{-# LANGUAGE CPP, BangPatterns, PatternGuards, DeriveDataTypeable #-}

module Codec.Archive.Tar.Index.StringTable (

    StringTable,

    lookup,

    index,

    construct,

    StringTableBuilder,

    empty,

    insert,

    inserts,

    finalise,

    unfinalise,

    serialise,

    serialiseSize,

    deserialiseV1,

    deserialiseV2,

#ifdef TESTS

    prop_valid,

    prop_sorted,

    prop_finalise_unfinalise,

    prop_serialise_deserialise,

    prop_serialiseSize,

#endif

 ) where

import Data.Typeable (Typeable)

import Prelude   hiding (lookup, id)

import Data.List hiding (lookup, insert)

import Data.Function (on)

import Data.Word (Word32)

import Data.Int  (Int32)

import Data.Bits

import Data.Monoid (Monoid(..))

#if (MIN_VERSION_base(4,5,0))

import Data.Monoid ((<>))

#endif

import Control.Exception (assert)

import qualified Data.Array.Unboxed as A

import           Data.Array.Unboxed ((!))

#if MIN_VERSION_containers(0,5,0)

import qualified Data.Map.Strict        as Map

import           Data.Map.Strict (Map)

#else

import qualified Data.Map               as Map

import           Data.Map (Map)

#endif

import qualified Data.ByteString        as BS

import qualified Data.ByteString.Unsafe as BS

import qualified Data.ByteString.Lazy   as LBS

#if MIN_VERSION_bytestring(0,10,2) || defined(MIN_VERSION_bytestring_builder)

import Data.ByteString.Builder          as BS

import Data.ByteString.Builder.Extra    as BS (byteStringCopy)

#else

import Data.ByteString.Lazy.Builder     as BS

import Data.ByteString.Lazy.Builder.Extras as BS (byteStringCopy)

#endif

-- | An effecient mapping from strings to a dense set of integers.

--

data StringTable id = StringTable

         {-# UNPACK #-} !BS.ByteString           -- all strings concatenated

         {-# UNPACK #-} !(A.UArray Int32 Word32) -- string offset table

         {-# UNPACK #-} !(A.UArray Int32 Int32)  -- string index to id table

         {-# UNPACK #-} !(A.UArray Int32 Int32)  -- string id to index table

  deriving (Show, Typeable)

instance (Eq id, Enum id) => Eq (StringTable id) where

  tbl1 == tbl2 = unfinalise tbl1 == unfinalise tbl2

-- | Look up a string in the token table. If the string is present, return

-- its corresponding index.

--

lookup :: Enum id => StringTable id -> BS.ByteString -> Maybe id

lookup (StringTable bs offsets ids _ixs) str =

    binarySearch 0 (topBound-1) str

  where

    (0, topBound) = A.bounds offsets

    binarySearch !a !b !key

      | a > b     = Nothing

      | otherwise = case compare key (index' bs offsets mid) of

          LT -> binarySearch a (mid-1) key

          EQ -> Just $! toEnum (fromIntegral (ids ! mid))

          GT -> binarySearch (mid+1) b key

      where mid = (a + b) `div` 2

index' :: BS.ByteString -> A.UArray Int32 Word32 -> Int32 -> BS.ByteString

index' bs offsets i = BS.unsafeTake len . BS.unsafeDrop start $ bs

  where

    start, end, len :: Int

    start = fromIntegral (offsets ! i)

    end   = fromIntegral (offsets ! (i+1))

    len   = end - start

-- | Given the index of a string in the table, return the string.

--

index :: Enum id => StringTable id -> id -> BS.ByteString

index (StringTable bs offsets _ids ixs) =

    index' bs offsets . (ixs !) . fromIntegral . fromEnum

-- | Given a list of strings, construct a 'StringTable' mapping those strings

-- to a dense set of integers. Also return the ids for all the strings used

-- in the construction.

--

construct :: Enum id => [BS.ByteString] -> StringTable id

construct = finalise . foldl' (\tbl s -> fst (insert s tbl)) empty

data StringTableBuilder id = StringTableBuilder

                                              !(Map BS.ByteString id)

                               {-# UNPACK #-} !Word32

  deriving (Eq, Show, Typeable)

empty :: StringTableBuilder id

empty = StringTableBuilder Map.empty 0

insert :: Enum id => BS.ByteString -> StringTableBuilder id -> (StringTableBuilder id, id)

insert str builder@(StringTableBuilder smap nextid) =

    case Map.lookup str smap of

      Just id -> (builder, id)

      Nothing -> let !id   = toEnum (fromIntegral nextid)

                     !smap' = Map.insert str id smap

                   in (StringTableBuilder smap' (nextid+1), id)

inserts :: Enum id => [BS.ByteString] -> StringTableBuilder id -> (StringTableBuilder id, [id])

inserts bss builder = mapAccumL (flip insert) builder bss

finalise :: Enum id => StringTableBuilder id -> StringTable id

finalise (StringTableBuilder smap _) =

    (StringTable strs offsets ids ixs)

  where

    strs    = BS.concat (Map.keys smap)

    offsets = A.listArray (0, fromIntegral (Map.size smap))

            . scanl (\off str -> off + fromIntegral (BS.length str)) 0

            $ Map.keys smap

    ids     = A.listArray (0, fromIntegral (Map.size smap) - 1)

            . map (fromIntegral . fromEnum)

            $ Map.elems smap

    ixs     = A.array (A.bounds ids) [ (id,ix) | (ix,id) <- A.assocs ids ]

unfinalise :: Enum id => StringTable id -> StringTableBuilder id

unfinalise (StringTable strs offsets ids _) =

    StringTableBuilder smap nextid

  where

    smap   = Map.fromAscList

               [ (index' strs offsets ix, toEnum (fromIntegral (ids ! ix)))

               | ix <- [0..h] ]

    (0,h)  = A.bounds ids

    nextid = fromIntegral (h+1)

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

-- (de)serialisation

--

serialise :: StringTable id -> BS.Builder

serialise (StringTable strs offs ids ixs) =

      let (_, !ixEnd) = A.bounds offs in

      BS.word32BE (fromIntegral (BS.length strs))

   <> BS.word32BE (fromIntegral ixEnd + 1)

   <> BS.byteStringCopy strs

   <> foldr (\n r -> BS.word32BE n <> r) mempty (A.elems offs)

   <> foldr (\n r -> BS.int32BE  n <> r) mempty (A.elems ids)

   <> foldr (\n r -> BS.int32BE  n <> r) mempty (A.elems ixs)

serialiseSize :: StringTable id -> Int

serialiseSize (StringTable strs offs _ids _ixs) =

    let (_, !ixEnd) = A.bounds offs

     in 4 * 2

      + BS.length strs

      + 4 * (fromIntegral ixEnd + 1)

      + 8 *  fromIntegral ixEnd

deserialiseV1 :: BS.ByteString -> Maybe (StringTable id, BS.ByteString)

deserialiseV1 bs

  | BS.length bs >= 8

  , let lenStrs = fromIntegral (readWord32BE bs 0)

        lenArr  = fromIntegral (readWord32BE bs 4)

        lenTotal= 8 + lenStrs + 4 * lenArr

  , BS.length bs >= lenTotal

  , let strs = BS.take lenStrs (BS.drop 8 bs)

        arr  = A.array (0, fromIntegral lenArr - 1)

                       [ (i, readWord32BE bs off)

                       | (i, off) <- zip [0 .. fromIntegral lenArr - 1]

                                         [offArrS,offArrS+4 .. offArrE]

                       ]

        ids  = A.array (0, fromIntegral lenArr - 1)

                       [ (i,i) | i <- [0 .. fromIntegral lenArr - 1] ]

        ixs  = ids -- two identity mappings

        offArrS = 8 + lenStrs

        offArrE = offArrS + 4 * lenArr - 1

        !stringTable = StringTable strs arr ids ixs

        !bs'         = BS.drop lenTotal bs

  = Just (stringTable, bs')

  | otherwise

  = Nothing

deserialiseV2 :: BS.ByteString -> Maybe (StringTable id, BS.ByteString)

deserialiseV2 bs

  | BS.length bs >= 8

  , let lenStrs = fromIntegral (readWord32BE bs 0)

        lenArr  = fromIntegral (readWord32BE bs 4)

        lenTotal= 8                   -- the two length prefixes

                + lenStrs

                + 4 * lenArr

                +(4 * (lenArr - 1)) * 2 -- offsets array is 1 longer

  , BS.length bs >= lenTotal

  , let strs = BS.take lenStrs (BS.drop 8 bs)

        offs = A.listArray (0, fromIntegral lenArr - 1)

                           [ readWord32BE bs off

                           | off <- offsets offsOff ]

        -- the second two arrays are 1 shorter

        ids  = A.listArray (0, fromIntegral lenArr - 2)

                           [ readInt32BE bs off

                           | off <- offsets idsOff ]

        ixs  = A.listArray (0, fromIntegral lenArr - 2)

                           [ readInt32BE bs off

                           | off <- offsets ixsOff ]

        offsOff = 8 + lenStrs

        idsOff  = offsOff + 4 * lenArr

        ixsOff  = idsOff  + 4 * (lenArr-1)

        offsets from = [from,from+4 .. from + 4 * (lenArr - 1)]

        !stringTable = StringTable strs offs ids ixs

        !bs'         = BS.drop lenTotal bs

  = Just (stringTable, bs')

  | otherwise

  = Nothing

readInt32BE :: BS.ByteString -> Int -> Int32

readInt32BE bs i = fromIntegral (readWord32BE bs i)

readWord32BE :: BS.ByteString -> Int -> Word32

readWord32BE bs i =

    assert (i >= 0 && i+3 <= BS.length bs - 1) $

    fromIntegral (BS.unsafeIndex bs (i + 0)) `shiftL` 24

  + fromIntegral (BS.unsafeIndex bs (i + 1)) `shiftL` 16

  + fromIntegral (BS.unsafeIndex bs (i + 2)) `shiftL` 8

  + fromIntegral (BS.unsafeIndex bs (i + 3))

#ifdef TESTS

prop_valid :: [BS.ByteString] -> Bool

prop_valid strs =

     all lookupIndex (enumStrings tbl)

  && all indexLookup (enumIds tbl)

  where

    tbl :: StringTable Int

    tbl = construct strs

    lookupIndex str = index tbl ident == str

      where Just ident = lookup tbl str

    indexLookup ident = lookup tbl str == Just ident

      where str       = index tbl ident

-- this is important so we can use Map.fromAscList

prop_sorted :: [BS.ByteString] -> Bool

prop_sorted strings =

    isSorted [ index' strs offsets ix

             | ix <- A.range (A.bounds ids) ]

  where

    _tbl :: StringTable Int

    _tbl@(StringTable strs offsets ids _ixs) = construct strings

    isSorted xs = and (zipWith (<) xs (tail xs))

prop_finalise_unfinalise :: [BS.ByteString] -> Bool

prop_finalise_unfinalise strs =

    builder == unfinalise (finalise builder)

  where

    builder :: StringTableBuilder Int

    builder = foldl' (\tbl s -> fst (insert s tbl)) empty strs

prop_serialise_deserialise :: [BS.ByteString] -> Bool

prop_serialise_deserialise strs =

    Just (strtable, BS.empty) == (deserialiseV2

                                . toStrict . BS.toLazyByteString

                                . serialise) strtable

  where

    strtable :: StringTable Int

    strtable = construct strs

prop_serialiseSize :: [BS.ByteString] -> Bool

prop_serialiseSize strs =

    (fromIntegral . LBS.length . BS.toLazyByteString . serialise) strtable

 == serialiseSize strtable

  where

    strtable :: StringTable Int

    strtable = construct strs

enumStrings :: Enum id => StringTable id -> [BS.ByteString]

enumStrings (StringTable bs offsets _ _) = map (index' bs offsets) [0..h-1]

  where (0,h) = A.bounds offsets

enumIds :: Enum id => StringTable id -> [id]

enumIds (StringTable _ offsets _ _) = [toEnum 0 .. toEnum (fromIntegral (h-1))]

  where (0,h) = A.bounds offsets

toStrict :: LBS.ByteString -> BS.ByteString

#if MIN_VERSION_bytestring(0,10,0)

toStrict = LBS.toStrict

#else

toStrict = BS.concat . LBS.toChunks

#endif

#endif

#if !(MIN_VERSION_base(4,5,0))

(<>) :: Monoid m => m -> m -> m

(<>) = mappend

#endif