require_relative 'core'

module RubyEmail

  # a Domain Name follows the Rfc1123: https://tools.ietf.org/html/rfc1123
  class Rfc1123 < Core
    # one valid character for domain part (first name first character)
    ATEXT_FIRST_FIRST = '([A-Za-z])'
    # one valid character for domain part (first name all other characters)
    ATEXT_FIRST_ALL = '([A-Za-z0-9])'
    # one valid character for domain part (all other names)
    ATEXT_ALL = '([A-Za-z0-9\-])'

    # a valid string for domain part (first name)
    ATOM_FIRST = "#{ATEXT_FIRST_FIRST}#{ATEXT_ALL}{0,62}"
    # a valid string for domain part (all other names)
    ATOM_ALL = "#{ATEXT_FIRST_ALL}#{ATEXT_ALL}{0,62}"

    # a valid string with subdomains, separated by dots for domain part as IPV4
    IPV4 = '(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)'
    # a valid string with subdomains, separated by dots for domain part as Domain Name
    DOT_ATOM_TEXT = "((#{ATOM_ALL}\\.)*#{ATOM_FIRST})"

    # email grammar
    VALIDE = "(?<domain>(?!.{254,})((#{DOT_ATOM_TEXT})|(#{IPV4})))"

    # regexp to validate complete email
    REGEXP = Regexp.new "\\A#{VALIDE}\\Z"

    module String
      # Check if the current [::String] instance is a valid domain
      # @return [TrueClass or FalseClass]
      def is_domain?
        RubyEmail::Rfc1123.validates? self
      end
    end

  end

end