lib/versioner: Reduce surface area (#6186)

* lib/versioner: Reduce surface area

This is a refactor while I was anyway rooting around in the versioner.
Instead of exporting every possible implementation and the factory and
letting the caller do whatever, this now encapsulates all that and
exposes a New() that takes a config.VersioningConfiguration.

Given that and that we don't know (from the outside) how a versioner
works or what state it keeps, we now just construct it once per folder
and keep it around. Previously it was recreated for each restore
request.

* unparam

* wip

lib/versioner/util.go

@@ -24,7 +24,7 @@ var errDirectory = fmt.Errorf("cannot restore on top of a directory")
 var errNotFound = fmt.Errorf("version not found")
 var errFileAlreadyExists = fmt.Errorf("file already exists")
 
-// Inserts ~tag just before the extension of the filename.
+// TagFilename inserts ~tag just before the extension of the filename.
 func TagFilename(name, tag string) string {
 	dir, file := filepath.Dir(name), filepath.Base(name)
 	ext := filepath.Ext(file)
@@ -34,8 +34,8 @@ func TagFilename(name, tag string) string {
 
 var tagExp = regexp.MustCompile(`.*~([^~.]+)(?:\.[^.]+)?$`)
 
-// Returns the tag from a filename, whether at the end or middle.
-func ExtractTag(path string) string {
+// extractTag returns the tag from a filename, whether at the end or middle.
+func extractTag(path string) string {
 	match := tagExp.FindStringSubmatch(path)
 	// match is []string{"whole match", "submatch"} when successful
 
@@ -45,9 +45,10 @@ func ExtractTag(path string) string {
 	return match[1]
 }
 
+// UntagFilename returns the filename without tag, and the extracted tag
 func UntagFilename(path string) (string, string) {
 	ext := filepath.Ext(path)
-	versionTag := ExtractTag(path)
+	versionTag := extractTag(path)
 
 	// Files tagged with old style tags cannot be untagged.
 	if versionTag == "" {
@@ -276,7 +277,7 @@ func findAllVersions(fs fs.Filesystem, filePath string) []string {
 	file := filepath.Base(filePath)
 
 	// Glob according to the new file~timestamp.ext pattern.
-	pattern := filepath.Join(inFolderPath, TagFilename(file, TimeGlob))
+	pattern := filepath.Join(inFolderPath, TagFilename(file, timeGlob))
 	versions, err := fs.Glob(pattern)
 	if err != nil {
 		l.Warnln("globbing:", err, "for", pattern)