function ibanMod97(iban) {
  const rearranged = iban.slice(4) + iban.slice(0, 4)
  const expanded = rearranged
    .split('')
    .map((char) => {
      const code = char.charCodeAt(0)
      if (code >= 65 && code <= 90) return String(code - 55)
      return char
    })
    .join('')

  let remainder = expanded
  while (remainder.length > 2) {
    const block = remainder.slice(0, 9)
    remainder = String(parseInt(block, 10) % 97) + remainder.slice(block.length)
  }
  return parseInt(remainder, 10) % 97
}

/** digits24: the 24 digits after the "IR" prefix */
function isValidIranSheba(digits24) {
  if (!/^\d{24}$/.test(String(digits24 || ''))) return false
  return ibanMod97(`IR${digits24}`) === 1
}

/** Standard Iranian national-code (کد ملی) checksum */
function isValidIranNationalCode(code) {
  const value = String(code || '')
  if (!/^\d{10}$/.test(value)) return false
  if (/^(\d)\1{9}$/.test(value)) return false

  const digits = value.split('').map(Number)
  const sum = digits
    .slice(0, 9)
    .reduce((acc, digit, index) => acc + digit * (10 - index), 0)
  const remainder = sum % 11
  const checkDigit = remainder < 2 ? remainder : 11 - remainder

  return checkDigit === digits[9]
}

module.exports = {
  isValidIranSheba,
  isValidIranNationalCode,
}