module Exercise_12 where

import Data.List -- (nub)
import Data.Maybe
{-H12-}
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]

{-WETT-}
encrypt :: String -> String
encrypt ws= map (ws!!) $table $length ws

--table :: Int -> [Int]
table n= map pred $primes n ++ (enumFromTo 1 n \\ primes n)

decrypt :: String -> String
decrypt ws= map fst $sortOn snd $zip ws $table $ length ws

{-TTEW-}