// Insert a user
func (s *UserStorage) Insert(c model.User) (string, error) {
	c.Chocolates = make([]model.Chocolate, len(c.ChocolatesIDs))
	err := s.updateChocolatesByChocolatesIDs(&c)
	if err != nil {
		return "", err
	}
	s.db.Create(&c)
	if s.db.Error != nil {
		return "", s.db.Error
	}
	return c.GetID(), nil
}