refactor: rule package

pkg/rule/enum.go

@@ -0,0 +1,17 @@
+package rule
+
+type RuleType string
+
+const (
+	FileNameRegex RuleType = "FILENAME-REGEX"
+	MessageRegex  RuleType = "MESSAGE-REGEX"
+	IsAlbum       RuleType = "IS-ALBUM"
+)
+
+func (r RuleType) String() string {
+	return string(r)
+}
+
+func Values() []RuleType {
+	return []RuleType{FileNameRegex, MessageRegex, IsAlbum}
+}