protected function compile($in, $out)
{
$start = microtime(true);
$css = $this->scss->compile(file_get_contents($in), $in);
$elapsed = round(microtime(true) - $start, 4);
$v = Version::VERSION;
$t = date('r');
$css = "/* compiled by scssphp {$v} on {$t} ({$elapsed}s) */\n\n" . $css;
$etag = md5($css);
file_put_contents($out, $css);
file_put_contents($this->metadataName($out), serialize(['etag' => $etag, 'imports' => $this->scss->getParsedFiles(), 'vars' => crc32(serialize($this->scss->getVariables()))]));
return [$css, $etag];
}