const UNITS: Array<[string, number]> = [
  ['year', 365 * 24 * 60 * 60],
  ['day', 24 * 60 * 60],
  ['hr', 60 * 60],
  ['min', 60],
];

// "just now", "1 min ago", "10 min ago", "3 days ago", …
export function formatRelativeTime(iso: string | null, now: number = Date.now()): string {
  if (!iso) {
    return 'never';
  }
  const seconds = Math.floor((now - new Date(iso).getTime()) / 1000);
  if (seconds < 45) {
    return 'just now';
  }
  for (const [label, secondsPerUnit] of UNITS) {
    const value = Math.floor(seconds / secondsPerUnit);
    if (value >= 1) {
      return `${value} ${label}${value === 1 ? '' : 's'} ago`;
    }
  }
  return 'just now';
}