module Encoding.LetterToNumber
  ( encltn
  , decltn
  ) where 

import Data.Char (ord, chr, isAscii, isAlpha, isSpace, isDigit, toUpper)
import Data.ByteString (ByteString)
import qualified Data.ByteString.Char8 as BC

-- This encodes ASCII characters only and ignores all other characters

charToNumber :: Char -> ByteString
charToNumber c
  | not (isAscii c) = BC.pack ""
  | isAlpha c = BC.pack $ show $ ord (toUpper c) - ord 'A' + 1
  | isSpace c = BC.pack "0"
  | otherwise = BC.singleton c

numberToChar :: ByteString -> ByteString
numberToChar s
  | s == BC.pack "0" = BC.singleton ' '
  | BC.all isDigit s = BC.singleton $ chr $ (read $ BC.unpack s) + ord 'A' - 1
  | otherwise = s

encltn :: ByteString -> ByteString
encltn input = BC.unwords $ filter (not . BC.null) $ map charToNumber $ BC.unpack input

decltn :: ByteString -> ByteString
decltn input = BC.concat $ map numberToChar $ BC.words input