import { Module, type OnApplicationBootstrap } from '@nestjs/common';
import client from 'prom-client';

import { MetricsModuleConfig } from './metrics.config';

@Module({})
export class MetricInitializingModule implements OnApplicationBootstrap {
  private static isBootstrapped = false;

  constructor(private readonly config: MetricsModuleConfig) {}

  /**
   * Configures prom-client
   */
  onApplicationBootstrap(): void {
    /**
     * This module initializes many times: forRoot, forFeature
     * but real prom-client should occur only once.
     */
    if (MetricInitializingModule.isBootstrapped) {
      return;
    }

    if (this.config.includeDefault) {
      client.collectDefaultMetrics();
    }

    MetricInitializingModule.isBootstrapped = true;
  }
}