Polyfill artist id in scrobble activity

lib/music_library/artists.ex

@@ -35,6 +35,15 @@ defmodule MusicLibrary.Artists do
     q |> Repo.all() |> MapSet.new()
   end
 
+  def get_all_artist_pairs do
+    q =
+      from ar in ArtistRecord,
+        distinct: true,
+        select: %{artist_id: ar.musicbrainz_id, record_id: ar.record_id}
+
+    q |> Repo.all()
+  end
+
   defp get_collected_artist_ids do
     q =
       from ar in ArtistRecord,

lib/music_library/scrobble_activity.ex

@@ -2,19 +2,20 @@ defmodule MusicLibrary.ScrobbleActivity do
   alias MusicLibrary.{Artists, Collection, Wishlist}
 
   def from_recent_tracks(recent_tracks, timezone) do
+    all_artist_pairs = Artists.get_all_artist_pairs()
+    recent_release_ids = recent_release_ids(recent_tracks)
+    collected_releases = Collection.collected_releases(recent_release_ids)
+    wishlisted_releases = Wishlist.wishlisted_releases(recent_release_ids)
+
     localized_recent_tracks =
       Enum.map(recent_tracks, fn t ->
         %{
           t
-          | scrobbled_at_label: localize_scrobbled_at(t.scrobbled_at_uts, timezone)
+          | scrobbled_at_label: localize_scrobbled_at(t.scrobbled_at_uts, timezone),
+            artist: polyfill_artist(t, collected_releases, wishlisted_releases, all_artist_pairs)
         }
       end)
 
-    recent_release_ids = recent_release_ids(localized_recent_tracks)
-
-    collected_releases = Collection.collected_releases(recent_release_ids)
-    wishlisted_releases = Wishlist.wishlisted_releases(recent_release_ids)
-
     all_artist_ids = Artists.get_all_artist_ids()
     recent_artist_ids = recent_artist_ids(localized_recent_tracks)
     artist_ids = MapSet.intersection(all_artist_ids, recent_artist_ids)
@@ -41,6 +42,39 @@ defmodule MusicLibrary.ScrobbleActivity do
     }
   end
 
+  defp polyfill_artist(track, collected_releases, wishlisted_releases, all_artist_pairs) do
+    %{
+      track.artist
+      | musicbrainz_id:
+          find_artist_id(track, collected_releases, wishlisted_releases, all_artist_pairs)
+    }
+  end
+
+  defguardp has_no_artist_id(track)
+            when is_nil(track.artist.musicbrainz_id) or track.artist.musicbrainz_id == ""
+
+  defp find_artist_id(track, collected_releases, wishlisted_releases, all_artist_pairs)
+       when has_no_artist_id(track) do
+    matched_release =
+      Enum.find(collected_releases ++ wishlisted_releases, fn r ->
+        r.release_id == track.album.musicbrainz_id
+      end)
+
+    record_id = if matched_release, do: matched_release.record_id, else: nil
+
+    if record_id do
+      Enum.find_value(all_artist_pairs, fn pair ->
+        if pair.record_id == record_id, do: pair.artist_id, else: nil
+      end)
+    else
+      nil
+    end
+  end
+
+  defp find_artist_id(track, _collected_releases, _wishlisted_releases, _all_artist_pairs) do
+    track.artist.musicbrainz_id
+  end
+
   defp localize_scrobbled_at(uts, timezone) do
     ldt =
       uts