class RecursiveExtensionFilterCallback

class RecursiveExtensionFilterCallback {
    
    /**
     * List of base extension type directory names to scan.
     *
     * Only these directory names are considered when starting a filesystem
     * recursion in a search path.
     *
     * @var string[]
     */
    protected array $allowedExtensionTypes = [
        'profiles',
        'modules',
        'themes',
    ];
    
    /**
     * List of directory names to skip when recursing.
     *
     * These directories are globally ignored in the recursive filesystem scan;
     * i.e., extensions (of all types) are not able to use any of these names,
     * because their directory names will be skipped.
     *
     * @var string[]
     */
    protected array $skippedFolders = [
        // Object-oriented code subdirectories.
'src',
        'lib',
        'vendor',
        // Front-end.
'assets',
        'css',
        'files',
        'images',
        'js',
        'misc',
        'templates',
        // Legacy subdirectories.
'includes',
        // Test subdirectories.
'fixtures',
        // @todo ./tests/Drupal should be ./tests/src/Drupal
'Drupal',
    ];
    
    /**
     * Construct a RecursiveExtensionFilterCallback.
     *
     * @param array $skipped_folders
     *   (optional) Add to the list of directories that should be filtered out
     *   during the iteration.
     * @param bool $accept_tests
     *   (optional) Pass FALSE to skip all test directories in the discovery. If
     *   TRUE, extensions in test directories will be discovered and only the
     *   global directory skip list in
     *   RecursiveExtensionFilterCallback::$skippedFolders and $skipped_folders
     *   are applied.
     */
    public function __construct(array $skipped_folders = [], bool $accept_tests = FALSE) {
        $this->skippedFolders = array_merge($this->skippedFolders, $skipped_folders);
        if (!$accept_tests) {
            $this->skippedFolders[] = 'tests';
        }
    }
    
    /**
     * Checks whether a given filesystem directory is acceptable.
     *
     * @param \RecursiveDirectoryIterator $filesystem_directory
     *   The filesystem directory to check.
     *
     * @return bool
     *   TRUE if the given filesystem directory is acceptable, otherwise FALSE.
     */
    public function accept(\RecursiveDirectoryIterator $filesystem_directory) : bool {
        $name = $filesystem_directory->getFilename();
        // FilesystemIterator::SKIP_DOTS only skips '.' and '..', but not hidden
        // directories (like '.git').
        if ($name[0] === '.') {
            return FALSE;
        }
        if ($filesystem_directory->isDir()) {
            // If this is a subdirectory of a base search path, only recurse into the
            // fixed list of expected extension type directory names. Required for
            // scanning the top-level/root directory; without this condition, we would
            // recurse into the whole filesystem tree that possibly contains other
            // files aside from Drupal.
            if ($filesystem_directory->getSubPath() === '') {
                return in_array($name, $this->allowedExtensionTypes, TRUE);
            }
            // 'config' directories are special-cased here, because every extension
            // contains one. However, those default configuration directories cannot
            // contain extensions. The directory name cannot be globally skipped,
            // because core happens to have a directory of an actual module that is
            // named 'config'. By explicitly testing for that case, we can skip all
            // other config directories, and at the same time, still allow the core
            // config module to be overridden/replaced in a profile/site directory
            // (whereas it must be located directly in a modules directory).
            if ($name === 'config') {
                return str_ends_with($filesystem_directory->getPathname(), 'modules/config');
            }
            // Accept the directory unless the folder is skipped.
            return !in_array($name, $this->skippedFolders, TRUE);
        }
        // Only accept extension info files.
        return str_ends_with($name, '.info.yml');
    }

}