Data/Aeson/Generic.hs

{-# LANGUAGE PatternGuards, Rank2Types, ScopedTypeVariables, CPP #-}

-- |
-- Module: Data.Aeson.Generic
-- Copyright: (c) 2011, 2012, 2013 Bryan O'Sullivan
-- (c) 2011 MailRank, Inc.
-- (c) 2008, 2009 Lennart Augustsson
-- License: BSD3
-- Maintainer: Bryan O'Sullivan <bos@serpentine.com>
-- Stability: DEPRECATED
-- Portability: portable
--
-- JSON handling using 'Data.Generics'.
--
-- This is based on the 'Text.JSON.Generic' package originally written
-- by Lennart Augustsson.

module Data.Aeson.Generic
{-# DEPRECATED "This module will be /REMOVED/ in version 0.7.0.0. Please switch to GHC generics or Data.Aeson.TH instead. These alternatives are less buggy, faster, and more configurable." #-}
 (
 -- * Decoding and encoding
 decode
 , decode'
 , encode
 -- * Lower-level conversion functions
 , fromJSON
 , toJSON
 ) where

import Control.Applicative ((<$>))
import Control.Arrow (first)
import Control.Monad.State.Strict
import Data.Aeson.Functions
import Data.Aeson.Types hiding (FromJSON(..), ToJSON(..), fromJSON)
import Data.Attoparsec.Number (Number)
import Data.Generics
import Data.Hashable (Hashable)
import Data.Int (Int8, Int16, Int32, Int64)
import Data.IntSet (IntSet)
import Data.Maybe (fromJust)
import Data.Text (Text, pack, unpack)
import Data.Time.Clock (UTCTime)
import Data.Word (Word, Word8, Word16, Word32, Word64)
import Data.Aeson.Parser.Internal (decodeWith, json, json')
import qualified Data.Aeson.Encode as E
import qualified Data.Aeson.Types as T
import qualified Data.ByteString.Lazy as L
import qualified Data.HashMap.Strict as H
import qualified Data.Map as Map
import qualified Data.Set as Set
import qualified Data.Text as DT
import qualified Data.Text.Lazy as LT
import qualified Data.Traversable as T
import qualified Data.Vector as V

-- | Efficiently serialize a JSON value as a lazy 'L.ByteString'.
encode :: (Data a) => a -> L.ByteString
encode = E.encode . toJSON
{-# INLINE encode #-}

-- | Efficiently deserialize a JSON value from a lazy 'L.ByteString'.
-- If this fails due to incomplete or invalid input, 'Nothing' is
-- returned.
--
-- This function parses immediately, but defers conversion. See
-- 'json' for details.
decode :: (Data a) => L.ByteString -> Maybe a
decode = decodeWith json fromJSON
{-# INLINE decode #-}

-- | Efficiently deserialize a JSON value from a lazy 'L.ByteString'.
-- If this fails due to incomplete or invalid input, 'Nothing' is
-- returned.
--
-- This function parses and performs conversion immediately. See
-- 'json'' for details.
decode' :: (Data a) => L.ByteString -> Maybe a
decode' = decodeWith json' fromJSON
{-# INLINE decode' #-}

type T a = a -> Value

toJSON :: (Data a) => a -> Value
toJSON = toJSON_generic
 `ext1Q` maybe Null toJSON
 `ext1Q` list
 `ext1Q` vector
 `ext1Q` set
 `ext2Q'` mapAny
 `ext2Q'` hashMapAny
 -- Use the standard encoding for all base types.
 `extQ` (T.toJSON :: T Integer)
 `extQ` (T.toJSON :: T Int)
 `extQ` (T.toJSON :: T Int8)
 `extQ` (T.toJSON :: T Int16)
 `extQ` (T.toJSON :: T Int32)
 `extQ` (T.toJSON :: T Int64)
 `extQ` (T.toJSON :: T Word)
 `extQ` (T.toJSON :: T Word8)
 `extQ` (T.toJSON :: T Word16)
 `extQ` (T.toJSON :: T Word32)
 `extQ` (T.toJSON :: T Word64)
 `extQ` (T.toJSON :: T Double)
 `extQ` (T.toJSON :: T Number)
 `extQ` (T.toJSON :: T Float)
 `extQ` (T.toJSON :: T Rational)
 `extQ` (T.toJSON :: T Char)
 `extQ` (T.toJSON :: T Text)
 `extQ` (T.toJSON :: T LT.Text)
 `extQ` (T.toJSON :: T String)
 `extQ` (T.toJSON :: T T.Value)
 `extQ` (T.toJSON :: T DotNetTime)
 `extQ` (T.toJSON :: T UTCTime)
 `extQ` (T.toJSON :: T IntSet)
 `extQ` (T.toJSON :: T Bool)
 `extQ` (T.toJSON :: T ())
 --`extQ` (T.toJSON :: T Ordering)
 where
 list xs = Array . V.fromList . map toJSON $ xs
 vector v = Array . V.map toJSON $ v
 set s = Array . V.fromList . map toJSON . Set.toList $ s

 mapAny m
 | tyrep == typeOf DT.empty = remap id
 | tyrep == typeOf LT.empty = remap LT.toStrict
 | tyrep == typeOf "" = remap pack
 | otherwise = modError "toJSON" $
 "cannot convert map keyed by type " ++ show tyrep
 where tyrep = typeOf . head . Map.keys $ m
 remap f = Object . mapHashKeyVal (f . fromJust . cast) toJSON $ m

 hashMapAny m
 | tyrep == typeOf DT.empty = remap id
 | tyrep == typeOf LT.empty = remap LT.toStrict
 | tyrep == typeOf "" = remap pack
 | otherwise = modError "toJSON" $
 "cannot convert map keyed by type " ++ show tyrep
 where tyrep = typeOf . head . H.keys $ m
 remap f = Object . mapKeyVal (f . fromJust . cast) toJSON $ m

toJSON_generic :: (Data a) => a -> Value
toJSON_generic = generic
 where
 -- Generic encoding of an algebraic data type.
 generic a =
 case dataTypeRep (dataTypeOf a) of
 -- No constructor, so it must be an error value. Code
 -- it anyway as Null.
 AlgRep [] -> Null
 -- Elide a single constructor and just code the arguments.
 AlgRep [c] -> encodeArgs c (gmapQ toJSON a)
 -- For multiple constructors, make an object with a
 -- field name that is the constructor (except lower
 -- case) and the data is the arguments encoded.
 AlgRep _ -> encodeConstr (toConstr a) (gmapQ toJSON a)
 rep -> err (dataTypeOf a) rep
 where
 err dt r = modError "toJSON" $ "not AlgRep " ++
 show r ++ "(" ++ show dt ++ ")"
 -- Encode nullary constructor as a string.
 -- Encode non-nullary constructors as an object with the constructor
 -- name as the single field and the arguments as the value.
 -- Use an array if the are no field names, but elide singleton arrays,
 -- and use an object if there are field names.
 encodeConstr c [] = String . constrString $ c
 encodeConstr c as = object [(constrString c, encodeArgs c as)]

 constrString = pack . showConstr

 encodeArgs c = encodeArgs' (constrFields c)
 encodeArgs' [] [j] = j
 encodeArgs' [] js = Array . V.fromList $ js
 encodeArgs' ns js = object $ zip (map pack ns) js


fromJSON :: (Data a) => Value -> Result a
fromJSON = parse parseJSON

type F a = Parser a

parseJSON :: (Data a) => Value -> Parser a
parseJSON j = parseJSON_generic j
 `ext1R` maybeP
 `ext1R` list
 `ext1R` vector
 `ext2R'` mapAny
 `ext2R'` hashMapAny
 -- Use the standard encoding for all base types.
 `extR` (value :: F Integer)
 `extR` (value :: F Int)
 `extR` (value :: F Int8)
 `extR` (value :: F Int16)
 `extR` (value :: F Int32)
 `extR` (value :: F Int64)
 `extR` (value :: F Word)
 `extR` (value :: F Word8)
 `extR` (value :: F Word16)
 `extR` (value :: F Word32)
 `extR` (value :: F Word64)
 `extR` (value :: F Double)
 `extR` (value :: F Number)
 `extR` (value :: F Float)
 `extR` (value :: F Rational)
 `extR` (value :: F Char)
 `extR` (value :: F Text)
 `extR` (value :: F LT.Text)
 `extR` (value :: F String)
 `extR` (value :: F T.Value)
 `extR` (value :: F DotNetTime)
 `extR` (value :: F UTCTime)
 `extR` (value :: F IntSet)
 `extR` (value :: F Bool)
 `extR` (value :: F ())
 where
 value :: (T.FromJSON a) => Parser a
 value = T.parseJSON j
 maybeP :: (Data a) => Parser (Maybe a)
 maybeP = if j == Null then return Nothing else Just <$> parseJSON j
 list :: (Data a) => Parser [a]
 list = V.toList <$> parseJSON j
 vector :: (Data a) => Parser (V.Vector a)
 vector = case j of
 Array js -> V.mapM parseJSON js
 _ -> myFail

 mapAny :: forall e f. (Data e, Data f) => Parser (Map.Map f e)
 mapAny
 | tyrep == typeOf DT.empty = process id
 | tyrep == typeOf LT.empty = process LT.fromStrict
 | tyrep == typeOf "" = process DT.unpack
 | otherwise = myFail
 where
 process f = maybe myFail return . cast =<< parseWith f
 parseWith :: (Ord c) => (Text -> c) -> Parser (Map.Map c e)
 parseWith f = case j of
 Object js -> Map.fromList . map (first f) . H.toList <$>
 T.mapM parseJSON js
 _ -> myFail
 tyrep = typeOf (undefined :: f)

 hashMapAny :: forall e f. (Data e, Data f) => Parser (H.HashMap f e)
 hashMapAny
 | tyrep == typeOf DT.empty = process id
 | tyrep == typeOf LT.empty = process LT.fromStrict
 | tyrep == typeOf "" = process DT.unpack
 | otherwise = myFail
 where
 process f = maybe myFail return . cast =<< parseWith f
 parseWith :: (Eq c, Hashable c) => (Text -> c) -> Parser (H.HashMap c e)
 parseWith f = case j of
 Object js -> mapKey f <$> T.mapM parseJSON js
 _ -> myFail
 tyrep = typeOf (undefined :: f)

 myFail = modFail "parseJSON" $ "bad data: " ++ show j

parseJSON_generic :: (Data a) => Value -> Parser a
parseJSON_generic j = generic
 where
 typ = dataTypeOf $ resType generic
 generic = case dataTypeRep typ of
 AlgRep [] -> case j of
 Null -> return (modError "parseJSON" "empty type")
 _ -> modFail "parseJSON" "no-constr bad data"
 AlgRep [_] -> decodeArgs (indexConstr typ 1) j
 AlgRep _ -> do (c, j') <- getConstr typ j; decodeArgs c j'
 rep -> modFail "parseJSON" $
 show rep ++ "(" ++ show typ ++ ")"
 getConstr t (Object o) | [(s, j')] <- fromJSObject o = do
 c <- readConstr' t s
 return (c, j')
 getConstr t (String js) = do c <- readConstr' t (unpack js)
 return (c, Null) -- handle nullary ctor
 getConstr _ _ = modFail "parseJSON" "bad constructor encoding"
 readConstr' t s =
 maybe (modFail "parseJSON" $ "unknown constructor: " ++ s ++ " " ++
 show t)
 return $ readConstr t s

 decodeArgs c0 = go (numConstrArgs (resType generic) c0) c0
 (constrFields c0)
 where
 go 0 c _ Null = construct c []
 go 1 c [] jd = construct c [jd] -- unary constructor
 go _ c [] (Array js) = construct c (V.toList js) -- no field names
 -- FIXME? We could allow reading an array into a constructor
 -- with field names.
 go _ c fs@(_:_) (Object o) = selectFields o fs >>=
 construct c -- field names
 go _ c _ jd = modFail "parseJSON" $
 "bad decodeArgs data " ++ show (c, jd)

 fromJSObject = map (first unpack) . H.toList

 -- Build the value by stepping through the list of subparts.
 construct c = evalStateT $ fromConstrM f c
 where f :: (Data a) => StateT [Value] Parser a
 f = do js <- get
 case js of
 [] -> lift $ modFail "construct" "empty list"
 (j':js') -> do put js'; lift $ parseJSON j'

 -- Select the named fields from a JSON object.
 selectFields fjs = mapM $ \f ->
 maybe (modFail "parseJSON" $ "field does not exist " ++ f) return $
 H.lookup (pack f) fjs

 -- Count how many arguments a constructor has. The value x is
 -- used to determine what type the constructor returns.
 numConstrArgs :: (Data a) => a -> Constr -> Int
 numConstrArgs x c = execState (fromConstrM f c `asTypeOf` return x) 0
 where f = do modify (+1); return undefined

 resType :: MonadPlus m => m a -> a
 resType _ = modError "parseJSON" "resType"

modFail :: (Monad m) => String -> String -> m a
modFail func err = fail $ "Data.Aeson.Generic." ++ func ++ ": " ++ err

modError :: String -> String -> a
modError func err = error $ "Data.Aeson.Generic." ++ func ++ ": " ++ err


-- Type extension for binary type constructors.

-- | Flexible type extension
#if MIN_VERSION_base(4,7,0)
ext2' :: (Data a, Typeable t)
#else
ext2' :: (Data a, Typeable2 t)
#endif
 => c a
 -> (forall d1 d2. (Data d1, Data d2) => c (t d1 d2))
 -> c a
ext2' def ext = maybe def id (dataCast2 ext)

-- | Type extension of queries for type constructors
#if MIN_VERSION_base(4,7,0)
ext2Q' :: (Data d, Typeable t)
#else
ext2Q' :: (Data d, Typeable2 t)
#endif
 => (d -> q)
 -> (forall d1 d2. (Data d1, Data d2) => t d1 d2 -> q)
 -> d -> q
ext2Q' def ext = unQ ((Q def) `ext2'` (Q ext))

-- | Type extension of readers for type constructors
#if MIN_VERSION_base(4,7,0)
ext2R' :: (Monad m, Data d, Typeable t)
#else
ext2R' :: (Monad m, Data d, Typeable2 t)
#endif
 => m d
 -> (forall d1 d2. (Data d1, Data d2) => m (t d1 d2))
 -> m d
ext2R' def ext = unR ((R def) `ext2'` (R ext))

-- | The type constructor for queries
newtype Q q x = Q { unQ :: x -> q }

-- | The type constructor for readers
newtype R m x = R { unR :: m x }