defmodule Toolshed.Core.Lsusb do
  @doc """
  Print out information on all of the connected USB devices.
  """
  @spec lsusb() :: :"do not show this result in output"
  def lsusb() do
    Enum.each(Path.wildcard("/sys/bus/usb/devices/*/uevent"), &print_usb/1)
    IEx.dont_display_result()
  end

  defp print_usb(uevent_path) do
    File.read!(uevent_path)
    |> parse_kv_config()
    |> find_more_usb_info(Path.dirname(uevent_path))
    |> print_usb_info()
  end

  defp print_usb_info(%{"DEVTYPE" => "usb_device"} = info) do
    vidpid = to_vidpid(info["PRODUCT"])

    IO.puts(
      "Bus #{info["BUSNUM"]} Device #{info["DEVNUM"]}: ID #{vidpid} #{info["manufacturer"]} #{info["product"]}"
    )
  end

  defp print_usb_info(_info), do: :ok

  defp to_vidpid(""), do: "?"

  defp to_vidpid(raw) do
    # The VIDPID comes in as "vid/pid/somethingelse"
    [vid_str, pid_str, _] = String.split(raw, "/", trim: true)
    vid = String.pad_leading(vid_str, 4, "0")
    pid = String.pad_leading(pid_str, 4, "0")
    vid <> ":" <> pid
  end

  defp parse_kv_config(contents) do
    contents
    |> String.split("\n")
    |> Enum.flat_map(&parse_kv/1)
    |> Enum.into(%{})
  end

  defp parse_kv(""), do: []
  defp parse_kv(<<"#", _rest::binary>>), do: []

  defp parse_kv(key_equals_value) do
    [key, value] = String.split(key_equals_value, "=", parts: 2, trim: true)
    [{key, value}]
  end

  defp find_more_usb_info(info, sysfs_path) do
    with {:ok, manufacturer} <- File.read(Path.join(sysfs_path, "manufacturer")),
         {:ok, product} <- File.read(Path.join(sysfs_path, "product")) do
      info
      |> Map.put("manufacturer", String.trim(manufacturer))
      |> Map.put("product", String.trim(product))
    else
      _ -> info
    end
  end
end