Moved logic of collapsing songs into albums to model package

(it should really be called domain.... maybe will rename it later)

model/mediafile_internal_test.go

@@ -0,0 +1,53 @@
+package model
+
+import (
+	"github.com/navidrome/navidrome/consts"
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("fixAlbumArtist", func() {
+	var album Album
+	BeforeEach(func() {
+		album = Album{}
+	})
+	Context("Non-Compilations", func() {
+		BeforeEach(func() {
+			album.Compilation = false
+			album.Artist = "Sparks"
+			album.ArtistID = "ar-123"
+		})
+		It("returns the track artist if no album artist is specified", func() {
+			al := fixAlbumArtist(album, nil)
+			Expect(al.AlbumArtistID).To(Equal("ar-123"))
+			Expect(al.AlbumArtist).To(Equal("Sparks"))
+		})
+		It("returns the album artist if it is specified", func() {
+			album.AlbumArtist = "Sparks Brothers"
+			album.AlbumArtistID = "ar-345"
+			al := fixAlbumArtist(album, nil)
+			Expect(al.AlbumArtistID).To(Equal("ar-345"))
+			Expect(al.AlbumArtist).To(Equal("Sparks Brothers"))
+		})
+	})
+	Context("Compilations", func() {
+		BeforeEach(func() {
+			album.Compilation = true
+			album.Name = "Sgt. Pepper Knew My Father"
+			album.AlbumArtistID = "ar-000"
+			album.AlbumArtist = "The Beatles"
+		})
+
+		It("returns VariousArtists if there's more than one album artist", func() {
+			al := fixAlbumArtist(album, []string{"ar-123", "ar-345"})
+			Expect(al.AlbumArtistID).To(Equal(consts.VariousArtistsID))
+			Expect(al.AlbumArtist).To(Equal(consts.VariousArtists))
+		})
+
+		It("returns the sole album artist if they are the same", func() {
+			al := fixAlbumArtist(album, []string{"ar-000", "ar-000"})
+			Expect(al.AlbumArtistID).To(Equal("ar-000"))
+			Expect(al.AlbumArtist).To(Equal("The Beatles"))
+		})
+	})
+})