import type { Filter } from "nostr-tools";
export interface RegisteredDirectMessageSubscription {
    token: number;
    addedAuthors: string[];
}
export declare function directMessageSubscriptionAuthors(filter: Filter): string[];
export declare function buildDirectMessageBackfillFilter(authors: Iterable<string>, since: number, limit?: number): Filter;
export declare class DirectMessageSubscriptionTracker {
    private nextToken;
    private authorsByToken;
    private authorRefCounts;
    registerFilter(filter: Filter): RegisteredDirectMessageSubscription;
    unregister(token: number): void;
    trackedAuthors(): string[];
}
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