module Encoding.Rotate
  ( rotate ) where

import Data.Maybe (fromMaybe)
import Data.ByteString as B
import qualified Data.ByteString.Char8 as BC

upperCase = BC.pack ['A' .. 'Z']
lowerCase = BC.pack ['a' .. 'z']

-- rotate :: Int -> String -> String
-- rotate n s = map (rotchar n) s
--   where
--     rotchar n c = 
--       case (lookup c $ transp n lowerCase) of
--         Just x -> x
--         Nothing -> fromMaybe c (lookup c $ transp n upperCase)
rotate :: Int -> BC.ByteString -> BC.ByteString
rotate n s = BC.map (rotchar n) s
  where
    rotchar :: Int -> Char -> Char
    rotchar n c =
      case (lookup c $ transp n lowerCase) of
        Just x -> x
        Nothing -> fromMaybe c (lookup c $ transp n upperCase)


-- transp :: Int -> [Char] -> [(Char, Char)]
-- transp n x = zip x ((drop n x) ++ (take n x))
transp :: Int -> BC.ByteString -> [(Char, Char)]
transp n x = Prelude.zip (BC.unpack x) (BC.unpack $  BC.append (BC.drop n x) (BC.take n x))