/**
 * Follow-mode — let a user "follow" another participant so their viewport
 * tracks wherever that participant navigates.
 *
 * The followed participant publishes their viewport via setPresence().
 * useFollowUser watches their presence and calls a callback whenever it
 * changes so the consumer can scroll/zoom to match.
 *
 * Viewport publishing is opt-in via setPresence("viewport", { ... }).
 * This module handles the consumer (follower) side only.
 */
import type { OtherPresence } from "./presence.js";
export interface ViewportDescriptor {
    /** Active document / file ID being viewed. */
    fileId?: string;
    /** Scroll position. */
    scrollX?: number;
    scrollY?: number;
    /** Zoom level (1.0 = 100%). */
    zoom?: number;
    /** Normalized cursor last seen (0–1). */
    cursorX?: number;
    cursorY?: number;
}
export interface UseFollowUserOptions {
    /** Remote participants list from usePresence. */
    others: OtherPresence[];
    /**
     * The client ID to follow. Pass null / undefined to stop following.
     */
    followingId: number | null | undefined;
    /**
     * Key inside presence payload that carries viewport info.
     * Default: "viewport"
     */
    viewportKey?: string;
    /**
     * Called whenever the followed participant's viewport changes.
     * Consumers should scroll/zoom to the described viewport in here.
     */
    onViewport: (viewport: ViewportDescriptor) => void;
}
export interface UseFollowUserResult {
    /** The currently followed client ID, or null. */
    followingId: number | null;
    /** True when actively following someone. */
    isFollowing: boolean;
    /** Stop following the current target. */
    stopFollowing: () => void;
}
/**
 * Watch a specific participant's viewport presence and invoke onViewport
 * when it changes.
 */
export declare function useFollowUser({ others, followingId, viewportKey, onViewport, }: UseFollowUserOptions): UseFollowUserResult;
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