create basic controller

pkg/repo/repo.go

@@ -21,13 +21,14 @@ func NewStateError(msg string) error {
 
 type Storage interface {
 	Lock() (func() error, error)
-	Exist(string) (bool, error)
+	Exists(string) (bool, error)
 	Write(string, encoding.BinaryMarshaler) error
 	Read(string, encoding.BinaryUnmarshaler) error
 }
 
 type repo struct {
-	s Storage
+	s       Storage
+	release func() error
 }
 
 func NewRepo(s Storage) (*repo, error) {
@@ -44,3 +45,38 @@ func NewFileRepo(path string) (*repo, error) {
 	}
 	return NewRepo(s)
 }
+
+func (r *repo) Lock() (err error) {
+	if r.s == nil {
+		return errors.New("storage is closed")
+	}
+	if r.release != nil {
+		return errors.New("storage already locked")
+	}
+	r.release, err = r.s.Lock()
+	if err != nil {
+		r.close()
+		return
+	}
+	return nil
+}
+
+func (r *repo) Release() (err error) {
+	if r.s == nil {
+		return errors.New("storage is closed")
+	}
+	if r.release == nil {
+		return errors.New("storage was never locked")
+	}
+	err = r.release()
+	if err != nil {
+		return
+	}
+	r.close()
+	return nil
+}
+
+func (r *repo) close() {
+	r.release = nil
+	r.s = nil
+}