trait RevisionLogEntityTrait

trait RevisionLogEntityTrait {
    
    /**
     * Provides revision-related base field definitions for an entity type.
     *
     * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
     *   The entity type definition.
     *
     * @return \Drupal\Core\Field\FieldDefinitionInterface[]
     *   An array of base field definitions for the entity type, keyed by field
     *   name.
     *
     * @see \Drupal\Core\Entity\FieldableEntityInterface::baseFieldDefinitions()
     */
    public static function revisionLogBaseFieldDefinitions(EntityTypeInterface $entity_type) {
        $fields[static::getRevisionMetadataKey($entity_type, 'revision_created')] = BaseFieldDefinition::create('created')->setLabel(t('Revision create time'))
            ->setDescription(t('The time that the current revision was created.'))
            ->setRevisionable(TRUE);
        $fields[static::getRevisionMetadataKey($entity_type, 'revision_user')] = BaseFieldDefinition::create('entity_reference')->setLabel(t('Revision user'))
            ->setDescription(t('The user ID of the author of the current revision.'))
            ->setSetting('target_type', 'user')
            ->setRevisionable(TRUE);
        $fields[static::getRevisionMetadataKey($entity_type, 'revision_log_message')] = BaseFieldDefinition::create('string_long')->setLabel(t('Revision log message'))
            ->setDescription(t('Briefly describe the changes you have made.'))
            ->setRevisionable(TRUE)
            ->setDefaultValue('')
            ->setDisplayOptions('form', [
            'type' => 'string_textarea',
            'weight' => 25,
            'settings' => [
                'rows' => 4,
            ],
        ]);
        return $fields;
    }
    
    /**
     * Implements \Drupal\Core\Entity\RevisionLogInterface::getRevisionCreationTime().
     */
    public function getRevisionCreationTime() {
        return $this->{static::getRevisionMetadataKey($this->getEntityType(), 'revision_created')}->value;
    }
    
    /**
     * Implements \Drupal\Core\Entity\RevisionLogInterface::setRevisionCreationTime().
     */
    public function setRevisionCreationTime($timestamp) {
        $this->{static::getRevisionMetadataKey($this->getEntityType(), 'revision_created')}->value = $timestamp;
        return $this;
    }
    
    /**
     * Implements \Drupal\Core\Entity\RevisionLogInterface::getRevisionUser().
     */
    public function getRevisionUser() {
        return $this->{static::getRevisionMetadataKey($this->getEntityType(), 'revision_user')}->entity;
    }
    
    /**
     * Implements \Drupal\Core\Entity\RevisionLogInterface::setRevisionUser().
     */
    public function setRevisionUser(UserInterface $account) {
        $this->{static::getRevisionMetadataKey($this->getEntityType(), 'revision_user')}->entity = $account;
        return $this;
    }
    
    /**
     * Implements \Drupal\Core\Entity\RevisionLogInterface::getRevisionUserId().
     */
    public function getRevisionUserId() {
        return $this->{static::getRevisionMetadataKey($this->getEntityType(), 'revision_user')}->target_id;
    }
    
    /**
     * Implements \Drupal\Core\Entity\RevisionLogInterface::setRevisionUserId().
     */
    public function setRevisionUserId($user_id) {
        $this->{static::getRevisionMetadataKey($this->getEntityType(), 'revision_user')}->target_id = $user_id;
        return $this;
    }
    
    /**
     * Implements \Drupal\Core\Entity\RevisionLogInterface::getRevisionLogMessage().
     */
    public function getRevisionLogMessage() {
        return $this->{static::getRevisionMetadataKey($this->getEntityType(), 'revision_log_message')}->value;
    }
    
    /**
     * Implements \Drupal\Core\Entity\RevisionLogInterface::setRevisionLogMessage().
     */
    public function setRevisionLogMessage($revision_log_message) {
        $this->{static::getRevisionMetadataKey($this->getEntityType(), 'revision_log_message')}->value = $revision_log_message;
        return $this;
    }
    
    /**
     * Gets the name of a revision metadata field.
     *
     * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
     *   A content entity type definition.
     * @param string $key
     *   The revision metadata key to get, must be one of 'revision_created',
     *   'revision_user' or 'revision_log_message'.
     *
     * @return string
     *   The name of the field for the specified $key.
     */
    protected static function getRevisionMetadataKey(EntityTypeInterface $entity_type, $key) {
        // We need to prevent ContentEntityType::getRevisionMetadataKey() from
        // providing fallback as that requires fetching the entity type's field
        // definition leading to an infinite recursion.
        
        /** @var \Drupal\Core\Entity\ContentEntityTypeInterface $entity_type */
        $revision_metadata_keys = $entity_type->getRevisionMetadataKeys(FALSE) + [
            'revision_created' => 'revision_created',
            'revision_user' => 'revision_user',
            'revision_log_message' => 'revision_log_message',
        ];
        return $revision_metadata_keys[$key];
    }

}