module Exercise_12 where

import Control.Applicative --why is this needed on the submission server, <*> should be part of Prelude (╯°□°）╯︵ ┻━┻)
import Control.Arrow
import Control.Monad
import Data.List

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 :: String -> String
-- encrypt s =
--   (map fst . ((++) <$> fst <*> snd))
--     (partition (isPrime . snd) (zip s [1 .. length s]))
-- decrypt :: String -> String
-- decrypt y = map fst $ sortOn snd (c ++ b)
--   where
--     a = splitAt ((length . primes) (length y)) y
--     b = (zip (fst a) (primes $ length y))
--     c = zip (snd a) ([1 .. length y] \\ primes (length y))
-- 1: 35
-- ges: 110
-- 67 token
{-WETT-}
encrypt :: String -> String
encrypt =
  zip (enumFrom 1) >>> partition (isPrime . fst) >>> uncurry (++) >>> map snd

decrypt :: String -> String
decrypt y =
  (splitAt ((length . primes) l) >>>
   zip (primes l) *** zip (enumFrom 1 \\ primes l) >>>
   uncurry (++) >>> sort >>> map snd)
    y
  where
    l = length y

{-TTEW-}