/**
 * Validates a CNPJ (Cadastro Nacional da Pessoa Jurídica)
 * Checks format and verifies check digits
 */
export function validateCNPJ(cnpj: string): boolean {
  // Remove non-numeric characters
  const cleaned = cnpj.replace(/\D/g, '')

  // Must have exactly 14 digits
  if (cleaned.length !== 14) {
    return false
  }

  // All same digits are invalid
  if (/^(\d)\1{13}$/.test(cleaned)) {
    return false
  }

  // Validate first check digit
  let sum = 0
  let position = 5
  for (let i = 0; i < 8; i++) {
    sum += parseInt(cleaned[i]) * position
    position -= 1
  }
  let remainder = sum % 11
  const firstDigit = remainder < 2 ? 0 : 11 - remainder

  if (parseInt(cleaned[8]) !== firstDigit) {
    return false
  }

  // Validate second check digit
  sum = 0
  position = 9
  for (let i = 0; i < 9; i++) {
    sum += parseInt(cleaned[i]) * position
    position -= 1
  }
  remainder = sum % 11
  const secondDigit = remainder < 2 ? 0 : 11 - remainder

  if (parseInt(cleaned[9]) !== secondDigit) {
    return false
  }

  return true
}

/**
 * Formats a CNPJ string to the standard format: 00.000.000/0000-00
 * Accepts both formatted and unformatted input
 */
export function formatCNPJ(value: string): string {
  const cleaned = value.replace(/\D/g, '').slice(0, 14)

  if (cleaned.length === 0) return ''
  if (cleaned.length <= 2) return cleaned
  if (cleaned.length <= 5) return `${cleaned.slice(0, 2)}.${cleaned.slice(2)}`
  if (cleaned.length <= 8) return `${cleaned.slice(0, 2)}.${cleaned.slice(2, 5)}.${cleaned.slice(5)}`
  if (cleaned.length <= 12) return `${cleaned.slice(0, 2)}.${cleaned.slice(2, 5)}.${cleaned.slice(5, 8)}/${cleaned.slice(8)}`
  return `${cleaned.slice(0, 2)}.${cleaned.slice(2, 5)}.${cleaned.slice(5, 8)}/${cleaned.slice(8, 12)}-${cleaned.slice(12)}`
}

/**
 * Removes CNPJ formatting, returning only digits
 */
export function removeCNPJFormatting(cnpj: string): string {
  return cnpj.replace(/\D/g, '')
}