-- |
-- Module      : Basement.Block.Mutable
-- License     : BSD-style
-- Maintainer  : Haskell Foundation
--
-- A block of memory that contains elements of a type,
-- very similar to an unboxed array but with the key difference:
--
-- * It doesn't have slicing capability (no cheap take or drop)
-- * It consume less memory: 1 Offset, 1 CountOf, 1 Pinning status trimmed
-- * It's unpackable in any constructor
-- * It uses unpinned memory by default
--
-- It should be rarely needed in high level API, but
-- in lowlevel API or some data structure containing lots
-- of unboxed array that will benefit from optimisation.
--
-- Because it's unpinned, the blocks are compactable / movable,
-- at the expense of making them less friendly to C layer / address.
--
-- Note that sadly the bytearray primitive type automatically create
-- a pinned bytearray if the size is bigger than a certain threshold
--
-- GHC Documentation associated:
--
-- includes/rts/storage/Block.h
--   * LARGE_OBJECT_THRESHOLD ((uint32_t)(BLOCK_SIZE * 8 / 10))
--   * BLOCK_SIZE   (1<<BLOCK_SHIFT)
--
-- includes/rts/Constant.h
--   * BLOCK_SHIFT  12
--
{-# LANGUAGE MagicHash           #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE UnboxedTuples       #-}
module Basement.Block.Mutable
    ( Block(..)
    , MutableBlock(..)
    , mutableLengthSize
    , mutableLengthBytes
    , mutableGetAddr
    , new
    , newPinned
    , mutableEmpty
    , iterSet
    , read
    , write
    , unsafeNew
    , unsafeWrite
    , unsafeRead
    , unsafeFreeze
    , unsafeThaw
    , unsafeCopyElements
    , unsafeCopyElementsRO
    , unsafeCopyBytes
    , unsafeCopyBytesRO
    ) where

import           GHC.Prim
import           GHC.Types
import           Basement.Compat.Base
import           Data.Proxy
import           Basement.Exception
import           Basement.Types.OffsetSize
import           Basement.Monad
import           Basement.Numerical.Additive
import           Basement.PrimType
import           Basement.Block.Base

-- | Return the length of a Mutable Block
--
-- note: we don't allow resizing yet, so this can remain a pure function
mutableLengthSize :: forall ty st . PrimType ty => MutableBlock ty st -> CountOf ty
mutableLengthSize (MutableBlock mba) =
    let !(CountOf (I# szBits)) = primSizeInBytes (Proxy :: Proxy ty)
        !elems              = quotInt# (sizeofMutableByteArray# mba) szBits
     in CountOf (I# elems)
{-# INLINE[1] mutableLengthSize #-}

mutableLengthBytes :: MutableBlock ty st -> CountOf Word8
mutableLengthBytes (MutableBlock mba) = CountOf (I# (sizeofMutableByteArray# mba))
{-# INLINE[1] mutableLengthBytes #-}

-- | Get the address of the context of the mutable block.
--
-- if the block is not pinned, this is a _dangerous_ operation
mutableGetAddr :: PrimMonad prim => MutableBlock ty (PrimState prim) -> prim (Ptr ty)
mutableGetAddr (MutableBlock mba) = primitive $ \s1 ->
    case unsafeFreezeByteArray# mba s1 of
        (# s2, ba #) -> (# s2, Ptr (byteArrayContents# ba) #)

-- | Set all mutable block element to a value
iterSet :: (PrimType ty, PrimMonad prim)
        => (Offset ty -> ty)
        -> MutableBlock ty (PrimState prim)
        -> prim ()
iterSet f ma = loop 0
  where
    !sz = mutableLengthSize ma
    loop i
        | i .==# sz = pure ()
        | otherwise = unsafeWrite ma i (f i) >> loop (i+1)
    {-# INLINE loop #-}

-- | read a cell in a mutable array.
--
-- If the index is out of bounds, an error is raised.
read :: (PrimMonad prim, PrimType ty) => MutableBlock ty (PrimState prim) -> Offset ty -> prim ty
read array n
    | isOutOfBound n len = primOutOfBound OOB_Read n len
    | otherwise          = unsafeRead array n
  where len = mutableLengthSize array
{-# INLINE read #-}

-- | Write to a cell in a mutable array.
--
-- If the index is out of bounds, an error is raised.
write :: (PrimMonad prim, PrimType ty) => MutableBlock ty (PrimState prim) -> Offset ty -> ty -> prim ()
write array n val
    | isOutOfBound n len = primOutOfBound OOB_Write n len
    | otherwise          = unsafeWrite array n val
  where
    len = mutableLengthSize array
{-# INLINE write #-}