Haskell Quiz/The Solitaire Cipher/Solution JFoutz

import Data.Char import Data.List import System

-- discard any non a to z characers, uppercase the rest -- split into groups of 5, padded with 'X'

prep ls = loop $ map toUpper $ filter (\x -> and [isAscii x, isLetter x]) ls

   where loop [] = []
         loop ls 
             | length ls < 5 = [take 5 (ls ++ "XXXX")]
             | otherwise = (take 5 ls) : loop (drop 5 ls)

drawMsg msg = concat $ intersperse " " (loop msg)

   where loop msg
             | length msg > 5 = (take 5 msg) : loop (drop 5 msg)
             | otherwise = [msg]

churn f msg = drawMsg $ toChr $ zipWith f (toNum $ concat $ prep msg) (keyStream [1..54]) crypt msg = churn solAdd msg decrypt msg = churn solSub msg

main = do { x <- getArgs

         ; case (head x) of
                "c" -> putStrLn $ crypt $ concat $ tail x
                "d" -> putStrLn $ decrypt $ concat $ tail x
                _ -> putStrLn "Try solitare c my message, or d my message"}

-- letters to numbers and back toNum = map (\x -> ord x - 65) toChr = map (\x -> chr (x + 65))

-- add and subtract base solitare style solAdd x y = mod (x + y) 26 solSub x y = mod (x + 26 - y) 26

--keyStream down1 x ls = move $ break (==x) ls

   where move (x:xs, t:[]) = x:t:xs
         move (xs, c:n:cx) = xs ++ n : c : cx

down2 x ls = down1 x $ down1 x ls

notEither a b = (\x y -> x /= a && y /= a && x /= b && y /= b) tripleCut a b ls = swap a b $ concat $ reverse $ groupBy (notEither a b) ls

swap a b [] = [] swap a b (x:xs)

    | a == x = b : swap a b xs
    | b == x = a : swap a b xs
    | otherwise = x : swap a b xs
                  

cardVal c = if c == 54 then 53 else c countCut ls = glue $ splitAt (cardVal $ last ls) (init ls)

   where glue (f,b) = b ++ f ++ [last ls]

jokerA = 53 jokerB = 54

keyStep deck = countCut $ tripleCut jokerA jokerB $ down2 jokerB $ down1 jokerA deck

getCard deck = deck !! (cardVal $ head deck)

keyStream deck = let d2 = keyStep deck

                    out = getCard d2
                in if out == jokerA || out == jokerB
                   then keyStream d2
                   else out : keyStream d2