export function calculateDurationInDays(
  startDate?: string | Date,
  endDate?: string | Date
): number | null {
  if (!startDate || !endDate) return null;

  const start = new Date(startDate);
  const end = new Date(endDate);

  if (isNaN(start.getTime()) || isNaN(end.getTime())) return null;

  const diffTime = end.getTime() - start.getTime();
  const diffDays = Math.ceil(diffTime / (1000 * 60 * 60 * 24));

  return diffDays >= 0 ? diffDays : null;
}