feat(wrtag): output covers with lowercase extension

closes #198

Author: sentriz

cmd/wrtag/testdata/scripts/cover-extension-lowercase.txtar

@@ -0,0 +1,30 @@
+exec tag write kat_moda/01.flac title 'Alarms'
+exec tag write kat_moda/02.flac title 'The Bells'
+exec tag write kat_moda/03.flac title 'The Bells (Festival mix)'
+
+exec tag write kat_moda/*.flac musicbrainz_albumid 'e47d04a4-7460-427d-a731-cc82386d85f1'
+exec tag write kat_moda/*.flac album               'Kat Moda'
+exec tag write kat_moda/*.flac albumartist         'Jeff Mills'
+exec tag write kat_moda/*.flac label               'Purpose Maker'
+exec tag write kat_moda/*.flac catalognumber       'PMD002'
+exec tag write kat_moda/*.flac media               'Digital Media'
+
+exec touch kat_moda/folder.PNG
+
+env WRTAG_PATH_FORMAT='albums/{{ .Release.Title }}/{{ .TrackNum }}{{ .Ext }}'
+
+exec wrtag move -yes kat_moda/
+
+exec find albums/
+cmp stdout exp-layout
+
+! exists 'albums/Kat Moda/cover.PNG'
+exists 'albums/Kat Moda/cover.png'
+
+-- exp-layout --
+albums
+albums/Kat Moda
+albums/Kat Moda/1.flac
+albums/Kat Moda/2.flac
+albums/Kat Moda/3.flac
+albums/Kat Moda/cover.png

wrtag.go

@@ -1004,7 +1004,8 @@ func processCover(
 	op FileSystemOperation, dc DirContext, release *musicbrainz.Release, destDir string, cover string,
 ) (string, error) {
 	coverPath := func(p string) string {
-		return filepath.Join(destDir, "cover"+filepath.Ext(p))
+		ext := strings.ToLower(filepath.Ext(p))
+		return filepath.Join(destDir, "cover"+ext)
 	}
 
 	if op.CanModifyDest() && (cover == "" || cfg.UpgradeCover) {
@@ -1078,7 +1079,7 @@ func tryDownloadMusicBrainzCover(ctx context.Context, caa *musicbrainz.CAAClient
 		return "", nil
 	}
 
-	ext := path.Ext(coverURL)
+	ext := strings.ToLower(path.Ext(coverURL))
 	tmpf, err := os.CreateTemp("", ".wrtag-cover-tmp-*"+ext)
 	if err != nil {
 		return "", fmt.Errorf("mktmp: %w", err)