class LayoutBuilderEntityViewDisplayForm

class LayoutBuilderEntityViewDisplayForm extends EntityViewDisplayEditForm {
    
    /**
     * The entity being used by this form.
     *
     * @var \Drupal\layout_builder\Entity\LayoutEntityDisplayInterface
     */
    protected $entity;
    
    /**
     * The storage section.
     *
     * @var \Drupal\layout_builder\DefaultsSectionStorageInterface
     */
    protected $sectionStorage;
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state, ?SectionStorageInterface $section_storage = NULL) {
        $this->sectionStorage = $section_storage;
        return parent::buildForm($form, $form_state);
    }
    
    /**
     * {@inheritdoc}
     */
    public function form(array $form, FormStateInterface $form_state) {
        $form = parent::form($form, $form_state);
        // Remove the Layout Builder field from the list.
        $form['#fields'] = array_diff($form['#fields'], [
            OverridesSectionStorage::FIELD_NAME,
        ]);
        unset($form['fields'][OverridesSectionStorage::FIELD_NAME]);
        $is_enabled = $this->entity
            ->isLayoutBuilderEnabled();
        if ($is_enabled) {
            // Hide the table of fields.
            $form['fields']['#access'] = FALSE;
            $form['#fields'] = [];
            $form['#extra'] = [];
        }
        $form['manage_layout'] = [
            '#type' => 'link',
            '#title' => $this->t('Manage layout'),
            '#weight' => -10,
            '#attributes' => [
                'class' => [
                    'button',
                ],
            ],
            '#url' => $this->sectionStorage
                ->getLayoutBuilderUrl(),
            '#access' => $is_enabled,
        ];
        $form['layout'] = [
            '#type' => 'details',
            '#open' => TRUE,
            '#title' => $this->t('Layout options'),
            '#tree' => TRUE,
        ];
        $form['layout']['enabled'] = [
            '#type' => 'checkbox',
            '#title' => $this->t('Use Layout Builder'),
            '#default_value' => $is_enabled,
        ];
        $form['#entity_builders']['layout_builder'] = '::entityFormEntityBuild';
        // @todo Expand to work for all view modes in
        //   https://www.drupal.org/node/2907413.
        if ($this->isCanonicalMode($this->entity
            ->getMode())) {
            $entity_type = $this->entityTypeManager
                ->getDefinition($this->entity
                ->getTargetEntityTypeId());
            $form['layout']['allow_custom'] = [
                '#type' => 'checkbox',
                '#title' => $this->t('Allow each @entity to have its layout customized.', [
                    '@entity' => $entity_type->getSingularLabel(),
                ]),
                '#default_value' => $this->entity
                    ->isOverridable(),
                '#states' => [
                    'disabled' => [
                        ':input[name="layout[enabled]"]' => [
                            'checked' => FALSE,
                        ],
                    ],
                    'invisible' => [
                        ':input[name="layout[enabled]"]' => [
                            'checked' => FALSE,
                        ],
                    ],
                ],
            ];
            if (!$is_enabled) {
                $form['layout']['allow_custom']['#attributes']['disabled'] = 'disabled';
            }
            // Prevent turning off overrides while any exist.
            if ($this->hasOverrides($this->entity)) {
                $form['layout']['enabled']['#disabled'] = TRUE;
                $form['layout']['enabled']['#description'] = $this->t('You must revert all customized layouts of this display before you can disable this option.');
                $form['layout']['allow_custom']['#disabled'] = TRUE;
                $form['layout']['allow_custom']['#description'] = $this->t('You must revert all customized layouts of this display before you can disable this option.');
                unset($form['layout']['allow_custom']['#states']);
                unset($form['#entity_builders']['layout_builder']);
            }
        }
        else {
            $form['layout']['allow_custom'] = [
                '#type' => 'value',
                '#value' => $this->entity
                    ->isOverridable(),
            ];
        }
        return $form;
    }
    
    /**
     * Determines if the mode is used by the canonical route.
     *
     * @param string $mode
     *   The view mode.
     *
     * @return bool
     *   TRUE if the mode is valid, FALSE otherwise.
     */
    protected function isCanonicalMode($mode) {
        // @todo This is a convention core uses but is not a given, nor is it easily
        //   introspectable. Address in https://www.drupal.org/node/2907413.
        $canonical_mode = 'full';
        if ($mode === $canonical_mode) {
            return TRUE;
        }
        // The default mode is valid if the canonical mode is not enabled.
        if ($mode === 'default') {
            
            /** @var \Drupal\Core\Config\Entity\ConfigEntityStorageInterface $storage */
            $storage = $this->entityTypeManager
                ->getStorage($this->entity
                ->getEntityTypeId());
            $query = $storage->getQuery()
                ->condition('targetEntityType', $this->entity
                ->getTargetEntityTypeId())
                ->condition('bundle', $this->entity
                ->getTargetBundle())
                ->condition('status', TRUE)
                ->condition('mode', $canonical_mode);
            return !$query->count()
                ->execute();
        }
        return FALSE;
    }
    
    /**
     * Determines if the defaults have any overrides.
     *
     * @param \Drupal\layout_builder\Entity\LayoutEntityDisplayInterface $display
     *   The entity display.
     *
     * @return bool
     *   TRUE if there are any overrides of this default, FALSE otherwise.
     */
    protected function hasOverrides(LayoutEntityDisplayInterface $display) {
        if (!$display->isOverridable()) {
            return FALSE;
        }
        $entity_type = $this->entityTypeManager
            ->getDefinition($display->getTargetEntityTypeId());
        $query = $this->entityTypeManager
            ->getStorage($display->getTargetEntityTypeId())
            ->getQuery()
            ->accessCheck(FALSE)
            ->exists(OverridesSectionStorage::FIELD_NAME);
        if ($bundle_key = $entity_type->getKey('bundle')) {
            $query->condition($bundle_key, $display->getTargetBundle());
        }
        return (bool) $query->count()
            ->execute();
    }
    
    /**
     * {@inheritdoc}
     */
    protected function copyFormValuesToEntity(EntityInterface $entity, array $form, FormStateInterface $form_state) {
        // Do not process field values if Layout Builder is or will be enabled.
        $set_enabled = (bool) $form_state->getValue([
            'layout',
            'enabled',
        ], FALSE);
        
        /** @var \Drupal\layout_builder\Entity\LayoutEntityDisplayInterface $entity */
        $already_enabled = $entity->isLayoutBuilderEnabled();
        if ($already_enabled || $set_enabled) {
            $form['#fields'] = [];
            $form['#extra'] = [];
        }
        parent::copyFormValuesToEntity($entity, $form, $form_state);
    }
    
    /**
     * Entity builder for layout options on the entity view display form.
     */
    public function entityFormEntityBuild($entity_type_id, LayoutEntityDisplayInterface $display, &$form, FormStateInterface &$form_state) {
        $set_enabled = (bool) $form_state->getValue([
            'layout',
            'enabled',
        ], FALSE);
        $already_enabled = $display->isLayoutBuilderEnabled();
        if ($set_enabled) {
            $overridable = (bool) $form_state->getValue([
                'layout',
                'allow_custom',
            ], FALSE);
            $display->setOverridable($overridable);
            if (!$already_enabled) {
                $display->enableLayoutBuilder();
            }
        }
        elseif ($already_enabled) {
            $form_state->setRedirectUrl($this->sectionStorage
                ->getLayoutBuilderUrl('disable'));
        }
    }
    
    /**
     * {@inheritdoc}
     */
    protected function buildFieldRow(FieldDefinitionInterface $field_definition, array $form, FormStateInterface $form_state) {
        if ($this->entity
            ->isLayoutBuilderEnabled()) {
            return [];
        }
        return parent::buildFieldRow($field_definition, $form, $form_state);
    }
    
    /**
     * {@inheritdoc}
     */
    protected function buildExtraFieldRow($field_id, $extra_field) {
        if ($this->entity
            ->isLayoutBuilderEnabled()) {
            return [];
        }
        return parent::buildExtraFieldRow($field_id, $extra_field);
    }

}