defmodule TcpWatcher do
  use GenServer

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

  def init({to_host, to_port, listen_socket}) do
    {:ok, {to_host, to_port, listen_socket}, {:continue, :accept}}
  end

  def handle_continue(:accept, {to_host, to_port, listen_socket} = _state) do
    {:ok, socket} = :gen_tcp.accept(listen_socket)
    start_link({to_host, to_port, listen_socket})
    {:ok, proxy_id} = TcpProxy.start_link({self(), to_host, to_port})
    {:noreply, {to_host, to_port, listen_socket, socket, proxy_id}}
  end

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

  def handle_info(
        {:tcp, _socket, data},
        {_to_host, _to_port, _listen_socket, _socket, proxy_id} = state
      ) do
    send(proxy_id, {:send, data})
    {:noreply, state}
  end

  def handle_info({:send, data}, {_to_host, _to_port, _listen_socket, socket, _proxy_id} = state) do
    :gen_tcp.send(socket, data)
    {:noreply, state}
  end
end