feat: add /song command

/song command will show the song currently playing.

lib/sergei/consumer.ex

@@ -18,7 +18,8 @@ defmodule Sergei.Consumer do
     {"ping", "Pong", []},
     {"play", "Play a song or resume playback", @play_opts},
     {"pause", "Pause media playback", []},
-    {"stop", "Stop media playback and leave the voice channel", []}
+    {"stop", "Stop media playback and leave the voice channel", []},
+    {"song", "What song is currently playing?", []}
   ]
 
   def start_link do
@@ -159,4 +160,15 @@ defmodule Sergei.Consumer do
         {:error, "This is embarrasing..."}
     end
   end
+
+  # /song
+  def do_command(%{guild_id: guild_id, data: %{name: "song"}}) do
+    case Sergei.Player.get_current_song(guild_id) do
+      :not_playing ->
+        {:ok, "I'm not playing anything right now."}
+
+      url ->
+        {:ok, url}
+    end
+  end
 end

lib/sergei/player.ex

@@ -35,6 +35,11 @@ defmodule Sergei.Player do
     GenServer.call(__MODULE__, {:stop, guild_id})
   end
 
+  @spec get_current_song(integer()) :: String.t() | :not_playing
+  def get_current_song(guild_id) do
+    GenServer.call(__MODULE__, {:get_current_song, guild_id})
+  end
+
   # Server
   @impl true
   def handle_info(:tick, state) do
@@ -103,6 +108,18 @@ defmodule Sergei.Player do
     {:reply, :ok, Map.delete(state, guild_id)}
   end
 
+  @impl true
+  def handle_call({:get_current_song, guild_id}, _from, state) do
+    res =
+      case Map.get(state, guild_id) do
+        %{url: url} -> url
+        nil -> :not_playing
+        _ -> Logger.error("error: Guild found, but no URL is given")
+      end
+
+    {:reply, res, state}
+  end
+
   def play_music(guild_id, channel_id, url) do
     cond do
       Voice.get_channel_id(guild_id) != channel_id ->