filebrozer/http/resource.go

package fbhttp

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"io/fs"
	"log"
	"net/http"
	"net/url"
	"os"
	"os/exec"
	"path"
	"path/filepath"
	"strings"
    "time"

	"github.com/shirou/gopsutil/v4/disk"
	"github.com/spf13/afero"

	fberrors "github.com/filebrowser/filebrowser/v2/errors"
	"github.com/filebrowser/filebrowser/v2/files"
	"github.com/filebrowser/filebrowser/v2/fileutils"
)

var resourceGetHandler = withUser(func(w http.ResponseWriter, r *http.Request, d *data) (int, error) {
	file, err := files.NewFileInfo(&files.FileOptions{
		Fs:         d.user.Fs,
		Path:       r.URL.Path,
		Modify:     d.user.Perm.Modify,
		Expand:     true,
		ReadHeader: d.server.TypeDetectionByHeader,
		Checker:    d,
		Content:    true,
	})
	if err != nil {
		return errToStatus(err), err
	}

	if file.IsDir {
		file.Sorting = d.user.Sorting
		file.ApplySort()
		return renderJSON(w, r, file)
	}

	if checksum := r.URL.Query().Get("checksum"); checksum != "" {
		err := file.Checksum(checksum)
		if errors.Is(err, fberrors.ErrInvalidOption) {
			return http.StatusBadRequest, nil
		} else if err != nil {
			return http.StatusInternalServerError, err
		}

		// do not waste bandwidth if we just want the checksum
		file.Content = ""
	}

	// If metadata requested, attempt to read audio tags and attach them
	if r.URL.Query().Get("metadata") == "1" {
		if err := file.ReadAudioTags(); err != nil {
			log.Printf("warning: failed reading audio tags for %s: %v", file.Path, err)
		}
	}

	return renderJSON(w, r, file)
})

func resourceDeleteHandler(fileCache FileCache) handleFunc {
	return withUser(func(_ http.ResponseWriter, r *http.Request, d *data) (int, error) {
		if r.URL.Path == "/" || !d.user.Perm.Delete {
			return http.StatusForbidden, nil
		}

		file, err := files.NewFileInfo(&files.FileOptions{
			Fs:         d.user.Fs,
			Path:       r.URL.Path,
			Modify:     d.user.Perm.Modify,
			Expand:     false,
			ReadHeader: d.server.TypeDetectionByHeader,
			Checker:    d,
		})
		if err != nil {
			return errToStatus(err), err
		}

		err = d.store.Share.DeleteWithPathPrefix(file.Path)
		if err != nil {
			log.Printf("WARNING: Error(s) occurred while deleting associated shares with file: %s", err)
		}

		// delete thumbnails
		err = delThumbs(r.Context(), fileCache, file)
		if err != nil {
			return errToStatus(err), err
		}

		err = d.RunHook(func() error {
			return d.user.Fs.RemoveAll(r.URL.Path)
		}, "delete", r.URL.Path, "", d.user)

		if err != nil {
			return errToStatus(err), err
		}

		return http.StatusNoContent, nil
	})
}

func resourcePostHandler(fileCache FileCache) handleFunc {
	return withUser(func(w http.ResponseWriter, r *http.Request, d *data) (int, error) {
		if !d.user.Perm.Create || !d.Check(r.URL.Path) {
			return http.StatusForbidden, nil
		}

		// Directories creation on POST.
		if strings.HasSuffix(r.URL.Path, "/") {
			err := d.user.Fs.MkdirAll(r.URL.Path, d.settings.DirMode)
			return errToStatus(err), err
		}

		file, err := files.NewFileInfo(&files.FileOptions{
			Fs:         d.user.Fs,
			Path:       r.URL.Path,
			Modify:     d.user.Perm.Modify,
			Expand:     false,
			ReadHeader: d.server.TypeDetectionByHeader,
			Checker:    d,
		})
		if err == nil {
			if r.URL.Query().Get("override") != "true" {
				return http.StatusConflict, nil
			}

			// Permission for overwriting the file
			if !d.user.Perm.Modify {
				return http.StatusForbidden, nil
			}

			err = delThumbs(r.Context(), fileCache, file)
			if err != nil {
				return errToStatus(err), err
			}
		}

		err = d.RunHook(func() error {
			info, writeErr := writeFile(d.user.Fs, r.URL.Path, r.Body, d.settings.FileMode, d.settings.DirMode)
			if writeErr != nil {
				return writeErr
			}

			etag := fmt.Sprintf(`"%x%x"`, info.ModTime().UnixNano(), info.Size())
			w.Header().Set("ETag", etag)
			return nil
		}, "upload", r.URL.Path, "", d.user)

		if err != nil {
			_ = d.user.Fs.RemoveAll(r.URL.Path)
		}

		return errToStatus(err), err
	})
}

var resourcePutHandler = withUser(func(w http.ResponseWriter, r *http.Request, d *data) (int, error) {
	if !d.user.Perm.Modify || !d.Check(r.URL.Path) {
		return http.StatusForbidden, nil
	}

	// Only allow PUT for files.
	if strings.HasSuffix(r.URL.Path, "/") {
		return http.StatusMethodNotAllowed, nil
	}

	exists, err := afero.Exists(d.user.Fs, r.URL.Path)
	if err != nil {
		return http.StatusInternalServerError, err
	}
	if !exists {
		return http.StatusNotFound, nil
	}

	err = d.RunHook(func() error {
		info, writeErr := writeFile(d.user.Fs, r.URL.Path, r.Body, d.settings.FileMode, d.settings.DirMode)
		if writeErr != nil {
			return writeErr
		}

		etag := fmt.Sprintf(`"%x%x"`, info.ModTime().UnixNano(), info.Size())
		w.Header().Set("ETag", etag)
		return nil
	}, "save", r.URL.Path, "", d.user)

	return errToStatus(err), err
})

func resourcePatchHandler(fileCache FileCache) handleFunc {
	return withUser(func(_ http.ResponseWriter, r *http.Request, d *data) (int, error) {
		src := r.URL.Path
		dst := r.URL.Query().Get("destination")
		action := r.URL.Query().Get("action")
		dst, err := url.QueryUnescape(dst)
		if !d.Check(src) || !d.Check(dst) {
			return http.StatusForbidden, nil
		}
		if err != nil {
			return errToStatus(err), err
		}
		if dst == "/" || src == "/" {
			return http.StatusForbidden, nil
		}

		// Only check parent relationship when a destination was provided.
		// Some actions (like metadata) don't provide a destination and calling
		// filepath.Rel with an empty dst returns an error "can't make relative to ...".
		if dst != "" {
			err = checkParent(src, dst)
			if err != nil {
				return http.StatusBadRequest, err
			}
		}

		override := r.URL.Query().Get("override") == "true"
		rename := r.URL.Query().Get("rename") == "true"
		// Only check destination existence when a destination was provided.
		if dst != "" && !override && !rename {
			if _, err = d.user.Fs.Stat(dst); err == nil {
				return http.StatusConflict, nil
			}
		}
		if rename {
			dst = addVersionSuffix(dst, d.user.Fs)
		}

		// Permission for overwriting the file
		if override && !d.user.Perm.Modify {
			return http.StatusForbidden, nil
		}

		// Special-case metadata action because it needs the request body
		if action == "metadata" {
			if !d.user.Perm.Modify {
				return http.StatusForbidden, nil
			}

			var tags map[string]string
			multi := map[string][]string{}
			var clear []string
			body, err := io.ReadAll(r.Body)
			if err != nil {
				return http.StatusBadRequest, err
			}
			// Accept both plain tag maps and objects with __clear__ array
			var raw map[string]any
			if err := json.Unmarshal(body, &raw); err == nil && raw != nil {
				// extract string-valued entries into tags
				tags = map[string]string{}
				for k, v := range raw {
					if k == "__clear__" {
						// parse array of strings
						if arr, ok := v.([]any); ok {
							for _, itm := range arr {
								if s, ok := itm.(string); ok {
									s = strings.TrimSpace(s)
									if s != "" {
										clear = append(clear, s)
									}
								}
							}
						}
						continue
					}
					if sv, ok := v.(string); ok {
						tags[k] = sv
						continue
					}
					if arr, ok := v.([]any); ok {
						vals := []string{}
						for _, itm := range arr {
							if s, ok := itm.(string); ok {
								s = strings.TrimSpace(s)
								if s != "" {
									vals = append(vals, s)
								}
							}
						}
						if len(vals) > 0 {
							multi[k] = vals
						}
					}
				}
			} else {
				// fallback to simple map
				tags = map[string]string{}
				if err := json.Unmarshal(body, &tags); err != nil {
					return http.StatusBadRequest, err
				}
			}

			// If the source is a directory, apply changes to all audio files within.
			// Otherwise, apply to the single file.
			err = d.RunHook(func() error {
				fi, statErr := files.NewFileInfo(&files.FileOptions{
					Fs:         d.user.Fs,
					Path:       src,
					Modify:     d.user.Perm.Modify,
					Expand:     false,
					ReadHeader: false,
					Checker:    d,
				})
				if statErr != nil {
					return statErr
				}
				if fi.IsDir {
					return applyMetadataToDir(r.Context(), d, src, tags, multi, clear)
				}
				return applyMetadataWithFFmpeg(r.Context(), d, src, tags, multi, clear)
			}, action, src, dst, d.user)

			return errToStatus(err), err
		}

		err = d.RunHook(func() error {
			return patchAction(r.Context(), action, src, dst, d, fileCache)
		}, action, src, dst, d.user)

		return errToStatus(err), err
	})
}

// applyMetadataWithFFmpeg attempts to write metadata using ffmpeg by creating
// a temporary file and replacing the original. This requires that the
// underlying filesystem exposes a real path (see FileInfo.RealPath()).
// For FLAC files with multi-valued tags (ARTISTS, ALBUMARTISTS), it uses
// metaflac directly since ffmpeg doesn't support true multi-valued Vorbis comments.
func applyMetadataWithFFmpeg(ctx context.Context, d *data, src string, tags map[string]string, multi map[string][]string, clear []string) error {
	fi, err := files.NewFileInfo(&files.FileOptions{
		Fs:         d.user.Fs,
		Path:       src,
		Modify:     d.user.Perm.Modify,
		Expand:     false,
		ReadHeader: false,
		Checker:    d,
	})
	if err != nil {
		return err
	}

	real := fi.RealPath()
	// If RealPath returns the same virtual path, we cannot run ffmpeg on it.
	if real == "" || real == fi.Path {
		return fmt.Errorf("unable to obtain underlying real file path for %s: %w", fi.Path, fberrors.ErrInvalidRequestParams)
	}

	// Ensure ffmpeg is available
	if _, err := exec.LookPath("ffmpeg"); err != nil {
		return fmt.Errorf("ffmpeg not found: %w", err)
	}

	dir := filepath.Dir(real)

	// Create a unique temporary filename in the same directory and keep the
	// same extension as the original so ffmpeg can infer the output format.
	ext := filepath.Ext(real)
	tmp := filepath.Join(dir, fmt.Sprintf(".metadata_tmp_%d%s", time.Now().UnixNano(), ext))

	// Ensure the temp file is removed on error
	defer func() {
		if _, statErr := os.Stat(tmp); statErr == nil {
			_ = os.Remove(tmp)
		}
	}()

	// Build ffmpeg args to preserve existing metadata and override only the
	// provided non-empty fields. We explicitly map input global metadata (0)
	// to output, and avoid `-map_metadata -1` which would clear everything.
	args := []string{"-y", "-i", real, "-map_metadata", "0", "-c", "copy"}
	// For MP3, prefer ID3v2.4 to support multi-valued tags properly
	isMP3 := strings.EqualFold(ext, ".mp3")
	// Treat M4A/MP4 similarly for metadata handling specifics
	isMP4 := strings.EqualFold(ext, ".m4a") || strings.EqualFold(ext, ".m4b") || strings.EqualFold(ext, ".mp4")
	// FLAC supports true multi-valued Vorbis comments via metaflac
	isFLAC := strings.EqualFold(ext, ".flac")
	if isMP3 {
		args = append(args, "-id3v2_version", "4")
	}

	// For FLAC files with multi-valued tags, use metaflac which properly supports
	// multiple values for the same tag (Vorbis comments).
	if isFLAC && len(multi) > 0 {
		if _, err := exec.LookPath("metaflac"); err == nil {
			// Use metaflac for multi-valued tags
			if err := applyMultiValuedTagsWithMetaflac(ctx, real, tags, multi, clear); err != nil {
				log.Printf("metaflac failed, falling back to ffmpeg: %v", err)
				// Fall through to ffmpeg
			} else {
				return nil
			}
		}
	}

	// If MP3 and there are clears, perform ID3v2 in-place removal first.
	// This avoids ffmpeg creating unwanted empty entries (e.g., TXXX artifacts).
	didID3Clear := false
	if isMP3 && len(clear) > 0 {
		frames := mapClearsToID3Frames(clear)
		txxx := mapClearsToTXXX(clear)
		removeNumeric := false
		for _, c := range clear {
			tok := normalizeKey(c)
			if tok == "artists" || tok == "albumartists" {
				removeNumeric = true
				break
			}
		}
		if err := clearID3v2Frames(real, frames, txxx, removeNumeric); err == nil {
			didID3Clear = true
		}
		// If ID3 clear failed, we'll still try ffmpeg below; but we won't add ffmpeg clears for MP3.
	}

	// Normalize incoming keys and map to ffmpeg keys
	norm := normalizeAndMapToFFmpeg(tags)
	changes := 0
	setKeys := map[string]struct{}{}
	for k, v := range norm {
		args = append(args, "-metadata", fmt.Sprintf("%s=%s", k, v))
		changes++
		setKeys[k] = struct{}{}
	}
	// Handle multi-valued tags (e.g., Artists, AlbumArtists)
	if len(multi) > 0 {
		mm := normalizeMultiToFFmpeg(multi)
		for ffk, vals := range mm {
			// MP4/M4A expects a single value; join for compatibility
			if isMP4 && (ffk == "artist" || ffk == "album_artist") {
				if len(vals) > 0 {
					joined := strings.Join(vals, "; ")
					args = append(args, "-metadata", fmt.Sprintf("%s=%s", ffk, joined))
					changes++
					setKeys[ffk] = struct{}{}
				}
				continue
			}
			// MP3 (ID3): prefer writing consolidated artist/album_artist rather than TXXX ARTISTS
			if isMP3 {
				if ffk == "ARTISTS" {
					if len(vals) > 0 {
						joined := strings.Join(vals, "; ")
						args = append(args, "-metadata", fmt.Sprintf("%s=%s", "artist", joined))
						changes++
						setKeys["artist"] = struct{}{}
					}
					continue
				}
				if ffk == "ALBUMARTISTS" {
					if len(vals) > 0 {
						joined := strings.Join(vals, "; ")
						args = append(args, "-metadata", fmt.Sprintf("%s=%s", "album_artist", joined))
						changes++
						setKeys["album_artist"] = struct{}{}
					}
					continue
				}
			}
			// Default: add repeated metadata entries for formats that support it (e.g., Vorbis)
			for _, v := range vals {
				args = append(args, "-metadata", fmt.Sprintf("%s=%s", ffk, v))
				changes++
			}
			setKeys[ffk] = struct{}{}
		}
	}
	// Map cleared canonical keys to ffmpeg keys and set to empty value.
	// For MP3, we skip ffmpeg-based clears because ID3v2 in-place removal is preferred.
	if len(clear) > 0 && !isMP3 {
		for ffk := range mapClearCanonicalsToFFmpeg(clear) {
			// Avoid clearing a key we are explicitly setting in this operation,
			// which could result in an empty extra value (e.g., trailing NUL).
			if _, isSet := setKeys[ffk]; isSet {
				continue
			}
			args = append(args, "-metadata", fmt.Sprintf("%s=", ffk))
			changes++
		}
	}

	// If no ffmpeg changes are needed (e.g., only clears on MP3), we can return.
	if changes == 0 {
		// If we performed ID3 clear or there was simply nothing to change, exit early.
		if didID3Clear || len(clear) == 0 {
			if isMP3 {
				// Best-effort cleanup of numeric/empty TXXX artifacts
				_ = cleanupNumericEmptyTXXX(real)
			}
			return nil
		}
		// Otherwise continue and let ffmpeg run (non-MP3 clears already added above).
	}
	args = append(args, tmp)

	cmd := exec.CommandContext(ctx, "ffmpeg", args...)
	// Capture combined output to provide actionable errors when ffmpeg fails
	out, err := cmd.CombinedOutput()
	if err != nil {
		return fmt.Errorf("ffmpeg error: %w: %s", err, strings.TrimSpace(string(out)))
	}

	// replace original
	if err := os.Rename(tmp, real); err != nil {
		return err
	}
	if isMP3 {
		// Post-write cleanup for numeric/empty TXXX artifacts
		_ = cleanupNumericEmptyTXXX(real)
	}
	return nil
}

// applyMetadataToDir iterates all immediate files in a directory and applies
// metadata changes to each supported audio file.
func applyMetadataToDir(ctx context.Context, d *data, dir string, tags map[string]string, multi map[string][]string, clear []string) error {
	// List directory entries
	f, err := d.user.Fs.Open(dir)
	if err != nil {
		return err
	}
	defer f.Close()

	names, err := f.Readdirnames(0)
	if err != nil {
		return err
	}

	// Supported audio extensions for metadata updates
	isAudio := func(ext string) bool {
		ext = strings.ToLower(ext)
		switch ext {
		case ".mp3", ".flac", ".m4a", ".mp4", ".ogg", ".wav":
			return true
		default:
			return false
		}
	}

	processed := 0
	failed := 0
	for _, name := range names {
		p := filepath.Join(dir, name)
		info, err := d.user.Fs.Stat(p)
		if err != nil {
			// skip entries we can't stat
			log.Printf("metadata: skip %s: %v", p, err)
			continue
		}
		if info.IsDir() {
			continue
		}
		if !isAudio(filepath.Ext(name)) {
			continue
		}
		if err := applyMetadataWithFFmpeg(ctx, d, p, tags, multi, clear); err != nil {
			failed++
			log.Printf("metadata: failed for %s: %v", p, err)
			continue
		}
		processed++
	}

	if processed == 0 {
		return fmt.Errorf("no audio files found in album: %w", fberrors.ErrInvalidRequestParams)
	}
	if failed > 0 {
		// Do not fail entire album operation; return success and rely on logs
		// to indicate which files failed. This avoids a 500 when some files
		// are temporarily locked or have unsupported formats.
		return nil
	}
	return nil
}

func checkParent(src, dst string) error {
	rel, err := filepath.Rel(src, dst)
	if err != nil {
		return err
	}

	rel = filepath.ToSlash(rel)
	if !strings.HasPrefix(rel, "../") && rel != ".." && rel != "." {
		return fberrors.ErrSourceIsParent
	}

	return nil
}

func addVersionSuffix(source string, afs afero.Fs) string {
	counter := 1
	dir, name := path.Split(source)
	ext := filepath.Ext(name)
	base := strings.TrimSuffix(name, ext)

	for {
		if _, err := afs.Stat(source); err != nil {
			break
		}
		renamed := fmt.Sprintf("%s(%d)%s", base, counter, ext)
		source = path.Join(dir, renamed)
		counter++
	}

	return source
}

func writeFile(afs afero.Fs, dst string, in io.Reader, fileMode, dirMode fs.FileMode) (os.FileInfo, error) {
	dir, _ := path.Split(dst)
	err := afs.MkdirAll(dir, dirMode)
	if err != nil {
		return nil, err
	}

	file, err := afs.OpenFile(dst, os.O_RDWR|os.O_CREATE|os.O_TRUNC, fileMode)
	if err != nil {
		return nil, err
	}
	defer file.Close()

	_, err = io.Copy(file, in)
	if err != nil {
		return nil, err
	}

	// Sync the file to ensure all data is written to storage.
	// to prevent file corruption.
	if err := file.Sync(); err != nil {
		return nil, err
	}

	// Gets the info about the file.
	info, err := file.Stat()
	if err != nil {
		return nil, err
	}

	return info, nil
}

func delThumbs(ctx context.Context, fileCache FileCache, file *files.FileInfo) error {
	for _, previewSizeName := range PreviewSizeNames() {
		size, _ := ParsePreviewSize(previewSizeName)
		if err := fileCache.Delete(ctx, previewCacheKey(file, size)); err != nil {
			return err
		}
	}

	return nil
}

func patchAction(ctx context.Context, action, src, dst string, d *data, fileCache FileCache) error {
	switch action {
	case "copy":
		if !d.user.Perm.Create {
			return fberrors.ErrPermissionDenied
		}

		return fileutils.Copy(d.user.Fs, src, dst, d.settings.FileMode, d.settings.DirMode)
	case "rename":
		if !d.user.Perm.Rename {
			return fberrors.ErrPermissionDenied
		}
		src = path.Clean("/" + src)
		dst = path.Clean("/" + dst)

		file, err := files.NewFileInfo(&files.FileOptions{
			Fs:         d.user.Fs,
			Path:       src,
			Modify:     d.user.Perm.Modify,
			Expand:     false,
			ReadHeader: false,
			Checker:    d,
		})
		if err != nil {
			return err
		}

		// delete thumbnails
		err = delThumbs(ctx, fileCache, file)
		if err != nil {
			return err
		}

		return fileutils.MoveFile(d.user.Fs, src, dst, d.settings.FileMode, d.settings.DirMode)
	default:
		return fmt.Errorf("unsupported action %s: %w", action, fberrors.ErrInvalidRequestParams)
	}
}

type DiskUsageResponse struct {
	Total uint64 `json:"total"`
	Used  uint64 `json:"used"`
}

var diskUsage = withUser(func(w http.ResponseWriter, r *http.Request, d *data) (int, error) {
	file, err := files.NewFileInfo(&files.FileOptions{
		Fs:         d.user.Fs,
		Path:       r.URL.Path,
		Modify:     d.user.Perm.Modify,
		Expand:     false,
		ReadHeader: false,
		Checker:    d,
		Content:    false,
	})
	if err != nil {
		return errToStatus(err), err
	}
	fPath := file.RealPath()
	if !file.IsDir {
		return renderJSON(w, r, &DiskUsageResponse{
			Total: 0,
			Used:  0,
		})
	}

	usage, err := disk.UsageWithContext(r.Context(), fPath)
	if err != nil {
		return errToStatus(err), err
	}
	return renderJSON(w, r, &DiskUsageResponse{
		Total: usage.Total,
		Used:  usage.Used,
	})
})

// applyMultiValuedTagsWithMetaflac uses metaflac to write tags to FLAC files.
// Unlike ffmpeg, metaflac properly supports multiple values for the same tag.
func applyMultiValuedTagsWithMetaflac(ctx context.Context, filepath string, tags map[string]string, multi map[string][]string, clear []string) error {
	// Normalize tags and multi to proper Vorbis comment names
	norm := normalizeAndMapToFFmpeg(tags)
	mm := normalizeMultiToFFmpeg(multi)

	// Build metaflac arguments
	// First, remove tags that we're going to set (to avoid duplicates)
	removeArgs := []string{}
	for k := range norm {
		upperK := strings.ToUpper(k)
		removeArgs = append(removeArgs, "--remove-tag="+upperK)
		// Also handle ALBUM_ARTIST vs "ALBUM ARTIST" variants
		if upperK == "ALBUM_ARTIST" {
			removeArgs = append(removeArgs, "--remove-tag=ALBUM ARTIST")
			removeArgs = append(removeArgs, "--remove-tag=ALBUMARTIST")
		}
	}
	for k := range mm {
		removeArgs = append(removeArgs, "--remove-tag="+k)
	}
	// Also remove cleared tags
	for _, c := range clear {
		token := normalizeKey(c)
		canonical, ok := canonicalMap[token]
		if !ok {
			if _, allowed := allowedCanonicals[c]; allowed {
				canonical = c
			} else {
				continue
			}
		}
		// Check multi-valued tags first
		if ffk, ok := ffmpegMultiKey[canonical]; ok {
			removeArgs = append(removeArgs, "--remove-tag="+ffk)
		}
		// Also check regular tags
		if ffk, ok := ffmpegKey[canonical]; ok {
			upperK := strings.ToUpper(ffk)
			removeArgs = append(removeArgs, "--remove-tag="+upperK)
			// Handle all variants of album artist
			if canonical == "AlbumArtist" {
				removeArgs = append(removeArgs, "--remove-tag=ALBUM ARTIST")
				removeArgs = append(removeArgs, "--remove-tag=ALBUMARTIST")
				removeArgs = append(removeArgs, "--remove-tag=ALBUM_ARTIST")
			}
			// Handle artist variants (lowercase/uppercase)
			if canonical == "Artist" {
				removeArgs = append(removeArgs, "--remove-tag=artist")
				removeArgs = append(removeArgs, "--remove-tag=ARTIST")
			}
		}
	}

	// Execute removal first if needed
	if len(removeArgs) > 0 {
		removeArgs = append(removeArgs, filepath)
		cmd := exec.CommandContext(ctx, "metaflac", removeArgs...)
		if out, err := cmd.CombinedOutput(); err != nil {
			return fmt.Errorf("metaflac remove failed: %w: %s", err, string(out))
		}
	}

	// Now set the new tags
	setArgs := []string{}
	for k, v := range norm {
		// Use uppercase for Vorbis comments (standard convention)
		setArgs = append(setArgs, fmt.Sprintf("--set-tag=%s=%s", strings.ToUpper(k), v))
	}
	// Add multi-valued tags (each value as a separate --set-tag)
	for k, vals := range mm {
		for _, v := range vals {
			setArgs = append(setArgs, fmt.Sprintf("--set-tag=%s=%s", k, v))
		}
	}

	// If nothing to set, we're done (removal was already executed above)
	if len(setArgs) == 0 {
		return nil
	}

	setArgs = append(setArgs, filepath)
	cmd := exec.CommandContext(ctx, "metaflac", setArgs...)
	if out, err := cmd.CombinedOutput(); err != nil {
		return fmt.Errorf("metaflac set failed: %w: %s", err, string(out))
	}

	return nil
}