{-# LANGUAGE CPP #-}
{-# OPTIONS_HADDOCK not-home #-}
{- HLINT ignore "Avoid restricted alias" -}

{-|
    Incremental construction functionality for the general-purpose fence pointer
    index.
-}
module Database.LSMTree.Internal.Index.OrdinaryAcc
(
    IndexOrdinaryAcc (IndexOrdinaryAcc),
    new,
    newWithDefaults,
    appendSingle,
    appendMulti,
    unsafeEnd
)
where

import           Prelude hiding (take)

import           Control.Exception (assert)
import           Control.Monad.ST.Strict (ST)
import           Data.Maybe (maybeToList)
import qualified Data.Vector.Primitive as Primitive (Vector, length)
import           Data.Word (Word16, Word32, Word8)
import           Database.LSMTree.Internal.Chunk (Baler, Chunk, createBaler,
                     feedBaler, unsafeEndBaler)
import           Database.LSMTree.Internal.Index.Ordinary
                     (IndexOrdinary (IndexOrdinary))
import           Database.LSMTree.Internal.Serialise
                     (SerialisedKey (SerialisedKey'))
import           Database.LSMTree.Internal.Unsliced (Unsliced, makeUnslicedKey)
import           Database.LSMTree.Internal.Vector (byteVectorFromPrim)
import           Database.LSMTree.Internal.Vector.Growing (GrowingVector)
import qualified Database.LSMTree.Internal.Vector.Growing as Growing (append,
                     freeze, new)
#ifdef NO_IGNORE_ASSERTS
import           Database.LSMTree.Internal.Unsliced (fromUnslicedKey)
import qualified Database.LSMTree.Internal.Vector.Growing as Growing
                     (readMaybeLast)
#endif

{-|
    A general-purpose fence pointer index under incremental construction.

    A value @IndexOrdinaryAcc unslicedLastKeys baler@ denotes a partially
    constructed index that assigns keys to pages according to @unslicedLastKeys@
    and uses @baler@ for incremental output of the serialised key list.
-}
data IndexOrdinaryAcc s = IndexOrdinaryAcc
                              !(GrowingVector s (Unsliced SerialisedKey))
                              !(Baler s)

-- | Creates a new, initially empty, index.
new :: Int                       -- ^ Initial size of the key buffer
    -> Int                       -- ^ Minimum chunk size in bytes
    -> ST s (IndexOrdinaryAcc s) -- ^ Construction of the index
new initialKeyBufferSize minChunkSize = IndexOrdinaryAcc                 <$>
                                        Growing.new initialKeyBufferSize <*>
                                        createBaler minChunkSize

{-|
    For a specification of this operation, see the documentation of [its
    type-agnostic version]('Database.LSMTree.Internal.Index.newWithDefaults').
-}
newWithDefaults :: ST s (IndexOrdinaryAcc s)
newWithDefaults = new 1024 4096

-- | Yields the serialisation of an element of a key list.
keyListElem :: SerialisedKey -> [Primitive.Vector Word8]
keyListElem (SerialisedKey' keyBytes) = [keySizeBytes, keyBytes] where

    keySize :: Int
    !keySize = Primitive.length keyBytes

    keySizeAsWord16 :: Word16
    !keySizeAsWord16 = assert (keySize <= fromIntegral (maxBound :: Word16)) $
                       fromIntegral keySize

    keySizeBytes :: Primitive.Vector Word8
    !keySizeBytes = byteVectorFromPrim keySizeAsWord16

{-|
    For a specification of this operation, see the documentation of [its
    type-agnostic version]('Database.LSMTree.Internal.Index.appendSingle').
-}
appendSingle :: (SerialisedKey, SerialisedKey)
             -> IndexOrdinaryAcc s
             -> ST s (Maybe Chunk)
appendSingle (firstKey, lastKey) (IndexOrdinaryAcc unslicedLastKeys baler)
    = assert (firstKey <= lastKey) $
      do
#ifdef NO_IGNORE_ASSERTS
          maybeLastUnslicedLastKey <- Growing.readMaybeLast unslicedLastKeys
          assert
              (all (< firstKey) (fromUnslicedKey <$> maybeLastUnslicedLastKey))
              (pure ())
#endif
          Growing.append unslicedLastKeys 1 (makeUnslicedKey lastKey)
          feedBaler (keyListElem lastKey) baler

{-|
    For a specification of this operation, see the documentation of [its
    type-agnostic version]('Database.LSMTree.Internal.Index.appendMulti').
-}
appendMulti :: (SerialisedKey, Word32)
            -> IndexOrdinaryAcc s
            -> ST s [Chunk]
appendMulti (key, overflowPageCount) (IndexOrdinaryAcc unslicedLastKeys baler)
    = do
#ifdef NO_IGNORE_ASSERTS
          maybeLastUnslicedLastKey <- Growing.readMaybeLast unslicedLastKeys
          assert (all (< key) (fromUnslicedKey <$> maybeLastUnslicedLastKey))
                 (pure ())
#endif
          Growing.append unslicedLastKeys pageCount (makeUnslicedKey key)
          maybeToList <$> feedBaler keyListElems baler
    where

    pageCount :: Int
    !pageCount = succ (fromIntegral overflowPageCount)

    keyListElems :: [Primitive.Vector Word8]
    keyListElems = concat (replicate pageCount (keyListElem key))

{-|
    For a specification of this operation, see the documentation of [its
    type-agnostic version]('Database.LSMTree.Internal.Index.unsafeEnd').
-}
unsafeEnd :: IndexOrdinaryAcc s -> ST s (Maybe Chunk, IndexOrdinary)
unsafeEnd (IndexOrdinaryAcc unslicedLastKeys baler) = do
    frozenUnslicedLastKeys <- Growing.freeze unslicedLastKeys
    remnant <- unsafeEndBaler baler
    pure (remnant, IndexOrdinary frozenUnslicedLastKeys)