export function calculateAge(birthDate: string): string {
  if (!birthDate) return "";
  const birth = new Date(birthDate);
  const now = new Date();
  let years = now.getFullYear() - birth.getFullYear();
  let months = now.getMonth() - birth.getMonth();
  let days = now.getDate() - birth.getDate();
  if (days < 0) {
    months--;
    days += new Date(now.getFullYear(), now.getMonth(), 0).getDate();
  }
  if (months < 0) { years--; months += 12; }
  const parts: string[] = [];
  if (years > 0) parts.push(`${years} year${years > 1 ? "s" : ""}`);
  if (months > 0) parts.push(`${months} month${months > 1 ? "s" : ""}`);
  if (days > 0) parts.push(`${days} day${days > 1 ? "s" : ""}`);
  return parts.length > 0 ? parts.join(", ") : "Newborn";
}

export function formatAge(birthDate: string, measurementDate?: string): string {
  const birth = new Date(birthDate);
  const ref = measurementDate ? new Date(measurementDate) : new Date();
  const totalDays = (ref.getTime() - birth.getTime()) / (1000 * 60 * 60 * 24);
  const years = Math.floor(totalDays / 365);
  const months = Math.floor((totalDays % 365) / 30);
  if (years > 0 && months > 0) return `${years}y ${months}mo`;
  if (years > 0) return `${years}y`;
  if (months > 0) return `${months}mo`;
  return "Newborn";
}

export function formatTimeAgo(dateStr: string | null | undefined): string | null {
  if (!dateStr) return null;
  const diffMs = Date.now() - new Date(dateStr).getTime();
  const mins = Math.floor(diffMs / 60_000);
  const hours = Math.floor(mins / 60);
  const days = Math.floor(hours / 24);
  if (mins < 1) return "just now";
  if (mins < 60) return `${mins}m ago`;
  if (hours < 24) return `${hours}h ago`;
  return `${days}d ago`;
}