private void IsRegisterInputCorrect(IPasswordGuardian parameter)
        {
            var password = parameter.Password;

            if (!(password != null && RegisterEmail != null && IsCorrectEmailFormat(RegisterEmail)))
            {
                RegisterErrorMessage = "Incorrect username or password format.";
            }
        }
        private async void TryRegisterCustomer(IPasswordGuardian parameter)
        {
            var password = parameter.Password;

            try
            {
                IsLoading = true;

                await _accountManager.RegisterUser(RegisterEmail, password);

                TryLogUser(RegisterEmail, parameter);
            }
            catch (Exception exception)
            {
                RegisterErrorMessage = exception.Message;
            }
            finally
            {
                IsLoading = false;
            }
        }
        private void ExecuteRegisterUser(IPasswordGuardian parameter)
        {
            RegisterErrorMessage = null;

            IsRegisterInputCorrect(parameter);

            if (string.IsNullOrEmpty(RegisterErrorMessage))
            {
                TryRegisterCustomer(parameter);
            }
        }
        private async void TryLogUser(string email, IPasswordGuardian parameter)
        {
            var password = parameter.Password;

            try
            {
                IsLoading = true;

                await _accountManager.LogUser(email, password);

                ExecuteNavigateToMainMenu();
            }
            catch (Exception exception)
            {
                LoginErrorMessage = exception.Message;
            }
            finally
            {
                IsLoading = false;
            }
        }
        private void IsLoginInputCorrect(IPasswordGuardian parameter)
        {
            var password = parameter.Password;

            if (!(password != null && LoginEmail != null && IsCorrectEmailFormat(LoginEmail)))
            {
                LoginErrorMessage = "Incorrect username or password format.";
            }         
        }
        private void ExecuteLogUser(IPasswordGuardian parameter)
        {
            LoginErrorMessage = null;
            
            IsLoginInputCorrect(parameter);

            if (string.IsNullOrEmpty(LoginErrorMessage))
            {
                TryLogUser(LoginEmail, parameter);
            }
        }