yeelight

# Discover request:
#
# M-SEARCH * HTTP/1.1\r\n
# HOST: 239.255.255.250:1982\r\n
# MAN: "ssdp:discover"\r\n
# ST: wifi_bulb\r\n

# Discover response:
# HTTP/1.1 200 OK
# Cache-Control: max-age=3600
# Date:
# Ext:
# Location: yeelight://192.168.1.239:55443
# Server: POSIX UPnP/1.0 YGLC/1
# id: 0x000000000015243f
# model: color
# fw_ver: 18
# support: get_prop set_default set_power toggle set_bright start_cf stop_cf set_scene
# cron_add cron_get cron_del set_ct_abx set_rgb
# 
power: on
# bright: 100
# color_mode: 2
# ct: 4000
# rgb: 16711680
# hue: 100
# sat: 35
# name: my_bulb
#
# ---------------------------------------------------------------------------------------------
#
# Notification message will have the following format:
# {method_pair, params_pair}\r\n
#
# with params_pair beeing an object type with the following format:
# {params_val_pair1, params_val_pair2, ...}
#
# Example => {"method": "props", "params":{"Power": "on", "bright: on"}}\r\n
#
# ---------------------------------------------------------------------------------------------

defmodule Discover do
  use GenServer

  defmodule State do
    defstruct udp: nil, devices: [], handlers: [], port: nil
  end

  @port 1982
  @multicast_group {239, 255, 255, 250}
  @discover_message """
  M-SEARCH * HTTP/1.1\r\n
  HOST: 239.255.255.250:1982\r\n
  MAN: "ssdp:discover"\r\n
  ST: wifi_bulb\r\n
  """

  def start_link, do: GenServer.start_link(__MODULE__, @port, name: __MODULE__)

  def start do
    start_link()
    GenServer.call(__MODULE__, :start)
  end

  def discover, do: GenServer.call(__MODULE__, :discover)

  def devices, do: GenServer.call(__MODULE__, :devices)

  @impl true
  def init(port) do
    {:ok, %State{:port => port}}
  end

  @impl true
  def handle_call(:start, _from, state) do
    {:reply, :ok,
     case state.udp do
       nil ->
         udp_options = [
           :binary,
           add_membership: {@multicast_group, {0, 0, 0, 0}},
           multicast_if: {0, 0, 0, 0},
           multicast_loop: false,
           multicast_ttl: 2,
           reuseaddr: true
         ]

         {:ok, udp} = :gen_udp.open(state.port, udp_options)

         Process.send_after(self(), :discover, 0)
         Map.update(state, :udp, udp, fn _ -> udp end)

       _exists ->
         state
     end}
  end

  def handle_call(:devices, _from, state) do
    {:reply, state.devices, state}
  end

  def handle_call(:send, _from, state) do
    :gen_udp.send(state.udp, @multicast_group, @port, discover())
    {:noreply, state}
  end

  @impl true
  def handle_info(:discover, state) do
    Process.send_after(self(), {:send, @discover_message}, (:rand.uniform() * 1000) |> round)
    Process.send_after(self(), :discover, 61000)
    {:noreply, state}
  end

  def handle_info({:send, discover}, state) do
    :gen_udp.send(state.udp, @multicast_group, @port, discover)
    {:noreply, state}
  end

  def handle_info(<<@discover_message, _::binary>>, state) do
    {:noreply, state}
  end

  def handle_info({:udp, _s, _ip, _port, <<"HTTP/1.1 200 OK\r\n", device::binary>>}, state) do
    {:noreply, device |> parse_device |> update_devices(state)}
  end

  def parse_device(body) do
    raw_params = String.split(body, ["\r\n", "\n"])

    mapped_params =
      Enum.map(raw_params, fn x ->
        case String.split(x, ":", parts: 2) do
          [k, v] -> {String.to_atom(String.downcase(k)), String.strip(v)}
          _ -> nil
        end
      end)

    map =
      Enum.reject(mapped_params, &(&1 == nil))
      |> Map.new()
      |> Map.delete(:"cache-control")
      |> Map.delete(:date)
      |> Map.delete(:ext)
      |> Map.delete(:server)

    struct!(Device, map)
  end

  def update_devices(device, state) when is_map(device) do
    case state.devices |> Enum.any?(fn d -> d.id == device.id end) do
      false -> Map.update(state, :devices, state.devices, &[device | &1])
      true -> state
    end
  end
end