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/downloading/media_download_worker.ex

@@ -0,0 +1,56 @@
+defmodule Pinchflat.Downloading.MediaDownloadWorker do
+  @moduledoc false
+
+  use Oban.Worker,
+    queue: :media_fetching,
+    unique: [period: :infinity, states: [:available, :scheduled, :retryable, :executing]],
+    tags: ["media_item", "media_fetching"]
+
+  alias Pinchflat.Repo
+  alias Pinchflat.Media
+  alias Pinchflat.Tasks
+  alias Pinchflat.Downloading.MediaDownloader
+  alias Pinchflat.Filesystem.FilesystemDataWorker
+
+  @impl Oban.Worker
+  @doc """
+  For a given media item, download the media alongside any options.
+  Does not download media if its source is set to not download media.
+
+  Returns :ok | {:ok, %MediaItem{}} | {:error, any, ...any}
+  """
+  def perform(%Oban.Job{args: %{"id" => media_item_id}}) do
+    media_item =
+      media_item_id
+      |> Media.get_media_item!()
+      |> Repo.preload(:source)
+
+    # If the source is set to not download media, perform a no-op
+    if media_item.source.download_media do
+      download_media_and_schedule_jobs(media_item)
+    else
+      :ok
+    end
+  end
+
+  defp download_media_and_schedule_jobs(media_item) do
+    case MediaDownloader.download_for_media_item(media_item) do
+      {:ok, _} ->
+        schedule_filesystem_data_worker(media_item)
+        {:ok, media_item}
+
+      err ->
+        err
+    end
+  end
+
+  defp schedule_filesystem_data_worker(media_item) do
+    %{id: media_item.id}
+    |> FilesystemDataWorker.new()
+    |> Tasks.create_job_with_task(media_item)
+    |> case do
+      {:ok, task} -> {:ok, task}
+      {:error, :duplicate_job} -> {:ok, :job_exists}
+    end
+  end
+end