{-# LANGUAGE BangPatterns  #-}
{-# LANGUAGE CPP           #-}
{-# LANGUAGE MagicHash     #-}
{-# LANGUAGE RankNTypes    #-}
{-# LANGUAGE UnboxedTuples #-}
-- |
-- Module      : Network.DNS.Pattern.Internal
-- Description : Internal DNS types and definitions
--
-- This module is not part of public API and may change even between patch versions.

module Network.DNS.Internal
  ( DomainLabel(..)
  , Domain(..)
  , DList(..)
  , toDList
  , fromDList
  , singleton
  , sbsMap
  , sbsSingleton
  , isLitChar
  , pprLabelsUtf16
  )

where

import           Data.ByteString.Internal (c2w)
import qualified Data.ByteString.Short as SBS
import           Data.Foldable (foldl')
import           Data.Function (on)
import qualified Data.Text as T
import           GHC.Word
import           Data.ByteString.Short.Internal (ShortByteString(SBS))
import qualified Data.Text.Array as T
import qualified Data.Text.Internal as T
import           GHC.ST (ST(..), runST)
#if !MIN_VERSION_bytestring(0,11,3)
import           GHC.Exts (Int(..), Int#, MutableByteArray#, indexWord8Array#,
                           isTrue#, newByteArray#, unsafeFreezeByteArray#,
                           writeWord8Array#, (+#), (<#))
#else
import           GHC.Exts (Int(..), Int#, MutableByteArray#, indexWord8Array#,
                           isTrue#, newByteArray#, unsafeFreezeByteArray#,
                           writeWord8Array#, (+#), (<#))
#endif

import           Network.DNS.Internal.Prim

isLitChar :: Word8 -> Bool
isLitChar c = (c >= c2w 'a' && c <= c2w 'z')
           || (c >= c2w '0' && c <= c2w '9')
           || (c >= c2w 'A' && c <= c2w 'Z')
           || (c == c2w '_')
           || (c == c2w '-')


-- | Domain label with case-insensitive 'Eq' and 'Ord' as per [RFC4343](https://datatracker.ietf.org/doc/html/rfc4343#section-3).
data DomainLabel = DomainLabel { getDomainLabel_ :: !SBS.ShortByteString
                               , getDomainLabelCF_ :: !SBS.ShortByteString }

-- | A domain parsed into labels. Each label is a 'SBS.ShortByteString' rather than 'T.Text' or 'String' because a label can contain arbitrary bytes.
-- However, the 'Ord' and 'Eq' instances do limited case-folding according to [RFC4343](https://datatracker.ietf.org/doc/html/rfc4343#section-3).
newtype Domain = Domain [DomainLabel] deriving (Eq, Ord)

instance Ord DomainLabel where
  (<=) = (<=) `on` getDomainLabelCF_
  compare = compare `on` getDomainLabelCF_

instance Eq DomainLabel where
  (==) = (==) `on` getDomainLabelCF_

-- | Difference list à la Huhges
newtype DList a = DList ([a] -> [a])

-- | Turn a list into 'DList'
{-# INLINE toDList #-}
toDList :: [a] -> DList a
toDList = DList . (++)

-- | Turn 'DList' back into a list.
{-# INLINE fromDList #-}
fromDList :: DList a -> [a]
fromDList (DList dl) = dl []

-- | Create a 'DList' containing just the specified element
{-# INLINE singleton #-}
singleton :: a -> DList a
singleton = DList . (:)

instance Semigroup (DList a) where
  {-# INLINE (<>) #-}
  DList l <> DList r = DList (l . r)

instance Monoid (DList a) where
  {-# INLINE mempty #-}
  mempty = DList id

{-# INLINE sbsSingleton #-}
sbsSingleton :: Word8 -> SBS.ShortByteString
#if MIN_VERSION_bytestring(0,11,3)
sbsSingleton = SBS.singleton
#else
sbsSingleton (W8# w) = runST $ ST $ \s1 ->
  case newByteArray# 1# s1 of
    (# s2, mba #) -> case writeWord8Array# mba 0# w s2 of
          s3 -> case unsafeFreezeByteArray# mba s3 of
             (# s4, ma #) -> (# s4, SBS ma #)

#endif

sbsMap :: (Word8 -> Word8) -> SBS.ShortByteString -> SBS.ShortByteString
#if MIN_VERSION_bytestring(0,11,3)
sbsMap = SBS.map
#else
sbsMap m sbs@(SBS ba) = runST $ ST $ \s1 ->
  case newByteArray# l# s1 of
    (# s2, mba #) -> case go mba 0# l# of
      ST f -> case f s2 of
        (# s3, _ #) -> case unsafeFreezeByteArray# mba s3 of
           (# s4, ma #) -> (# s4, SBS ma #)
  where
    !(I# l#) = SBS.length sbs
    go :: MutableByteArray# s -> Int# -> Int# -> ST s ()
    go !mba !i !l
      | I# i >= I# l = return ()
      | otherwise = (ST $ \s ->
          let !(W8# w') = m (W8# (indexWord8Array# ba i)) in
          (# writeWord8Array# mba i w' s, () #)
       ) >> go mba (i +# 1#) l
#endif

pprLabelsUtf16 :: [SBS.ShortByteString] -> T.Text
pprLabelsUtf16 xs@(_:_) = let SBS ba = createSBS (codePoints * 2) (go xs 0#)
                           in T.text (T.Array ba) 0 codePoints
  where
    -- We adjust for an extra codepoint to account per label for the dot separators.
    -- The case of root zone domain names (empty list, pretty-prints to ".") is handled
    -- in a separate `domainEncoderUtf16` definition below.
    codePoints = foldl' (\a x -> a + pprLabelCodepoints x + 1) 0 xs

    go (a:as) off mba  = do I# off' <- labelWriterUtf16 a off mba
                            writeWord8Array0 mba off' (c2w '.')
                            go as (off' +# 2#) mba

    go []     off _mba = pure ()
pprLabelsUtf16 [] = T.pack "."

domainEncoderUtf16 :: [a] -> ShortByteString
domainEncoderUtf16 [] = SBS.pack [c2w '.']

createSBS :: Int -> (forall s. MBA s -> ST s a) -> SBS.ShortByteString
createSBS len fill = runST $ do
  mba <- newByteArray len
  fill mba
  BA# ba# <- unsafeFreezeByteArray mba
  pure (SBS ba#)

pprLabelUtf16 :: SBS.ShortByteString -> SBS.ShortByteString
pprLabelUtf16 bs = createSBS (pprLabelCodepoints bs * 2) (labelWriterUtf16 bs 0#)

pprLabelCodepoints :: SBS.ShortByteString -> Int
pprLabelCodepoints sbs@(SBS ba) = go 0#
  where
    !(I# len) = SBS.length sbs
    go i# | isTrue# (i# <# len) =
            let a = W8# (indexWord8Array# ba i#)
             in case () of
                       _ | isLitChar a    -> go (i# +# 1#)
                         | a == c2w '\\'  -> go (i# +# 2#)
                         | a == c2w '.'   -> go (i# +# 2#)
                         | otherwise      -> go (i# +# 3#)
    go i = I# i

-- Create an ST action to write to a mutable byte array, starting at some offset. Returns
-- the new offset where we can resume writing to.
labelWriterUtf16 :: SBS.ShortByteString -> Int# -> MBA s -> ST s Int
labelWriterUtf16 sbs@(SBS ba) off mba = go 0# off
  where
    !(I# len) = SBS.length sbs

    go i# off | isTrue# (i# <# len)
           = let a = W8# (indexWord8Array# ba i#)
             in case () of
                       _ | isLitChar a
                         -> do writeWord8Array0 mba (off) a
                               go (i# +# 1#) (off +# 2#)

                         | a == c2w '\\'
                         -> do writeWord8Array0 mba (off)       (c2w '\\')
                               writeWord8Array0 mba (off +# 2#) (c2w '\\')
                               go (i# +# 1#) (off +# 4#)

                         | a == c2w '.'
                         -> do writeWord8Array0 mba (off)       (c2w '\\')
                               writeWord8Array0 mba (off +# 2#) (c2w '.')
                               go (i# +# 1#) (off +# 4#)

                         | otherwise
                         -> do writeWord8Array0 mba (off)       (c2w '\\')
                               writeWord8Array0 mba (off +# 2#) (c2w '0' + o1)
                               writeWord8Array0 mba (off +# 4#) (c2w '0' + o2)
                               writeWord8Array0 mba (off +# 6#) (c2w '0' + o3)
                               go (i# +# 1#) (off +# 8#)
                           where
                            (# o1, o2, o3 #) = case quotRem a 8 of
                                (v1, r3) -> case quotRem v1 8 of
                                    (v2, r2) -> case quotRem v2 8 of
                                      (_, r1) -> (# r1, r2, r3 #)
           | otherwise
           = pure (I# off)