public function input($filename, $input)
    {
        if (substr($filename, strlen($this->_settings['ext']) * -1) !== $this->_settings['ext']) {
            return $input;
        }
        if (!class_exists('Leafo\\ScssPhp\\Compiler')) {
            throw new \Exception(sprintf('Cannot not load filter class "%s".', 'Leafo\\ScssPhp\\Compiler'));
        }
        $sc = new Compiler();
        $sc->addImportPath(dirname($filename));
        return $sc->compile($input);
    }