{-
Convert big-endian hexadecimal to big-endian decimal with zero-padding
so that the decimal may be losslessly converted back to data.
-}
{-
    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 #-}
module Main(main) where {
import Data.List;
import Data.Text.Read(hexadecimal);
import qualified Data.Text as Text;

main :: IO();
main = getContents >>= mapM_ putStrLn . map (to_dec_padded . head . words) . lines;
-- designed for a pipe of input from, say, sha1sum

read_hex :: String -> Integer;
read_hex s = case hexadecimal $ Text.pack s of {
Left string -> error string;
Right (i,remainder) -> if Text.null remainder
then i
else error "leftover text";
};

equivalent_decimal_length :: Integer -> Integer;
equivalent_decimal_length hex_length = genericLength $ show $ read_hex $ genericReplicate hex_length 'f';

to_dec_padded :: String -> String;
to_dec_padded s = reverse $ genericTake (equivalent_decimal_length $ genericLength s) $ (reverse $ show $ read_hex s) ++ repeat '0';

} --end