class FieldLayoutBuilder

class FieldLayoutBuilder implements ContainerInjectionInterface {
    
    /**
     * The layout plugin manager.
     *
     * @var \Drupal\Core\Layout\LayoutPluginManagerInterface
     */
    protected $layoutPluginManager;
    
    /**
     * The entity field manager.
     *
     * @var \Drupal\Core\Entity\EntityFieldManagerInterface
     */
    protected $entityFieldManager;
    
    /**
     * Constructs a new FieldLayoutBuilder.
     *
     * @param \Drupal\Core\Layout\LayoutPluginManagerInterface $layout_plugin_manager
     *   The layout plugin manager.
     * @param \Drupal\Core\Entity\EntityFieldManagerInterface $entity_field_manager
     *   The entity field manager.
     */
    public function __construct(LayoutPluginManagerInterface $layout_plugin_manager, EntityFieldManagerInterface $entity_field_manager) {
        $this->layoutPluginManager = $layout_plugin_manager;
        $this->entityFieldManager = $entity_field_manager;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container) {
        return new static($container->get('plugin.manager.core.layout'), $container->get('entity_field.manager'));
    }
    
    /**
     * Applies the layout to an entity build.
     *
     * @param array $build
     *   A renderable array representing the entity content or form.
     * @param \Drupal\field_layout\Display\EntityDisplayWithLayoutInterface $display
     *   The entity display holding the display options configured for the entity
     *   components.
     */
    public function buildView(array &$build, EntityDisplayWithLayoutInterface $display) {
        $layout_definition = $this->layoutPluginManager
            ->getDefinition($display->getLayoutId(), FALSE);
        if ($layout_definition && ($fields = $this->getFields($build, $display, 'view'))) {
            // Add the regions to the $build in the correct order.
            $regions = array_fill_keys($layout_definition->getRegionNames(), []);
            foreach ($fields as $name => $field) {
                // If the region is controlled by the layout, move the field from the
                // top-level of $build into a region-specific section. Custom regions
                // could be set by other code at run-time; these should be ignored.
                // @todo Ideally the array structure would remain unchanged, see
                //   https://www.drupal.org/node/2846393.
                if (isset($regions[$field['region']])) {
                    $regions[$field['region']][$name] = $build[$name];
                    unset($build[$name]);
                }
            }
            // Ensure this will not conflict with any existing array elements by
            // prefixing with an underscore.
            $build['_field_layout'] = $display->getLayout()
                ->build($regions);
        }
    }
    
    /**
     * Applies the layout to an entity form.
     *
     * @param array $build
     *   A renderable array representing the entity content or form.
     * @param \Drupal\field_layout\Display\EntityDisplayWithLayoutInterface $display
     *   The entity display holding the display options configured for the entity
     *   components.
     */
    public function buildForm(array &$build, EntityDisplayWithLayoutInterface $display) {
        $layout_definition = $this->layoutPluginManager
            ->getDefinition($display->getLayoutId(), FALSE);
        if ($layout_definition && ($fields = $this->getFields($build, $display, 'form'))) {
            $fill = [];
            $fill['#process'][] = '\\Drupal\\Core\\Render\\Element\\RenderElement::processGroup';
            $fill['#pre_render'][] = '\\Drupal\\Core\\Render\\Element\\RenderElement::preRenderGroup';
            // Add the regions to the $build in the correct order.
            $regions = array_fill_keys($layout_definition->getRegionNames(), $fill);
            foreach ($fields as $name => $field) {
                // As this is a form, #group can be used to relocate the fields. This
                // avoids breaking hook_form_alter() implementations by not actually
                // moving the field in the form structure. If a #group is already set,
                // do not overwrite it.
                if (isset($regions[$field['region']]) && !isset($build[$name]['#group'])) {
                    $build[$name]['#group'] = $field['region'];
                }
            }
            // Ensure this will not conflict with any existing array elements by
            // prefixing with an underscore.
            $build['_field_layout'] = $display->getLayout()
                ->build($regions);
        }
    }
    
    /**
     * Gets the fields that need to be processed.
     *
     * @param array $build
     *   A renderable array representing the entity content or form.
     * @param \Drupal\field_layout\Display\EntityDisplayWithLayoutInterface $display
     *   The entity display holding the display options configured for the entity
     *   components.
     * @param string $display_context
     *   The display context, either 'form' or 'view'.
     *
     * @return array
     *   An array of configurable fields present in the build.
     */
    protected function getFields(array $build, EntityDisplayWithLayoutInterface $display, $display_context) {
        $components = $display->getComponents();
        // Ignore any extra fields from the list of field definitions. Field
        // definitions can have a non-configurable display, but all extra fields are
        // always displayed.
        $field_definitions = array_diff_key($this->entityFieldManager
            ->getFieldDefinitions($display->getTargetEntityTypeId(), $display->getTargetBundle()), $this->entityFieldManager
            ->getExtraFields($display->getTargetEntityTypeId(), $display->getTargetBundle()));
        $fields_to_exclude = array_filter($field_definitions, function (FieldDefinitionInterface $field_definition) use ($display_context) {
            // Remove fields with a non-configurable display.
            return !$field_definition->isDisplayConfigurable($display_context);
        });
        $components = array_diff_key($components, $fields_to_exclude);
        // Only include fields present in the build.
        $components = array_intersect_key($components, $build);
        return $components;
    }

}