Ruby Implementation of a Rotational Cipher. Wrote in https://coderpad.io/966172

rotationalCipher.rb

$ALPHABET = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
$alphabet = 'abcdefghijklmnopqurstvwxyz'

# Get an index of an alphabetic letter based on the index and offset
def calculateOffset(index, offset)
  index += offset
  index -= 26 while index >= 26 # keep subtracting until we get to the right range
  index
end

# Get a char from the alphabet based on an offset
def getCharByOffset(char, offset=0)
  # Chars could be in the upper alphabet, the lower alphabet, or neither.
  indexUpper = $ALPHABET.index(char)
  indexLower = $alphabet.index(char)
  if indexUpper
    i = calculateOffset(indexUpper, offset)
    char = $ALPHABET[i].chr # Get the char at that index
  elsif indexLower
    i = calculateOffset(indexLower, offset)
    char = $alphabet[i].chr
  end
  char
end

# Rotationally encode a string
def rotx(x, string, encrypt=true)
  newString = ''
  x = -x unless encrypt
  # for each char in the string
  string.each_char do |char|
    # TODO: support decryption
    newString << getCharByOffset(char, x)
  end
  # get a new char that is `x` away in the alphabet
  newString
end



# ------------------------------------------------ Assertions
puts rotx 10, 'Hello, World'
# => "Rovvy, Gybvn" # Shouldn't this be "Rovvy, Gycvn"?
puts rotx 10, 'Rovvy, Gycvn', false
# => "Hello, World"

# Rotation numbers greater than 26 should work as well
puts rotx 36, 'Hello, World'
# => "Rovvy, Gybvn"