{-# language BangPatterns #-}
{-# language DuplicateRecordFields #-}
{-# language LambdaCase #-}
{-# language MagicHash #-}
{-# language RankNTypes #-}
{-# language ScopedTypeVariables #-}
{-# language UnboxedTuples #-}

module Data.ByteArray.Builder.Small
  ( -- * Unsafe Primitives
    Builder(..)
  , construct
  , fromUnsafe
    -- * Evaluation
  , run
  , pasteST
  , pasteIO
  , pasteGrowST
  , pasteGrowIO
  , pasteArrayST
  , pasteArrayIO
    -- * Materialized Byte Sequences
  , bytes
  , bytearray
    -- * Encode Integral Types
    -- ** Human-Readable
  , word64Dec
  , int64Dec
  , word64PaddedUpperHex
  , word32PaddedUpperHex
  , word16PaddedUpperHex
  , word8PaddedUpperHex
    -- ** Machine-Readable
  , word64BE
  , word32BE
  , word16BE
    -- * Encode Floating-Point Types
    -- ** Human-Readable
  , doubleDec
  ) where

import Control.Monad.Primitive
import Control.Monad.ST
import Control.Monad.ST.Run (runByteArrayST)
import Data.Bytes.Types
import Data.Primitive
import Data.Int (Int64)
import GHC.Exts
import GHC.ST
import GHC.Word
import GHC.TypeLits (KnownNat,natVal')
import Data.Primitive.ByteArray.Offset (MutableByteArrayOffset(..))

import qualified Data.Primitive as PM
import qualified Data.Vector as V
import qualified Data.ByteArray.Builder.Small.Unsafe as Unsafe

-- | An unmaterialized sequence of bytes that may be pasted
-- into a mutable byte array.
newtype Builder = Builder
  -- This functions takes an offset and a number of remaining bytes
  -- and returns the new offset.
  (forall s. MutableByteArray# s -> Int# -> Int# -> State# s -> (# State# s, Int# #))

instance Semigroup Builder where
  {-# inline (<>) #-}
  Builder f <> Builder g = Builder $ \arr off0 len0 s0 -> case f arr off0 len0 s0 of
    (# s1, r #) -> case r /=# (-1#) of
      1# -> g arr r (len0 +# (off0 -# r)) s1
      _ -> (# s1, (-1#) #)

instance Monoid Builder where
  mempty = Builder $ \_ off0 _ s0 -> (# s0, off0 #)

-- | Run a builder. An accurate size hint is important for good performance.
-- The size hint should be slightly larger than the actual size.
run ::
     Int -- ^ Hint for upper bound on size
  -> Builder -- ^ Builder
  -> ByteArray
run hint b = runByteArrayST $ do
  let go !n = do
        arr <- newByteArray n
        pasteST b (MutableBytes arr 0 n) >>= \case
          Nothing -> go (n + 64)
          Just len -> do
            shrinkMutableByteArray arr len
            unsafeFreezeByteArray arr
  go hint

-- | Variant of 'pasteArrayST' that runs in 'IO'.
pasteArrayIO ::
     MutableBytes RealWorld -- ^ Buffer
  -> (a -> Builder) -- ^ Builder
  -> V.Vector a -- ^ Elements to serialize
  -> IO (V.Vector a, MutableBytes RealWorld) -- ^ Shifted vector, shifted buffer
pasteArrayIO !arr f !xs = stToIO (pasteArrayST arr f xs)

-- | Fold over a vector, applying the builder to each element until
-- the buffer cannot accomodate any more.
pasteArrayST ::
     MutableBytes s -- ^ Buffer
  -> (a -> Builder) -- ^ Builder
  -> V.Vector a -- ^ Elements to serialize
  -> ST s (V.Vector a, MutableBytes s) -- ^ Shifted vector, shifted buffer
pasteArrayST (MutableBytes arr off0 len0) f !xs0 = do
  let go !xs !ixBufA !lenBufA = if V.length xs > 0
        then do
          let a = V.unsafeHead xs
          pasteST (f a) (MutableBytes arr ixBufA lenBufA) >>= \case
            Nothing -> pure (xs,MutableBytes arr ixBufA lenBufA)
            Just ixBufB ->
              go (V.unsafeTail xs) ixBufB (lenBufA + (ixBufA - ixBufB))
        else pure (xs,MutableBytes arr ixBufA lenBufA)
  go xs0 off0 len0

-- | Paste the builder into the byte array starting at offset zero.
-- This repeatedly reallocates the byte array if it cannot accomodate
-- the builder, replaying the builder each time.
pasteGrowST ::
     Int -- ^ How many bytes to grow by at a time
  -> Builder
  -> MutableByteArrayOffset s
     -- ^ Initial buffer, used linearly. Do not reuse this argument.
  -> ST s (MutableByteArrayOffset s)
     -- ^ Final buffer that accomodated the builder.
pasteGrowST !n b !(MutableByteArrayOffset arr0 off0) = do
  let go !arr !sz = pasteST b (MutableBytes arr off0 (sz - off0)) >>= \case
        Nothing -> do
          let szNext = sz + n
          arrNext <- PM.resizeMutableByteArray arr szNext
          go arrNext szNext
        Just ix -> pure (MutableByteArrayOffset{array=arr,offset=ix})
  go arr0 =<< PM.getSizeofMutableByteArray arr0

-- | Variant of 'pasteGrowST' that runs in 'IO'.
pasteGrowIO ::
     Int -- ^ How many bytes to grow by at a time
  -> Builder
  -> MutableByteArrayOffset RealWorld
     -- ^ Initial buffer, used linearly. Do not reuse this argument.
  -> IO (MutableByteArrayOffset RealWorld)
     -- ^ Final buffer that accomodated the builder.
pasteGrowIO !n b !arr = stToIO (pasteGrowST n b arr)

-- | Execute the builder, pasting its contents into a buffer.
-- If the buffer is not large enough, this returns 'Nothing'.
-- Otherwise, it returns the index in the buffer that follows
-- the payload just written.
pasteST :: Builder -> MutableBytes s -> ST s (Maybe Int)
{-# inline pasteST #-}
pasteST (Builder f) (MutableBytes (MutableByteArray arr) (I# off) (I# len)) =
  ST $ \s0 -> case f arr off len s0 of
    (# s1, r #) -> if isTrue# (r /=# (-1#))
      then (# s1, Just (I# r) #)
      else (# s1, Nothing #)

-- | Variant of 'pasteST' that runs in 'IO'.
pasteIO :: Builder -> MutableBytes RealWorld -> IO (Maybe Int)
{-# inline pasteIO #-}
pasteIO b m = stToIO (pasteST b m)

-- | Constructor for 'Builder' that works on a function with lifted
-- arguments instead of unlifted ones. This is just as unsafe as the
-- actual constructor.
construct :: (forall s. MutableBytes s -> ST s (Maybe Int)) -> Builder
construct f = Builder
  $ \arr off len s0 ->
    case unST (f (MutableBytes (MutableByteArray arr) (I# off) (I# len))) s0 of
      (# s1, m #) -> case m of
        Nothing -> (# s1, (-1#) #)
        Just (I# n) -> (# s1, n #)

fromUnsafe :: forall n. KnownNat n => Unsafe.Builder n -> Builder
{-# inline fromUnsafe #-}
fromUnsafe (Unsafe.Builder f) = Builder $ \arr off len s0 ->
  case fromIntegral (natVal' (proxy# :: Proxy# n)) of
    I# req -> case len >=# req of
      1# -> f arr off s0
      _ -> (# s0, (-1#) #)

-- | Create a builder from an unsliced byte sequence.
bytearray :: ByteArray -> Builder
bytearray a = bytes (Bytes a 0 (sizeofByteArray a))

-- | Create a builder from a sliced byte sequence.
bytes :: Bytes -> Builder
bytes (Bytes src soff slen) = construct $ \(MutableBytes arr off len) -> if len >= slen
  then do
    copyByteArray arr off src soff slen
    pure (Just (off + slen))
  else pure Nothing

-- | Encodes an unsigned 64-bit integer as decimal.
-- This encoding never starts with a zero unless the
-- argument was zero.
word64Dec :: Word64 -> Builder
word64Dec w = fromUnsafe (Unsafe.word64Dec w)

-- | Encode a double-floating-point number, using decimal notation or
-- scientific notation depending on the magnitude. This has undefined
-- behavior when representing @+inf@, @-inf@, and @NaN@. It will not
-- crash, but the generated numbers will be nonsense.
doubleDec :: Double -> Builder
doubleDec w = fromUnsafe (Unsafe.doubleDec w)

-- | Encodes a signed 64-bit integer as decimal.
-- This encoding never starts with a zero unless the argument was zero.
-- Negative numbers are preceded by a minus sign. Positive numbers
-- are not preceded by anything.
int64Dec :: Int64 -> Builder
int64Dec w = fromUnsafe (Unsafe.int64Dec w)

-- | Encode a 64-bit unsigned integer as hexadecimal, zero-padding
-- the encoding to 16 digits. This uses uppercase for the alphabetical
-- digits. For example, this encodes the number 1022 as @00000000000003FE@.
word64PaddedUpperHex :: Word64 -> Builder
word64PaddedUpperHex w =
  fromUnsafe (Unsafe.word64PaddedUpperHex w)

-- | Encode a 32-bit unsigned integer as hexadecimal, zero-padding
-- the encoding to 8 digits. This uses uppercase for the alphabetical
-- digits. For example, this encodes the number 1022 as @000003FE@.
word32PaddedUpperHex :: Word32 -> Builder
word32PaddedUpperHex w =
  fromUnsafe (Unsafe.word32PaddedUpperHex w)

-- | Encode a 16-bit unsigned integer as hexadecimal, zero-padding
-- the encoding to 4 digits. This uses uppercase for the alphabetical
-- digits. For example, this encodes the number 1022 as @03FE@.
word16PaddedUpperHex :: Word16 -> Builder
word16PaddedUpperHex w =
  fromUnsafe (Unsafe.word16PaddedUpperHex w)

-- | Encode a 8-bit unsigned integer as hexadecimal, zero-padding
-- the encoding to 2 digits. This uses uppercase for the alphabetical
-- digits. For example, this encodes the number 11 as @0B@.
word8PaddedUpperHex :: Word8 -> Builder
word8PaddedUpperHex w =
  fromUnsafe (Unsafe.word8PaddedUpperHex w)

unST :: ST s a -> State# s -> (# State# s, a #)
unST (ST f) = f

shrinkMutableByteArray :: MutableByteArray s -> Int -> ST s ()
shrinkMutableByteArray (MutableByteArray arr) (I# sz) =
  primitive_ (shrinkMutableByteArray# arr sz)

-- | Requires exactly 8 bytes. Dump the octets of a 64-bit
-- word in a big-endian fashion.
word64BE :: Word64 -> Builder
word64BE w = fromUnsafe (Unsafe.word64BE w)

-- | Requires exactly 4 bytes. Dump the octets of a 32-bit
-- word in a big-endian fashion.
word32BE :: Word32 -> Builder
word32BE w = fromUnsafe (Unsafe.word32BE w)

-- | Requires exactly 2 bytes. Dump the octets of a 16-bit
-- word in a big-endian fashion.
word16BE :: Word16 -> Builder
word16BE w = fromUnsafe (Unsafe.word16BE w)