@Injectable()
export class CompareMenuFormService {
  public get nowBeingCompared$(): Observable<UsingChannel[]> {
    return this.nowBeingComparedMulticast$;
  }
  public readonly form: { [index: number]: UsingChannel|undefined } = {}
  private readonly nowBeingComparedMulticast$ = new ReplaySubject<UsingChannel[]>();
  public selectChannel(channel: UsingChannel): void {
    this.form[channel.index] = channel;
    this.emitNowBeingCompared();
  }
  public unSelectChannel(channel: UsingChannel): void {
    this.form[channel.index] = undefined;
    this.emitNowBeingCompared();
  }
  private emitNowBeingCompared(): void {
    const beingCompared = Object.values(this.form).filter(value => value !== undefined) as UsingChannel[];
    this.nowBeingComparedMulticast$.next(beingCompared);
  }
}