Hex.hs

-- | Collection of functions to deal with hexadecimal encoding.
module System.Hardware.ELM327.Utils.Hex where

import Data.List (intercalate)
import Data.List.Split (chunksOf)
import Data.Word (Word8)
import Numeric (readHex)
import Text.Printf (printf)

-- | Convert an even list of hexadecimal characters to a list of Word8 values.
--
-- If the list is not even, or the string contains a non-hexadecimal
-- character, 'Nothing' is returned.
hexToBytes :: String -> Maybe [Word8]
hexToBytes = mapM pairToWord8 . chunksOf 2
  where
    pairToWord8 s@[_, _] | [(x, "")] <- readHex s = Just x
                         | otherwise = Nothing
    pairToWord8 _ = Nothing

-- | Convert a list of bytes to a hexadecimal string.
--
-- Use seperator as a seperator between each byte in the resulting string.
bytesToHex :: String -> [Word8] -> String
bytesToHex sep = intercalate sep . map (printf "%02X")