module.exports = function inet_pton(a) {
  //  discuss at: https://locutus.io/php/inet_pton/
  // original by: Theriault (https://github.com/Theriault)
  // improved by: alromh87 and JamieSlome
  //   example 1: inet_pton('::')
  //   returns 1: '\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0'
  //   example 2: inet_pton('127.0.0.1')
  //   returns 2: '\x7F\x00\x00\x01'

  let m
  let i
  let j
  const f = String.fromCharCode

  // IPv4
  m = a.match(/^(?:\d{1,3}(?:\.|$)){4}/)
  if (m) {
    m = m[0].split('.')
    m = f(m[0], m[1], m[2], m[3])
    // Return if 4 bytes, otherwise false.
    return m.length === 4 ? m : false
  }

  // IPv6
  if (a.length > 39) {
    return false
  }

  m = a.split('::')

  if (m.length > 2) {
    return false
  } // :: can't be used more than once in IPv6.

  const reHexDigits = /^[\da-f]{1,4}$/i

  for (j = 0; j < m.length; j++) {
    if (m[j].length === 0) {
      // Skip if empty.
      continue
    }
    m[j] = m[j].split(':')
    for (i = 0; i < m[j].length; i++) {
      let hextet = m[j][i]
      // check if valid hex string up to 4 chars
      if (!reHexDigits.test(hextet)) {
        return false
      }

      hextet = parseInt(hextet, 16)

      // Would be NaN if it was blank, return false.
      if (isNaN(hextet)) {
        // Invalid IP.
        return false
      }
      m[j][i] = f(hextet >> 8, hextet & 0xff)
    }
    m[j] = m[j].join('')
  }

  return m.join('\x00'.repeat(16 - m.reduce((tl, m) => tl + m.length, 0)))
}