Implement ML-143: Cart-style multi record import

Closes ML-143.

lib/music_library/worker/import_from_musicbrainz_release_group.ex

@@ -0,0 +1,32 @@
+defmodule MusicLibrary.Worker.ImportFromMusicbrainzReleaseGroup do
+  @moduledoc """
+  Imports a record from a MusicBrainz release group in the background.
+
+  Used by the cart-style multi-record import when there are two or more
+  records to import at once.
+  """
+
+  use Oban.Worker, queue: :music_brainz, max_attempts: 3
+
+  alias MusicLibrary.Records
+
+  @impl Oban.Worker
+  def perform(%Oban.Job{args: %{"release_group_id" => release_group_id} = args}) do
+    opts = [
+      format: args["format"],
+      purchased_at: parse_datetime(args["purchased_at"])
+    ]
+
+    case Records.import_from_musicbrainz_release_group(release_group_id, opts) do
+      {:ok, _record} -> :ok
+      {:error, reason} -> {:error, reason}
+    end
+  end
+
+  defp parse_datetime(nil), do: nil
+
+  defp parse_datetime(str) do
+    {:ok, datetime, _offset} = DateTime.from_iso8601(str)
+    datetime
+  end
+end