Caesar cipher in Sass.

SassMeister-input.scss

// ----
// Sass (v3.3.8)
// Compass (v1.0.0.alpha.19)
// ----


// Caesar cipher
// https://en.wikipedia.org/wiki/Caesar_cipher


// Get char code from `$str` at `$index` in range [1-52][A-Za-z].
// ––––––––
// @param [string] $str
// @param [number] $index
// ––––––––
// @return [number]

@function char-code-at($str, $index: 1) {
  $chars: 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz';
  @return str-index($chars, str-slice($str, $index, $index));
}


// Get char at `$index` in range [1-52][A-Za-z].
// ––––––––
// @param [number] $index
// ––––––––
// @return [string]

@function from-char-code($index) {
  $chars: 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz';
  @return str-slice($chars, $index, $index);
}


// Test whether `$value` is containedd between `$min` and `$max`.
// --------
// @param [number] $min: minimum range value
// @param [number] $max: maximum range value
// @param [number] $value: the value to be tested
// --------
// @return [boolean]

@function is-in-range($min, $max, $value) {
  @return ($value >= $min) and ($value <= $max);
}


// Caesar cipher encoder/decoder.
// --------
// @param [stringr] $message
// @param [number] $shift
// @param [string] $op: encrypt | decrupt
// --------
// @return [string]

@function caesar($message, $shift: 1, $op: 'encrypt') {
  @if type-of($shift) != number {
    @warn '`$shift` must be a number, type-of($shift) given.';
  }
  @if not is-in-range(0, 26, abs($shift)) {
    @warn '`$shift` must in range [0-26].';
  }
  
  $result: '';
  
  @if $op == 'decrypt' {
   $shift: (26 - $shift);
  }
  
  @for $i from 1 through str-length($message) {
    $code: char-code-at($message, $i);

    @if $code {
      // Uppercase $col <= 26
      // Lowercase $col > 26
      $start: if($code > 26, 27, 1);
      $match: ((($code - $start) + $shift) % 26) + $start;
      $result: $result + from-char-code($match);
    }
    @else {
      // Non [A-Za-z] char.
      $result: $result + str-slice($message, $i, $i);
    }
  }
  
  @return $result;
}

// Alias
@function rot($message, $shift: 1, $op: 'encrypt') {
  @return caesar($message, $shift, $op);
}


// Tests
caesar {
  $fixture: (
    ('ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz', 13, 'NOPQRSTUVWXYZABCDEFGHIJKLMnopqrstuvwxyzabcdefghijklm'),
    ('Caesar cipher', 1, 'Dbftbs djqifs'),
    ('Caesar cipher', 3, 'Fdhvdu flskhu'),
    ('Caesar cipher', 5, 'Hfjxfw hnumjw'),
    ('Caesar cipher', -6, 'Wuymul wcjbyl')
  );
  
   /* Encrypt */
  $tests: '';
  @each $test in $fixture {
    $pass: rot(nth($test, 1), nth($test, 2)) == nth($test, 3);
    $tests: $tests + if($pass, '✔ ', 'X ');
  }
  tests: $tests;
  
  /* Decrypt */
  $tests: '';
  @each $test in $fixture {
    $pass: rot(nth($test, 3), nth($test, 2), 'decrypt') == nth($test, 1);
    $tests: $tests + if($pass, '✔ ', 'X ');
  }
  tests: $tests;
}

SassMeister-output.css

@charset "UTF-8";
caesar {
  /* Encrypt */
  tests: "✔ ✔ ✔ ✔ ✔ ";
  /* Decrypt */
  tests: "✔ ✔ ✔ ✔ ✔ ";
}