# frozen_string_literal: true
require 'resolv'
require 'socket'
require 'net/ping/tcp'

module Netchk
  class DNSServerVerifier
    def verify
      nameservers = self.nameservers
      if nameservers.empty?
        $stderr.puts "No DNS server found. Verify your configuration."
      else
        puts "Using DNS servers #{nameservers.map { |ns| ns.join('#') }.join(', ')}"
        nameservers.map do |ns|
          verify_nameserver(*ns)
        end
      end
    end


    private
      def verify_nameserver(ip, port)
        ping = Net::Ping::TCP.new(ip, port)
        unless ping.ping?
          $stderr.puts "Failed to ping DNS server #{ip}:#{port}"
        end
      end

      def nameservers
        # Dirty trick to get default nameserver list from /etc/resolv.conf
        # without parsing the file manually.
        ::Resolv::DNS.open do |dns|
          dns.lazy_initialize
          dns.instance_variable_get("@config").instance_variable_get("@nameserver_port")
        end
      end
  end
end