feat(server/m7-353): coverart.FindSidecar shared helper + tests

internal/coverart/sidecar.go

@@ -0,0 +1,35 @@
+// Package coverart finds and fetches album cover artwork.
+//
+// Two-layer model: a directory-walking sidecar lookup (cover.jpg / folder.jpg
+// next to the audio files) and a MusicBrainz Cover Art Archive (MBCAA)
+// fallback for albums with an MBID but no sidecar. The Enricher orchestrates
+// the two; the API and Subsonic packages reuse the sidecar helper directly.
+package coverart
+
+import (
+	"os"
+	"path/filepath"
+)
+
+// SidecarNames is the lookup order for cover art living next to audio files.
+// Matches common library conventions: cover.* wins over folder.*; JPEG wins
+// over PNG when both are present.
+var SidecarNames = []string{
+	"cover.jpg", "cover.jpeg", "cover.png",
+	"folder.jpg", "folder.jpeg", "folder.png",
+}
+
+// FindSidecar returns the absolute path to a sidecar cover image in
+// albumDir, or "" when none of the conventional names are present as a
+// regular file. Directories named like sidecar files are skipped.
+func FindSidecar(albumDir string) string {
+	for _, name := range SidecarNames {
+		candidate := filepath.Join(albumDir, name)
+		info, err := os.Stat(candidate)
+		if err != nil || info.IsDir() {
+			continue
+		}
+		return candidate
+	}
+	return ""
+}

internal/coverart/sidecar_test.go

@@ -0,0 +1,54 @@
+package coverart
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestFindSidecar_PrefersCoverJpgOverFolderJpg(t *testing.T) {
+	dir := t.TempDir()
+	must(t, os.WriteFile(filepath.Join(dir, "folder.jpg"), []byte("f"), 0o644))
+	must(t, os.WriteFile(filepath.Join(dir, "cover.jpg"), []byte("c"), 0o644))
+	got := FindSidecar(dir)
+	want := filepath.Join(dir, "cover.jpg")
+	if got != want {
+		t.Errorf("got %q, want %q", got, want)
+	}
+}
+
+func TestFindSidecar_PrefersJpegOverPng(t *testing.T) {
+	dir := t.TempDir()
+	must(t, os.WriteFile(filepath.Join(dir, "cover.png"), []byte("p"), 0o644))
+	must(t, os.WriteFile(filepath.Join(dir, "cover.jpeg"), []byte("j"), 0o644))
+	got := FindSidecar(dir)
+	want := filepath.Join(dir, "cover.jpeg")
+	if got != want {
+		t.Errorf("got %q, want %q", got, want)
+	}
+}
+
+func TestFindSidecar_EmptyDir_ReturnsEmpty(t *testing.T) {
+	dir := t.TempDir()
+	if got := FindSidecar(dir); got != "" {
+		t.Errorf("expected empty string, got %q", got)
+	}
+}
+
+func TestFindSidecar_DirectoryNamedCoverJpg_Skipped(t *testing.T) {
+	dir := t.TempDir()
+	must(t, os.MkdirAll(filepath.Join(dir, "cover.jpg"), 0o755))
+	must(t, os.WriteFile(filepath.Join(dir, "folder.png"), []byte("p"), 0o644))
+	got := FindSidecar(dir)
+	want := filepath.Join(dir, "folder.png")
+	if got != want {
+		t.Errorf("got %q, want %q", got, want)
+	}
+}
+
+func must(t *testing.T, err error) {
+	t.Helper()
+	if err != nil {
+		t.Fatalf("setup: %v", err)
+	}
+}