private void btnAddTeacher_Click(object sender, RoutedEventArgs e)
        {
            try
            {
                AddTeacherWindow addTeacherWindow = new AddTeacherWindow();
                if (addTeacherWindow.ShowDialog() == true)
                {
                    Teacher teacher = new Teacher()
                    {
                        Username   = addTeacherWindow.Username,
                        FirstName  = addTeacherWindow.FirstName,
                        MiddleName = addTeacherWindow.MiddleName,
                        LastName   = addTeacherWindow.LastName
                    };

                    string secret = Crypto.GenerateRandomSecret();
                    teacher.Username = Crypto.EncryptStringAES(teacher.Username, secret);
                    string password = Crypto.EncryptStringAES(addTeacherWindow.Password, secret);

                    if (client.RegisterTeacher(teacher, password, secret))
                    {
                        UpdateTeacherViews();
                        MessageBox.Show("Учителят беше добавен успешно");
                    }
                    else
                    {
                        MessageBox.Show("Учителят не е валиден или вече съществува");
                    }
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(Application.Current.Resources["defaultErrorMessage"].ToString(),
                                "Грешка", MessageBoxButton.OK, MessageBoxImage.Error);
            }
        }
        private void btnAddTeacher_Click(object sender, RoutedEventArgs e)
        {
            try
            {
                AddTeacherWindow addTeacherWindow = new AddTeacherWindow();
                if (addTeacherWindow.ShowDialog() == true)
                {
                    Teacher teacher = new Teacher()
                    {
                        Username = addTeacherWindow.Username,
                        FirstName = addTeacherWindow.FirstName,
                        MiddleName = addTeacherWindow.MiddleName,
                        LastName = addTeacherWindow.LastName
                    };

                    string secret = Crypto.GenerateRandomSecret();
                    teacher.Username = Crypto.EncryptStringAES(teacher.Username, secret);
                    string password = Crypto.EncryptStringAES(addTeacherWindow.Password, secret);

                    if(client.RegisterTeacher(teacher, password, secret))
                    {
                        UpdateTeacherViews();
                        MessageBox.Show("Учителят беше добавен успешно");   
                    }
                    else
                    {
                        MessageBox.Show("Учителят не е валиден или вече съществува");
                    }
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(Application.Current.Resources["defaultErrorMessage"].ToString(), 
                    "Грешка", MessageBoxButton.OK, MessageBoxImage.Error);
            }
        }