refactor(scanner): enhance ScanTarget struct with String method for better target representation

Signed-off-by: Deluan <deluan@navidrome.org>

scanner/controller.go

@@ -27,11 +27,16 @@ var (
 )
 
 // ScanTarget represents a specific folder within a library to be scanned.
+// NOTE: This struct is used as a map key, so it should only contain comparable types.
 type ScanTarget struct {
 	LibraryID  int
 	FolderPath string // Relative path within the library, or "" for entire library
 }
 
+func (st ScanTarget) String() string {
+	return fmt.Sprintf("%d:%s", st.LibraryID, st.FolderPath)
+}
+
 type Scanner interface {
 	// ScanAll starts a full scan of the music library. This is a blocking operation.
 	ScanAll(ctx context.Context, fullScan bool) (warnings []string, err error)

scanner/external.go

@@ -8,10 +8,11 @@ import (
 	"io"
 	"os"
 	"os/exec"
-	"strconv"
+	"strings"
 
 	"github.com/navidrome/navidrome/conf"
 	"github.com/navidrome/navidrome/log"
+	"github.com/navidrome/navidrome/utils/slice"
 )
 
 // scannerExternal is a scanner that runs an external process to do the scanning. It is used to avoid
@@ -49,13 +50,7 @@ func (s *scannerExternal) scan(ctx context.Context, fullScan bool, targets []Sca
 
 	// Add targets if provided
 	if len(targets) > 0 {
-		var targetsStr string
-		for i, target := range targets {
-			if i > 0 {
-				targetsStr += ","
-			}
-			targetsStr += strconv.Itoa(target.LibraryID) + ":" + target.FolderPath
-		}
+		targetsStr := strings.Join(slice.Map(targets, func(t ScanTarget) string { return t.String() }), ",")
 		args = append(args, "--targets", targetsStr)
 		log.Debug(ctx, "Spawning external scanner process with targets", "fullScan", fullScan, "path", exe, "targets", targetsStr)
 	} else {

scanner/watcher.go

@@ -121,10 +121,11 @@ func (w *watcher) Run(ctx context.Context) error {
 			folderPath := notification.FolderPath
 
 			// If already scheduled for scan, skip
-			if _, exists := targets[ScanTarget{LibraryID: lib.ID, FolderPath: folderPath}]; exists {
+			target := ScanTarget{LibraryID: lib.ID, FolderPath: folderPath}
+			if _, exists := targets[target]; exists {
 				continue
 			}
-			targets[ScanTarget{LibraryID: lib.ID, FolderPath: folderPath}] = struct{}{}
+			targets[target] = struct{}{}
 			trigger.Reset(w.triggerWait)
 
 			log.Debug(ctx, "Watcher: Detected changes. Waiting for more changes before triggering scan",