{-# LANGUAGE BangPatterns #-}
{-# LANGUAGE CPP #-}
{-# LANGUAGE OverloadedStrings #-}
#if MIN_VERSION_ghc_prim(0,3,1)
{-# LANGUAGE MagicHash #-}
#endif

-- |
-- Module:      Data.Aeson.Parser.Internal
-- Copyright:   (c) 2011-2016 Bryan O'Sullivan
--              (c) 2011 MailRank, Inc.
-- License:     BSD3
-- Maintainer:  Bryan O'Sullivan <bos@serpentine.com>
-- Stability:   experimental
-- Portability: portable
--
-- Efficiently and correctly parse a JSON string.  The string must be
-- encoded as UTF-8.

module Data.Aeson.Parser.Internal
    (
    -- * Lazy parsers
      json, jsonEOF
    , value
    , jstring
    -- * Strict parsers
    , json', jsonEOF'
    , value'
    -- * Helpers
    , decodeWith
    , decodeStrictWith
    , eitherDecodeWith
    , eitherDecodeStrictWith
    ) where

import Prelude ()
import Prelude.Compat

import Data.Aeson.Types.Internal (IResult(..), JSONPath, Result(..), Value(..))
import Data.Attoparsec.ByteString.Char8 (Parser, char, endOfInput, scientific, skipSpace, string)
import Data.Attoparsec.ByteString.Char8 (Parser, char, endOfInput, scientific, skipSpace, string)
import Data.Bits ((.|.), shiftL)
import Data.ByteString.Internal (ByteString(..))
import Data.Char (chr)
import Data.Text (Text)
import Data.Vector as Vector (Vector, empty, fromListN, reverse)
import qualified Data.Attoparsec.ByteString as A
import qualified Data.Attoparsec.Lazy as L
import qualified Data.ByteString as B
import qualified Data.ByteString.Lazy as L
import qualified Data.HashMap.Strict as H
import Data.Aeson.Parser.Unescape

#if MIN_VERSION_ghc_prim(0,3,1)
import GHC.Base (Int#, (==#), isTrue#, word2Int#)
import GHC.Word (Word8(W8#))
#endif

#define BACKSLASH 92
#define CLOSE_CURLY 125
#define CLOSE_SQUARE 93
#define COMMA 44
#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

-- | Parse a top-level JSON value.
--
-- 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.
--
-- This function is an alias for 'value'. In aeson 0.8 and earlier, it
-- parsed only object or array types, in conformance with the
-- now-obsolete RFC 4627.
json :: Parser Value
json = value

-- | Parse a top-level JSON value.
--
-- 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.
--
-- This function is an alias for 'value''. In aeson 0.8 and earlier, it
-- parsed only object or array types, in conformance with the
-- now-obsolete RFC 4627.
json' :: Parser Value
json' = value'

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

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

objectValues :: Parser Text -> Parser Value -> Parser (H.HashMap Text Value)
objectValues str val = do
  skipSpace
  w <- A.peekWord8'
  if w == CLOSE_CURLY
    then A.anyWord8 >> return H.empty
    else loop []
 where
  -- Why use acc pattern here, you may ask? because 'H.fromList' use 'unsafeInsert'
  -- and it's much faster because it's doing in place update to the 'HashMap'!
  loop acc = do
    k <- str <* skipSpace <* char ':'
    v <- val <* skipSpace
    ch <- A.satisfy $ \w -> w == COMMA || w == CLOSE_CURLY
    let acc' = (k, v) : acc
    if ch == COMMA
      then skipSpace >> loop acc'
      else return (H.fromList acc')
{-# INLINE objectValues #-}

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

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

arrayValues :: Parser Value -> Parser (Vector Value)
arrayValues val = do
  skipSpace
  w <- A.peekWord8'
  if w == CLOSE_SQUARE
    then A.anyWord8 >> return Vector.empty
    else loop [] 1
  where
    loop acc !len = do
      v <- val <* skipSpace
      ch <- A.satisfy $ \w -> w == COMMA || w == CLOSE_SQUARE
      if ch == COMMA
        then skipSpace >> loop (v:acc) (len+1)
        else return (Vector.reverse (Vector.fromListN len (v:acc)))
{-# 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 :: Parser Value
value = do
  skipSpace
  w <- A.peekWord8'
  case w of
    DOUBLE_QUOTE  -> A.anyWord8 *> (String <$> jstring_)
    OPEN_CURLY    -> A.anyWord8 *> object_
    OPEN_SQUARE   -> A.anyWord8 *> array_
    C_f           -> string "false" *> pure (Bool False)
    C_t           -> string "true" *> pure (Bool True)
    C_n           -> string "null" *> pure Null
    _              | w >= 48 && w <= 57 || w == 45
                  -> Number <$> scientific
      | otherwise -> fail "not a valid json value"

-- | Strict version of 'value'. See also 'json''.
value' :: Parser Value
value' = do
  skipSpace
  w <- A.peekWord8'
  case w of
    DOUBLE_QUOTE  -> do
                     !s <- A.anyWord8 *> jstring_
                     return (String s)
    OPEN_CURLY    -> A.anyWord8 *> object_'
    OPEN_SQUARE   -> A.anyWord8 *> array_'
    C_f           -> string "false" *> pure (Bool False)
    C_t           -> string "true" *> pure (Bool True)
    C_n           -> string "null" *> pure Null
    _              | w >= 48 && w <= 57 || w == 45
                  -> do
                     !n <- scientific
                     return (Number n)
      | otherwise -> fail "not a valid json value"

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

-- | Parse a string without a leading quote.
jstring_ :: Parser Text
{-# INLINE jstring_ #-}
jstring_ = {-# SCC "jstring_" #-} do
  s <- A.scan startState go <* A.anyWord8
  case unescapeText s of
    Right r  -> return r
    Left err -> fail $ show err
 where
#if MIN_VERSION_ghc_prim(0,3,1)
    startState              = S 0#
    go (S a) (W8# c)
      | isTrue# a                     = Just (S 0#)
      | isTrue# (word2Int# c ==# 34#) = Nothing   -- double quote
      | otherwise = let a' = word2Int# c ==# 92#  -- backslash
                    in Just (S a')

data S = S Int#
#else
    startState              = False
    go a c
      | a                  = Just False
      | c == DOUBLE_QUOTE  = Nothing
      | otherwise = let a' = c == backslash
                    in Just a'
      where backslash = BACKSLASH
#endif

decodeWith :: Parser Value -> (Value -> Result a) -> L.ByteString -> Maybe a
decodeWith p to s =
    case L.parse p s of
      L.Done _ v -> case to v of
                      Success a -> Just a
                      _         -> Nothing
      _          -> Nothing
{-# INLINE decodeWith #-}

decodeStrictWith :: Parser Value -> (Value -> Result a) -> B.ByteString
                 -> Maybe a
decodeStrictWith p to s =
    case either Error to (A.parseOnly p s) of
      Success a -> Just a
      _         -> Nothing
{-# INLINE decodeStrictWith #-}

eitherDecodeWith :: Parser Value -> (Value -> IResult a) -> L.ByteString
                 -> Either (JSONPath, String) a
eitherDecodeWith p to s =
    case L.parse p s of
      L.Done _ v     -> case to v of
                          ISuccess a      -> Right a
                          IError path msg -> Left (path, msg)
      L.Fail _ _ msg -> Left ([], msg)
{-# INLINE eitherDecodeWith #-}

eitherDecodeStrictWith :: Parser Value -> (Value -> IResult a) -> B.ByteString
                       -> Either (JSONPath, String) a
eitherDecodeStrictWith p to s =
    case either (IError []) to (A.parseOnly p s) of
      ISuccess a      -> Right a
      IError path msg -> Left (path, msg)
{-# INLINE eitherDecodeStrictWith #-}

-- $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 :: Parser Value
jsonEOF = json <* skipSpace <* endOfInput

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