import Char
import List

caesar :: String -> (Int, Int) -> String
caesar [] (_, _) = []
caesar (x:xs) (shift, dec) = enc : caesar xs (shift, dec)
  where
    enc = [ 'A'..'Z'] !! (mod (ord x - 65 + (dec * shift)) 26)

vigenere :: String -> String -> (Int, Int) -> String
vigenere [] _ (_, _) = []
vigenere (x:xs) ks (idx, dec) = enc : vigenere xs ks (newIdx, dec)
  where
    alph = [ 'A'..'Z']
    newIdx = mod (idx + 1) (length ks)
    enc = alph !! (mod (ord x - 65 + (dec * (shift (ks !! idx, 0)))) 26)
    shift (k, i) = if i > 25 then 1 else if alph !! i == k then i else shift (k, i+1)

main :: IO()
main = do
  putStrLn $ "FELIX -> " ++ caesar "FELIX" (3, 1)
  putStrLn $ "IHOLA -> " ++ caesar "IHOLA" (3, -1)
  putStrLn $ "GEHEIMNIS -> " ++ vigenere "GEHEIMNIS" "AKEY" (0, 1)
  putStrLn $ "GOLCIWRGS -> " ++ vigenere "GOLCIWRGS" "AKEY" (0, -1)