export interface AisReceiverStatus {
    receiver_seen: boolean;
    first_seen_ts: number | null;
}
export declare class AisReceiverMemory {
    private readonly file;
    private seen;
    private written;
    private firstSeenTs;
    private writeChain;
    constructor(dataDir: string);
    load(): void;
    note(now: number): void;
    status(): AisReceiverStatus;
    flush(): Promise<void>;
    private write;
}