First pass at uniformed types, specs and docs

- spec public functions (skipping controllers, views, live views and
components)
- use types instead of explanations in docs
- remove redundant docs
- fix typos

lib/music_library/assets/asset.ex

@@ -14,6 +14,9 @@ defmodule MusicLibrary.Assets.Asset do
     timestamps(type: :utc_datetime)
   end
 
+  @type t :: %__MODULE__{}
+
+  @spec changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
   def changeset(asset, attrs) do
     asset
     |> cast(attrs, [:content, :format, :properties])
@@ -22,6 +25,7 @@ defmodule MusicLibrary.Assets.Asset do
     |> unique_constraint(:hash)
   end
 
+  @spec image_changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
   def image_changeset(asset, attrs) do
     asset
     |> cast(attrs, [:content, :format])
@@ -60,6 +64,7 @@ defmodule MusicLibrary.Assets.Asset do
     }
   end
 
+  @spec hash(binary()) :: String.t()
   def hash(content) do
     :crypto.hash(:sha256, content) |> Base.encode16()
   end

lib/music_library/assets/cache.ex

@@ -1,13 +1,16 @@
 defmodule MusicLibrary.Assets.Cache do
+  @spec new() :: :ets.table()
   def new do
     :ets.new(__MODULE__, [:named_table, :public, :compressed, read_concurrency: true])
   end
 
+  @spec set(String.t(), String.t(), binary()) :: true
   def set(payload, format, content) do
     inserted_at = DateTime.utc_now() |> DateTime.to_unix()
     :ets.insert(__MODULE__, {{payload, format}, inserted_at, content})
   end
 
+  @spec get(String.t(), String.t()) :: {:found, binary()} | :not_found
   def get(payload, format) do
     case :ets.lookup(__MODULE__, {payload, format}) do
       [{{^payload, ^format}, _inserted_at, content}] -> {:found, content}
@@ -15,6 +18,7 @@ defmodule MusicLibrary.Assets.Cache do
     end
   end
 
+  @spec total_content_size() :: non_neg_integer()
   def total_content_size do
     :ets.foldl(
       fn {_key, _inserted_at, content}, acc -> acc + byte_size(content) end,
@@ -23,6 +27,7 @@ defmodule MusicLibrary.Assets.Cache do
     )
   end
 
+  @spec prune(non_neg_integer()) :: non_neg_integer()
   def prune(older_than_seconds) do
     threshold =
       DateTime.utc_now()

lib/music_library/assets/image.ex

@@ -9,13 +9,16 @@ defmodule MusicLibrary.Assets.Image do
   @default_size 2000
   @default_format "image/jpeg"
 
+  @spec fallback_data() :: binary()
   def fallback_data, do: unquote(fallback_data)
 
+  @spec resize(binary(), pos_integer(), String.t()) :: {:ok, binary()} | {:error, term()}
   def resize(cover_data, size \\ @default_size, format \\ @default_format) do
     {:ok, thumb} = Operation.thumbnail_buffer(cover_data, size)
     Image.write_to_buffer(thumb, extension(format))
   end
 
+  @spec convert(binary(), String.t(), String.t()) :: {:ok, binary()}
   def convert(cover_data, data_format, target_format) do
     if data_format == target_format do
       {:ok, cover_data}

lib/music_library/assets/transform.ex

@@ -5,6 +5,7 @@ defmodule MusicLibrary.Assets.Transform do
   @type t :: %__MODULE__{}
   @type payload :: String.t()
 
+  @spec new(map()) :: t()
   def new(attrs \\ %{}), do: struct!(__MODULE__, attrs)
 
   @doc """