{-# LANGUAGE MagicHash #-}
{-# OPTIONS_GHC -fwarn-unused-binds -fwarn-unused-imports #-}

module Noun.Jam.Fast (jam, jamBS, jamFat, jamFatBS) where

import ClassyPrelude hiding (hash)

import Control.Lens              (view, to, from)
import Data.Bits                 (shiftL, shiftR, setBit, clearBit, xor, (.|.))
import Noun.Atom                 (Atom(MkAtom), toAtom, bitWidth, takeBitsWord)
import Noun.Atom                 (wordBitWidth, wordBitWidth# , atomBitWidth#)
import Noun                      (Noun(Atom, Cell))
import Noun.Fat
import Noun.Pill                 (bigNatWords, atomBS)
import Data.Vector.Primitive     ((!))
import Foreign.Marshal.Alloc     (callocBytes, free)
import Foreign.Ptr               (Ptr, castPtr, plusPtr)
import Foreign.Storable          (poke)
import GHC.Integer.GMP.Internals (BigNat)
import GHC.Int                   (Int(I#))
import GHC.Natural               (Natural(NatS#, NatJ#))
import GHC.Prim                  (Word#, plusWord#, word2Int#)
import GHC.Word                  (Word(W#))
import System.IO.Unsafe          (unsafePerformIO)

import qualified Data.ByteString.Unsafe as BS
import qualified Data.Hashable          as Hash
import qualified Data.HashTable.IO      as H
import qualified Data.Vector.Primitive  as VP


-- Exports ---------------------------------------------------------------------

jamFatBS :: FatNoun -> ByteString
jamFatBS n = doPut bt sz (writeNoun n)
  where
    (sz, bt) = unsafePerformIO (compress n)

jamFat :: FatNoun -> Atom
jamFat = view (from atomBS) . jamFatBS

jamBS :: Noun -> ByteString
jamBS = jamFatBS . toFatNoun

jam :: Noun -> Atom
jam = jamFat . toFatNoun


-- Types -----------------------------------------------------------------------

{-|
    The encoder state.

    - ptr: Pointer into the output buffer.
    - reg: Next 64 bits of output, partially written.
    - off: Number of bits already written into `reg`
    - pos: Total number of bits written.
-}
data S = S
  { ptr :: {-# UNPACK #-} !(Ptr Word)
  , reg :: {-# UNPACK #-} !Word
  , off :: {-# UNPACK #-} !Int
  , pos :: {-# UNPACK #-} !Word
  } deriving (Show,Eq,Ord)

data PutResult a = PutResult {-# UNPACK #-} !S !a
  deriving Functor

newtype Put a = Put
  { runPut :: H.CuckooHashTable Word Word
           -> S
           -> IO (PutResult a)
  }

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

{-# INLINE getRef #-}
getRef :: Put (Maybe Word)
getRef = Put \tbl s -> PutResult s <$> H.lookup tbl (pos s)

{-
  1. Write the register to the output, and increment the output pointer.
-}
{-# INLINE flush #-}
flush :: Put ()
flush = Put $ \tbl s@S{..} -> do
    poke ptr reg
    pure $ PutResult (s { ptr = ptr `plusPtr` 8 }) ()

{-# INLINE update #-}
update :: (S -> S) -> Put ()
update f = Put \tbl s@S{..} -> pure (PutResult (f s) ())

{-# INLINE setRegOff #-}
setRegOff :: Word -> Int -> Put ()
setRegOff r o = update \s@S{..} -> (s {reg=r, off=o})

{-# INLINE setReg #-}
setReg :: Word -> Put ()
setReg r = update \s@S{..} -> (s { reg=r })

{-# INLINE getS #-}
getS :: Put S
getS = Put $ \tbl s -> pure (PutResult s s)

{-# INLINE putS #-}
putS :: S -> Put ()
putS s = Put $ \tbl _ -> pure (PutResult s ())

{-
    To write a bit:

    | reg  |= 1 << off
    | off <- (off + 1) % 64
    | if (!off):
    |     buf[w++] <- reg
    |     reg      <- 0
-}
{-# INLINE writeBit #-}
writeBit :: Bool -> Put ()
writeBit b = Put $ \tbl s@S{..} -> do
    let s' = s { reg = (if b then setBit else clearBit) reg off
               , off = (off + 1) `mod` 64
               , pos = pos + 1
               }

    if off == 63
    then runPut (flush >> setRegOff 0 0) tbl s'
    else pure $ PutResult s' ()

{-
    To write a 64bit word:

    | reg |= w << off
    | buf[bufI++] = reg
    | reg = w >> (64 - off)
-}
{-# INLINE writeWord #-}
writeWord :: Word -> Put ()
writeWord wor = do
    S{..} <- getS
    setReg (reg .|. shiftL wor off)
    flush
    update \s -> s { pos = 64 + pos
                   , reg = shiftR wor (64 - off)
                   }

{-
    To write some bits (< 64) from a word:

    | wor = takeBits(wid, wor)
    | reg = reg .|. (wor << off)
    | off = (off + wid) % 64
    |
    | if (off + wid >= 64)
    |     buf[w] = x
    |     reg    = wor >> (wid - off)
-}
{-# INLINE writeBitsFromWord #-}
writeBitsFromWord :: Int -> Word -> Put ()
writeBitsFromWord wid wor = do
    wor <- pure (takeBitsWord wid wor)

    oldSt <- getS

    let newSt = oldSt { reg = reg oldSt .|. shiftL wor (off oldSt)
                      , off = (off oldSt + wid) `mod` 64
                      , pos = fromIntegral wid + pos oldSt
                      }

    putS newSt

    when (wid + off oldSt >= 64) $ do
        flush
        setReg (shiftR wor (wid - off newSt))
{-
  Write all of the the signficant bits of a direct atom.
-}
{-# INLINE writeAtomWord# #-}
writeAtomWord# :: Word# -> Put ()
writeAtomWord# w = do
    writeBitsFromWord (I# (word2Int# (wordBitWidth# w))) (W# w)

{-# INLINE writeAtomWord #-}
writeAtomWord :: Word -> Put ()
writeAtomWord (W# w) = writeAtomWord# w

{-
  Write all of the the signficant bits of an indirect atom.

  TODO Use memcpy when the bit-offset of the output is divisible by 8.
-}
{-# INLINE writeAtomBigNat #-}
writeAtomBigNat :: BigNat -> Put ()
writeAtomBigNat (view bigNatWords -> words) = do
  let lastIdx = VP.length words - 1
  for_ [0..(lastIdx-1)] \i ->
      writeWord (words ! i)
  writeAtomWord (words ! lastIdx)

{-# INLINE writeAtomBits #-}
writeAtomBits :: Atom -> Put ()
writeAtomBits = \case MkAtom (NatS# wd) -> writeAtomWord# wd
                      MkAtom (NatJ# bn) -> writeAtomBigNat bn


-- Put Instances ---------------------------------------------------------------

instance Functor Put where
    fmap f g = Put $ \tbl s -> do
        PutResult s' a <- runPut g tbl s
        pure $ PutResult s' (f a)
    {-# INLINE fmap #-}

instance Applicative Put where
    pure x = Put (\_ s -> return $ PutResult s x)
    {-# INLINE pure #-}

    Put f <*> Put g = Put $ \tbl s1 -> do
        PutResult s2 f' <- f tbl s1
        PutResult s3 g' <- g tbl s2
        return $ PutResult s3 (f' g')
    {-# INLINE (<*>) #-}

    Put f *> Put g = Put $ \tbl s1 -> do
        PutResult s2 _ <- f tbl s1
        g tbl s2
    {-# INLINE (*>) #-}

instance Monad Put where
    return = pure
    {-# INLINE return #-}

    (>>) = (*>)
    {-# INLINE (>>) #-}

    Put x >>= f = Put $ \tbl s -> do
        PutResult s' x' <- x tbl s
        runPut (f x') tbl s'
    {-# INLINE (>>=) #-}


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

doPut :: H.CuckooHashTable Word Word -> Word -> Put () -> ByteString
doPut tbl sz m =
    unsafePerformIO $ do
        -- traceM "doPut"
        buf <- callocBytes (fromIntegral (wordSz*8))
        _   <- runPut (m >> mbFlush) tbl (S buf 0 0 0)
        BS.unsafePackCStringFinalizer (castPtr buf) byteSz (free buf)
  where
    wordSz = fromIntegral (sz `divUp` 64)
    byteSz = fromIntegral (sz `divUp` 8)
    divUp  = \x y -> (x `div` y) + (if x `mod` y == 0 then 0 else 1)

    mbFlush :: Put ()
    mbFlush = do
      shouldFlush <- (/= 0) . off <$> getS
      when shouldFlush flush


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

{-
    TODO Handle back references
-}
writeNoun :: FatNoun -> Put ()
writeNoun n =
  getRef >>= \case
    Just bk -> writeBackRef bk
    Nothing -> case n of FatAtom _ n     -> writeAtom (MkAtom $ NatJ# n)
                         FatWord (W# w)  -> writeAtom (MkAtom $ NatS# w)
                         FatCell _ _ h t -> writeCell h t

{-# INLINE writeMat #-}
writeMat :: Atom -> Put ()
writeMat 0   = writeBit True
writeMat atm = do
    writeBitsFromWord (preWid+1) (shiftL 1 preWid)
    writeBitsFromWord (preWid-1) atmWid
    writeAtomBits atm
  where
    atmWid = bitWidth atm
    preWid = fromIntegral (wordBitWidth atmWid)

{-# INLINE writeCell #-}
writeCell :: FatNoun -> FatNoun -> Put ()
writeCell h t = do
    writeBit True
    writeBit False
    writeNoun h
    writeNoun t

{-# INLINE writeAtom #-}
writeAtom :: Atom -> Put ()
writeAtom a = do
    writeBit False
    writeMat a

{-# INLINE writeBackRef #-}
writeBackRef :: Word -> Put ()
writeBackRef a = do
    p <- pos <$> getS
    writeBit True
    writeBit True
    writeMat (toAtom a)


-- Calculate Jam Size and Backrefs ---------------------------------------------

{-# INLINE matSz #-}
matSz :: Atom -> Word
matSz a = W# (matSz# a)

{-# INLINE matSz# #-}
matSz# :: Atom -> Word#
matSz# 0 = 1##
matSz# a = preW `plusWord#` preW `plusWord#` atmW
  where
    atmW = atomBitWidth# a
    preW = wordBitWidth# atmW

{-# INLINE atomSz #-}
atomSz :: Atom -> Word
atomSz = (1+) . matSz

{-# INLINE refSz #-}
refSz :: Word -> Word
refSz = (1+) . jamWordSz

{-# INLINE jamWordSz #-}
jamWordSz :: Word -> Word
jamWordSz 0      = 2
jamWordSz (W# w) = 1 + 2*(W# preW) + (W# atmW)
  where
    atmW = wordBitWidth# w
    preW = wordBitWidth# atmW

compress :: FatNoun -> IO (Word, H.CuckooHashTable Word Word)
compress top = do
    -- traceM "<compress>"
    let sz =  10 ^ (floor $ logBase 600 (fromIntegral $ fatSize top))

    -- traceM ("inp(" <> show (fatSize top) <> ")")
    -- traceM ("sz(" <> show sz <> ")")

    nodes :: H.BasicHashTable  FatNoun Word <- H.newSized sz
    backs :: H.CuckooHashTable Word    Word <- H.newSized sz

    let proc :: Word -> FatNoun -> IO Word
        proc pos = \case
            n@(FatAtom _ a) -> pure $ atomSz (MkAtom (NatJ# a))
            FatWord w       -> pure (jamWordSz w)
            FatCell _ _ h t -> do
                !hSz <- go (pos+2) h
                !tSz <- go (pos+2+hSz) t
                pure (2+hSz+tSz)


        go :: Word -> FatNoun -> IO Word
        go p inp = do
            H.lookup nodes inp >>= \case
                Nothing -> do
                    H.insert nodes inp p
                    proc p inp
                Just bak -> do
                    let rs    = refSz bak
                        doRef = H.insert backs p bak $> rs
                        noRef = proc p inp
                    case inp of
                        FatCell _ _ _ _                              -> doRef
                        FatWord w   | rs < atomSz (fromIntegral w)   -> doRef
                        FatAtom _ a | rs < atomSz (MkAtom (NatJ# a)) -> doRef
                        _                                            -> noRef

    res <- go 0 top
    -- traceM "</compress>"
    -- print res
    pure (res, backs)


-- Stolen from Hashable Library ------------------------------------------------

{-# INLINE combine #-}
combine :: Int -> Int -> Int
combine h1 h2 = (h1 * 16777619) `xor` h2

{-# INLINE defaultHashWithSalt #-}
defaultHashWithSalt :: Hashable a => Int -> a -> Int
defaultHashWithSalt salt x = salt `combine` Hash.hash x