class DbtngExampleAddForm

class DbtngExampleAddForm implements FormInterface, ContainerInjectionInterface {
    use StringTranslationTrait;
    use MessengerTrait;
    
    /**
     * Our database repository service.
     *
     * @var \Drupal\dbtng_example\DbtngExampleRepository
     */
    protected $repository;
    
    /**
     * The current user.
     *
     * We'll need this service in order to check if the user is logged in.
     *
     * @var \Drupal\Core\Session\AccountProxyInterface
     */
    protected $currentUser;
    
    /**
     * {@inheritdoc}
     *
     * We'll use the ContainerInjectionInterface pattern here to inject the
     * current user and also get the string_translation service.
     */
    public static function create(ContainerInterface $container) {
        $form = new static($container->get('dbtng_example.repository'), $container->get('current_user'));
        // The StringTranslationTrait trait manages the string translation service
        // for us. We can inject the service here.
        $form->setStringTranslation($container->get('string_translation'));
        $form->setMessenger($container->get('messenger'));
        return $form;
    }
    
    /**
     * Construct the new form object.
     */
    public function __construct(DbtngExampleRepository $repository, AccountProxyInterface $current_user) {
        $this->repository = $repository;
        $this->currentUser = $current_user;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return 'dbtng_add_form';
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state) {
        $form = [];
        $form['message'] = [
            '#markup' => $this->t('Add an entry to the dbtng_example table.'),
        ];
        $form['add'] = [
            '#type' => 'fieldset',
            '#title' => $this->t('Add a person entry'),
        ];
        $form['add']['name'] = [
            '#type' => 'textfield',
            '#title' => $this->t('Name'),
            '#size' => 15,
        ];
        $form['add']['surname'] = [
            '#type' => 'textfield',
            '#title' => $this->t('Surname'),
            '#size' => 15,
        ];
        $form['add']['age'] = [
            '#type' => 'textfield',
            '#title' => $this->t('Age'),
            '#size' => 5,
            '#description' => $this->t("Values greater than 127 will cause an exception. Try it - it's a great example why exception handling is needed with DTBNG."),
        ];
        $form['add']['submit'] = [
            '#type' => 'submit',
            '#value' => $this->t('Add'),
        ];
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function validateForm(array &$form, FormStateInterface $form_state) {
        // Verify that the user is logged-in.
        if ($this->currentUser
            ->isAnonymous()) {
            $form_state->setError($form['add'], $this->t('You must be logged in to add values to the database.'));
        }
        // Confirm that age is numeric.
        if (!intval($form_state->getValue('age'))) {
            $form_state->setErrorByName('age', $this->t('Age needs to be a number'));
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
        // Gather the current user so the new record has ownership.
        $account = $this->currentUser;
        // Save the submitted entry.
        $entry = [
            'name' => $form_state->getValue('name'),
            'surname' => $form_state->getValue('surname'),
            'age' => $form_state->getValue('age'),
            'uid' => $account->id(),
        ];
        $return = $this->repository
            ->insert($entry);
        if ($return) {
            $this->messenger()
                ->addMessage($this->t('Created entry @entry', [
                '@entry' => print_r($entry, TRUE),
            ]));
        }
    }

}