{-# LANGUAGE BangPatterns #-}
{-# LANGUAGE CPP #-}
{-# LANGUAGE MagicHash #-}
#if __GLASGOW_HASKELL__ >= 702
{-# LANGUAGE Trustworthy #-}
#endif
-- |
-- Module      : Data.ByteString.Base16
-- Copyright   : (c) 2011 MailRank, Inc.
--
-- License     : BSD
-- Maintainer  : Herbert Valerio Riedel <hvr@gnu.org>,
--               Mikhail Glushenkov <mikhail.glushenkov@gmail.com>,
--               Emily Pillmore <emilypi@cohomolo.gy>
-- Stability   : stable
-- Portability : non-portable
--
-- RFC 4648-compliant Base16 (Hexadecimal) encoding for 'ByteString' values.
-- For a complete Base16 encoding specification, please see <https://tools.ietf.org/html/rfc4648#section-8 RFC-4648 section 8>.
--
module Data.ByteString.Base16
( encode
, decode
, decodeLenient
) where

import Data.ByteString (empty)
import Data.ByteString.Base16.Internal (encodeLoop, decodeLoop, lenientLoop, mkBS, withBS)
import Data.ByteString.Internal (ByteString)

import Foreign.ForeignPtr (withForeignPtr)
import Foreign.Ptr (plusPtr)

import GHC.ForeignPtr (mallocPlainForeignPtrBytes)

-- | Encode a 'ByteString' value in base16 (i.e. hexadecimal).
-- Encoded values will always have a length that is a multiple of 2.
--
-- === __Examples__:
--
-- > encode "foo"  == "666f6f"
--
encode :: ByteString -> ByteString
encode bs = withBS bs go
  where
    go !sptr !slen
      | slen > maxBound `div` 2 =
        error "Data.ByteString.Base16.encode: input too long"
      | otherwise = do
          let l = slen * 2
          dfp <- mallocPlainForeignPtrBytes l
          withForeignPtr dfp $ \dptr ->
            encodeLoop dptr sptr (sptr `plusPtr` slen)
          return $ mkBS dfp l

-- | Decode a base16-encoded 'ByteString' value.
-- If errors are encountered during the decoding process,
-- then an error message and character offset will be returned in
-- the @Left@ clause of the coproduct.
--
-- === __Examples__:
--
-- > decode "666f6f"  == Right "foo"
-- > decode "66quux"  == Left "invalid character at offset: 2"
-- > decode "666quux" == Left "invalid character at offset: 3"
--
-- @since 1.0.0.0
--
decode :: ByteString -> Either String ByteString
decode bs = withBS bs go
  where
    go !sptr !slen
      | slen == 0 = return $ Right empty
      | r /= 0 = return $ Left "invalid bytestring size"
      | otherwise = do
        dfp <- mallocPlainForeignPtrBytes q
        withForeignPtr dfp $ \dptr ->
          decodeLoop dfp dptr sptr (plusPtr sptr slen)
      where
        !q = slen `quot` 2
        !r = slen `rem` 2

-- | Decode a Base16-encoded 'ByteString' value leniently, using a
-- strategy that never fails.
--
-- /N.B./: this is not RFC 4648-compliant
--
-- === __Examples__:
--
-- > decodeLenient "666f6f"  == "foo"
-- > decodeLenient "66quuxx" == "f"
-- > decodeLenient "666quux" == "f"
-- > decodeLenient "666fquu" -- "fo"
--
-- @since 1.0.0.0
--
decodeLenient :: ByteString -> ByteString
decodeLenient bs = withBS bs go
  where
    go !sptr !slen
      | slen == 0 = return empty
      | otherwise = do
        dfp <- mallocPlainForeignPtrBytes (q * 2)
        withForeignPtr dfp $ \dptr ->
          lenientLoop dfp dptr sptr (plusPtr sptr slen)
      where
        !q = slen `quot` 2