class EntityDisplayBase

abstract class EntityDisplayBase extends ConfigEntityBase implements EntityDisplayInterface {
    
    /**
     * The mode used to render entities with arbitrary display options.
     *
     * @todo Prevent creation of a mode with this ID
     *   https://www.drupal.org/node/2410727
     */
    const CUSTOM_MODE = '_custom';
    
    /**
     * Unique ID for the config entity.
     *
     * @var string
     */
    protected $id;
    
    /**
     * Entity type to be displayed.
     *
     * @var string
     */
    protected $targetEntityType;
    
    /**
     * Bundle to be displayed.
     *
     * @var string
     */
    protected $bundle;
    
    /**
     * A list of field definitions eligible for configuration in this display.
     *
     * @var \Drupal\Core\Field\FieldDefinitionInterface[]
     */
    protected $fieldDefinitions;
    
    /**
     * View or form mode to be displayed.
     *
     * @var string
     */
    protected $mode = self::CUSTOM_MODE;
    
    /**
     * Whether this display is enabled or not.
     *
     * If the entity (form) display is disabled, we'll fall back to the 'default'
     * display.
     *
     * @var bool
     */
    protected $status;
    
    /**
     * List of component display options, keyed by component name.
     *
     * @var array
     */
    protected $content = [];
    
    /**
     * List of components that are set to be hidden.
     *
     * @var array
     */
    protected $hidden = [];
    
    /**
     * The original view or form mode that was requested.
     *
     * Case of view/form modes being configured to fall back to the 'default'
     * display.
     *
     * @var string
     */
    protected $originalMode;
    
    /**
     * The plugin objects used for this display, keyed by field name.
     *
     * @var array
     */
    protected $plugins = [];
    
    /**
     * Context in which this entity will be used (e.g. 'view', 'form').
     *
     * @var string
     */
    protected $displayContext;
    
    /**
     * The plugin manager used by this entity type.
     *
     * @var \Drupal\Component\Plugin\PluginManagerBase
     */
    protected $pluginManager;
    
    /**
     * The renderer.
     *
     * @var \Drupal\Core\Render\RendererInterface
     */
    protected $renderer;
    
    /**
     * {@inheritdoc}
     */
    public function __construct(array $values, $entity_type) {
        if (!isset($values['targetEntityType']) || !isset($values['bundle'])) {
            throw new \InvalidArgumentException('Missing required properties for an EntityDisplay entity.');
        }
        if (!$this->entityTypeManager()
            ->getDefinition($values['targetEntityType'])
            ->entityClassImplements(FieldableEntityInterface::class)) {
            throw new \InvalidArgumentException('EntityDisplay entities can only handle fieldable entity types.');
        }
        $this->renderer = \Drupal::service('renderer');
        // A plugin manager and a context type needs to be set by extending classes.
        if (!isset($this->pluginManager)) {
            throw new \RuntimeException('Missing plugin manager.');
        }
        if (!isset($this->displayContext)) {
            throw new \RuntimeException('Missing display context type.');
        }
        parent::__construct($values, $entity_type);
        $this->originalMode = $this->mode;
        $this->init();
    }
    
    /**
     * Initializes the display.
     *
     * This fills in default options for components:
     * - that are not explicitly known as either "visible" or "hidden" in the
     *   display,
     * - or that are not supposed to be configurable.
     */
    protected function init() {
        // Only populate defaults for "official" view modes and form modes.
        if ($this->mode !== static::CUSTOM_MODE) {
            $default_region = $this->getDefaultRegion();
            // Fill in defaults for extra fields.
            $context = $this->displayContext == 'view' ? 'display' : $this->displayContext;
            $extra_fields = \Drupal::service('entity_field.manager')->getExtraFields($this->targetEntityType, $this->bundle);
            $extra_fields = $extra_fields[$context] ?? [];
            foreach ($extra_fields as $name => $definition) {
                if (!isset($this->content[$name]) && !isset($this->hidden[$name])) {
                    // Extra fields are visible by default unless they explicitly say so.
                    if (!isset($definition['visible']) || $definition['visible'] == TRUE) {
                        $this->setComponent($name, [
                            'weight' => $definition['weight'],
                        ]);
                    }
                    else {
                        $this->removeComponent($name);
                    }
                }
                // Ensure extra fields have a 'region'.
                if (isset($this->content[$name])) {
                    $this->content[$name] += [
                        'region' => $default_region,
                    ];
                }
            }
            // Fill in defaults for fields.
            $fields = $this->getFieldDefinitions();
            foreach ($fields as $name => $definition) {
                if (!$definition->isDisplayConfigurable($this->displayContext) || !isset($this->content[$name]) && !isset($this->hidden[$name])) {
                    $options = $definition->getDisplayOptions($this->displayContext);
                    if (!empty($options['region']) && $options['region'] === 'hidden') {
                        $this->removeComponent($name);
                    }
                    elseif ($options) {
                        $options += [
                            'region' => $default_region,
                        ];
                        $this->setComponent($name, $options);
                    }
                    // Note: (base) fields that do not specify display options are not
                    // tracked in the display at all, in order to avoid cluttering the
                    // configuration that gets saved back.
                }
            }
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function getTargetEntityTypeId() {
        return $this->targetEntityType;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getMode() {
        return $this->get('mode');
    }
    
    /**
     * {@inheritdoc}
     */
    public function getOriginalMode() {
        return $this->get('originalMode');
    }
    
    /**
     * {@inheritdoc}
     */
    public function getTargetBundle() {
        return $this->bundle;
    }
    
    /**
     * {@inheritdoc}
     */
    public function setTargetBundle($bundle) {
        $this->set('bundle', $bundle);
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function id() {
        return $this->targetEntityType . '.' . $this->bundle . '.' . $this->mode;
    }
    
    /**
     * {@inheritdoc}
     */
    public function preSave(EntityStorageInterface $storage) {
        // Ensure that a region is set on each component.
        foreach ($this->getComponents() as $name => $component) {
            // Ensure that a region is set.
            if (isset($this->content[$name]) && !isset($component['region'])) {
                // Directly set the component to bypass other changes in setComponent().
                $this->content[$name]['region'] = $this->getDefaultRegion();
            }
        }
        ksort($this->content);
        ksort($this->hidden);
        parent::preSave($storage);
    }
    
    /**
     * {@inheritdoc}
     */
    public function calculateDependencies() {
        parent::calculateDependencies();
        $target_entity_type = $this->entityTypeManager()
            ->getDefinition($this->targetEntityType);
        // Create dependency on the bundle.
        $bundle_config_dependency = $target_entity_type->getBundleConfigDependency($this->bundle);
        $this->addDependency($bundle_config_dependency['type'], $bundle_config_dependency['name']);
        // If field.module is enabled, add dependencies on 'field_config' entities
        // for both displayed and hidden fields. We intentionally leave out base
        // field overrides, since the field still exists without them.
        if (\Drupal::moduleHandler()->moduleExists('field')) {
            $components = $this->content + $this->hidden;
            $field_definitions = \Drupal::service('entity_field.manager')->getFieldDefinitions($this->targetEntityType, $this->bundle);
            foreach (array_intersect_key($field_definitions, $components) as $field_definition) {
                if ($field_definition instanceof ConfigEntityInterface && $field_definition->getEntityTypeId() == 'field_config') {
                    $this->addDependency('config', $field_definition->getConfigDependencyName());
                }
            }
        }
        // Depend on configured modes.
        if ($this->mode != 'default') {
            $mode_entity = $this->entityTypeManager()
                ->getStorage('entity_' . $this->displayContext . '_mode')
                ->load($target_entity_type->id() . '.' . $this->mode);
            $this->addDependency('config', $mode_entity->getConfigDependencyName());
        }
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function toArray() {
        $properties = parent::toArray();
        // Do not store options for fields whose display is not set to be
        // configurable.
        foreach ($this->getFieldDefinitions() as $field_name => $definition) {
            if (!$definition->isDisplayConfigurable($this->displayContext)) {
                unset($properties['content'][$field_name]);
                unset($properties['hidden'][$field_name]);
            }
        }
        return $properties;
    }
    
    /**
     * {@inheritdoc}
     */
    public function createCopy($mode) {
        $display = $this->createDuplicate();
        $display->mode = $display->originalMode = $mode;
        return $display;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getComponents() {
        return $this->content;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getComponent($name) {
        return $this->content[$name] ?? NULL;
    }
    
    /**
     * {@inheritdoc}
     */
    public function setComponent($name, array $options = []) {
        // If no weight specified, make sure the field sinks at the bottom.
        if (!isset($options['weight'])) {
            $max = $this->getHighestWeight();
            $options['weight'] = isset($max) ? $max + 1 : 0;
        }
        // For a field, fill in default options.
        if ($field_definition = $this->getFieldDefinition($name)) {
            $options = $this->pluginManager
                ->prepareConfiguration($field_definition->getType(), $options);
        }
        // Ensure we always have an empty settings and array.
        $options += [
            'settings' => [],
            'third_party_settings' => [],
        ];
        $this->content[$name] = $options;
        unset($this->hidden[$name]);
        unset($this->plugins[$name]);
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function removeComponent($name) {
        $this->hidden[$name] = TRUE;
        unset($this->content[$name]);
        unset($this->plugins[$name]);
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getHighestWeight() {
        $weights = [];
        // Collect weights for the components in the display.
        foreach ($this->content as $options) {
            if (isset($options['weight'])) {
                $weights[] = $options['weight'];
            }
        }
        // Let other modules feedback about their own additions.
        $weights = array_merge($weights, \Drupal::moduleHandler()->invokeAll('field_info_max_weight', [
            $this->targetEntityType,
            $this->bundle,
            $this->displayContext,
            $this->mode,
        ]));
        return $weights ? max($weights) : NULL;
    }
    
    /**
     * Gets the field definition of a field.
     */
    protected function getFieldDefinition($field_name) {
        $definitions = $this->getFieldDefinitions();
        return $definitions[$field_name] ?? NULL;
    }
    
    /**
     * Gets the definitions of the fields that are candidate for display.
     */
    protected function getFieldDefinitions() {
        if (!isset($this->fieldDefinitions)) {
            $definitions = \Drupal::service('entity_field.manager')->getFieldDefinitions($this->targetEntityType, $this->bundle);
            // For "official" view modes and form modes, ignore fields whose
            // definition states they should not be displayed.
            if ($this->mode !== static::CUSTOM_MODE) {
                $definitions = array_filter($definitions, [
                    $this,
                    'fieldHasDisplayOptions',
                ]);
            }
            $this->fieldDefinitions = $definitions;
        }
        return $this->fieldDefinitions;
    }
    
    /**
     * Determines if a field has options for a given display.
     *
     * @param \Drupal\Core\Field\FieldDefinitionInterface $definition
     *   A field definition.
     *
     * @return array|null
     */
    private function fieldHasDisplayOptions(FieldDefinitionInterface $definition) {
        // The display only cares about fields that specify display options.
        // Discard base fields that are not rendered through formatters / widgets.
        return $definition->getDisplayOptions($this->displayContext);
    }
    
    /**
     * {@inheritdoc}
     */
    public function onDependencyRemoval(array $dependencies) {
        $changed = parent::onDependencyRemoval($dependencies);
        foreach ($dependencies['config'] as $entity) {
            if ($entity->getEntityTypeId() == 'field_config') {
                // Remove components for fields that are being deleted.
                $this->removeComponent($entity->getName());
                unset($this->hidden[$entity->getName()]);
                $changed = TRUE;
            }
        }
        foreach ($this->getComponents() as $name => $component) {
            if ($renderer = $this->getRenderer($name)) {
                if (in_array($renderer->getPluginDefinition()['provider'], $dependencies['module'])) {
                    // Revert to the defaults if the plugin that supplies the widget or
                    // formatter depends on a module that is being uninstalled.
                    $this->setComponent($name);
                    $changed = TRUE;
                }
                // Give this component the opportunity to react on dependency removal.
                $component_removed_dependencies = $this->getPluginRemovedDependencies($renderer->calculateDependencies(), $dependencies);
                if ($component_removed_dependencies) {
                    if ($renderer->onDependencyRemoval($component_removed_dependencies)) {
                        // Update component settings to reflect changes.
                        $component['settings'] = $renderer->getSettings();
                        $component['third_party_settings'] = [];
                        foreach ($renderer->getThirdPartyProviders() as $module) {
                            $component['third_party_settings'][$module] = $renderer->getThirdPartySettings($module);
                        }
                        $this->setComponent($name, $component);
                        $changed = TRUE;
                    }
                    // If there are unresolved deleted dependencies left, disable this
                    // component to avoid the removal of the entire display entity.
                    if ($this->getPluginRemovedDependencies($renderer->calculateDependencies(), $dependencies)) {
                        $this->removeComponent($name);
                        $arguments = [
                            '@display' => (string) $this->getEntityType()
                                ->getLabel(),
                            '@id' => $this->id(),
                            '@name' => $name,
                        ];
                        $this->getLogger()
                            ->warning("@display '@id': Component '@name' was disabled because its settings depend on removed dependencies.", $arguments);
                        $changed = TRUE;
                    }
                }
            }
        }
        return $changed;
    }
    
    /**
     * Returns the plugin dependencies being removed.
     *
     * The function recursively computes the intersection between all plugin
     * dependencies and all removed dependencies.
     *
     * Note: The two arguments do not have the same structure.
     *
     * @param array[] $plugin_dependencies
     *   A list of dependencies having the same structure as the return value of
     *   ConfigEntityInterface::calculateDependencies().
     * @param array[] $removed_dependencies
     *   A list of dependencies having the same structure as the input argument of
     *   ConfigEntityInterface::onDependencyRemoval().
     *
     * @return array
     *   A recursively computed intersection.
     *
     * @see \Drupal\Core\Config\Entity\ConfigEntityInterface::calculateDependencies()
     * @see \Drupal\Core\Config\Entity\ConfigEntityInterface::onDependencyRemoval()
     */
    protected function getPluginRemovedDependencies(array $plugin_dependencies, array $removed_dependencies) {
        $intersect = [];
        foreach ($plugin_dependencies as $type => $dependencies) {
            if ($removed_dependencies[$type]) {
                // Config and content entities have the dependency names as keys while
                // module and theme dependencies are indexed arrays of dependency names.
                // @see \Drupal\Core\Config\ConfigManager::callOnDependencyRemoval()
                if (in_array($type, [
                    'config',
                    'content',
                ])) {
                    $removed = array_intersect_key($removed_dependencies[$type], array_flip($dependencies));
                }
                else {
                    $removed = array_values(array_intersect($removed_dependencies[$type], $dependencies));
                }
                if ($removed) {
                    $intersect[$type] = $removed;
                }
            }
        }
        return $intersect;
    }
    
    /**
     * Gets the default region.
     *
     * @return string
     *   The default region for this display.
     */
    protected function getDefaultRegion() {
        return 'content';
    }
    
    /**
     * {@inheritdoc}
     */
    public function __sleep() {
        // Only store the definition, not external objects or derived data.
        $keys = array_keys($this->toArray());
        // In addition, we need to keep the entity type and the "is new" status.
        $keys[] = 'entityTypeId';
        $keys[] = 'enforceIsNew';
        // Keep track of the serialized keys, to avoid calling toArray() again in
        // __wakeup(). Because of the way __sleep() works, the data has to be
        // present in the object to be included in the serialized values.
        $keys[] = '_serializedKeys';
        $this->_serializedKeys = $keys;
        return $keys;
    }
    
    /**
     * {@inheritdoc}
     */
    public function __wakeup() {
        // Determine what were the properties from toArray() that were saved in
        // __sleep().
        $keys = $this->_serializedKeys;
        unset($this->_serializedKeys);
        $values = array_intersect_key(get_object_vars($this), array_flip($keys));
        // Run those values through the __construct(), as if they came from a
        // regular entity load.
        $this->__construct($values, $this->entityTypeId);
    }
    
    /**
     * Provides the 'system' channel logger service.
     *
     * @return \Psr\Log\LoggerInterface
     *   The 'system' channel logger.
     */
    protected function getLogger() {
        return \Drupal::logger('system');
    }

}