class ExpressionContainerBase

abstract class ExpressionContainerBase extends ExpressionBase implements ExpressionContainerInterface {
    
    /**
     * The expression manager.
     *
     * @var \Drupal\rules\Engine\ExpressionManagerInterface
     */
    protected $expressionManager;
    
    /**
     * The rules debug logger channel.
     *
     * @var \Drupal\Core\Logger\LoggerChannelInterface
     */
    protected $rulesDebugLogger;
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
        return new static($configuration, $plugin_id, $plugin_definition, $container->get('plugin.manager.rules_expression'), $container->get('logger.channel.rules_debug'));
    }
    
    /**
     * Sorts an array of expressions by 'weight' property.
     *
     * Callback for uasort().
     *
     * @param \Drupal\rules\Engine\ExpressionInterface $a
     *   First item for comparison.
     * @param \Drupal\rules\Engine\ExpressionInterface $b
     *   Second item for comparison.
     *
     * @return int
     *   The comparison result for uasort().
     */
    public static function sortByWeightProperty(ExpressionInterface $a, ExpressionInterface $b) {
        $a_weight = $a->getWeight();
        $b_weight = $b->getWeight();
        if ($a_weight == $b_weight) {
            return 0;
        }
        return $a_weight < $b_weight ? -1 : 1;
    }
    
    /**
     * {@inheritdoc}
     */
    public function addExpression($plugin_id, ContextConfig $config = NULL) {
        return $this->addExpressionObject($this->expressionManager
            ->createInstance($plugin_id, $config ? $config->toArray() : []));
    }
    
    /**
     * Determines whether child-expressions are allowed to assert metadata.
     *
     * @return bool
     *   Whether child-expressions are allowed to assert metadata.
     *
     * @see \Drupal\rules\Engine\ExpressionInterface::prepareExecutionMetadataState()
     */
    protected abstract function allowsMetadataAssertions();
    
    /**
     * {@inheritdoc}
     */
    public function checkIntegrity(ExecutionMetadataStateInterface $metadata_state, $apply_assertions = TRUE) {
        $violation_list = new IntegrityViolationList();
        $this->prepareExecutionMetadataStateBeforeTraversal($metadata_state);
        $apply_assertions = $apply_assertions && $this->allowsMetadataAssertions();
        foreach ($this as $child_expression) {
            $child_violations = $child_expression->checkIntegrity($metadata_state, $apply_assertions);
            $violation_list->addAll($child_violations);
        }
        $this->prepareExecutionMetadataStateAfterTraversal($metadata_state);
        return $violation_list;
    }
    
    /**
     * {@inheritdoc}
     */
    public function prepareExecutionMetadataState(ExecutionMetadataStateInterface $metadata_state, ExpressionInterface $until = NULL, $apply_assertions = TRUE) {
        if ($until && $this->getUuid() === $until->getUuid()) {
            return TRUE;
        }
        $this->prepareExecutionMetadataStateBeforeTraversal($metadata_state);
        $apply_assertions = $apply_assertions && $this->allowsMetadataAssertions();
        foreach ($this as $child_expression) {
            $found = $child_expression->prepareExecutionMetadataState($metadata_state, $until, $apply_assertions);
            // If the expression was found, we need to stop.
            if ($found) {
                return TRUE;
            }
        }
        $this->prepareExecutionMetadataStateAfterTraversal($metadata_state);
    }
    
    /**
     * Prepares execution metadata state before traversing through children.
     *
     * @see ::prepareExecutionMetadataState()
     * @see ::checkIntegrity()
     */
    protected function prepareExecutionMetadataStateBeforeTraversal(ExecutionMetadataStateInterface $metadata_state) {
        // Any pre-traversal preparations need to be added here.
    }
    
    /**
     * Prepares execution metadata state after traversing through children.
     *
     * @see ::prepareExecutionMetadataState()
     * @see ::checkIntegrity()
     */
    protected function prepareExecutionMetadataStateAfterTraversal(ExecutionMetadataStateInterface $metadata_state) {
        // Any post-traversal preparations need to be added here.
    }

}