ListenBrainz: Handle missing loves metadata for merged recordings

If a loved recording MBID got merged into another recording, the love on
ListenBrainz has no metadata. Lookup the metadata directly from
MusicBrainz.

go.mod

@@ -57,6 +57,7 @@ require (
 	github.com/spf13/pflag v1.0.6 // indirect
 	github.com/subosito/gotenv v1.6.0 // indirect
 	go.uber.org/multierr v1.11.0 // indirect
+	go.uploadedlobster.com/musicbrainzws2 v0.13.1 // indirect
 	golang.org/x/image v0.26.0 // indirect
 	golang.org/x/mod v0.24.0 // indirect
 	golang.org/x/net v0.39.0 // indirect

go.sum

@@ -132,6 +132,8 @@ go.uber.org/multierr v1.11.0 h1:blXXJkSxSSfBVBlC76pxqeO+LN3aDfLQo+309xJstO0=
 go.uber.org/multierr v1.11.0/go.mod h1:20+QtiLqy0Nd6FdQB9TLXag12DsQkrbs3htMFfDN80Y=
 go.uploadedlobster.com/mbtypes v0.4.0 h1:D5asCgHsRWufj4Yn5u0IuH2J9z1UuYImYkYIp1Z1Q7s=
 go.uploadedlobster.com/mbtypes v0.4.0/go.mod h1:Bu1K1Hl77QTAE2Z7QKiW/JAp9KqYWQebkRRfG02dlZM=
+go.uploadedlobster.com/musicbrainzws2 v0.13.1 h1:34GKI7l9eTCyh9ozNOHmlwAAUTDK9WVRsFZK5trxcwQ=
+go.uploadedlobster.com/musicbrainzws2 v0.13.1/go.mod h1:TVln70Fzp/++fw0/jCP1xXwgilVwDkzTwRbV8GwUYLA=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/crypto v0.0.0-20210921155107-089bfa567519/go.mod h1:GvvjBRRGRdwPK5ydBHafDWAxML/pGHZbMvKqRZ5+Abc=
 golang.org/x/crypto v0.37.0 h1:kJNSjF/Xp7kU0iB2Z+9viTPMW4EqqsrywMXLJOOsXSE=

internal/backends/listenbrainz/listenbrainz.go

@@ -22,6 +22,7 @@ import (
 	"time"
 
 	"go.uploadedlobster.com/mbtypes"
+	"go.uploadedlobster.com/musicbrainzws2"
 	"go.uploadedlobster.com/scotty/internal/config"
 	"go.uploadedlobster.com/scotty/internal/i18n"
 	"go.uploadedlobster.com/scotty/internal/models"
@@ -31,6 +32,7 @@ import (
 
 type ListenBrainzApiBackend struct {
 	client          Client
+	mbClient        musicbrainzws2.Client
 	username        string
 	checkDuplicates bool
 	existingMBIDs   map[mbtypes.MBID]bool
@@ -56,6 +58,7 @@ func (b *ListenBrainzApiBackend) Options() []models.BackendOption {
 
 func (b *ListenBrainzApiBackend) FromConfig(config *config.ServiceConfig) models.Backend {
 	b.client = NewClient(config.GetString("token"))
+	b.mbClient = *musicbrainzws2.NewClient(version.AppName, version.AppVersion)
 	b.client.MaxResults = MaxItemsPerGet
 	b.username = config.GetString("username")
 	b.checkDuplicates = config.GetBool("check-duplicate-listens", false)
@@ -228,6 +231,16 @@ out:
 		}
 
 		for _, feedback := range result.Feedback {
+			// Missing track metadata indicates that the recording MBID is no
+			// longer available and might have been merged. Try fetching details
+			// from MusicBrainz.
+			if feedback.TrackMetadata == nil {
+				track, err := b.lookupRecording(feedback.RecordingMBID)
+				if err == nil {
+					feedback.TrackMetadata = track
+				}
+			}
+
 			love := feedback.AsLove()
 			if love.Created.Unix() > oldestTimestamp.Unix() {
 				loves = append(loves, love)
@@ -265,6 +278,12 @@ func (b *ListenBrainzApiBackend) ImportLoves(export models.LovesResult, importRe
 
 			for _, love := range existingLoves.Items {
 				b.existingMBIDs[love.RecordingMBID] = true
+				// In case the loved MBID got merged the track MBID represents the
+				// actual recording MBID.
+				if love.Track.RecordingMBID != "" &&
+					love.Track.RecordingMBID != love.RecordingMBID {
+					b.existingMBIDs[love.Track.RecordingMBID] = true
+				}
 			}
 		}
 	}
@@ -347,6 +366,31 @@ func (b *ListenBrainzApiBackend) checkDuplicateListen(listen models.Listen) (boo
 	return false, nil
 }
 
+func (b *ListenBrainzApiBackend) lookupRecording(mbid mbtypes.MBID) (*Track, error) {
+	filter := musicbrainzws2.IncludesFilter{
+		Includes: []string{"artist-credits"},
+	}
+	recording, err := b.mbClient.LookupRecording(mbid, filter)
+	if err != nil {
+		return nil, err
+	}
+
+	artistMBIDs := make([]mbtypes.MBID, 0, len(recording.ArtistCredit))
+	for _, artist := range recording.ArtistCredit {
+		artistMBIDs = append(artistMBIDs, artist.Artist.ID)
+	}
+	track := Track{
+		TrackName:  recording.Title,
+		ArtistName: recording.ArtistCredit.String(),
+		MBIDMapping: &MBIDMapping{
+			// In case of redirects this MBID differs from the looked up MBID
+			RecordingMBID: recording.ID,
+			ArtistMBIDs:   artistMBIDs,
+		},
+	}
+	return &track, nil
+}
+
 func (lbListen Listen) AsListen() models.Listen {
 	listen := models.Listen{
 		ListenedAt: time.Unix(lbListen.ListenedAt, 0),