feat: initial implementation of metadata aggregator

- gRPC service with MusicBrainz provider
- PostgreSQL schema with migrations
- Service layer with database-first caching
- Repository pattern for data access
- YAML configuration support
- Research documentation for 17 music metadata projects

internal/server/mapper.go

@@ -0,0 +1,161 @@
+package server
+
+import (
+	"github.com/metadata-agregator/internal/domain"
+	metadatav1 "github.com/metadata-agregator/pkg/gen/metadata/v1"
+)
+
+func toProtoArtist(d *domain.Artist) *metadatav1.Artist {
+	if d == nil {
+		return nil
+	}
+
+	a := &metadatav1.Artist{
+		Id:          d.ID,
+		Name:        d.Name,
+		SortName:    d.SortName,
+		ArtistType:  d.Type,
+		Country:     d.Country,
+		Description: d.Description,
+		ImageUrl:    d.ImageURL,
+	}
+
+	if d.FormedDate != nil {
+		a.FormedDate = d.FormedDate.Format("2006-01-02")
+	}
+	if d.DisbandedDate != nil {
+		a.DisbandedDate = d.DisbandedDate.Format("2006-01-02")
+	}
+
+	for _, g := range d.Genres {
+		a.Genres = append(a.Genres, &metadatav1.Genre{
+			Id:   g.ID,
+			Name: g.Name,
+		})
+	}
+
+	for _, e := range d.ExternalIDs {
+		a.ExternalIds = append(a.ExternalIds, &metadatav1.ExternalID{
+			Source:   e.Source,
+			SourceId: e.SourceID,
+			Url:      e.URL,
+		})
+	}
+
+	return a
+}
+
+func toProtoAlbum(d *domain.Album) *metadatav1.Album {
+	if d == nil {
+		return nil
+	}
+
+	a := &metadatav1.Album{
+		Id:          d.ID,
+		Title:       d.Title,
+		AlbumType:   d.Type,
+		Upc:         d.UPC,
+		TotalTracks: int32(d.TotalTracks),
+		TotalDiscs:  int32(d.TotalDiscs),
+		CoverUrl:    d.CoverURL,
+	}
+
+	if d.ReleaseDate != nil {
+		a.ReleaseDate = d.ReleaseDate.Format("2006-01-02")
+	}
+
+	for _, ac := range d.Artists {
+		a.Artists = append(a.Artists, toProtoArtistCredit(&ac))
+	}
+
+	if d.Label != nil {
+		a.Label = &metadatav1.Label{
+			Id:      d.Label.ID,
+			Name:    d.Label.Name,
+			Country: d.Label.Country,
+		}
+	}
+
+	for _, g := range d.Genres {
+		a.Genres = append(a.Genres, &metadatav1.Genre{
+			Id:   g.ID,
+			Name: g.Name,
+		})
+	}
+
+	for _, e := range d.ExternalIDs {
+		a.ExternalIds = append(a.ExternalIds, &metadatav1.ExternalID{
+			Source:   e.Source,
+			SourceId: e.SourceID,
+			Url:      e.URL,
+		})
+	}
+
+	return a
+}
+
+func toProtoTrack(d *domain.Track) *metadatav1.Track {
+	if d == nil {
+		return nil
+	}
+
+	t := &metadatav1.Track{
+		Id:          d.ID,
+		Title:       d.Title,
+		DurationMs:  int32(d.DurationMs),
+		Isrc:        d.ISRC,
+		Explicit:    d.Explicit,
+		DiscNumber:  int32(d.DiscNumber),
+		TrackNumber: int32(d.TrackNumber),
+	}
+
+	for _, ac := range d.Artists {
+		t.Artists = append(t.Artists, toProtoArtistCredit(&ac))
+	}
+
+	if d.Work != nil {
+		t.Work = toProtoWork(d.Work)
+	}
+
+	for _, e := range d.ExternalIDs {
+		t.ExternalIds = append(t.ExternalIds, &metadatav1.ExternalID{
+			Source:   e.Source,
+			SourceId: e.SourceID,
+			Url:      e.URL,
+		})
+	}
+
+	return t
+}
+
+func toProtoWork(d *domain.Work) *metadatav1.Work {
+	if d == nil {
+		return nil
+	}
+
+	w := &metadatav1.Work{
+		Id:       d.ID,
+		Title:    d.Title,
+		WorkType: d.Type,
+		Language: d.Language,
+	}
+
+	for _, c := range d.Composers {
+		w.Composers = append(w.Composers, toProtoArtistCredit(&c))
+	}
+
+	return w
+}
+
+func toProtoArtistCredit(d *domain.ArtistCredit) *metadatav1.ArtistCredit {
+	if d == nil {
+		return nil
+	}
+
+	return &metadatav1.ArtistCredit{
+		Artist:     toProtoArtist(&d.Artist),
+		Role:       d.Role,
+		Position:   int32(d.Position),
+		JoinPhrase: d.JoinPhrase,
+	}
+}