frontend/src/hooks/usePolling.js

import { useEffect, useRef } from "react";

/**
 * usePolling — self-rescheduling setTimeout-based polling.
 *
 * Calls `callback` every `interval` ms while `active` is true.
 * Stops automatically when `active` becomes false.
 * Cleans up on unmount.
 *
 * Uses setTimeout (not setInterval) so each poll waits for the
 * previous one to finish before scheduling the next — identical
 * to the pattern used in Documents.jsx.
 *
 * @param {() => Promise<void>} callback  Async function to call each tick.
 * @param {number}              interval  Milliseconds between polls.
 * @param {boolean}             active    Poll only while this is true.
 */
export function usePolling(callback, interval, active) {
    const timerRef = useRef(null);
    const callbackRef = useRef(callback);

    // Keep callbackRef current without restarting the effect.
    useEffect(() => {
        callbackRef.current = callback;
    }, [callback]);

    useEffect(() => {
        if (!active) {
            clearTimeout(timerRef.current);
            timerRef.current = null;
            return;
        }

        timerRef.current = setTimeout(async () => {
            await callbackRef.current();
        }, interval);

        return () => {
            clearTimeout(timerRef.current);
            timerRef.current = null;
        };
    // Re-run whenever active or the data that drives active changes.
    // interval is stable so including it has no cost.
    }, [active, interval]);
}