module Exercise_12 where

import Data.List
import Data.Ord
import Data.Foldable
import Control.Arrow
import Data.Function ((&))
import Control.Applicative ((<$>))

isPrime :: Int -> Bool
isPrime n
  | n <= 1 = False
  | otherwise = primeAux (n-1)
  where
    primeAux 1 = True
    primeAux i = n `mod` i /= 0 && primeAux (i-1)

-- returns all primes up to the passed number
primes :: Int -> [Int]
primes n = [i | i<-[2..n], isPrime i]

-- Functions have, as requested, been carefully crafted for 
-- your viewing (dis)pleasure :,)
-- There is a version below that disambiguates things, but where's the fun int that? :D
{-WETT-}
encrypt :: String -> String
encrypt = concatMap toList.sortOn (isPrime <$> fst >>> Down) <$> zip ft1

decrypt :: String -> String
decrypt s = map fst `fmap` sortOn snd <<< zip s $ flip union ft1 $ length s & primes

ft1 :: [Int]
ft1 = enumFrom 1
{-TTEW-}


{- MCCOMMENT
 - A bit easier on the eyes (but using the same ammount of tokens!) :
encrypt' :: String -> String
encrypt' = map snd.sortOn (not.isPrime.fst).zip (enumFrom 1)

decrypt' :: String -> String
decrypt' s = map fst $ sortOn snd $ zip s $ (primes $ length s) `union` enumFrom 1
-}