function isValidDateKey(value) {
  if (!/^\d{4}-\d{2}-\d{2}$/.test(String(value || ""))) return false;
  const date = new Date(`${value}T00:00:00Z`);
  return (
    !Number.isNaN(date.getTime()) && date.toISOString().slice(0, 10) === value
  );
}

module.exports = { isValidDateKey };