class Tar

class Tar {
    public static function getComposerJson(string $pathToArchive) : ?string {
        $phar = new \PharData($pathToArchive);
        if (!$phar->valid()) {
            return null;
        }
        return self::extractComposerJsonFromFolder($phar);
    }
    
    /**
     * @throws \RuntimeException
     */
    private static function extractComposerJsonFromFolder(\PharData $phar) : string {
        if (isset($phar['composer.json'])) {
            return $phar['composer.json']->getContent();
        }
        $topLevelPaths = [];
        foreach ($phar as $folderFile) {
            $name = $folderFile->getBasename();
            if ($folderFile->isDir()) {
                $topLevelPaths[$name] = true;
                if (\count($topLevelPaths) > 1) {
                    throw new \RuntimeException('Archive has more than one top level directories, and no composer.json was found on the top level, so it\'s an invalid archive. Top level paths found were: ' . implode(',', array_keys($topLevelPaths)));
                }
            }
        }
        $composerJsonPath = key($topLevelPaths) . '/composer.json';
        if ($topLevelPaths && isset($phar[$composerJsonPath])) {
            return $phar[$composerJsonPath]->getContent();
        }
        throw new \RuntimeException('No composer.json found either at the top level or within the topmost directory');
    }

}