Added way to track media filesize (#48)

lib/pinchflat/tasks/media_item_tasks.ex

@@ -0,0 +1,22 @@
+defmodule Pinchflat.Tasks.MediaItemTasks do
+  @moduledoc """
+  This module contains methods used by or used to control tasks (aka workers)
+  related to media items.
+  """
+  alias Pinchflat.Media
+
+  @doc """
+  Fetches the file size of a media item and saves it to the database.
+
+  Returns {:ok, media_item} | {:error, any()}
+  """
+  def compute_and_save_media_filesize(media_item) do
+    case File.stat(media_item.media_filepath) do
+      {:ok, %{size: size}} ->
+        Media.update_media_item(media_item, %{media_size_bytes: size})
+
+      err ->
+        err
+    end
+  end
+end