-- |

-- Module    : Codec.Binary.Base64

-- Copyright : (c) 2007 Magnus Therning

-- License   : BSD3

--

-- Implemented as specified in RFC 4648

-- (<http://tools.ietf.org/html/rfc4648>).

--

-- Further documentation and information can be found at

-- <http://www.haskell.org/haskellwiki/Library/Data_encoding>.

module Codec.Binary.Base64

    ( 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

-- {{{1 enc/dec map

_encMap =

    [ (0, 'A'), (1, 'B'), (2, 'C'), (3, 'D'), (4, 'E')

    , (5, 'F') , (6, 'G'), (7, 'H'), (8, 'I'), (9, 'J')

    , (10, 'K'), (11, 'L'), (12, 'M'), (13, 'N'), (14, 'O')

    , (15, 'P'), (16, 'Q'), (17, 'R'), (18, 'S'), (19, 'T')

    , (20, 'U'), (21, 'V'), (22, 'W'), (23, 'X'), (24, 'Y')

    , (25, 'Z'), (26, 'a'), (27, 'b'), (28, 'c'), (29, 'd')

    , (30, 'e'), (31, 'f'), (32, 'g'), (33, 'h'), (34, 'i')

    , (35, 'j'), (36, 'k'), (37, 'l'), (38, 'm'), (39, 'n')

    , (40, 'o'), (41, 'p'), (42, 'q'), (43, 'r'), (44, 's')

    , (45, 't'), (46, 'u'), (47, 'v'), (48, 'w'), (49, 'x')

    , (50, 'y'), (51, 'z'), (52, '0'), (53, '1'), (54, '2')

    , (55, '3'), (56, '4'), (57, '5'), (58, '6'), (59, '7')

    , (60, '8'), (61, '9'), (62, '+'), (63, '/') ]

-- {{{1 encodeArray

encodeArray :: Array Word8 Char

encodeArray = array (0, 64) _encMap

-- {{{1 decodeMap

decodeMap :: M.Map Char Word8

decodeMap  = M.fromList [(snd i, fst i) | i <- _encMap]

-- {{{1 encode

-- | Encode data.

encode :: [Word8]

    -> String

encode = let

        pad n = take n $ repeat 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 (\ i s -> (encodeArray ! i) : s) "" [i1, i2, i3, i4]) ++ enc os

    in enc

-- {{{1 decode

-- | Decode data (lazy).

decode' :: String

    -> [Maybe Word8]

decode' = let

        pad n = take n $ repeat $ 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) . takeWhile (/= '=')

-- | Decode data (strict).

decode :: String

    -> Maybe [Word8]

decode = sequence . decode'

-- {{{1 chop

-- | Chop up a string in parts.

--

--   The length given is rounded down to the nearest multiple of 4.

--

--   /Notes:/

--

--   * PEM requires lines that are 64 characters long.

--

--   * MIME requires lines that are at most 76 characters long.

chop :: Int     -- ^ length of individual lines

    -> String

    -> [String]

chop n "" = []

chop n s = let

        enc_len | n < 4 = 4

                | otherwise = n `div` 4 * 4

    in (take enc_len s) : chop n (drop enc_len s)

-- {{{1 unchop

-- | Concatenate the strings into one long string.

unchop :: [String]

    -> String

unchop = foldr (++) ""