// Short "Xs/m/h/d/mo/y" relative time without "ago" suffix (ProjectSidebar).
export function relTime(iso: string): string {
  const now = Date.now();
  const t = Date.parse(iso);
  if (Number.isNaN(t)) return '';
  const sec = Math.max(0, Math.floor((now - t) / 1000));
  if (sec < 60) return `${sec}s`;
  const min = Math.floor(sec / 60);
  if (min < 60) return `${min}m`;
  const hr = Math.floor(min / 60);
  if (hr < 24) return `${hr}h`;
  const day = Math.floor(hr / 24);
  if (day < 30) return `${day}d`;
  const mo = Math.floor(day / 30);
  if (mo < 12) return `${mo}mo`;
  return `${Math.floor(mo / 12)}y`;
}

// "just now / Xm ago / Xh ago / Xd ago" with locale-date fallback for >7d
// (SessionLandingPage).
export function formatRelative(iso: string): string {
  const then = new Date(iso).getTime();
  if (Number.isNaN(then)) return '';
  const s = Math.max(0, Math.round((Date.now() - then) / 1000));
  if (s < 60) return 'just now';
  const m = Math.round(s / 60);
  if (m < 60) return `${m}m ago`;
  const h = Math.round(m / 60);
  if (h < 24) return `${h}h ago`;
  const d = Math.round(h / 24);
  if (d < 7) return `${d}d ago`;
  return new Date(iso).toLocaleDateString();
}

// "just now / Xm ago / Xh ago / Xd ago" with no full-date fallback (AgentPicker).
export function formatAgo(iso: string): string {
  const then = new Date(iso).getTime();
  if (Number.isNaN(then)) return '—';
  const diff = Date.now() - then;
  if (diff < 60_000) return 'just now';
  if (diff < 3_600_000) return `${Math.round(diff / 60_000)}m ago`;
  if (diff < 86_400_000) return `${Math.round(diff / 3_600_000)}h ago`;
  return `${Math.round(diff / 86_400_000)}d ago`;
}