module Codec.Binary.Uu
( encode
, decode
, decode'
, chop
, unchop
) where
import Control.Monad
import Data.Array
import Data.Bits
import Data.Maybe
import Data.Word
import qualified Data.Map as M
_encMap = zip [0..] "`!\"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_"
encodeArray :: Array Word8 Char
encodeArray = array (0, 64) _encMap
decodeMap :: M.Map Char Word8
decodeMap = M.fromList [(snd i, fst i) | i <- _encMap]
encode :: [Word8]
-> String
encode = let
pad n = replicate n 0
enc [] = ""
enc l@[o] = take 2 . enc $ l ++ pad 2
enc l@[o1, o2] = take 3 . enc $ l ++ pad 1
enc (o1 : o2 : o3 : os) = let
i1 = o1 `shiftR` 2
i2 = (o1 `shiftL` 4 .|. o2 `shiftR` 4) .&. 0x3f
i3 = (o2 `shiftL` 2 .|. o3 `shiftR` 6) .&. 0x3f
i4 = o3 .&. 0x3f
in foldr ((:) . (encodeArray !)) "" [i1, i2, i3, i4] ++ enc os
in enc
decode' :: String
-> [Maybe Word8]
decode' = let
pad n = replicate n $ Just 0
dec [] = []
dec l@[Just eo1, Just eo2] = take 1 . dec $ l ++ pad 2
dec l@[Just eo1, Just eo2, Just eo3] = take 2 . dec $ l ++ pad 1
dec (Just eo1 : Just eo2 : Just eo3 : Just eo4 : eos) = let
o1 = eo1 `shiftL` 2 .|. eo2 `shiftR` 4
o2 = eo2 `shiftL` 4 .|. eo3 `shiftR` 2
o3 = eo3 `shiftL` 6 .|. eo4
in Just o1 : Just o2 : Just o3 : dec eos
dec _ = [Nothing]
in
dec . map (flip M.lookup decodeMap)
decode :: String
-> Maybe [Word8]
decode = sequence . decode'
chop :: Int
-> String
-> [String]
chop n "" = []
chop n s = let
enc_len | n < 5 = 4
| n >= 85 = 84
| otherwise = (n 1) `div` 4 * 4
enc_line = take enc_len s
act_len = fromIntegral $ case (length enc_line `divMod` 4) of
(l, 0) -> l * 3
(l, 2) -> l * 3 + 1
(l, 3) -> l * 3 + 2
len = (encodeArray ! act_len)
in (len : enc_line) : chop n (drop enc_len s)
unchop :: [String]
-> String
unchop ss = let
singleUnchop (l : cs) = let
act_len = fromIntegral $ decodeMap M.! l
enc_len = case (act_len `divMod` 3) of
(n, 0) -> n * 4
(n, 1) -> n * 4 + 2
(n, 2) -> n * 4 + 3
in take enc_len cs
in foldr ((++) . singleUnchop) "" ss