feat(scanner): implement selective folder scanning and file system watcher improvements (#4674)

* feat: Add selective folder scanning capability

Implement targeted scanning of specific library/folder pairs without
full recursion. This enables efficient rescanning of individual folders
when changes are detected, significantly reducing scan time for large
libraries.

Key changes:
- Add ScanTarget struct and ScanFolders API to Scanner interface
- Implement CLI flag --targets for specifying libraryID:folderPath pairs
- Add FolderRepository.GetByPaths() for batch folder info retrieval
- Create loadSpecificFolders() for non-recursive directory loading
- Scope GC operations to affected libraries only (with TODO for full impl)
- Add comprehensive tests for selective scanning behavior

The selective scan:
- Only processes specified folders (no subdirectory recursion)
- Maintains library isolation
- Runs full maintenance pipeline scoped to affected libraries
- Supports both full and quick scan modes

Examples:
  navidrome scan --targets "1:Music/Rock,1:Music/Jazz"
  navidrome scan --full --targets "2:Classical"

* feat(folder): replace GetByPaths with GetFolderUpdateInfo for improved folder updates retrieval

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

* test: update parseTargets test to handle folder names with spaces

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

* refactor(folder): remove unused LibraryPath struct and update GC logging message

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

* refactor(folder): enhance external scanner to support target-specific scanning

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

* refactor(scanner): simplify scanner methods

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

* feat(watcher): implement folder scanning notifications with deduplication

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

* refactor(watcher): add resolveFolderPath function for testability

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

* feat(watcher): implement path ignoring based on .ndignore patterns

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

* refactor(scanner): implement IgnoreChecker for managing .ndignore patterns

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

* refactor(ignore_checker): rename scanner to lineScanner for clarity

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

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

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

* fix(scanner): validate library ID to prevent negative values

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

* refactor(scanner): simplify GC method by removing library ID parameter

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

* feat(scanner): update folder scanning to include all descendants of specified folders

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

* feat(subsonic): allow selective scan in the /startScan endpoint

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

* refactor(scanner): update CallScan to handle specific library/folder pairs

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

* refactor(scanner): streamline scanning logic by removing scanAll method

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

* test: enhance mockScanner for thread safety and improve test reliability

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

* refactor(scanner): move scanner.ScanTarget to model.ScanTarget

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

* refactor: move scanner types to model,implement MockScanner

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

* refactor(scanner): update scanner interface and implementations to use model.Scanner

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

* refactor(folder_repository): normalize target path handling by using filepath.Clean

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

* test(folder_repository): add comprehensive tests for folder retrieval and child exclusion

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

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

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

* refactor(scanner): streamline phase folder and album creation by removing unnecessary library parameter

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

* refactor(scanner): move initialization logic from phase_1 to the scanner itself

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

* refactor(tests): rename selective scan test file to scanner_selective_test.go

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

* feat(configuration): add DevSelectiveWatcher configuration option

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

* feat(watcher): enhance .ndignore handling for folder deletions and file changes

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

* docs(scanner): comments

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

* refactor(scanner): enhance walkDirTree to support target folder scanning

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

* fix(scanner, watcher): handle errors when pushing ignore patterns for folders

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

* Update scanner/phase_1_folders.go

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* refactor(scanner): replace parseTargets function with direct call to scanner.ParseTargets

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

* test(scanner): add tests for ScanBegin and ScanEnd functionality

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

* fix(library): update PRAGMA optimize to check table sizes without ANALYZE

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

* test(scanner): refactor tests

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

* feat(ui): add selective scan options and update translations

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

* feat(ui): add quick and full scan options for individual libraries

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

* feat(ui): add Scan buttonsto the LibraryList

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

* feat(scan): update scanning parameters from 'path' to 'target' for selective scans.

* refactor(scan): move ParseTargets function to model package

* test(scan): suppress unused return value from SetUserLibraries in tests

* feat(gc): enhance garbage collection to support selective library purging

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

* fix(scanner): prevent race condition when scanning deleted folders

When the watcher detects changes in a folder that gets deleted before
the scanner runs (due to the 10-second delay), the scanner was
prematurely removing these folders from the tracking map, preventing
them from being marked as missing.

The issue occurred because `newFolderEntry` was calling `popLastUpdate`
before verifying the folder actually exists on the filesystem.

Changes:
- Move fs.Stat check before newFolderEntry creation in loadDir to
  ensure deleted folders remain in lastUpdates for finalize() to handle
- Add early existence check in walkDirTree to skip non-existent target
  folders with a warning log
- Add unit test verifying non-existent folders aren't removed from
  lastUpdates prematurely
- Add integration test for deleted folder scenario with ScanFolders

Fixes the issue where deleting entire folders (e.g., /music/AC_DC)
wouldn't mark tracks as missing when using selective folder scanning.

* refactor(scan): streamline folder entry creation and update handling

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

* feat(scan): add '@Recycle' (QNAP) to ignored directories list

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

* fix(log): improve thread safety in logging level management

* test(scan): move unit tests for ParseTargets function

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

* review

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

---------

Signed-off-by: Deluan <deluan@navidrome.org>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: deluan <deluan.quintao@mechanical-orchard.com>

scanner/external.go

@@ -8,10 +8,12 @@ import (
 	"io"
 	"os"
 	"os/exec"
+	"strings"
 
 	"github.com/navidrome/navidrome/conf"
 	"github.com/navidrome/navidrome/log"
-	. "github.com/navidrome/navidrome/utils/gg"
+	"github.com/navidrome/navidrome/model"
+	"github.com/navidrome/navidrome/utils/slice"
 )
 
 // scannerExternal is a scanner that runs an external process to do the scanning. It is used to avoid
@@ -23,19 +25,41 @@ import (
 // process will forward them to the caller.
 type scannerExternal struct{}
 
-func (s *scannerExternal) scanAll(ctx context.Context, fullScan bool, progress chan<- *ProgressInfo) {
+func (s *scannerExternal) scanFolders(ctx context.Context, fullScan bool, targets []model.ScanTarget, progress chan<- *ProgressInfo) {
+	s.scan(ctx, fullScan, targets, progress)
+}
+
+func (s *scannerExternal) scan(ctx context.Context, fullScan bool, targets []model.ScanTarget, progress chan<- *ProgressInfo) {
 	exe, err := os.Executable()
 	if err != nil {
 		progress <- &ProgressInfo{Error: fmt.Sprintf("failed to get executable path: %s", err)}
 		return
 	}
-	log.Debug(ctx, "Spawning external scanner process", "fullScan", fullScan, "path", exe)
-	cmd := exec.CommandContext(ctx, exe, "scan",
+
+	// Build command arguments
+	args := []string{
+		"scan",
 		"--nobanner", "--subprocess",
 		"--configfile", conf.Server.ConfigFile,
 		"--datafolder", conf.Server.DataFolder,
 		"--cachefolder", conf.Server.CacheFolder,
-		If(fullScan, "--full", ""))
+	}
+
+	// Add targets if provided
+	if len(targets) > 0 {
+		targetsStr := strings.Join(slice.Map(targets, func(t model.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 {
+		log.Debug(ctx, "Spawning external scanner process", "fullScan", fullScan, "path", exe)
+	}
+
+	// Add full scan flag if needed
+	if fullScan {
+		args = append(args, "--full")
+	}
+
+	cmd := exec.CommandContext(ctx, exe, args...)
 
 	in, out := io.Pipe()
 	defer in.Close()