class FormTestClickedButtonForm

class FormTestClickedButtonForm extends FormBase {
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return 'form_test_clicked_button';
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state, $first = NULL, $second = NULL, $third = NULL) {
        // A single text field. In IE, when a form has only one non-button input field
        // and the ENTER key is pressed while that field has focus, the form is
        // submitted without any information identifying the button responsible for
        // the submission. In other browsers, the form is submitted as though the
        // first button were clicked.
        $form['text'] = [
            '#title' => 'Text',
            '#type' => 'textfield',
        ];
        // Loop through each path argument, adding buttons based on the information
        // in the argument. For example, if the path is
        // form-test/clicked-button/s/i/rb, then 3 buttons are added: a 'submit', an
        // 'image_button', and a 'button' with #access=FALSE. This enables form.test
        // to test a variety of combinations.
        $i = 0;
        $args = [
            $first,
            $second,
            $third,
        ];
        foreach ($args as $arg) {
            $name = 'button' . ++$i;
            // 's', 'b', or 'i' in the argument define the button type wanted.
            if (strpos($arg, 's') !== FALSE) {
                $type = 'submit';
            }
            elseif (strpos($arg, 'b') !== FALSE) {
                $type = 'button';
            }
            elseif (strpos($arg, 'i') !== FALSE) {
                $type = 'image_button';
            }
            else {
                $type = NULL;
            }
            if (isset($type)) {
                $form[$name] = [
                    '#type' => $type,
                    '#name' => $name,
                ];
                // Image buttons need a #src; the others need a #value.
                if ($type == 'image_button') {
                    $form[$name]['#src'] = 'core/misc/druplicon.png';
                }
                else {
                    $form[$name]['#value'] = $name;
                }
                // 'r' for restricted, so we can test that button click detection code
                // correctly takes #access security into account.
                if (strpos($arg, 'r') !== FALSE) {
                    $form[$name]['#access'] = FALSE;
                }
            }
        }
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function validateForm(array &$form, FormStateInterface $form_state) {
        if ($triggering_element = $form_state->getTriggeringElement()) {
            $this->messenger()
                ->addStatus(t('The clicked button is %name.', [
                '%name' => $triggering_element['#name'],
            ]));
        }
        else {
            $this->messenger()
                ->addStatus('There is no clicked button.');
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
        $this->messenger()
            ->addStatus('Submit handler for form_test_clicked_button executed.');
    }

}