bin2block.hs

{-# LANGUAGE DeriveDataTypeable #-}
module Main (main) where

import System.Environment
import Text.Read
import Data.Word
import Data.Bits
import Data.Char
import Data.Typeable
import Control.Exception
import qualified Data.ByteString as BS
import System.Posix

-- Split an unsigned 16 bit int into a pair) of unsigned 8 bit ints
splitWord16_8 :: Word16 -> [Word8]
splitWord16_8 a = [fromIntegral a, fromIntegral (shiftR a 8)]

-- Calculates the block's checksum byte
checkSum :: [Word8] -> Word8
checkSum = foldl xor 0

-- Takes a block of data, adds the flag (for header or data) and prepends
-- the .tap format length field
block :: [Word8] -> BS.ByteString
block blockData = let payload = [255] ++ blockData ++ [checkSum ([255] ++ blockData)] in
    BS.pack (splitWord16_8 (fromIntegral (length payload)) ++ payload)

-- for parsing all the command line arguments
parseArgs :: [String] -> Maybe (String)
parseArgs args = let l = length args in
    if l /= 1 then Nothing
    else Just (args !! 0)

data Bin2TapException
    = InvalidArgs
    deriving (Eq, Typeable)

instance Show Bin2TapException where
    show InvalidArgs =
        "Usage: bin2block <filename>\n"

instance Exception Bin2TapException

-- Main conversion function
tapeConversion :: String -> IO ()
tapeConversion filename = do
    -- get the contents of the binary
    filedata <- BS.readFile filename;
    -- save a new file that contains...
    BS.writeFile outfilename ( block (BS.unpack filedata))
    where outfilename = filename ++ ".tap"

main :: IO ()
main = do
  args <- getArgs
  case parseArgs args of
    Nothing -> throw InvalidArgs
    Just file -> tapeConversion file