module Net # :nodoc:
  module DNS
    class RR

      #
      # = Mail Exchange Record (MX)
      #
      # Class for DNS MX resource records.
      #
      # A MX record specifies the name and relative preference of mail servers
      # (mail exchangers in the DNS jargon) for the zone.
      # The MX RR is used by SMTP (Mail) Agents to route mail for the domain.
      #
      class MX < RR

        # Gets the preference value.
        #
        # Returns an Integer.
        def preference
          @preference
        end

        # Gets the exchange value.
        #
        # Returns a String.
        def exchange
          @exchange
        end

        # Gets the standardized value for this record,
        # represented by the value of <tt>preference</tt> and <tt>exchange</tt>.
        #
        # Returns a String.
        def value
          "#{preference} #{exchange}"
        end


        private

          def subclass_new_from_hash(options)
            if options.has_key?(:preference) && options.has_key?(:exchange)
              @preference = options[:preference].to_i
              @exchange = options[:exchange]
            else
              raise ArgumentError, ":preference and :exchange fields are mandatory"
            end
          end

          def subclass_new_from_string(str)
            @preference, @exchange = check_mx(str)
          end

          def subclass_new_from_binary(data, offset)
            @preference = data.unpack("@#{offset} n")[0]
            offset += 2
            @exchange, offset = dn_expand(data, offset)
            offset
          end


          def set_type
            @type = Net::DNS::RR::Types.new("MX")
          end

          def get_inspect
            value
          end


          def check_mx(input)
            str = input.to_s
            unless str.strip =~ /^(\d+)\s+(\S+)$/
              raise ArgumentError, "Invalid MX section `#{str}'"
            end
            [$1.to_i, $2]
          end

          def build_pack
            @mx_pack = [@preference].pack("n") + pack_name(@exchange)
            @rdlength = @mx_pack.size
          end

          def get_data
            @mx_pack
          end

      end

    end
  end
end