class UringMachine::DNSResolver

def do_resolve(hostname, type, try_count = 0)
  fd = socket_fd
  req = prepare_request_packet(hostname, type)
  msg = req.encode
  @machine.send(fd, msg, msg.bytesize, 0)
  buf = +''
  @machine.recv(fd, buf, 16384, 0)
  msg = Resolv::DNS::Message.decode buf
  addrs = []
  msg.each_answer do |name, ttl, data|
    p [name, ttl, data]
    if data.kind_of?(Resolv::DNS::Resource::IN::A) ||
      data.kind_of?(Resolv::DNS::Resource::IN::AAAA)
      addrs << data.address.to_s
    end
  end
  addrs
end

def get_nameservers
  nameservers = []
  IO.readlines('/etc/resolv.conf').each do |line|
    if line =~ /^nameserver (.+)$/
      nameservers << $1.split(/\s+/).first
    end
  end
  nameservers
end

def handle_requests_loop
  while true
    hostname, type, fiber = @machine.shift(@requests)
    res = do_resolve(hostname, type)
    @machine.schedule(fiber, res)
  end
end

def initialize(machine)
  @machine = machine
  @requests = UM::Queue.new
  @nameservers = get_nameservers
  @fiber = @machine.spin { handle_requests_loop }
  @last_id = 0
  @cache = {}
end

def msg_type(type)
  # TODO: add support for other types
  Resolv::DNS::Resource::IN::A
end

def prepare_request_packet(hostname, type)
  msg = Resolv::DNS::Message.new
  msg.id = (@last_id += 1)
  msg.rd = 1
  msg.add_question hostname, msg_type(type)
  msg
end

def prepare_socket
  fd = @machine.socket(UM::AF_INET, UM::SOCK_DGRAM, 0, 0)
  @machine.bind(fd, '0.0.0.0', 0)
  @machine.connect(fd, @nameservers.sample, 53)
  fd
end

def resolve(hostname, type)
  @machine.push(@requests, [hostname, type, Fiber.current])
  @machine.yield
end

def socket_fd
  @socket_fd ||= prepare_socket
end