Refactoring of Media context

lib/mobilizon/media/file.ex

@@ -1,9 +1,22 @@
 defmodule Mobilizon.Media.File do
   @moduledoc """
-  Represents a file entity
+  Represents a file entity.
   """
+
   use Ecto.Schema
-  import Ecto.Changeset
+
+  import Ecto.Changeset, only: [cast: 3, validate_required: 2]
+
+  @type t :: %__MODULE__{
+          name: String.t(),
+          url: String.t(),
+          content_type: String.t(),
+          size: integer
+        }
+
+  @required_attrs [:name, :url]
+  @optional_attrs [:content_type, :size]
+  @attrs @required_attrs ++ @optional_attrs
 
   embedded_schema do
     field(:name, :string)
@@ -15,9 +28,10 @@ defmodule Mobilizon.Media.File do
   end
 
   @doc false
-  def changeset(picture, attrs) do
-    picture
-    |> cast(attrs, [:name, :url, :content_type, :size])
-    |> validate_required([:name, :url])
+  @spec changeset(t | Ecto.Changeset.t(), map) :: Ecto.Changeset.t()
+  def changeset(file, attrs) do
+    file
+    |> cast(attrs, @attrs)
+    |> validate_required(@required_attrs)
   end
 end