class Button

class Button extends FormElementBase {
    
    /**
     * {@inheritdoc}
     */
    public function getInfo() {
        return [
            '#input' => TRUE,
            '#name' => 'op',
            '#is_button' => TRUE,
            '#submit_button' => TRUE,
            '#executes_submit_callback' => FALSE,
            '#limit_validation_errors' => FALSE,
            '#process' => [
                [
                    static::class,
                    'processButton',
                ],
                [
                    static::class,
                    'processAjaxForm',
                ],
            ],
            '#pre_render' => [
                [
                    static::class,
                    'preRenderButton',
                ],
            ],
            '#theme_wrappers' => [
                'input__submit',
            ],
        ];
    }
    
    /**
     * Processes a form button element.
     */
    public static function processButton(&$element, FormStateInterface $form_state, &$complete_form) {
        // If this is a button intentionally allowing incomplete form submission
        // (e.g., a "Previous" or "Add another item" button), then also skip
        // client-side validation.
        if (isset($element['#limit_validation_errors']) && $element['#limit_validation_errors'] !== FALSE) {
            $element['#attributes']['formnovalidate'] = 'formnovalidate';
        }
        return $element;
    }
    
    /**
     * Prepares a #type 'button' render element for input.html.twig.
     *
     * @param array $element
     *   An associative array containing the properties of the element.
     *   Properties used: #attributes, #button_type, #name, #submit_button,
     *   #value. The #button_type property accepts any value, though core themes
     *   have CSS that styles the following button_types appropriately:
     *   'primary', 'danger'.
     *
     * @return array
     *   The $element with prepared variables ready for input.html.twig.
     */
    public static function preRenderButton($element) {
        if ($element['#submit_button']) {
            $element['#attributes']['type'] = 'submit';
        }
        else {
            $element['#attributes']['type'] = 'button';
        }
        Element::setAttributes($element, [
            'id',
            'name',
            'value',
        ]);
        $element['#attributes']['class'][] = 'button';
        if (!empty($element['#button_type'])) {
            $element['#attributes']['class'][] = 'button--' . $element['#button_type'];
        }
        $element['#attributes']['class'][] = 'js-form-submit';
        $element['#attributes']['class'][] = 'form-submit';
        if (!empty($element['#attributes']['disabled'])) {
            $element['#attributes']['class'][] = 'is-disabled';
        }
        return $element;
    }

}