{-# LANGUAGE BangPatterns, CPP, OverloadedStrings #-}
{-# OPTIONS_GHC -fno-warn-unused-binds #-}

module AesonBP where

import Data.ByteString.Builder
  (Builder, byteString, toLazyByteString, charUtf8, word8)

import Data.Bits ((.|.), shiftL)
import Data.ByteString (ByteString)
import Data.Char (chr)
import Data.Text (Text)
import Data.Text.Encoding (decodeUtf8')
import Data.Vector as Vector (Vector, fromList)
import Data.Word (Word8)
import System.FilePath ((</>))
import qualified Data.Attoparsec.Zepto as Z
import Data.Binary.Get (Get)
import qualified Data.Binary.Parser as BP
import qualified Data.ByteString as B
import qualified Data.ByteString.Lazy as L
import qualified Data.ByteString.Unsafe as B
import qualified Data.HashMap.Strict as H
import System.Directory (doesDirectoryExist)
import Aeson (Value(..))

#define BACKSLASH 92
#define CLOSE_CURLY 125
#define CLOSE_SQUARE 93
#define COMMA 44
#define COLON 58
#define DOUBLE_QUOTE 34
#define OPEN_CURLY 123
#define OPEN_SQUARE 91
#define C_0 48
#define C_9 57
#define C_A 65
#define C_F 70
#define C_a 97
#define C_f 102
#define C_n 110
#define C_t 116

pathTo :: String -> IO FilePath
pathTo wat = do
  exists <- doesDirectoryExist "bench"
  return $ if exists
           then "bench" </> wat
           else wat

data Result a = Error String
              | Success a
                deriving (Eq, Show)


-- | A JSON \"object\" (key\/value map).
type Object = H.HashMap Text Value

-- | A JSON \"array\" (sequence).
type Array = Vector Value

-- | Parse a top-level JSON value.  This must be either an object or
-- an array, per RFC 4627.
--
-- The conversion of a parsed value to a Haskell value is deferred
-- until the Haskell value is needed.  This may improve performance if
-- only a subset of the results of conversions are needed, but at a
-- cost in thunk allocation.
json :: Get Value
json = json_ object_ array_

-- | Parse a top-level JSON value.  This must be either an object or
-- an array, per RFC 4627.
--
-- This is a strict version of 'json' which avoids building up thunks
-- during parsing; it performs all conversions immediately.  Prefer
-- this version if most of the JSON data needs to be accessed.
json' :: Get Value
json' = json_ object_' array_'

json_ :: Get Value -> Get Value -> Get Value
json_ obj ary = do
  w <- BP.skipSpaces *> BP.satisfy (\w -> w == OPEN_CURLY || w == OPEN_SQUARE)
  if w == OPEN_CURLY
    then obj
    else ary
{-# INLINE json_ #-}

object_ :: Get Value
object_ = {-# SCC "object_" #-} Object <$> objectValues jstring value

object_' :: Get Value
object_' = {-# SCC "object_'" #-} do
  !vals <- objectValues jstring' value'
  return (Object vals)
 where
  jstring' = do
    !s <- jstring
    return s

objectValues :: Get Text -> Get Value -> Get (H.HashMap Text Value)
objectValues str val = do
  BP.skipSpaces
  let pair = liftA2 (,) (str <* BP.skipSpaces) (BP.word8 COLON *> BP.skipSpaces *> val)
  H.fromList <$> commaSeparated pair CLOSE_CURLY
{-# INLINE objectValues #-}

array_ :: Get Value
array_ = {-# SCC "array_" #-} Array <$> arrayValues value

array_' :: Get Value
array_' = {-# SCC "array_'" #-} do
  !vals <- arrayValues value'
  return (Array vals)

commaSeparated :: Get a -> Word8 -> Get [a]
commaSeparated item endByte = do
  w <- BP.peek
  if w == endByte
    then BP.skipN 1 >> return []
    else loop
  where
    loop = do
      v <- item <* BP.skipSpaces
      ch <- BP.satisfy $ \w -> w == COMMA || w == endByte
      if ch == COMMA
        then BP.skipSpaces >> (v:) <$> loop
        else return [v]
{-# INLINE commaSeparated #-}

arrayValues :: Get Value -> Get (Vector Value)
arrayValues val = do
  BP.skipSpaces
  Vector.fromList <$> commaSeparated val CLOSE_SQUARE
{-# INLINE arrayValues #-}

-- | Parse any JSON value.  You should usually 'json' in preference to
-- this function, as this function relaxes the object-or-array
-- requirement of RFC 4627.
--
-- In particular, be careful in using this function if you think your
-- code might interoperate with Javascript.  A na&#xef;ve Javascript
-- library that parses JSON data using @eval@ is vulnerable to attack
-- unless the encoded data represents an object or an array.  JSON
-- implementations in other languages conform to that same restriction
-- to preserve interoperability and security.
value :: Get Value
value = do
  w <- BP.peek
  case w of
    DOUBLE_QUOTE  -> BP.skipN 1 *> (String <$> jstring_)
    OPEN_CURLY    -> BP.skipN 1 *> object_
    OPEN_SQUARE   -> BP.skipN 1 *> array_
    C_f           -> BP.string "false" *> pure (Bool False)
    C_t           -> BP.string "true" *> pure (Bool True)
    C_n           -> BP.string "null" *> pure Null
    _              | w >= 48 && w <= 57 || w == 45
                  -> Number <$> BP.scientific
      | otherwise -> fail "not a valid json value"

-- | Strict version of 'value'. See also 'json''.
value' :: Get Value
value' = do
  w <- BP.peek
  case w of
    DOUBLE_QUOTE  -> do
                     !s <- BP.skipN 1 *> jstring_
                     return (String s)
    OPEN_CURLY    -> BP.skipN 1 *> object_'
    OPEN_SQUARE   -> BP.skipN 1 *> array_'
    C_f           -> BP.string "false" *> pure (Bool False)
    C_t           -> BP.string "true" *> pure (Bool True)
    C_n           -> BP.string "null" *> pure Null
    _              | w >= 48 && w <= 57 || w == 45
                  -> do
                     !n <- BP.scientific
                     return (Number n)
      | otherwise -> fail "not a valid json value"

-- | Parse a quoted JSON string.
jstring :: Get Text
jstring = BP.word8 DOUBLE_QUOTE *> jstring_

-- | Parse a string without a leading quote.
jstring_ :: Get Text
jstring_ = {-# SCC "jstring_" #-} do
  s <- BP.scan False $ \s c -> if s then Just False
                                   else if c == DOUBLE_QUOTE
                                        then Nothing
                                        else Just (c == BACKSLASH)
  BP.word8 DOUBLE_QUOTE
  s1 <- if BACKSLASH `B.elem` s
        then case Z.parse unescape s of
            Right r  -> return r
            Left err -> fail err
         else return s

  case decodeUtf8' s1 of
      Right r  -> return r
      Left err -> fail $ show err

{-# INLINE jstring_ #-}

unescape :: Z.Parser ByteString
unescape = toByteString <$> go mempty where
  go acc = do
    h <- Z.takeWhile (/=BACKSLASH)
    let rest = do
          start <- Z.take 2
          let !slash = B.unsafeHead start
              !t = B.unsafeIndex start 1
              escape = case B.findIndex (==t) "\"\\/ntbrfu" of
                         Just i -> i
                         _      -> 255
          if slash /= BACKSLASH || escape == 255
            then fail "invalid JSON escape sequence"
            else do
            let cont m = go (acc `mappend` byteString h `mappend` m)
                {-# INLINE cont #-}
            if t /= 117 -- 'u'
              then cont (word8 (B.unsafeIndex mapping escape))
              else do
                   a <- hexQuad
                   if a < 0xd800 || a > 0xdfff
                     then cont (charUtf8 (chr a))
                     else do
                       b <- Z.string "\\u" *> hexQuad
                       if a <= 0xdbff && b >= 0xdc00 && b <= 0xdfff
                         then let !c = ((a - 0xd800) `shiftL` 10) +
                                       (b - 0xdc00) + 0x10000
                              in cont (charUtf8 (chr c))
                         else fail "invalid UTF-16 surrogates"
    done <- Z.atEnd
    if done
      then return (acc `mappend` byteString h)
      else rest
  mapping = "\"\\/\n\t\b\r\f"

hexQuad :: Z.Parser Int
hexQuad = do
  s <- Z.take 4
  let hex n | w >= C_0 && w <= C_9 = w - C_0
            | w >= C_a && w <= C_f = w - 87
            | w >= C_A && w <= C_F = w - 55
            | otherwise          = 255
        where w = fromIntegral $ B.unsafeIndex s n
      a = hex 0; b = hex 1; c = hex 2; d = hex 3
  if (a .|. b .|. c .|. d) /= 255
    then return $! d .|. (c `shiftL` 4) .|. (b `shiftL` 8) .|. (a `shiftL` 12)
    else fail "invalid hex escape"

-- $lazy
--
-- The 'json' and 'value' parsers decouple identification from
-- conversion.  Identification occurs immediately (so that an invalid
-- JSON document can be rejected as early as possible), but conversion
-- to a Haskell value is deferred until that value is needed.
--
-- This decoupling can be time-efficient if only a smallish subset of
-- elements in a JSON value need to be inspected, since the cost of
-- conversion is zero for uninspected elements.  The trade off is an
-- increase in memory usage, due to allocation of thunks for values
-- that have not yet been converted.

-- $strict
--
-- The 'json'' and 'value'' parsers combine identification with
-- conversion.  They consume more CPU cycles up front, but have a
-- smaller memory footprint.

-- | Parse a top-level JSON value followed by optional whitespace and
-- end-of-input.  See also: 'json'.
jsonEOF :: Get Value
jsonEOF = json <* BP.skipSpaces

-- | Parse a top-level JSON value followed by optional whitespace and
-- end-of-input.  See also: 'json''.
jsonEOF' :: Get Value
jsonEOF' = json' <* BP.skipSpaces

toByteString :: Builder -> ByteString
toByteString = L.toStrict . toLazyByteString
{-# INLINE toByteString #-}