class FieldLayoutHooks

class FieldLayoutHooks {
    
    /**
     * Implements hook_help().
     */
    public function help($route_name, RouteMatchInterface $route_match) {
        switch ($route_name) {
            case 'help.page.field_layout':
                $output = '<h2>' . t('About') . '</h2>';
                $output .= '<p>' . t('The Field Layout module allows you to arrange fields into regions on forms and displays of entities such as nodes and users.') . '</p>';
                $output .= '<p>' . t('For more information, see the <a href=":field-layout-documentation">online documentation for the Field Layout module</a>.', [
                    ':field-layout-documentation' => 'https://www.drupal.org/documentation/modules/field_layout',
                ]) . '</p>';
                return $output;
        }
    }
    
    /**
     * Implements hook_entity_type_alter().
     */
    public function entityTypeAlter(array &$entity_types) : void {
        
        /** @var \Drupal\Core\Entity\EntityTypeInterface[] $entity_types */
        $entity_types['entity_view_display']->setClass(FieldLayoutEntityViewDisplay::class);
        $entity_types['entity_form_display']->setClass(FieldLayoutEntityFormDisplay::class);
        // The form classes are only needed when Field UI is installed.
        if (\Drupal::moduleHandler()->moduleExists('field_ui')) {
            $entity_types['entity_view_display']->setFormClass('edit', FieldLayoutEntityViewDisplayEditForm::class);
            $entity_types['entity_form_display']->setFormClass('edit', FieldLayoutEntityFormDisplayEditForm::class);
        }
    }
    
    /**
     * Implements hook_entity_view_alter().
     */
    public function entityViewAlter(array &$build, EntityInterface $entity, EntityViewDisplayInterface $display) {
        if ($display instanceof EntityDisplayWithLayoutInterface) {
            \Drupal::classResolver(FieldLayoutBuilder::class)->buildView($build, $display);
        }
    }
    
    /**
     * Implements hook_form_alter().
     */
    public function formAlter(&$form, FormStateInterface $form_state, $form_id) : void {
        $form_object = $form_state->getFormObject();
        if ($form_object instanceof ContentEntityFormInterface && ($display = $form_object->getFormDisplay($form_state))) {
            if ($display instanceof EntityDisplayWithLayoutInterface) {
                \Drupal::classResolver(FieldLayoutBuilder::class)->buildForm($form, $display);
            }
        }
    }

}