{-
Convert raw data (little-endian base-256 bytes) to little-endian octal
with zero-padding so that the octal may be losslessly converted back
to data.  Note: little-endian octal is a very unusual way of
expressing octal, not the standard way which is big-endian.
-}
{-
    Copyright 2015 Ken Takusagawa

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.

-}

{-# LANGUAGE ScopedTypeVariables, LambdaCase, MagicHash #-}
module Main(main) where {
import Data.List;
import qualified Data.ByteString.Lazy as B;
import GHC.Integer(mkInteger);
import Data.Bits(testBit);
import Data.Word(Word8);
import Data.Char(intToDigit);

main :: IO();
main = B.getContents >>= putStrLn . to_oct;


oct_show_unpadded :: B.ByteString -> String;
oct_show_unpadded =  map (intToDigit . fromIntegral . bool_to_integer) . nchunk 3 . concatMap to_bits . B.unpack;

{-
expected_octal_digits :: Integer -> Integer;
expected_octal_digits byte_length = case divMod (8*byte_length) 3 of {
(q,0) -> q;
(q,_) -> q+1;
}; -}

to_oct :: B.ByteString -> String;
-- to_oct s = genericTake (expected_octal_digits $ fromIntegral $ B.length s) $ (reverse $ oct_show_unpadded s) ++ repeat '0';
to_oct = oct_show_unpadded;  -- no need to estimate width because leading zeros don't get converted to nothing as does going through Integer


to_bits :: Word8 -> [Bool];
to_bits x = map (testBit x) [0..7];

from_bits :: [Bool] -> Int;
from_bits = foldr (\b accum -> accum * 2 + if b then 1 else 0) 0;

nchunk :: Integer -> [a] -> [[a]];
nchunk n = unfoldr $ \l -> if null l
then Nothing else Just $ genericSplitAt n l;

bool_to_integer :: [Bool] -> Integer;
bool_to_integer = mkInteger True . map from_bits . nchunk 31;

} --end