class PreOperationStageEvent

abstract class PreOperationStageEvent extends StageEvent {
    
    /**
     * The validation results.
     *
     * @var \Drupal\package_manager\ValidationResult[]
     */
    protected $results = [];
    
    /**
     * Gets the validation results.
     *
     * @param int|null $severity
     *   (optional) The severity for the results to return. Should be one of the
     *   SystemManager::REQUIREMENT_* constants.
     *
     * @return \Drupal\package_manager\ValidationResult[]
     *   The validation results.
     */
    public function getResults(?int $severity = NULL) : array {
        if ($severity !== NULL) {
            return array_filter($this->results, function ($result) use ($severity) {
                return $result->severity === $severity;
            });
        }
        return $this->results;
    }
    
    /**
     * Convenience method to flag a validation error.
     *
     * @param \Drupal\Core\StringTranslation\TranslatableMarkup[] $messages
     *   The error messages.
     * @param \Drupal\Core\StringTranslation\TranslatableMarkup|null $summary
     *   The summary of error messages. Must be passed if there is more than one
     *   message.
     */
    public function addError(array $messages, ?TranslatableMarkup $summary = NULL) : void {
        $this->addResult(ValidationResult::createError(array_values($messages), $summary));
    }
    
    /**
     * Convenience method, adds an error validation result from a throwable.
     *
     * @param \Throwable $throwable
     *   The throwable.
     * @param \Drupal\Core\StringTranslation\TranslatableMarkup|null $summary
     *   (optional) The summary of error messages.
     */
    public function addErrorFromThrowable(\Throwable $throwable, ?TranslatableMarkup $summary = NULL) : void {
        $this->addResult(ValidationResult::createErrorFromThrowable($throwable, $summary));
    }
    
    /**
     * Adds a validation result to the event.
     *
     * @param \Drupal\package_manager\ValidationResult $result
     *   The validation result to add.
     *
     * @throws \InvalidArgumentException
     *   Thrown if the validation result is not an error.
     */
    public function addResult(ValidationResult $result) : void {
        // Only errors are allowed for this event.
        if ($result->severity !== SystemManager::REQUIREMENT_ERROR) {
            throw new \InvalidArgumentException('Only errors are allowed.');
        }
        $this->results[] = $result;
    }
    
    /**
     * {@inheritdoc}
     */
    public function stopPropagation() : void {
        if (empty($this->getResults(SystemManager::REQUIREMENT_ERROR))) {
            $this->addErrorFromThrowable(new \LogicException('Event propagation stopped without any errors added to the event. This bypasses the package_manager validation system.'));
        }
        parent::stopPropagation();
    }

}