.redownlaod with suffix, isrc variable

backend/isrc_helper.go

@@ -0,0 +1,22 @@
+package backend
+
+import "strings"
+
+func ResolveTrackISRC(spotifyTrackID string) string {
+	spotifyTrackID = strings.TrimSpace(spotifyTrackID)
+	if spotifyTrackID == "" {
+		return ""
+	}
+
+	if cachedISRC, err := GetCachedISRC(spotifyTrackID); err == nil && cachedISRC != "" {
+		return strings.ToUpper(strings.TrimSpace(cachedISRC))
+	}
+
+	client := NewSongLinkClient()
+	isrc, err := client.GetISRCDirect(spotifyTrackID)
+	if err != nil {
+		return ""
+	}
+
+	return strings.ToUpper(strings.TrimSpace(isrc))
+}