private function getLevel2DirectoryName(Attachment $attachment)
{
if ($attachment->getId()) {
$level2Dir = $attachment->getId() / $this->config['file_num_dirs_level_2'] % $this->config['file_num_dirs_level_1'];
} else {
$level2Dir = 0;
}
$level2ZeroPad = strlen($this->config['file_num_dirs_level_2']);
return sprintf('%0' . $level2ZeroPad . 'd', $level2Dir);
}