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import Data.Char (ord)
import Data.Word (Word8)
import Data.Tuple.Extra
import Data.Tuple (swap)
import Data.Array (array,(!),Array)
import Data.Bits (shiftL,shiftR,(.&.))
import System.Environment (getArgs,getProgName,withArgs)
import Test.Hspec (hspec,describe,it,shouldBe)
import qualified Data.ByteString.Lazy as BL
import qualified Data.ByteString.Lazy.Char8 as Char8
main = do args<-getArgs
let arg=args!!0
prg<-getProgName
if length args == 0
then BL.getContents >>= BL.putStr . encode64
else if length args == 1 && arg == "-t"
then withArgs [] test
else if length args == 1 && arg == "-d"
then BL.getContents >>= BL.putStr . decode64
else putStrLn $ unlines
[ "usage: "++prg++" [FLAG]"
,"reads from stdin"
,"default mode is encode"
,"flags: -d decode, -t unit test"]
encode64 = chunkBL 76 (flip BL.append (Char8.pack "\n")) . chunkBL 3 (from 6 4.to 8)
decode64 = chunkBL 4 (from 8 3.to 6)
tab64enc :: Array Int Word8
tab64enc = array (0,63) $ zip [0..] $ map (fromIntegral.ord) $
['A'..'Z']++['a'..'z']++['0'..'9']++['+','/']
to s = (\(v,l)->(v`shiftL`((3-fromIntegral l)*s),l+1)) . first (BL.foldl' f 0) . second (BL.length) . dupe
where f a v = a `shiftL` s + fromIntegral v
from s l (x,m) = BL.take (fromIntegral l) . BL.pack $ (++repeat 61) $ map f (take (fromIntegral m) $ reverse [0..l-1])
where f v = tab64enc ! (x `shiftR` (v*s) .&. (2^s-1))
chunkBL n f b | BL.null b = b
| otherwise = let l = f . BL.take n $ b
r = chunkBL n f . BL.drop n $ b
in BL.append l r
-- |Unit Testing
tests=[ ("any carnal pleasure.","YW55IGNhcm5hbCBwbGVhc3VyZS4=\n")
,("any carnal pleasure","YW55IGNhcm5hbCBwbGVhc3VyZQ==\n")
,("any carnal pleasur","YW55IGNhcm5hbCBwbGVhc3Vy\n")
,("any carnal pleasu","YW55IGNhcm5hbCBwbGVhc3U=\n")
,("any carnal pleas","YW55IGNhcm5hbCBwbGVhcw==\n") ]
test = hspec $ do describe "Base64" $ do
it "encode" $ do mapM_ (tst encode64) tests
it "decode" $ do mapM_ (tst decode64) (map swap tests)
where tst f (d,e) = (f (Char8.pack d)) `shouldBe` (Char8.pack e)
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