26. Countdown — odliczanie do dat

function useCountdown(targetDate) {
  const [timeLeft, setTimeLeft] = useState(calculateTimeLeft(targetDate));

  useEffect(() => {
    const interval = setInterval(() => {
      setTimeLeft(calculateTimeLeft(targetDate));
    }, 1000);
    return () => clearInterval(interval);
  }, [targetDate]);

  return timeLeft;
}

function calculateTimeLeft(targetDate) {
  const diff = new Date(targetDate) - new Date();
  if (diff <= 0) return { days: 0, hours: 0, minutes: 0, seconds: 0, passed: true };

  return {
    days: Math.floor(diff / (1000 * 60 * 60 * 24)),
    hours: Math.floor((diff % (1000 * 60 * 60 * 24)) / (1000 * 60 * 60)),
    minutes: Math.floor((diff % (1000 * 60 * 60)) / (1000 * 60)),
    seconds: Math.floor((diff % (1000 * 60)) / 1000),
    passed: false,
  };
}