relative-timestamp.tsx

import { differenceInDays, format, formatDistanceToNow } from 'date-fns';
import { ja } from 'date-fns/locale';

export default function RelativeTimestamp({ date }: { date: Date }) {
  const diffInDays = differenceInDays(new Date(), date);

  if (diffInDays < 8) {
    return formatDistanceToNow(date, {
      locale: ja,
      addSuffix: true,
    });
  } else if (diffInDays < 365) {
    return format(date, 'MM月dd日');
  } else {
    return format(date, 'yyyy年MM月dd日');
  }
}