package musicfs

import (
	"path/filepath"
	"strings"

	"github.com/rs/zerolog/log"
)

func DeriveSubdir(originRoot, contentPath string) string {
	rel, err := filepath.Rel(originRoot, contentPath)
	if err != nil || strings.HasPrefix(rel, "..") {
		log.Warn().
			Str("origin_root", originRoot).
			Str("content_path", contentPath).
			Msg("content path outside origin root, falling back to full rescan")
		return ""
	}
	return rel
}