Parse an IP Address

# title: Parse an IP Address
# source: https://rosettacode.org/wiki/Parse_an_IP_Address
# category: Rosetta Code
# difficulty: Easy
# summary: Parse dotted IPv4 strings into four validated octets.
# tags: popular, strings, parsing, networking
# vibe: 0.2

def digit_value(char)
  digits = "0123456789"
  digits.index(char)
end

def parse_octet(text)
  if text == ""
    return nil
  end

  value = 0
  index = 0

  while index < text.length
    digit = digit_value(text.slice(index))
    if digit == nil
      return nil
    end
    value = (value * 10) + digit
    index = index + 1
  end

  if value < 0 || value > 255
    return nil
  end

  value
end

def parse_ipv4(text)
  parts = text.split(".")
  if parts.size != 4
    return nil
  end

  octets = []
  index = 0
  while index < parts.size
    octet = parse_octet(parts[index])
    if octet == nil
      return nil
    end
    octets = octets + [octet]
    index = index + 1
  end

  octets
end

def run
  {
    localhost: parse_ipv4("127.0.0.1"),
    docs: parse_ipv4("192.168.10.42"),
    invalid_range: parse_ipv4("256.1.1.1"),
    invalid_shape: parse_ipv4("10.20.30")
  }
end