class WritableFileSystemValidator

class WritableFileSystemValidator implements EventSubscriberInterface {
    use BaseRequirementValidatorTrait;
    use StringTranslationTrait;
    public function __construct(PathLocator $pathLocator) {
    }
    
    /**
     * Checks that the file system is writable.
     *
     * @todo Determine if 'is_writable()' is a sufficiently robust test across
     *   different operating systems in https://drupal.org/i/3348253.
     */
    public function validate(PreOperationStageEvent $event) : void {
        $messages = [];
        $project_root = $this->pathLocator
            ->getProjectRoot();
        // If the web (Drupal) root and project root are different, validate the
        // web root separately.
        $web_root = $this->pathLocator
            ->getWebRoot();
        if ($web_root) {
            $drupal_root = $project_root . DIRECTORY_SEPARATOR . $web_root;
            if (!is_writable($drupal_root)) {
                $messages[] = $this->t('The Drupal directory "@dir" is not writable.', [
                    '@dir' => $drupal_root,
                ]);
            }
        }
        if (!is_writable($project_root)) {
            $messages[] = $this->t('The project root directory "@dir" is not writable.', [
                '@dir' => $project_root,
            ]);
        }
        $dir = $this->pathLocator
            ->getVendorDirectory();
        if (!is_writable($dir)) {
            $messages[] = $this->t('The vendor directory "@dir" is not writable.', [
                '@dir' => $dir,
            ]);
        }
        // During pre-apply don't check whether the staging root is writable.
        if ($event instanceof PreApplyEvent) {
            if ($messages) {
                $event->addError($messages, $this->t('The file system is not writable.'));
            }
            return;
        }
        // Ensure the staging root is writable. If it doesn't exist, ensure we will
        // be able to create it.
        $dir = $this->pathLocator
            ->getStagingRoot();
        if (!file_exists($dir)) {
            $dir = dirname($dir);
            if (!is_writable($dir)) {
                $messages[] = $this->t('The stage root directory will not able to be created at "@dir".', [
                    '@dir' => $dir,
                ]);
            }
        }
        elseif (!is_writable($dir)) {
            $messages[] = $this->t('The stage root directory "@dir" is not writable.', [
                '@dir' => $dir,
            ]);
        }
        if ($messages) {
            $event->addError($messages, $this->t('The file system is not writable.'));
        }
    }

}