refactor(scanner): simplify selective scan logic using slice.Filter

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

scanner/scanner.go

@@ -15,6 +15,7 @@ import (
 	"github.com/navidrome/navidrome/log"
 	"github.com/navidrome/navidrome/model"
 	"github.com/navidrome/navidrome/utils/run"
+	"github.com/navidrome/navidrome/utils/slice"
 )
 
 type scannerImpl struct {
@@ -30,7 +31,6 @@ type scanState struct {
 	changesDetected atomic.Bool
 	libraries       model.Libraries  // Store libraries list for consistency across phases
 	targets         map[int][]string // Optional: map[libraryID][]folderPaths for selective scans
-	affectedLibIDs  []int            // IDs of libraries involved in the scan (for GC scoping)
 }
 
 func (s *scanState) sendProgress(info *ProgressInfo) {
@@ -74,7 +74,6 @@ func (s *scannerImpl) scanFolders(ctx context.Context, fullScan bool, targets []
 	if isSelectiveScan {
 		// Selective scan: filter libraries and build targets map
 		state.targets = make(map[int][]string)
-		affectedLibIDSet := make(map[int]bool)
 
 		for _, target := range targets {
 			folderPath := target.FolderPath
@@ -82,15 +81,12 @@ func (s *scannerImpl) scanFolders(ctx context.Context, fullScan bool, targets []
 				folderPath = "."
 			}
 			state.targets[target.LibraryID] = append(state.targets[target.LibraryID], folderPath)
-			affectedLibIDSet[target.LibraryID] = true
 		}
 
-		for _, lib := range allLibs {
-			if affectedLibIDSet[lib.ID] {
-				libs = append(libs, lib)
-				state.affectedLibIDs = append(state.affectedLibIDs, lib.ID)
-			}
-		}
+		// Filter libraries to only those in targets
+		libs = slice.Filter(allLibs, func(lib model.Library) bool {
+			return len(state.targets[lib.ID]) > 0
+		})
 
 		log.Info(ctx, "Scanner: Starting selective scan", "fullScan", state.fullScan, "numLibraries", len(libs), "numTargets", len(targets))
 	} else {

utils/slice/slice.go

@@ -171,3 +171,14 @@ func SeqFunc[I, O any](s []I, f func(I) O) iter.Seq[O] {
 		}
 	}
 }
+
+// Filter returns a new slice containing only the elements of s for which filterFunc returns true
+func Filter[T any](s []T, filterFunc func(T) bool) []T {
+	var result []T
+	for _, item := range s {
+		if filterFunc(item) {
+			result = append(result, item)
+		}
+	}
+	return result
+}

utils/slice/slice_test.go

@@ -172,4 +172,42 @@ var _ = Describe("Slice Utils", func() {
 			Expect(result).To(ConsistOf("2", "4", "6", "8"))
 		})
 	})
+
+	Describe("Filter", func() {
+		It("returns empty slice for an empty input", func() {
+			filterFunc := func(v int) bool { return v > 0 }
+			result := slice.Filter([]int{}, filterFunc)
+			Expect(result).To(BeEmpty())
+		})
+
+		It("returns all elements when filter matches all", func() {
+			filterFunc := func(v int) bool { return v > 0 }
+			result := slice.Filter([]int{1, 2, 3, 4}, filterFunc)
+			Expect(result).To(HaveExactElements(1, 2, 3, 4))
+		})
+
+		It("returns empty slice when filter matches none", func() {
+			filterFunc := func(v int) bool { return v > 10 }
+			result := slice.Filter([]int{1, 2, 3, 4}, filterFunc)
+			Expect(result).To(BeEmpty())
+		})
+
+		It("returns only matching elements", func() {
+			filterFunc := func(v int) bool { return v%2 == 0 }
+			result := slice.Filter([]int{1, 2, 3, 4, 5, 6}, filterFunc)
+			Expect(result).To(HaveExactElements(2, 4, 6))
+		})
+
+		It("works with string slices", func() {
+			filterFunc := func(s string) bool { return len(s) > 3 }
+			result := slice.Filter([]string{"a", "abc", "abcd", "ab", "abcde"}, filterFunc)
+			Expect(result).To(HaveExactElements("abcd", "abcde"))
+		})
+
+		It("preserves order of elements", func() {
+			filterFunc := func(v int) bool { return v%2 == 1 }
+			result := slice.Filter([]int{9, 8, 7, 6, 5, 4, 3, 2, 1}, filterFunc)
+			Expect(result).To(HaveExactElements(9, 7, 5, 3, 1))
+		})
+	})
 })