export function isValidIso(iso: string): boolean {
  if (!/^\d{4}-\d{2}-\d{2}$/.test(iso)) return false
  const [y, m, d] = iso.split('-').map(Number)
  const date = new Date(y, m - 1, d)
  return date.getFullYear() === y && date.getMonth() === m - 1 && date.getDate() === d
}

export function formatIsoToDisplay(iso: string | null): string {
  if (!iso || !isValidIso(iso)) return ''
  const [y, m, d] = iso.split('-')
  return `${d}/${m}/${y}`
}

export function parseDisplayToIso(display: string): string | null {
  const match = /^(\d{2})\/(\d{2})\/(\d{4})$/.exec(display.trim())
  if (!match) return null
  const [, dd, mm, yyyy] = match
  const iso = `${yyyy}-${mm}-${dd}`
  return isValidIso(iso) ? iso : null
}

export function isDateInRange(iso: string, min?: string, max?: string): boolean {
  if (min && iso < min) return false
  if (max && iso > max) return false
  return true
}

export function isMonthInRange(year: number, month: number, min?: string, max?: string): boolean {
  const ym = `${year}-${String(month + 1).padStart(2, '0')}`
  if (min && ym < min.slice(0, 7)) return false
  if (max && ym > max.slice(0, 7)) return false
  return true
}

export function isYearInRange(year: number, min?: string, max?: string): boolean {
  if (min && year < Number(min.slice(0, 4))) return false
  if (max && year > Number(max.slice(0, 4))) return false
  return true
}