ValueParser.hs

{-
 *  Programmer:	Piotr Borek
 *  E-mail:     piotrborek@op.pl
 *  Copyright 2016 Piotr Borek
 *
 *  Distributed under the terms of the GPL (GNU Public License)
 *
 *  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 2 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, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
-}

module Coin.Utils.ValueParser (
    parseValue,
    valueShow
) where

charToInt :: Char -> Maybe Int
charToInt '0' = Just 0
charToInt '1' = Just 1
charToInt '2' = Just 2
charToInt '3' = Just 3
charToInt '4' = Just 4
charToInt '5' = Just 5
charToInt '6' = Just 6
charToInt '7' = Just 7
charToInt '8' = Just 8
charToInt '9' = Just 9
charToInt _   = Nothing

parseValue :: String -> Maybe Int
parseValue []   = Nothing
parseValue text = parseValueA (reverse text) 0 100

parseValueA :: String -> Int -> Int -> Maybe Int
parseValueA [] acc _ = return acc
parseValueA (x:xs) acc mult =
    if or [x == ',', x == '.']
        then
            if mult == 10000
                then parseValueB xs (acc `div` 100) (mult `div` 100)
                else Nothing
        else do
            digit <- charToInt x
            parseValueA xs (acc + mult * digit) (mult * 10)

parseValueB :: String -> Int -> Int -> Maybe Int
parseValueB [] acc _ = return acc
parseValueB (x:xs) acc mult = do
    digit <- charToInt x
    parseValueB xs (acc + mult * digit) (mult * 10)

valueShow :: (Num n, Show n) => n -> String
valueShow val = let (a, b) = splitAt 2 $ reverse val'
                in reverse b ++ "." ++ reverse a
  where
      val' = let text = show val
             in case length text of
                    0 -> "000"
                    1 -> "00" ++ text
                    2 -> "0" ++ text
                    _ -> text