class ContentEntityBase

abstract class ContentEntityBase extends EntityBase implements \IteratorAggregate, ContentEntityInterface, TranslationStatusInterface {
    use EntityChangesDetectionTrait {
        getFieldsToSkipFromTranslationChangesCheck as traitGetFieldsToSkipFromTranslationChangesCheck;
    }
    use SynchronizableEntityTrait;
    
    /**
     * The plain data values of the contained fields.
     *
     * This always holds the original, unchanged values of the entity. The values
     * are keyed by language code, whereas LanguageInterface::LANGCODE_DEFAULT
     * is used for values in default language.
     *
     * @todo: Add methods for getting original fields and for determining
     * changes.
     * @todo: Provide a better way for defining default values.
     *
     * @var array
     */
    protected $values = [];
    
    /**
     * The array of fields, each being an instance of FieldItemListInterface.
     *
     * @var array
     */
    protected $fields = [];
    
    /**
     * Local cache for field definitions.
     *
     * @see ContentEntityBase::getFieldDefinitions()
     *
     * @var array
     */
    protected $fieldDefinitions;
    
    /**
     * Local cache for the available language objects.
     *
     * @var \Drupal\Core\Language\LanguageInterface[]
     */
    protected $languages;
    
    /**
     * The language entity key.
     *
     * @var string
     */
    protected $langcodeKey;
    
    /**
     * The default langcode entity key.
     *
     * @var string
     */
    protected $defaultLangcodeKey;
    
    /**
     * Language code identifying the entity active language.
     *
     * This is the language field accessors will use to determine which field
     * values manipulate.
     *
     * @var string
     */
    protected $activeLangcode = LanguageInterface::LANGCODE_DEFAULT;
    
    /**
     * Local cache for the default language code.
     *
     * @var string
     */
    protected $defaultLangcode;
    
    /**
     * An array of entity translation metadata.
     *
     * An associative array keyed by translation language code. Every value is an
     * array containing the translation status and the translation object, if it has
     * already been instantiated.
     *
     * @var array
     */
    protected $translations = [];
    
    /**
     * A flag indicating whether a translation object is being initialized.
     *
     * @var bool
     */
    protected $translationInitialize = FALSE;
    
    /**
     * Boolean indicating whether a new revision should be created on save.
     *
     * @var bool
     */
    protected $newRevision = FALSE;
    
    /**
     * Indicates whether this is the default revision.
     *
     * @var bool
     */
    protected $isDefaultRevision = TRUE;
    
    /**
     * Holds untranslatable entity keys such as the ID, bundle, and revision ID.
     *
     * @var array
     */
    protected $entityKeys = [];
    
    /**
     * Holds translatable entity keys such as the label.
     *
     * @var array
     */
    protected $translatableEntityKeys = [];
    
    /**
     * Whether entity validation was performed.
     *
     * @var bool
     */
    protected $validated = FALSE;
    
    /**
     * Whether entity validation is required before saving the entity.
     *
     * @var bool
     */
    protected $validationRequired = FALSE;
    
    /**
     * The loaded revision ID before the new revision was set.
     *
     * @var int
     */
    protected $loadedRevisionId;
    
    /**
     * The revision translation affected entity key.
     *
     * @var string
     */
    protected $revisionTranslationAffectedKey;
    
    /**
     * Whether the revision translation affected flag has been enforced.
     *
     * An array, keyed by the translation language code.
     *
     * @var bool[]
     */
    protected $enforceRevisionTranslationAffected = [];
    
    /**
     * Local cache for fields to skip from the checking for translation changes.
     *
     * @var array
     */
    protected static $fieldsToSkipFromTranslationChangesCheck = [];
    
    /**
     * {@inheritdoc}
     */
    public function __construct(array $values, $entity_type, $bundle = FALSE, $translations = []) {
        $this->entityTypeId = $entity_type;
        $this->entityKeys['bundle'] = $bundle ? $bundle : $this->entityTypeId;
        $this->langcodeKey = $this->getEntityType()
            ->getKey('langcode');
        $this->defaultLangcodeKey = $this->getEntityType()
            ->getKey('default_langcode');
        $this->revisionTranslationAffectedKey = $this->getEntityType()
            ->getKey('revision_translation_affected');
        foreach ($values as $key => $value) {
            // If the key matches an existing property set the value to the property
            // to set properties like isDefaultRevision.
            // @todo: Should this be converted somehow?
            if (property_exists($this, $key) && isset($value[LanguageInterface::LANGCODE_DEFAULT])) {
                $this->{$key} = $value[LanguageInterface::LANGCODE_DEFAULT];
            }
        }
        $this->values = $values;
        foreach ($this->getEntityType()
            ->getKeys() as $key => $field_name) {
            if (isset($this->values[$field_name])) {
                if (is_array($this->values[$field_name])) {
                    // We store untranslatable fields into an entity key without using a
                    // langcode key.
                    if (!$this->getFieldDefinition($field_name)
                        ->isTranslatable()) {
                        if (isset($this->values[$field_name][LanguageInterface::LANGCODE_DEFAULT])) {
                            if (is_array($this->values[$field_name][LanguageInterface::LANGCODE_DEFAULT])) {
                                if (isset($this->values[$field_name][LanguageInterface::LANGCODE_DEFAULT][0]['value'])) {
                                    $this->entityKeys[$key] = $this->values[$field_name][LanguageInterface::LANGCODE_DEFAULT][0]['value'];
                                }
                            }
                            else {
                                $this->entityKeys[$key] = $this->values[$field_name][LanguageInterface::LANGCODE_DEFAULT];
                            }
                        }
                    }
                    else {
                        // We save translatable fields such as the publishing status of a node
                        // into an entity key array keyed by langcode as a performance
                        // optimization, so we don't have to go through TypedData when we
                        // need these values.
                        foreach ($this->values[$field_name] as $langcode => $field_value) {
                            if (is_array($this->values[$field_name][$langcode])) {
                                if (isset($this->values[$field_name][$langcode][0]['value'])) {
                                    $this->translatableEntityKeys[$key][$langcode] = $this->values[$field_name][$langcode][0]['value'];
                                }
                            }
                            else {
                                $this->translatableEntityKeys[$key][$langcode] = $this->values[$field_name][$langcode];
                            }
                        }
                    }
                }
            }
        }
        // Initialize translations. Ensure we have at least an entry for the default
        // language.
        // We determine if the entity is new by checking in the entity values for
        // the presence of the id entity key, as the usage of ::isNew() is not
        // possible in the constructor.
        $data = isset($values[$this->getEntityType()
            ->getKey('id')]) ? [
            'status' => static::TRANSLATION_EXISTING,
        ] : [
            'status' => static::TRANSLATION_CREATED,
        ];
        $this->translations[LanguageInterface::LANGCODE_DEFAULT] = $data;
        $this->setDefaultLangcode();
        if ($translations) {
            foreach ($translations as $langcode) {
                if ($langcode != $this->defaultLangcode && $langcode != LanguageInterface::LANGCODE_DEFAULT) {
                    $this->translations[$langcode] = $data;
                }
            }
        }
        if ($this->getEntityType()
            ->isRevisionable()) {
            // Store the loaded revision ID the entity has been loaded with to
            // keep it safe from changes.
            $this->updateLoadedRevisionId();
        }
    }
    
    /**
     * {@inheritdoc}
     */
    protected function getLanguages() {
        if (empty($this->languages)) {
            $this->languages = $this->languageManager()
                ->getLanguages(LanguageInterface::STATE_ALL);
            // If the entity references a language that is not or no longer available,
            // we return a mock language object to avoid disrupting the consuming
            // code.
            if (!isset($this->languages[$this->defaultLangcode])) {
                $this->languages[$this->defaultLangcode] = new Language([
                    'id' => $this->defaultLangcode,
                ]);
            }
        }
        return $this->languages;
    }
    
    /**
     * {@inheritdoc}
     */
    public function postCreate(EntityStorageInterface $storage) {
        $this->newRevision = TRUE;
    }
    
    /**
     * {@inheritdoc}
     */
    public function setNewRevision($value = TRUE) {
        if (!$this->getEntityType()
            ->hasKey('revision')) {
            throw new \LogicException("Entity type {$this->getEntityTypeId()} does not support revisions.");
        }
        if ($value && !$this->newRevision) {
            // When saving a new revision, set any existing revision ID to NULL so as
            // to ensure that a new revision will actually be created.
            $this->set($this->getEntityType()
                ->getKey('revision'), NULL);
        }
        elseif (!$value && $this->newRevision) {
            // If ::setNewRevision(FALSE) is called after ::setNewRevision(TRUE) we
            // have to restore the loaded revision ID.
            $this->set($this->getEntityType()
                ->getKey('revision'), $this->getLoadedRevisionId());
        }
        $this->newRevision = $value;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getLoadedRevisionId() {
        return $this->loadedRevisionId;
    }
    
    /**
     * {@inheritdoc}
     */
    public function updateLoadedRevisionId() {
        $this->loadedRevisionId = $this->getRevisionId() ?: $this->loadedRevisionId;
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function isNewRevision() {
        return $this->newRevision || $this->getEntityType()
            ->hasKey('revision') && !$this->getRevisionId();
    }
    
    /**
     * {@inheritdoc}
     */
    public function isDefaultRevision($new_value = NULL) {
        $return = $this->isDefaultRevision;
        if (isset($new_value)) {
            $this->isDefaultRevision = (bool) $new_value;
        }
        // New entities should always ensure at least one default revision exists,
        // creating an entity without a default revision is an invalid state.
        return $this->isNew() || $return;
    }
    
    /**
     * {@inheritdoc}
     */
    public function wasDefaultRevision() {
        
        /** @var \Drupal\Core\Entity\ContentEntityTypeInterface $entity_type */
        $entity_type = $this->getEntityType();
        if (!$entity_type->isRevisionable()) {
            return TRUE;
        }
        $revision_default_key = $entity_type->getRevisionMetadataKey('revision_default');
        $value = $this->isNew() || $this->get($revision_default_key)->value;
        return $value;
    }
    
    /**
     * {@inheritdoc}
     */
    public function isLatestRevision() {
        
        /** @var \Drupal\Core\Entity\ContentEntityStorageInterface $storage */
        $storage = $this->entityTypeManager()
            ->getStorage($this->getEntityTypeId());
        return $this->getLoadedRevisionId() == $storage->getLatestRevisionId($this->id());
    }
    
    /**
     * {@inheritdoc}
     */
    public function isLatestTranslationAffectedRevision() {
        
        /** @var \Drupal\Core\Entity\ContentEntityStorageInterface $storage */
        $storage = $this->entityTypeManager()
            ->getStorage($this->getEntityTypeId());
        return $this->getLoadedRevisionId() == $storage->getLatestTranslationAffectedRevisionId($this->id(), $this->language()
            ->getId());
    }
    
    /**
     * {@inheritdoc}
     */
    public function isRevisionTranslationAffected() {
        return $this->hasField($this->revisionTranslationAffectedKey) ? $this->get($this->revisionTranslationAffectedKey)->value : TRUE;
    }
    
    /**
     * {@inheritdoc}
     */
    public function setRevisionTranslationAffected($affected) {
        if ($this->hasField($this->revisionTranslationAffectedKey)) {
            $this->set($this->revisionTranslationAffectedKey, $affected);
        }
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function isRevisionTranslationAffectedEnforced() {
        return !empty($this->enforceRevisionTranslationAffected[$this->activeLangcode]);
    }
    
    /**
     * {@inheritdoc}
     */
    public function setRevisionTranslationAffectedEnforced($enforced) {
        $this->enforceRevisionTranslationAffected[$this->activeLangcode] = $enforced;
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function isDefaultTranslation() {
        return $this->activeLangcode === LanguageInterface::LANGCODE_DEFAULT;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getRevisionId() {
        return $this->getEntityKey('revision');
    }
    
    /**
     * {@inheritdoc}
     */
    public function isTranslatable() {
        // Check the bundle is translatable, the entity has a language defined, and
        // the site has more than one language.
        $bundles = $this->entityTypeBundleInfo()
            ->getBundleInfo($this->entityTypeId);
        return !empty($bundles[$this->bundle()]['translatable']) && !$this->getUntranslated()
            ->language()
            ->isLocked() && $this->languageManager()
            ->isMultilingual();
    }
    
    /**
     * {@inheritdoc}
     */
    public function preSave(EntityStorageInterface $storage) {
        // An entity requiring validation should not be saved if it has not been
        // actually validated.
        if ($this->validationRequired && !$this->validated) {
            // @todo Make this an assertion in https://www.drupal.org/node/2408013.
            throw new \LogicException('Entity validation was skipped.');
        }
        else {
            $this->validated = FALSE;
        }
        parent::preSave($storage);
    }
    
    /**
     * {@inheritdoc}
     */
    public function preSaveRevision(EntityStorageInterface $storage, \stdClass $record) {
    }
    
    /**
     * {@inheritdoc}
     */
    public function postSave(EntityStorageInterface $storage, $update = TRUE) {
        parent::postSave($storage, $update);
        // Update the status of all saved translations.
        $removed = [];
        foreach ($this->translations as $langcode => &$data) {
            if ($data['status'] == static::TRANSLATION_REMOVED) {
                $removed[$langcode] = TRUE;
            }
            else {
                $data['status'] = static::TRANSLATION_EXISTING;
            }
        }
        $this->translations = array_diff_key($this->translations, $removed);
        // Reset the new revision flag.
        $this->newRevision = FALSE;
        // Reset the enforcement of the revision translation affected flag.
        $this->enforceRevisionTranslationAffected = [];
    }
    
    /**
     * {@inheritdoc}
     */
    public function validate() {
        $this->validated = TRUE;
        $violations = $this->getTypedData()
            ->validate();
        return new EntityConstraintViolationList($this, iterator_to_array($violations));
    }
    
    /**
     * {@inheritdoc}
     */
    public function isValidationRequired() {
        return (bool) $this->validationRequired;
    }
    
    /**
     * {@inheritdoc}
     */
    public function setValidationRequired($required) {
        $this->validationRequired = $required;
        return $this;
    }
    
    /**
     * Clear entity translation object cache to remove stale references.
     */
    protected function clearTranslationCache() {
        foreach ($this->translations as &$translation) {
            unset($translation['entity']);
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function __sleep() {
        // Get the values of instantiated field objects, only serialize the values.
        foreach ($this->fields as $name => $fields) {
            foreach ($fields as $langcode => $field) {
                $this->values[$name][$langcode] = $field->getValue();
            }
        }
        $this->fields = [];
        $this->fieldDefinitions = NULL;
        $this->languages = NULL;
        $this->clearTranslationCache();
        return parent::__sleep();
    }
    
    /**
     * {@inheritdoc}
     */
    public function id() {
        return $this->getEntityKey('id');
    }
    
    /**
     * {@inheritdoc}
     */
    public function bundle() {
        return $this->getEntityKey('bundle');
    }
    
    /**
     * {@inheritdoc}
     */
    public function uuid() {
        return $this->getEntityKey('uuid');
    }
    
    /**
     * {@inheritdoc}
     */
    public function hasField($field_name) {
        return (bool) $this->getFieldDefinition($field_name);
    }
    
    /**
     * {@inheritdoc}
     */
    public function get($field_name) {
        if (!isset($this->fields[$field_name][$this->activeLangcode])) {
            return $this->getTranslatedField($field_name, $this->activeLangcode);
        }
        return $this->fields[$field_name][$this->activeLangcode];
    }
    
    /**
     * Gets a translated field.
     *
     * @return \Drupal\Core\Field\FieldItemListInterface
     */
    protected function getTranslatedField($name, $langcode) {
        if ($this->translations[$this->activeLangcode]['status'] == static::TRANSLATION_REMOVED) {
            throw new \InvalidArgumentException("The entity object refers to a removed translation ({$this->activeLangcode}) and cannot be manipulated.");
        }
        // Populate $this->fields to speed-up further look-ups and to keep track of
        // fields objects, possibly holding changes to field values.
        if (!isset($this->fields[$name][$langcode])) {
            $definition = $this->getFieldDefinition($name);
            if (!$definition) {
                throw new \InvalidArgumentException("Field {$name} is unknown.");
            }
            // Non-translatable fields are always stored with
            // LanguageInterface::LANGCODE_DEFAULT as key.
            $default = $langcode == LanguageInterface::LANGCODE_DEFAULT;
            if (!$default && !$definition->isTranslatable()) {
                if (!isset($this->fields[$name][LanguageInterface::LANGCODE_DEFAULT])) {
                    $this->fields[$name][LanguageInterface::LANGCODE_DEFAULT] = $this->getTranslatedField($name, LanguageInterface::LANGCODE_DEFAULT);
                }
                $this->fields[$name][$langcode] =& $this->fields[$name][LanguageInterface::LANGCODE_DEFAULT];
            }
            else {
                $value = NULL;
                if (isset($this->values[$name][$langcode])) {
                    $value = $this->values[$name][$langcode];
                }
                $field = \Drupal::service('plugin.manager.field.field_type')->createFieldItemList($this->getTranslation($langcode), $name, $value);
                if ($default) {
                    // $this->defaultLangcode might not be set if we are initializing the
                    // default language code cache, in which case there is no valid
                    // langcode to assign.
                    $field_langcode = isset($this->defaultLangcode) ? $this->defaultLangcode : LanguageInterface::LANGCODE_NOT_SPECIFIED;
                }
                else {
                    $field_langcode = $langcode;
                }
                $field->setLangcode($field_langcode);
                $this->fields[$name][$langcode] = $field;
            }
        }
        return $this->fields[$name][$langcode];
    }
    
    /**
     * {@inheritdoc}
     */
    public function set($name, $value, $notify = TRUE) {
        // Assign the value on the child and overrule notify such that we get
        // notified to handle changes afterwards. We can ignore notify as there is
        // no parent to notify anyway.
        $this->get($name)
            ->setValue($value, TRUE);
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getFields($include_computed = TRUE) {
        $fields = [];
        foreach ($this->getFieldDefinitions() as $name => $definition) {
            if ($include_computed || !$definition->isComputed()) {
                $fields[$name] = $this->get($name);
            }
        }
        return $fields;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getTranslatableFields($include_computed = TRUE) {
        $fields = [];
        foreach ($this->getFieldDefinitions() as $name => $definition) {
            if (($include_computed || !$definition->isComputed()) && $definition->isTranslatable()) {
                $fields[$name] = $this->get($name);
            }
        }
        return $fields;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getIterator() {
        return new \ArrayIterator($this->getFields());
    }
    
    /**
     * {@inheritdoc}
     */
    public function getFieldDefinition($name) {
        if (!isset($this->fieldDefinitions)) {
            $this->getFieldDefinitions();
        }
        if (isset($this->fieldDefinitions[$name])) {
            return $this->fieldDefinitions[$name];
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function getFieldDefinitions() {
        if (!isset($this->fieldDefinitions)) {
            $this->fieldDefinitions = \Drupal::service('entity_field.manager')->getFieldDefinitions($this->entityTypeId, $this->bundle());
        }
        return $this->fieldDefinitions;
    }
    
    /**
     * {@inheritdoc}
     */
    public function toArray() {
        $values = [];
        foreach ($this->getFields() as $name => $property) {
            $values[$name] = $property->getValue();
        }
        return $values;
    }
    
    /**
     * {@inheritdoc}
     */
    public function access($operation, AccountInterface $account = NULL, $return_as_object = FALSE) {
        if ($operation == 'create') {
            return $this->entityTypeManager()
                ->getAccessControlHandler($this->entityTypeId)
                ->createAccess($this->bundle(), $account, [], $return_as_object);
        }
        return $this->entityTypeManager()
            ->getAccessControlHandler($this->entityTypeId)
            ->access($this, $operation, $account, $return_as_object);
    }
    
    /**
     * {@inheritdoc}
     */
    public function language() {
        $language = NULL;
        if ($this->activeLangcode != LanguageInterface::LANGCODE_DEFAULT) {
            if (!isset($this->languages[$this->activeLangcode])) {
                $this->getLanguages();
            }
            $language = $this->languages[$this->activeLangcode];
        }
        else {
            // @todo Avoid this check by getting the language from the language
            //   manager directly in https://www.drupal.org/node/2303877.
            if (!isset($this->languages[$this->defaultLangcode])) {
                $this->getLanguages();
            }
            $language = $this->languages[$this->defaultLangcode];
        }
        return $language;
    }
    
    /**
     * Populates the local cache for the default language code.
     */
    protected function setDefaultLangcode() {
        // Get the language code if the property exists.
        // Try to read the value directly from the list of entity keys which got
        // initialized in __construct(). This avoids creating a field item object.
        if (isset($this->translatableEntityKeys['langcode'][$this->activeLangcode])) {
            $this->defaultLangcode = $this->translatableEntityKeys['langcode'][$this->activeLangcode];
        }
        elseif ($this->hasField($this->langcodeKey) && ($item = $this->get($this->langcodeKey)) && isset($item->language)) {
            $this->defaultLangcode = $item->language
                ->getId();
            $this->translatableEntityKeys['langcode'][$this->activeLangcode] = $this->defaultLangcode;
        }
        if (empty($this->defaultLangcode)) {
            // Make sure we return a proper language object, if the entity has a
            // langcode field, default to the site's default language.
            if ($this->hasField($this->langcodeKey)) {
                $this->defaultLangcode = $this->languageManager()
                    ->getDefaultLanguage()
                    ->getId();
            }
            else {
                $this->defaultLangcode = LanguageInterface::LANGCODE_NOT_SPECIFIED;
            }
        }
        // This needs to be initialized manually as it is skipped when instantiating
        // the language field object to avoid infinite recursion.
        if (!empty($this->fields[$this->langcodeKey])) {
            $this->fields[$this->langcodeKey][LanguageInterface::LANGCODE_DEFAULT]
                ->setLangcode($this->defaultLangcode);
        }
    }
    
    /**
     * Updates language for already instantiated fields.
     */
    protected function updateFieldLangcodes($langcode) {
        foreach ($this->fields as $name => $items) {
            if (!empty($items[LanguageInterface::LANGCODE_DEFAULT])) {
                $items[LanguageInterface::LANGCODE_DEFAULT]->setLangcode($langcode);
            }
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function onChange($name) {
        // Check if the changed name is the value of any entity keys and if any of
        // those values are currently cached, if so, reset it. Exclude the bundle
        // from that check, as it ready only and must not change, unsetting it could
        // lead to recursions.
        foreach (array_keys($this->getEntityType()
            ->getKeys(), $name, TRUE) as $key) {
            if ($key != 'bundle') {
                if (isset($this->entityKeys[$key])) {
                    unset($this->entityKeys[$key]);
                }
                elseif (isset($this->translatableEntityKeys[$key][$this->activeLangcode])) {
                    unset($this->translatableEntityKeys[$key][$this->activeLangcode]);
                }
                // If the revision identifier field is being populated with the original
                // value, we need to make sure the "new revision" flag is reset
                // accordingly.
                if ($key === 'revision' && $this->getRevisionId() == $this->getLoadedRevisionId() && !$this->isNew()) {
                    $this->newRevision = FALSE;
                }
            }
        }
        switch ($name) {
            case $this->langcodeKey:
                if ($this->isDefaultTranslation()) {
                    // Update the default internal language cache.
                    $this->setDefaultLangcode();
                    if (isset($this->translations[$this->defaultLangcode])) {
                        $message = new FormattableMarkup('A translation already exists for the specified language (@langcode).', [
                            '@langcode' => $this->defaultLangcode,
                        ]);
                        throw new \InvalidArgumentException($message);
                    }
                    $this->updateFieldLangcodes($this->defaultLangcode);
                }
                else {
                    // @todo Allow the translation language to be changed. See
                    //   https://www.drupal.org/node/2443989.
                    $items = $this->get($this->langcodeKey);
                    if ($items->value != $this->activeLangcode) {
                        $items->setValue($this->activeLangcode, FALSE);
                        $message = new FormattableMarkup('The translation language cannot be changed (@langcode).', [
                            '@langcode' => $this->activeLangcode,
                        ]);
                        throw new \LogicException($message);
                    }
                }
                break;
            case $this->defaultLangcodeKey:
                // @todo Use a standard method to make the default_langcode field
                //   read-only. See https://www.drupal.org/node/2443991.
                if (isset($this->values[$this->defaultLangcodeKey]) && $this->get($this->defaultLangcodeKey)->value != $this->isDefaultTranslation()) {
                    $this->get($this->defaultLangcodeKey)
                        ->setValue($this->isDefaultTranslation(), FALSE);
                    $message = new FormattableMarkup('The default translation flag cannot be changed (@langcode).', [
                        '@langcode' => $this->activeLangcode,
                    ]);
                    throw new \LogicException($message);
                }
                break;
            case $this->revisionTranslationAffectedKey:
                // If the revision translation affected flag is being set then enforce
                // its value.
                $this->setRevisionTranslationAffectedEnforced(TRUE);
                break;
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function getTranslation($langcode) {
        // Ensure we always use the default language code when dealing with the
        // original entity language.
        if ($langcode != LanguageInterface::LANGCODE_DEFAULT && $langcode == $this->defaultLangcode) {
            $langcode = LanguageInterface::LANGCODE_DEFAULT;
        }
        // Populate entity translation object cache so it will be available for all
        // translation objects.
        if (!isset($this->translations[$this->activeLangcode]['entity'])) {
            $this->translations[$this->activeLangcode]['entity'] = $this;
        }
        // If we already have a translation object for the specified language we can
        // just return it.
        if (isset($this->translations[$langcode]['entity'])) {
            $translation = $this->translations[$langcode]['entity'];
        }
        elseif (isset($this->translations[$langcode])) {
            $translation = $this->initializeTranslation($langcode);
            $this->translations[$langcode]['entity'] = $translation;
        }
        if (empty($translation)) {
            throw new \InvalidArgumentException("Invalid translation language ({$langcode}) specified.");
        }
        return $translation;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getUntranslated() {
        return $this->getTranslation(LanguageInterface::LANGCODE_DEFAULT);
    }
    
    /**
     * Instantiates a translation object for an existing translation.
     *
     * The translated entity will be a clone of the current entity with the
     * specified $langcode. All translations share the same field data structures
     * to ensure that all of them deal with fresh data.
     *
     * @param string $langcode
     *   The language code for the requested translation.
     *
     * @return \Drupal\Core\Entity\EntityInterface
     *   The translation object. The content properties of the translation object
     *   are stored as references to the main entity.
     */
    protected function initializeTranslation($langcode) {
        // If the requested translation is valid, clone it with the current language
        // as the active language. The $translationInitialize flag triggers a
        // shallow (non-recursive) clone.
        $this->translationInitialize = TRUE;
        $translation = clone $this;
        $this->translationInitialize = FALSE;
        $translation->activeLangcode = $langcode;
        // Ensure that changes to fields, values and translations are propagated
        // to all the translation objects.
        // @todo Consider converting these to ArrayObject.
        $translation->values =& $this->values;
        $translation->fields =& $this->fields;
        $translation->translations =& $this->translations;
        $translation->enforceIsNew =& $this->enforceIsNew;
        $translation->newRevision =& $this->newRevision;
        $translation->entityKeys =& $this->entityKeys;
        $translation->translatableEntityKeys =& $this->translatableEntityKeys;
        $translation->translationInitialize = FALSE;
        $translation->typedData = NULL;
        $translation->loadedRevisionId =& $this->loadedRevisionId;
        $translation->isDefaultRevision =& $this->isDefaultRevision;
        $translation->enforceRevisionTranslationAffected =& $this->enforceRevisionTranslationAffected;
        $translation->isSyncing =& $this->isSyncing;
        return $translation;
    }
    
    /**
     * {@inheritdoc}
     */
    public function hasTranslation($langcode) {
        if ($langcode == $this->defaultLangcode) {
            $langcode = LanguageInterface::LANGCODE_DEFAULT;
        }
        return !empty($this->translations[$langcode]['status']);
    }
    
    /**
     * {@inheritdoc}
     */
    public function isNewTranslation() {
        return $this->translations[$this->activeLangcode]['status'] == static::TRANSLATION_CREATED;
    }
    
    /**
     * {@inheritdoc}
     */
    public function addTranslation($langcode, array $values = []) {
        // Make sure we do not attempt to create a translation if an invalid
        // language is specified or the entity cannot be translated.
        $this->getLanguages();
        if (!isset($this->languages[$langcode]) || $this->hasTranslation($langcode) || $this->languages[$langcode]
            ->isLocked()) {
            throw new \InvalidArgumentException("Invalid translation language ({$langcode}) specified.");
        }
        if ($this->languages[$this->defaultLangcode]
            ->isLocked()) {
            throw new \InvalidArgumentException("The entity cannot be translated since it is language neutral ({$this->defaultLangcode}).");
        }
        // Initialize the translation object.
        
        /** @var \Drupal\Core\Entity\ContentEntityStorageInterface $storage */
        $storage = $this->entityTypeManager()
            ->getStorage($this->getEntityTypeId());
        $this->translations[$langcode]['status'] = !isset($this->translations[$langcode]['status_existed']) ? static::TRANSLATION_CREATED : static::TRANSLATION_EXISTING;
        return $storage->createTranslation($this, $langcode, $values);
    }
    
    /**
     * {@inheritdoc}
     */
    public function removeTranslation($langcode) {
        if (isset($this->translations[$langcode]) && $langcode != LanguageInterface::LANGCODE_DEFAULT && $langcode != $this->defaultLangcode) {
            foreach ($this->getFieldDefinitions() as $name => $definition) {
                if ($definition->isTranslatable()) {
                    unset($this->values[$name][$langcode]);
                    unset($this->fields[$name][$langcode]);
                }
            }
            // If removing a translation which has not been saved yet, then we have
            // to remove it completely so that ::getTranslationStatus returns the
            // proper status.
            if ($this->translations[$langcode]['status'] == static::TRANSLATION_CREATED) {
                unset($this->translations[$langcode]);
            }
            else {
                if ($this->translations[$langcode]['status'] == static::TRANSLATION_EXISTING) {
                    $this->translations[$langcode]['status_existed'] = TRUE;
                }
                $this->translations[$langcode]['status'] = static::TRANSLATION_REMOVED;
            }
        }
        else {
            throw new \InvalidArgumentException("The specified translation ({$langcode}) cannot be removed.");
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function getTranslationStatus($langcode) {
        if ($langcode == $this->defaultLangcode) {
            $langcode = LanguageInterface::LANGCODE_DEFAULT;
        }
        return isset($this->translations[$langcode]) ? $this->translations[$langcode]['status'] : NULL;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getTranslationLanguages($include_default = TRUE) {
        $translations = array_filter($this->translations, function ($translation) {
            return $translation['status'];
        });
        unset($translations[LanguageInterface::LANGCODE_DEFAULT]);
        if ($include_default) {
            $translations[$this->defaultLangcode] = TRUE;
        }
        // Now load language objects based upon translation langcodes.
        return array_intersect_key($this->getLanguages(), $translations);
    }
    
    /**
     * Updates the original values with the interim changes.
     */
    public function updateOriginalValues() {
        if (!$this->fields) {
            return;
        }
        foreach ($this->getFieldDefinitions() as $name => $definition) {
            if (!$definition->isComputed() && !empty($this->fields[$name])) {
                foreach ($this->fields[$name] as $langcode => $item) {
                    $item->filterEmptyItems();
                    $this->values[$name][$langcode] = $item->getValue();
                }
            }
        }
    }
    
    /**
     * Implements the magic method for getting object properties.
     *
     * @todo: A lot of code still uses non-fields (e.g. $entity->content in view
     *   builders) by reference. Clean that up.
     */
    public function &__get($name) {
        // If this is an entity field, handle it accordingly. We first check whether
        // a field object has been already created. If not, we create one.
        if (isset($this->fields[$name][$this->activeLangcode])) {
            return $this->fields[$name][$this->activeLangcode];
        }
        // Inline getFieldDefinition() to speed things up.
        if (!isset($this->fieldDefinitions)) {
            $this->getFieldDefinitions();
        }
        if (isset($this->fieldDefinitions[$name])) {
            $return = $this->getTranslatedField($name, $this->activeLangcode);
            return $return;
        }
        // Else directly read/write plain values. That way, non-field entity
        // properties can always be accessed directly.
        if (!isset($this->values[$name])) {
            $this->values[$name] = NULL;
        }
        return $this->values[$name];
    }
    
    /**
     * Implements the magic method for setting object properties.
     *
     * Uses default language always.
     */
    public function __set($name, $value) {
        // Inline getFieldDefinition() to speed things up.
        if (!isset($this->fieldDefinitions)) {
            $this->getFieldDefinitions();
        }
        // Handle Field API fields.
        if (isset($this->fieldDefinitions[$name])) {
            // Support setting values via property objects.
            if ($value instanceof TypedDataInterface) {
                $value = $value->getValue();
            }
            // If a FieldItemList object already exists, set its value.
            if (isset($this->fields[$name][$this->activeLangcode])) {
                $this->fields[$name][$this->activeLangcode]
                    ->setValue($value);
            }
            else {
                $this->getTranslatedField($name, $this->activeLangcode)
                    ->setValue($value);
            }
        }
        elseif ($name == 'translations') {
            $this->translations = $value;
        }
        else {
            $this->values[$name] = $value;
        }
    }
    
    /**
     * Implements the magic method for isset().
     */
    public function __isset($name) {
        // "Official" Field API fields are always set. For non-field properties,
        // check the internal values.
        return $this->hasField($name) ? TRUE : isset($this->values[$name]);
    }
    
    /**
     * Implements the magic method for unset().
     */
    public function __unset($name) {
        // Unsetting a field means emptying it.
        if ($this->hasField($name)) {
            $this->get($name)
                ->setValue([]);
        }
        else {
            unset($this->values[$name]);
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function createDuplicate() {
        if ($this->translations[$this->activeLangcode]['status'] == static::TRANSLATION_REMOVED) {
            throw new \InvalidArgumentException("The entity object refers to a removed translation ({$this->activeLangcode}) and cannot be manipulated.");
        }
        $duplicate = clone $this;
        $entity_type = $this->getEntityType();
        if ($entity_type->hasKey('id')) {
            $duplicate->{$entity_type->getKey('id')}->value = NULL;
        }
        $duplicate->enforceIsNew();
        // Check if the entity type supports UUIDs and generate a new one if so.
        if ($entity_type->hasKey('uuid')) {
            $duplicate->{$entity_type->getKey('uuid')}->value = $this->uuidGenerator()
                ->generate();
        }
        // Check whether the entity type supports revisions and initialize it if so.
        if ($entity_type->isRevisionable()) {
            $duplicate->{$entity_type->getKey('revision')}->value = NULL;
            $duplicate->loadedRevisionId = NULL;
        }
        return $duplicate;
    }
    
    /**
     * Magic method: Implements a deep clone.
     */
    public function __clone() {
        // Avoid deep-cloning when we are initializing a translation object, since
        // it will represent the same entity, only with a different active language.
        if ($this->translationInitialize) {
            return;
        }
        // The translation is a different object, and needs its own TypedData
        // adapter object.
        $this->typedData = NULL;
        $definitions = $this->getFieldDefinitions();
        // The translation cache has to be cleared before cloning the fields
        // below so that the call to getTranslation() does not re-use the
        // translation objects of the old entity but instead creates new
        // translation objects from the newly cloned entity. Otherwise the newly
        // cloned field item lists would hold references to the old translation
        // objects in their $parent property after the call to setContext().
        $this->clearTranslationCache();
        // Because the new translation objects that are created below are
        // themselves created by *cloning* the newly cloned entity we need to
        // make sure that the references to property values are properly cloned
        // before cloning the fields. Otherwise calling
        // $items->getEntity()->isNew(), for example, would return the
        // $enforceIsNew value of the old entity.
        // Ensure the translations array is actually cloned by overwriting the
        // original reference with one pointing to a copy of the array.
        $translations = $this->translations;
        $this->translations =& $translations;
        // Ensure that the following properties are actually cloned by
        // overwriting the original references with ones pointing to copies of
        // them: enforceIsNew, newRevision, loadedRevisionId, fields, entityKeys,
        // translatableEntityKeys, values, isDefaultRevision and
        // enforceRevisionTranslationAffected.
        $enforce_is_new = $this->enforceIsNew;
        $this->enforceIsNew =& $enforce_is_new;
        $new_revision = $this->newRevision;
        $this->newRevision =& $new_revision;
        $original_revision_id = $this->loadedRevisionId;
        $this->loadedRevisionId =& $original_revision_id;
        $fields = $this->fields;
        $this->fields =& $fields;
        $entity_keys = $this->entityKeys;
        $this->entityKeys =& $entity_keys;
        $translatable_entity_keys = $this->translatableEntityKeys;
        $this->translatableEntityKeys =& $translatable_entity_keys;
        $values = $this->values;
        $this->values =& $values;
        $default_revision = $this->isDefaultRevision;
        $this->isDefaultRevision =& $default_revision;
        $is_revision_translation_affected_enforced = $this->enforceRevisionTranslationAffected;
        $this->enforceRevisionTranslationAffected =& $is_revision_translation_affected_enforced;
        $is_syncing = $this->isSyncing;
        $this->isSyncing =& $is_syncing;
        foreach ($this->fields as $name => $fields_by_langcode) {
            $this->fields[$name] = [];
            // Untranslatable fields may have multiple references for the same field
            // object keyed by language. To avoid creating different field objects
            // we retain just the original value, as references will be recreated
            // later as needed.
            if (!$definitions[$name]->isTranslatable() && count($fields_by_langcode) > 1) {
                $fields_by_langcode = array_intersect_key($fields_by_langcode, [
                    LanguageInterface::LANGCODE_DEFAULT => TRUE,
                ]);
            }
            foreach ($fields_by_langcode as $langcode => $items) {
                $this->fields[$name][$langcode] = clone $items;
                $this->fields[$name][$langcode]
                    ->setContext($name, $this->getTranslation($langcode)
                    ->getTypedData());
            }
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function label() {
        $label = NULL;
        $entity_type = $this->getEntityType();
        if (($label_callback = $entity_type->get('label_callback')) && is_callable($label_callback)) {
            @trigger_error('Entity type ' . $this->getEntityTypeId() . ' defines a label callback. Support for that is deprecated in drupal:8.0.0 and will be removed in drupal:9.0.0. Override the EntityInterface::label() method instead. See https://www.drupal.org/node/3050794', E_USER_DEPRECATED);
            $label = call_user_func($label_callback, $this);
        }
        elseif ($label_key = $entity_type->getKey('label')) {
            $label = $this->getEntityKey('label');
        }
        return $label;
    }
    
    /**
     * {@inheritdoc}
     */
    public function referencedEntities() {
        $referenced_entities = [];
        // Gather a list of referenced entities.
        foreach ($this->getFields() as $field_items) {
            foreach ($field_items as $field_item) {
                // Loop over all properties of a field item.
                foreach ($field_item->getProperties(TRUE) as $property) {
                    if ($property instanceof EntityReference && ($entity = $property->getValue())) {
                        $referenced_entities[] = $entity;
                    }
                }
            }
        }
        return $referenced_entities;
    }
    
    /**
     * Gets the value of the given entity key, if defined.
     *
     * @param string $key
     *   Name of the entity key, for example id, revision or bundle.
     *
     * @return mixed
     *   The value of the entity key, NULL if not defined.
     */
    protected function getEntityKey($key) {
        // If the value is known already, return it.
        if (isset($this->entityKeys[$key])) {
            return $this->entityKeys[$key];
        }
        if (isset($this->translatableEntityKeys[$key][$this->activeLangcode])) {
            return $this->translatableEntityKeys[$key][$this->activeLangcode];
        }
        // Otherwise fetch the value by creating a field object.
        $value = NULL;
        if ($this->getEntityType()
            ->hasKey($key)) {
            $field_name = $this->getEntityType()
                ->getKey($key);
            $definition = $this->getFieldDefinition($field_name);
            $property = $definition->getFieldStorageDefinition()
                ->getMainPropertyName();
            $value = $this->get($field_name)->{$property};
            // Put it in the right array, depending on whether it is translatable.
            if ($definition->isTranslatable()) {
                $this->translatableEntityKeys[$key][$this->activeLangcode] = $value;
            }
            else {
                $this->entityKeys[$key] = $value;
            }
        }
        else {
            $this->entityKeys[$key] = $value;
        }
        return $value;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function baseFieldDefinitions(EntityTypeInterface $entity_type) {
        $fields = [];
        if ($entity_type->hasKey('id')) {
            $fields[$entity_type->getKey('id')] = BaseFieldDefinition::create('integer')->setLabel(new TranslatableMarkup('ID'))
                ->setReadOnly(TRUE)
                ->setSetting('unsigned', TRUE);
        }
        if ($entity_type->hasKey('uuid')) {
            $fields[$entity_type->getKey('uuid')] = BaseFieldDefinition::create('uuid')->setLabel(new TranslatableMarkup('UUID'))
                ->setReadOnly(TRUE);
        }
        if ($entity_type->hasKey('revision')) {
            $fields[$entity_type->getKey('revision')] = BaseFieldDefinition::create('integer')->setLabel(new TranslatableMarkup('Revision ID'))
                ->setReadOnly(TRUE)
                ->setSetting('unsigned', TRUE);
        }
        if ($entity_type->hasKey('langcode')) {
            $fields[$entity_type->getKey('langcode')] = BaseFieldDefinition::create('language')->setLabel(new TranslatableMarkup('Language'))
                ->setDisplayOptions('view', [
                'region' => 'hidden',
            ])
                ->setDisplayOptions('form', [
                'type' => 'language_select',
                'weight' => 2,
            ]);
            if ($entity_type->isRevisionable()) {
                $fields[$entity_type->getKey('langcode')]
                    ->setRevisionable(TRUE);
            }
            if ($entity_type->isTranslatable()) {
                $fields[$entity_type->getKey('langcode')]
                    ->setTranslatable(TRUE);
            }
        }
        if ($entity_type->hasKey('bundle')) {
            if ($bundle_entity_type_id = $entity_type->getBundleEntityType()) {
                $fields[$entity_type->getKey('bundle')] = BaseFieldDefinition::create('entity_reference')->setLabel($entity_type->getBundleLabel())
                    ->setSetting('target_type', $bundle_entity_type_id)
                    ->setRequired(TRUE)
                    ->setReadOnly(TRUE);
            }
            else {
                $fields[$entity_type->getKey('bundle')] = BaseFieldDefinition::create('string')->setLabel($entity_type->getBundleLabel())
                    ->setRequired(TRUE)
                    ->setReadOnly(TRUE);
            }
        }
        return $fields;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function bundleFieldDefinitions(EntityTypeInterface $entity_type, $bundle, array $base_field_definitions) {
        return [];
    }
    
    /**
     * Returns an array of field names to skip in ::hasTranslationChanges.
     *
     * @return array
     *   An array of field names.
     */
    protected function getFieldsToSkipFromTranslationChangesCheck() {
        $bundle = $this->bundle();
        if (!isset(static::$fieldsToSkipFromTranslationChangesCheck[$this->entityTypeId][$bundle])) {
            static::$fieldsToSkipFromTranslationChangesCheck[$this->entityTypeId][$bundle] = $this->traitGetFieldsToSkipFromTranslationChangesCheck($this);
        }
        return static::$fieldsToSkipFromTranslationChangesCheck[$this->entityTypeId][$bundle];
    }
    
    /**
     * {@inheritdoc}
     */
    public function hasTranslationChanges() {
        if ($this->isNew()) {
            return TRUE;
        }
        // $this->original only exists during save. See
        // \Drupal\Core\Entity\EntityStorageBase::save(). If it exists we re-use it
        // here for performance reasons.
        
        /** @var \Drupal\Core\Entity\ContentEntityBase $original */
        $original = $this->original ? $this->original : NULL;
        if (!$original) {
            $id = $this->getOriginalId() !== NULL ? $this->getOriginalId() : $this->id();
            $original = $this->entityTypeManager()
                ->getStorage($this->getEntityTypeId())
                ->loadUnchanged($id);
        }
        // If the current translation has just been added, we have a change.
        $translated = count($this->translations) > 1;
        if ($translated && !$original->hasTranslation($this->activeLangcode)) {
            return TRUE;
        }
        // Compare field item current values with the original ones to determine
        // whether we have changes. If a field is not translatable and the entity is
        // translated we skip it because, depending on the use case, it would make
        // sense to mark all translations as changed or none of them. We skip also
        // computed fields as comparing them with their original values might not be
        // possible or be meaningless.
        
        /** @var \Drupal\Core\Entity\ContentEntityBase $translation */
        $translation = $original->getTranslation($this->activeLangcode);
        $langcode = $this->language()
            ->getId();
        // The list of fields to skip from the comparision.
        $skip_fields = $this->getFieldsToSkipFromTranslationChangesCheck();
        // We also check untranslatable fields, so that a change to those will mark
        // all translations as affected, unless they are configured to only affect
        // the default translation.
        $skip_untranslatable_fields = !$this->isDefaultTranslation() && $this->isDefaultTranslationAffectedOnly();
        foreach ($this->getFieldDefinitions() as $field_name => $definition) {
            // @todo Avoid special-casing the following fields. See
            //    https://www.drupal.org/node/2329253.
            if (in_array($field_name, $skip_fields, TRUE) || $skip_untranslatable_fields && !$definition->isTranslatable()) {
                continue;
            }
            $items = $this->get($field_name)
                ->filterEmptyItems();
            $original_items = $translation->get($field_name)
                ->filterEmptyItems();
            if ($items->hasAffectingChanges($original_items, $langcode)) {
                return TRUE;
            }
        }
        return FALSE;
    }
    
    /**
     * {@inheritdoc}
     */
    public function isDefaultTranslationAffectedOnly() {
        $bundle_name = $this->bundle();
        $bundle_info = \Drupal::service('entity_type.bundle.info')->getBundleInfo($this->getEntityTypeId());
        return !empty($bundle_info[$bundle_name]['untranslatable_fields.default_translation_affected']);
    }

}