module Exercise_12 where

import System.IO
import Data.Function
import Data.List (nub, sortBy, groupBy, partition)
import Data.Bifoldable (biconcat)

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]
--encrypt s = [s!!pred i | i <- 1 `enumFromTo` length s, isPrime i] ++ [s!!pred i | i <- 1 `enumFromTo` length s, not $ isPrime i]
{-WETT-}
encrypt :: String -> String
encrypt s = map (s!!) . map pred . biconcat . partition isPrime $ 1 `enumFromTo` length s

decrypt :: String -> String
decrypt s = map fst $ sortBy (compare `on` snd) $ s `zip` (biconcat . partition isPrime $ 1 `enumFromTo` length s)
{-TTEW-}