A solution to a Caesar cipher challenge in which only letters are offset and in which spaces are a handful of special characters; the original challenge featured only lowercase letters and an offset of four, but this is intended to scale easily.

cipher.rb

def north_korean_cipher message, offset = 4
  unexaggerate message.chars.map{|char| decode char, offset}.join('')
end

def unexaggerate message
  message.gsub(/\d+/) { |num| num.to_i / 100 }
end

def decode char, offset
  case
  when lowercase?(char) then shift_by offset, char, 'a'
  when uppercase?(char) then shift_by offset, char, 'A'
  when space?(char) then ' '
  else char
  end
end

def shift_by offset, char, base_char, alphabet_length = 26
  ((char.ord - base_char.ord - offset) % alphabet_length + base_char.ord).chr
end

def lowercase? char
  'a' <= char && 'z' >= char
end

def uppercase? char
  lowercase? char.downcase
end

def space? char
  '@#$%^&*'.include? char
end