export declare class NotificationService {
    private readonly options;
    private timer;
    private draining;
    private lastMaintenanceAt;
    constructor(options: {
        publish: (type: string, payload: unknown) => void;
        fetch?: typeof fetch;
    });
    start(): void;
    stop(): void;
    handleGatewayEvent(type: string, payload: unknown): void;
    drain(): Promise<void>;
    private deliverPending;
    private send;
    private checkReceipts;
    private retryOrFail;
}