const dateTimeFmt = new Intl.DateTimeFormat(undefined, { dateStyle: 'medium', timeStyle: 'short' });
const timeFmt = new Intl.DateTimeFormat(undefined, { timeStyle: 'medium' });
const relFmt = new Intl.RelativeTimeFormat(undefined, { numeric: 'auto' });

const REL_UNITS = [
  ['year', 31_536_000], ['month', 2_592_000], ['week', 604_800],
  ['day', 86_400], ['hour', 3_600], ['minute', 60],
];

export function parseDate(value) {
  if (!value) return null;
  const d = new Date(value);
  return Number.isNaN(d.getTime()) ? null : d;
}

export const formatDateTime = (d) => (d ? dateTimeFmt.format(d) : '—');
export const formatTime = (d) => timeFmt.format(d);

export function formatRelative(d, now = Date.now()) {
  if (!d) return '';
  const diffSec = Math.round((d.getTime() - now) / 1000);
  for (const [unit, secs] of REL_UNITS) {
    if (Math.abs(diffSec) >= secs) return relFmt.format(Math.round(diffSec / secs), unit);
  }
  return relFmt.format(diffSec, 'second');
}

export function formatDuration(totalSec) {
  if (totalSec == null || Number.isNaN(Number(totalSec))) return null;
  const s = Math.max(0, Math.round(totalSec));
  const h = Math.floor(s / 3600);
  const m = Math.floor((s % 3600) / 60);
  const sec = s % 60;
  return [h && `${h}h`, (h || m) && `${m}m`, `${sec}s`].filter(Boolean).join(' ');
}

export function formatBytes(bytes) {
  if (bytes == null || Number.isNaN(Number(bytes))) return null;
  const units = ['B', 'KB', 'MB', 'GB', 'TB', 'PB'];
  let n = Number(bytes);
  let i = 0;
  while (n >= 1024 && i < units.length - 1) { n /= 1024; i++; }
  return `${n.toFixed(i === 0 ? 0 : 1)} ${units[i]}`;
}