public function metrics()
    {
        $this->_metrics = new Metrics();
        foreach ($this->_coverage as $file => $rawCoverage) {
            $root = $this->parse($file);
            $coverage = $this->export($file);
            $this->_processed = [
                'loc'      => -1,
                'nlloc'    => -1,
                'lloc'     => -1,
                'cloc'     => -1,
                'coverage' => -1
            ];
            $this->_processTree($file, $root->tree, $coverage);
        }
        return $this->_metrics;
    }