defmodule P2pChat.Transport.GenTun do
  require Logger
  require P2pChat.Transport.PrimTun, as: PrimTun

  @behaviour GenServer

  defstruct [:tun_handle]

  #
  # Server API
  # 
  @impl true
  def init(_args) do
    {:ok, tun_handle} = PrimTun.make_tun_device(true)
    state = %__MODULE__{tun_handle: tun_handle}
    { :ok, state, { :continue, :recv } }
  end

  @impl true
  def handle_continue(:recv, state) do
    case PrimTun.tun_recv(state.tun_handle, 2**16) do
       {:ok, buf} ->
         Logger.debug("Received #{byte_size(buf)} bytes")
       {:error, :would_block} -> {}
       {:error, e} ->
         Logger.error("Error during receive: #{e}")
    end
    
    {:noreply, state}
  end

  @impl true
  def handle_call({:get_addrs}, _from, state) do
    result = PrimTun.get_addrs(state.tun_handle)
    {:reply, result, state}
  end

  #
  # Client API
  # 
  def open() do
    GenServer.start_link(__MODULE__, nil)
  end

  def get_addrs(pid) do
    GenServer.call(pid, {:get_addrs})
  end
end