Refactor modules into contexts (#78)

* [WIP] break out a few contexts, start refactoring fast index modules

* [WIP] more contexts, this time around slow indexing and downloads

* [WIP] got all tests passing

* [WIP] Added moduledocs

* Built a genserver to rename old jobs on boot

* Added a module naming check; moved things around

* Fixed specs

lib/pinchflat/filesystem/filesystem_helpers.ex

@@ -0,0 +1,38 @@
+defmodule Pinchflat.Filesystem.FilesystemHelpers do
+  @moduledoc """
+  Utility methods for working with the filesystem
+  """
+  alias Pinchflat.Media
+  alias Pinchflat.Utils.StringUtils
+
+  @doc """
+  Generates a temporary file and returns its path. The file is empty and has the given type.
+  Generates all the directories in the path if they don't exist.
+
+  Returns binary()
+  """
+  def generate_metadata_tmpfile(type) do
+    tmpfile_directory = Application.get_env(:pinchflat, :tmpfile_directory)
+    filepath = Path.join([tmpfile_directory, "#{StringUtils.random_string(64)}.#{type}"])
+
+    :ok = File.mkdir_p!(Path.dirname(filepath))
+    :ok = File.write(filepath, "")
+
+    filepath
+  end
+
+  @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