/// Rotate all characters from the alphabet in `$string` by `$rot` positions.
/// @since 1.2.0
/// @param {String} $string   - string to rotate
/// @param {Number} $rot (13) - number of positions to switch in alphabet
/// @return {String}
@function _ss-str-rot($string, $rot: 13) {
  $alphabet: a b c d e f g h i j k l m n o p q r s t u v w x y z;
  $result: "";

  @for $i from 1 through str-length($string) {
    $char: str-slice($string, $i, $i);
    $index: index($alphabet, to-lower-case($char));
    $is-caps: $index and (index($alphabet, to-lower-case($char)) != index($alphabet, $char));
    $new-char: if($index,
      if($index + $rot > length($alphabet),
        nth($alphabet, $index + $rot - length($alphabet)),
        nth($alphabet, $index + $rot)
      ),
      $char
    );

    @if $is-caps {
      $new-char: to-upper-case($new-char);
    }

    $result: $result + $new-char;
  }

  @return $result;
}