{-# LANGUAGE CPP #-}

{-|
    Atom implementation with fast conversions between bytestrings
    and atoms.

    TODO Support Big Endian.
-}

module Urbit.Atom.Internal where

import Prelude

import Control.Monad.Primitive   (primitive_)
import Data.Bits                 (shiftL, shiftR, (.&.), (.|.))
import Data.ByteString           (ByteString)
import Data.Vector.Primitive     (Vector(..))
import Data.Word                 (Word8)
import GHC.Exts                  (Ptr(Ptr), sizeofByteArray#)
import GHC.Exts                  (Int(..))
import GHC.Integer.GMP.Internals (BigNat(..), bigNatToWord, sizeofBigNat#)
import GHC.Integer.GMP.Internals (indexBigNat#)
import GHC.Integer.GMP.Internals (byteArrayToBigNat#, wordToBigNat, zeroBigNat)
import GHC.Natural               (Natural(..))
import GHC.Prim                  (Int#, clz#, minusWord#, plusWord#)
import GHC.Prim                  (Word#, int2Word#, subIntC#, timesWord#)
import GHC.Prim                  (copyByteArrayToAddr#)
import GHC.Word                  (Word(..))
import System.IO.Unsafe          (unsafePerformIO)

import qualified Data.ByteString           as BS
import qualified Data.ByteString.Internal  as BS
import qualified Data.ByteString.Unsafe    as BS
import qualified Data.Primitive.ByteArray  as Prim
import qualified Data.Vector.Primitive     as VP
import qualified Foreign.ForeignPtr.Unsafe as Ptr


-- Setup BIT and BYT macros. ---------------------------------------------------

#include <MachDeps.h>

#if WORD_SIZE_IN_BITS == 64
#define BIT 64
#define BYT 8
#elif WORD_SIZE_IN_BITS == 32
#define BIT 32
#define BYT 4
#else
#error WORD_SIZE_IN_BITS must be either 32 or 64
#endif


--------------------------------------------------------------------------------

wordBitWidth# :: Word# -> Word#
wordBitWidth# w = minusWord# BIT## (clz# w)

wordBitWidth :: Word -> Word
wordBitWidth (W# w) = W# (wordBitWidth# w)

bigNatBitWidth# :: BigNat -> Word#
bigNatBitWidth# nat =
  lswBits `plusWord#` ((int2Word# lastIdx) `timesWord#` BIT##)
 where
  (# lastIdx, _ #) = subIntC# (sizeofBigNat# nat) 1#
  lswBits          = wordBitWidth# (indexBigNat# nat lastIdx)

atomBitWidth# :: Natural -> Word#
atomBitWidth# (NatS# gl) = wordBitWidth# gl
atomBitWidth# (NatJ# bn) = bigNatBitWidth# bn

bitWidth :: Num a => Natural -> a
bitWidth a = fromIntegral (W# (atomBitWidth# a))

--------------------------------------------------------------------------------

{-# INLINE takeBitsWord #-}
takeBitsWord :: Int -> Word -> Word
takeBitsWord wid wor = wor .&. (shiftL 1 wid - 1)


--------------------------------------------------------------------------------

{-
    A `Pill` is a bytestring without trailing zeros.
-}
newtype Pill = Pill { unPill :: ByteString }

instance Eq Pill where
  (==) x y = pillBytes x == pillBytes y

instance Show Pill where
  show = show . pillBytes


--------------------------------------------------------------------------------

strip :: ByteString -> ByteString
strip buf = BS.take (len - go 0 (len - 1)) buf
 where
  len = BS.length buf
  go n i | i < 0                     = n
         | 0 == BS.unsafeIndex buf i = go (n + 1) (i - 1)
         | otherwise                 = n

pillBytes :: Pill -> ByteString
pillBytes = strip . unPill

bytesPill :: ByteString -> Pill
bytesPill = Pill . strip


--------------------------------------------------------------------------------

{-
    Cast a BigNat to a vector without a copy.
-}
bigNatWords :: BigNat -> Vector Word
bigNatWords (BN# bArr) =
  Vector 0 (I# (sizeofByteArray# bArr) `div` BYT) (Prim.ByteArray bArr)

{-|
    Cast a vector to a BigNat. This will not copy.

    TODO Don't crash if given a slice.
-}
wordsBigNat :: Vector Word -> BigNat
wordsBigNat v@(Vector off (I# len) (Prim.ByteArray buf)) = case VP.length v of
  0 -> zeroBigNat
  1 -> case VP.unsafeIndex v 0 of
    W# w -> wordToBigNat w
  n ->
    if off /= 0 then error "words2Nat: bad-vec" else byteArrayToBigNat# buf len

{-|
    More careful version of `wordsBigNat`, but not yet tested.

    Cast a vector to a BigNat. This will not copy unless input is a slice.

    Note that the length of the vector is in words, and the length passed
    to `byteArrayToBigNat#` is also in words.
-}
wordsBigNat' :: Vector Word -> BigNat
wordsBigNat' v = case VP.length v of
  0 -> zeroBigNat
  1 -> wordToBigNat w where W# w = VP.unsafeIndex v 0
  n -> if offset v == 0 then extract v else extract (VP.force v)
 where
  offset (Vector off _ _) = off

  extract (Vector _ (I# len) (Prim.ByteArray buf)) = byteArrayToBigNat# buf len


--------------------------------------------------------------------------------

-- | Cast a nat to a vector (no copy)
natWords :: Natural -> Vector Word
natWords = bigNatWords . natBigNat

-- | Cast a vector to a nat (no copy)
wordsNat :: Vector Word -> Natural
wordsNat = bigNatNat . wordsBigNat

-- | Cast a Nat to a BigNat (no copy).
natBigNat :: Natural -> BigNat
natBigNat (NatS# w ) = wordToBigNat w
natBigNat (NatJ# bn) = bn

-- | Cast a BigNat to a Nat (no copy).
bigNatNat :: BigNat -> Natural
bigNatNat bn = case sizeofBigNat# bn of
  0# -> 0
  1# -> NatS# (bigNatToWord bn)
  _  -> NatJ# bn


--------------------------------------------------------------------------------

wordBytes :: Word -> ByteString
wordBytes wor = BS.reverse $ BS.pack $ go 0 []
 where
  go i acc | i >= BYT  = acc
  go i acc | otherwise = go (i + 1) (fromIntegral (shiftR wor (i * BYT)) : acc)

bytesFirstWord :: ByteString -> Word
bytesFirstWord buf = go 0 0
 where
  top = min BYT (BS.length buf)
  i idx off = shiftL (fromIntegral $ BS.index buf idx) off
  go acc idx =
    if idx >= top then acc else go (acc .|. i idx (BYT * idx)) (idx + 1)


--------------------------------------------------------------------------------

pillWords :: Pill -> Vector Word
pillWords = bsToWords . pillBytes

wordsPill :: Vector Word -> Pill
wordsPill = bytesPill . vecBytes . wordsToBytes


--------------------------------------------------------------------------------

wordsToBytes :: Vector Word -> Vector Word8
wordsToBytes (Vector off sz buf) = Vector (off * BYT) (sz * BYT) buf

bsToWords :: ByteString -> Vector Word
bsToWords bs = VP.generate (1 + BS.length bs `div` BYT)
  $ \i -> bytesFirstWord (BS.drop (i * BYT) bs)


--------------------------------------------------------------------------------

vecBytes :: Vector Word8 -> ByteString
vecBytes (Vector off sz buf) = unsafePerformIO $ do
  fp <- BS.mallocByteString sz
  let Ptr a = Ptr.unsafeForeignPtrToPtr fp -- Safe b/c returning fp
  copyByteArrayToAddr a buf 0 sz
  pure (BS.PS fp off sz)
 where
  unI# :: Int -> Int#
  unI# (I# n#) = n#

  --  Hack to get GHCJS build working, since it has an old version of the
  --  `primitive` library.
  copyByteArrayToAddr dst# (Prim.ByteArray src#) soff sz =
    primitive_ (copyByteArrayToAddr# src# (unI# soff) dst# (unI# sz))

bytesVec :: ByteString -> Vector Word8
bytesVec bs = VP.generate (BS.length bs) (BS.index bs)


--------------------------------------------------------------------------------

natPill :: Natural -> Pill
natPill = wordsPill . natWords

pillNat :: Pill -> Natural
pillNat = wordsNat . bsToWords . pillBytes