defmodule TcpProxy do
  use GenServer

  def start_link({watch_pid, to_host, to_port}) do
    GenServer.start_link(__MODULE__, {watch_pid, to_host, to_port})
  end

  def init({watch_pid, to_host, to_port}) do
    {:ok, socket} =
      :gen_tcp.connect(String.to_charlist(to_host), to_port, [:binary, active: true])

    {:ok, {watch_pid, socket}}
  end

  def handle_info({:tcp, _socket, data}, {watch_pid, _socket} = state) do
    send(watch_pid, {:send, data})
    {:noreply, state}
  end

  def handle_info({:send, data}, {watch_pid, socket} = state) do
    :gen_tcp.send(socket, data)
    {:noreply, state}
  end

  def handle_info({:tcp_closed, _port}, state) do
    {:stop, :normal, state}
  end
end