digital-pilates/hooks/useCountdown.ts

import { useEffect, useMemo, useRef, useState } from 'react';
import { formatCountdown } from '@/utils/fasting';

interface CountdownOptions {
  target: Date | null | undefined;
  intervalMs?: number;
  autoStart?: boolean;
}

export const useCountdown = ({ target, intervalMs = 1000, autoStart = true }: CountdownOptions) => {
  const [now, setNow] = useState(() => new Date());
  const timerRef = useRef<ReturnType<typeof setInterval> | null>(null);
  const targetTimestamp = target instanceof Date ? target.getTime() : null;

  useEffect(() => {
    if (!autoStart) return undefined;
    if (targetTimestamp == null) return undefined;

    timerRef.current && clearInterval(timerRef.current);
    timerRef.current = setInterval(() => {
      setNow(new Date());
    }, intervalMs);

    return () => {
      if (timerRef.current) {
        clearInterval(timerRef.current);
        timerRef.current = null;
      }
    };
  }, [targetTimestamp, intervalMs, autoStart]);

  useEffect(() => {
    if (targetTimestamp == null) return;
    setNow(new Date());
  }, [targetTimestamp]);

  const diffMs = useMemo(() => {
    if (targetTimestamp == null) return 0;
    return targetTimestamp - now.getTime();
  }, [targetTimestamp, now]);

  const formatted = useMemo(() => {
    if (targetTimestamp == null) return '--:--:--';
    return formatCountdown(new Date(targetTimestamp), now);
  }, [targetTimestamp, now]);

  return {
    now,
    diffMs,
    formatted,
    isExpired: diffMs <= 0,
    hasTarget: targetTimestamp != null,
  };
};