protected function _generateCFS()
    {
        $cfsFile = $this->_directory->createFile($this->_name . '.cfs');
        $cfsFile->writeVInt(count($this->_files));

        $dataOffsetPointers = array();
        foreach ($this->_files as $fileName) {
            $dataOffsetPointers[$fileName] = $cfsFile->tell();
            $cfsFile->writeLong(0); // write dummy data
            $cfsFile->writeString($fileName);
        }

        foreach ($this->_files as $fileName) {
            // Get actual data offset
            $dataOffset = $cfsFile->tell();
            // Seek to the data offset pointer
            $cfsFile->seek($dataOffsetPointers[$fileName]);
            // Write actual data offset value
            $cfsFile->writeLong($dataOffset);
            // Seek back to the end of file
            $cfsFile->seek($dataOffset);

            $dataFile = $this->_directory->getFileObject($fileName);

            $byteCount = $this->_directory->fileLength($fileName);
            while ($byteCount > 0) {
                $data = $dataFile->readBytes(min($byteCount, 131072 /*128Kb*/));
                $byteCount -= strlen($data);
                $cfsFile->writeBytes($data);
            }

            $this->_directory->deleteFile($fileName);
        }
    }