import { useCallback, useEffect, useRef } from 'react';
import { viewerEpoch } from '../utils/writeThroughHold';

// Call it as an action starts; the check it returns says whether the page that started it is still shown to the same
// viewer, so a completion that arrives later does nothing on the page or app that replaced it.
export const useLifetime = (): (() => () => boolean) => {
    const mountedRef = useRef(true);
    useEffect(() => {
        mountedRef.current = true;
        return () => { mountedRef.current = false; };
    }, []);
    return useCallback(() => {
        const viewer = viewerEpoch();
        return () => mountedRef.current && viewer === viewerEpoch();
    }, []);
};