greeting-service.module.ts

import { ModuleWithProviders, NgModule } from '@angular/core';
import { GreetingService } from './greeting.service';
import { GreetingServiceConfig } from './greeting-service.config';

import { GREETING_SERVICE_CONFIG_INJECTION_TOKEN } from './greeting-service.token';

@NgModule({
  providers: [GreetingService],
})
export class GreetingServiceModule {
  constructor(greetingService: GreetingService) {
    greetingService.initialize();
  }

  static config(
    config?: Partial<GreetingServiceConfig>
  ): ModuleWithProviders<GreetingServiceModule> {
    return {
      ngModule: GreetingServiceModule,
      providers: [
        {
          provide: GREETING_SERVICE_CONFIG_INJECTION_TOKEN,
          useValue: Object.assign(new GreetingServiceConfig(), config),
        },
      ],
    };
  }
}