Add types and specs for LastFm module

lib/last_fm/album.ex

@@ -1,3 +1,8 @@
 defmodule LastFm.Album do
   defstruct [:musicbrainz_id, :title]
+
+  @type t :: %__MODULE__{
+          musicbrainz_id: String.t(),
+          title: String.t()
+        }
 end

lib/last_fm/api_behaviour.ex

@@ -3,5 +3,5 @@ defmodule LastFm.APIBehaviour do
 
   @type user :: String.t()
   @type api_key :: String.t()
-  @callback get_recent_tracks(user, api_key) :: {:ok, [%Track{}]} | {:error, String.t()}
+  @callback get_recent_tracks(user, api_key) :: {:ok, [Track.t()]} | {:error, String.t()}
 end

lib/last_fm/artist.ex

@@ -1,3 +1,8 @@
 defmodule LastFm.Artist do
   defstruct [:musicbrainz_id, :name]
+
+  @type t :: %__MODULE__{
+          musicbrainz_id: String.t(),
+          name: String.t()
+        }
 end

lib/last_fm/feed.ex

@@ -6,11 +6,14 @@ defmodule LastFm.Feed do
   is technically prone to collision, it's very unlikely for that to happen due to the
   nature of the data.
   """
+
+  @spec create_table!() :: :ok | no_return
   def create_table! do
     __MODULE__ = :ets.new(__MODULE__, [:ordered_set, :named_table, :public])
     :ok
   end
 
+  @spec update([LastFm.Track.t()]) :: :ok | no_return
   def update(tracks) do
     data = Enum.map(tracks, fn t -> {t.scrobbled_at_uts, t} end)
 
@@ -20,6 +23,7 @@ defmodule LastFm.Feed do
     Phoenix.PubSub.broadcast(LastFm.PubSub, "feed:update", %{tracks: tracks})
   end
 
+  @spec all() :: [LastFm.Track.t()]
   def all do
     m = [
       {
@@ -29,9 +33,11 @@ defmodule LastFm.Feed do
       }
     ]
 
+    # reversing to get tracks in DESC order
     :ets.select_reverse(__MODULE__, m)
   end
 
+  @spec subscribe() :: :ok
   def subscribe do
     Phoenix.PubSub.subscribe(LastFm.PubSub, "feed:update")
   end

lib/last_fm/refresh.ex

@@ -5,11 +5,20 @@ defmodule LastFm.Refresh do
 
   alias LastFm.Feed
 
+  @type config :: %{
+          api: module(),
+          api_key: String.t(),
+          user: String.t(),
+          refresh_interval: pos_integer()
+        }
+
+  @spec start_link(config) :: GenServer.on_start()
   def start_link(config) do
     GenServer.start_link(__MODULE__, config, name: __MODULE__)
   end
 
   @impl true
+  @spec init(config) :: {:ok, config, {:continue, :refresh}} | :ignore
   def init(config) do
     config = Map.new(config)
 
@@ -21,9 +30,11 @@ defmodule LastFm.Refresh do
   end
 
   @impl true
+  @spec handle_continue(atom(), config) :: {:noreply, config}
   def handle_continue(:refresh, config), do: refresh(config)
 
   @impl true
+  @spec handle_info(atom(), config) :: {:noreply, config}
   def handle_info(:refresh, config), do: refresh(config)
 
   defp refresh(config) do

lib/last_fm/track.ex

@@ -17,6 +17,16 @@ defmodule LastFm.Track do
     :scrobbled_at_label
   ]
 
+  @type t :: %__MODULE__{
+          musicbrainz_id: String.t(),
+          title: String.t(),
+          artist: Artist.t(),
+          album: Album.t(),
+          cover_url: String.t(),
+          scrobbled_at_uts: integer(),
+          scrobbled_at_label: String.t()
+        }
+
   def from_api_response(raw_tracks) do
     Enum.map(raw_tracks, fn t ->
       album = %Album{