code: protected function getCommonPath($first, $second)
      {
          $first  = explode('/', $first);
          $second = explode('/', $second);
          for ($i = 0; $i < min(count($first), count($second)); $i++) {
              if ($first[$i] != $second[$i]) {
                  return implode('/', array_slice($first, 0, $i)) . '/';
              }
          }
  
          return implode('/', $first) . '/';
      }
docs: Finds the common starting path.
  
  @param string $first        Path to compare.
  @param string $second       Path to compare.
  
  @return string              Common directories.