defmodule DNS do
  import Socket.Datagram, only: [send!: 3, recv!: 1]

  @doc """
  TODO: docs
  TODO: handle errors
  """
  @spec resolve(char_list | char_list, { String.t, :inet.port }) :: {atom, :inet.ip} | {atom, atom}
  def resolve(domain, dns_server \\ { "8.8.8.8", 53 }) do
    case query(domain, dns_server).anlist do
      answers when is_list(answers) and length(answers) > 0 ->
        data =
          answers
          |> Enum.map(&(&1.data))
          |> Enum.reject(&is_nil/1)

        {:ok, data}
      _ ->
        {:error, :not_found}
    end
  end

  @doc """
  TODO: docs
  """
  @spec query(char_list | char_list, { String.t, :inet.port }) :: DNS.Record.t
  def query(domain, dns_server \\ { "8.8.8.8", 53 }) do
    record = %DNS.Record{
      header: %DNS.Header{rd: true},
      qdlist: [%DNS.Query{domain: to_char_list(domain), type: :a, class: :in}]
    }

    client = Socket.UDP.open!(0)

    send!(client, DNS.Record.encode(record), dns_server)

    { data, _server } = recv!(client)
    DNS.Record.decode(data)
  end
end