--
-- Miguel's Naive
-- Base64 Encoder -- Coded on a winter afterfnoon on 19th Feb 2018 A.D.
--                   to fully understand base64 encoding and play with 
--                   haskell, which is always an indisputable pleasure.
--
--                   The following lines were written in full awareness 
--                   that 'libraries' for this purpose, which perform way 
--                   better, are in existence.
--
-- Coded in big anger due to nick's stories about saving his binary 
-- format, encrypted passwords in an ascii config file, featuring 
-- strange letters and characters.
-- 
-- Example Usage: echo "just testing" | stack runghc base64.hs  | stack runghc base64 -- -d
-- (You can cross check with base64 / base64 -d) 

import System.Environment
import qualified Data.List.Split as T
import qualified Data.List as L
import qualified Data.Map.Strict as M
import qualified Data.ByteString.Lazy as B
import Text.Printf
import Data.Maybe
import Data.Char
import Control.Monad

main = do args<-getArgs
          if length args == 0 then go encode64 
          else when (args!!0 == "-d") $ go decode64
          where go f = getContents >>= putStr.(++"\n").f

fromBase64 x  = (['A'..'Z']++['a'..'z']++['0'..'9']++['+','/']) !! x
mapBase64     = M.fromList $ map (\x-> (fromBase64 x,x)) [0..63]
binToDec      = sum . map (2^) . L.findIndices (=='1') . reverse 

encode64 x = pad64 (length x) . map (fromBase64 . binToDec) . T.chunksOf 6 . 
             concat . map (printf "%08b" ) $ x ++ cycle "\000"

decode64 x = map (chr . binToDec) . T.chunksOf 8 . 
             concat . map ( printf "%06b" . fromJust) . filter isJust . 
             map (flip M.lookup mapBase64) $ x

pad64 l = (++(take m ((cycle "=")))) . take ((l+m)*3 `div` 2 -3-m)
          where m = mod (3 - mod l 3) 3