app.component2.ts

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.scss']
})
export class AppComponent implements AfterViewInit{
  protected undoConfigurationSubject = new BehaviorSubject<TopologyCommand | null>(null);
  undoConfiguration$ = this.undoConfigurationSubject.asObservable();

  protected resetConfigurationSubject = new BehaviorSubject<boolean | null>(null);
  resetConfiguration$ = this.resetConfigurationSubject.asObservable();

  ..,

  get isUndoButtonDisplayed(): boolean {
    return this.commandStack.length > 0;
  }

  get undoButtonText() {
    return `Undo (${this.commandStack.length})`;
  }

  protected onUndoButtonClicked() {
    if (this.commandStack.length === 0) {
      return;
    }
    this.undoConfigurationSubject.next(this.commandStack[0]);
  }

  protected onResetButtonClicked() {
    const length = this.commandStack.length;
    for (let i = 0; i < length; i++) {
      this.commandStack.pop();
    }

    this.resetConfigurationSubject.next(true);
  }
  
}