protected function resolveConfigFile()
    {
        $ruleSet = $this->getInput()->getOption('ruleSet');

        if (null === $ruleSet && file_exists('phpsemver.xml')) {
            return 'phpsemver.xml';
        }

        if (null === $ruleSet) {
            $ruleSet = 'SemVer2';
        }

        if (file_exists($ruleSet)) {
            return $ruleSet;
        }

        $defaultPath = PHPSEMVER_LIB_PATH . '/PHPSemVer/Rules/';
        if (file_exists($defaultPath . $ruleSet . '.xml')) {
            return $defaultPath . $ruleSet . '.xml';
        }

        throw new \InvalidArgumentException(
            'Could not find rule set: ' . $ruleSet
        );
    }