import { NgModule, Optional, SkipSelf } from '@angular/core';
import { CommonModule } from '@angular/common';
import { ContactService } from './contact.service';

@NgModule({
  declarations: [],
  imports: [
    CommonModule
  ]
})
export class ContactModule { 
  constructor(
    @Optional()
    @SkipSelf()
    parentModule: ContactModule
  ) {
    if (parentModule) {
      throw new Error('ContactModule is already loaded. Import it in the AppModule only');
    }
  }

  static forRoot() {
    return {
      ngModule: ContactModule,
      providers: [ ContactService ]
    }
  }
}