance.removeAllListeners(eventResult);
      expired = true;
      resolve(result);
    });

    setTimeout(() => {
      // expiring failed events
      if (!expired) {
        eventInstance.removeAllListeners(eventResult);
        resolve(null);
      }
    }, 5000);

    if (values.length === 1) {
      values = values[0];
    }

    Logger.verbose(
      `Emmiting new event: ${event}`,
      'EmitEventAndSubscribeResult',
    );
    eventInstance.emit(event, values, eventParam);
  });
};