Almost abstract Begging app

BegginApp.ts

class BeggingApp {
    private static readonly defaultMessage = '';
    private static readonly reason = 'because its so awesome and i would like to take part at testing it';
    private static readonly responseOnSuccess = 'Thank you dear very much for the key !';
    
    private static serviceBag: Collection<Injectable[]>;

    public static main(param: MainParams): void {
        const beggar = new Beggar(BeggingApp.serviceBag.getItem(BeggingService));

        timer(0, 2000)
            .pipe(
                switchMap(() => beggar.begForKeys(param.message || BeggingApp.defaultMessage, BeggingApp.reason)),
                takeWhile((res) => res.responseMessage !== 'Ok Ok, Here is the key')
            )
            .subscribe((response) => {
                const fs = BeggingApp.serviceBag.getItem(FileSystem);
                const mailer = BeggingApp.serviceBag.getItem(Mailer);
                fs.save(response.key);
                mailer.sendMail(DEVS_EMAIL, BeggingApp.responseOnSuccess);
            });
    }
}

class Beggar {
    constructor(private beggingService: BeggingService) {
    }

    public begForKeys(requestMessage: string, reason: string): Observable<BeggarResponse> {
        return this.beggingService.sendRequest({
            requestMessage: requestMessage,
            reason: reason
        });
    }
}

@Service()
class BeggingService {
    private beggingProtocol;

    sendRequest(request: BeggarRequest): Observable<BeggarResponse> {
        return this.beggingProtocol.send(request);
    }
}

interface MainParams {
    message: string;
}

interface BeggarRequest {
    requestMessage: string;
    reason: string;
}

interface BeggarResponse {
    responseMessage: string;
    key?: string;
}