Add IncryBy and DecrBy methods to increase or decrease a value

pkg/modules/keyvalue/error/error.go

@@ -27,3 +27,26 @@ type ErrValueNotFoundForKey struct {
 func (e *ErrValueNotFoundForKey) Error() string {
 	return fmt.Sprintf("could not find value for key %s", e.Key)
 }
+
+// IsErrValueNotFoundForKey checks if an error is ErrValueNotFoundForKey
+func IsErrValueNotFoundForKey(err error) bool {
+	_, is := err.(*ErrValueNotFoundForKey)
+	return is
+}
+
+// ErrValueHasWrongType represents an error where a value saved at key has the wrong value
+type ErrValueHasWrongType struct {
+	Key           string
+	ExpectedValue string
+}
+
+// Error is the error implementation
+func (e *ErrValueHasWrongType) Error() string {
+	return fmt.Sprintf("value at key %s has the wrong value, expexted was %s", e.Key, e.ExpectedValue)
+}
+
+// IsErrValueHasWrongType checks if an error is ErrValueHasWrongType
+func IsErrValueHasWrongType(err error) bool {
+	_, is := err.(*ErrValueHasWrongType)
+	return is
+}

pkg/modules/keyvalue/keyvalue.go

@@ -28,6 +28,8 @@ type Storage interface {
 	Put(key string, value interface{}) (err error)
 	Get(key string) (value interface{}, err error)
 	Del(key string) (err error)
+	IncrBy(key string, update int64) (err error)
+	DecrBy(key string, update int64) (err error)
 }
 
 var store Storage

pkg/modules/keyvalue/memory/memory.go

@@ -64,3 +64,39 @@ func (s *Storage) Del(key string) (err error) {
 	delete(s.store, key)
 	return nil
 }
+
+// IncrBy increases the value saved at key by the amount provided through update
+// It assumes the value saved for the key either does not exist or has a type of int64
+func (s *Storage) IncrBy(key string, update int64) (err error) {
+	s.mutex.Lock()
+	defer s.mutex.Unlock()
+
+	v, err := s.Get(key)
+	if err != nil && !e.IsErrValueNotFoundForKey(err) {
+		return err
+	}
+	val, is := v.(int64)
+	if !is {
+		return &e.ErrValueHasWrongType{Key: key, ExpectedValue: "int64"}
+	}
+	s.store[key] = val + update
+	return nil
+}
+
+// DecrBy decreases the value saved at key by the amount provided through update
+// It assumes the value saved for the key either does not exist or has a type of int64
+func (s *Storage) DecrBy(key string, update int64) (err error) {
+	s.mutex.Lock()
+	defer s.mutex.Unlock()
+
+	v, err := s.Get(key)
+	if err != nil && !e.IsErrValueNotFoundForKey(err) {
+		return err
+	}
+	val, is := v.(int64)
+	if !is {
+		return &e.ErrValueHasWrongType{Key: key, ExpectedValue: "int64"}
+	}
+	s.store[key] = val - update
+	return nil
+}

pkg/modules/keyvalue/redis/redis.go

@@ -66,3 +66,13 @@ func (s *Storage) Get(key string) (value interface{}, err error) {
 func (s *Storage) Del(key string) (err error) {
 	return s.client.Del(key).Err()
 }
+
+// IncrBy increases the value saved at key by the amount provided through update
+func (s *Storage) IncrBy(key string, update int64) (err error) {
+	return s.client.IncrBy(key, update).Err()
+}
+
+// DecrBy decreases the value saved at key by the amount provided through update
+func (s *Storage) DecrBy(key string, update int64) (err error) {
+	return s.client.DecrBy(key, update).Err()
+}