private function getLevel1DirectoryName(Attachment $attachment)
{
if ($attachment->getId()) {
$level1Dir = floor($attachment->getId() / ($this->config['file_num_dirs_level_1'] * $this->config['file_num_dirs_level_2']));
} else {
$level1Dir = 0;
}
$level1ZeroPad = strlen($this->config['file_num_dirs_level_1']);
return sprintf('%0' . $level1ZeroPad . 'd', $level1Dir);
}