serviceFinal.ts

@Injectable()
export class NastyService {
  constructor(@Inject(CASE_LOGIC_HANDLER) private caseHandlers: CaseLogicHandler[]) {
  }

  doNastyOperation(key: any) {
    const handler = this.caseHandlers.find(h => h.key === key);
    if (!handler) throw new Error(`No case handler provided for key: ${key}`);
    handler.doLogic();
  }
}