Source

aeson / Data / Aeson / Generic.hs

{-# LANGUAGE PatternGuards #-}

-- Module:      Data.Aeson.Generic
-- Copyright:   (c) 2011 MailRank, Inc.
--              (c) 2008, 2009 Lennart Augustsson
-- License:     BSD3
-- Maintainer:  Bryan O'Sullivan <bos@mailrank.com>
-- Stability:   experimental
-- 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
    (
      fromJSON
    , toJSON
    ) where

import Control.Applicative ((<$>))
import Control.Arrow (first)
import Control.Monad.State.Strict
import Data.Aeson.Functions (transformMap)
import Data.Aeson.Types hiding (FromJSON(..), ToJSON(..), fromJSON)
import Data.Generics
import Data.Int (Int8, Int16, Int32, Int64)
import Data.IntSet (IntSet)
import Data.Text (Text, pack, unpack)
import Data.Time.Clock (UTCTime)
import Data.Word (Word, Word8, Word16, Word32, Word64)
import qualified Data.Aeson.Types as T
import qualified Data.ByteString as B
import qualified Data.ByteString.Lazy as L
import qualified Data.Map as Map
import qualified Data.Traversable as T
import qualified Data.Set as Set
import qualified Data.Text.Lazy as L
import qualified Data.Vector as V

type T a = a -> Value

toJSON :: (Data a) => a -> Value
toJSON = toJSON_generic
         `ext1Q` list
         `ext1Q` vector
         `ext1Q` set
         `ext1Q` mapText
         `ext1Q` mapLazyText
         `ext1Q` mapString
         -- 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 Float)
         `extQ` (T.toJSON :: T Rational)
         `extQ` (T.toJSON :: T Char)
         `extQ` (T.toJSON :: T Text)
         `extQ` (T.toJSON :: T L.Text)
         `extQ` (T.toJSON :: T String)
         `extQ` (T.toJSON :: T B.ByteString)
         `extQ` (T.toJSON :: T L.ByteString)
         `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
    mapText m = Object . Map.map toJSON $ m
    mapLazyText m = Object . transformMap L.toStrict toJSON $ m
    mapString m = Object . transformMap pack 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 = error $ "Data.Aeson.Generic.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 mungeField ns) js

        -- Skip leading '_' in field name so we can use keywords
        -- etc. as field names.
        mungeField ('_':cs) = pack cs
        mungeField cs       = pack cs

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` list
             `ext1R` vector
             `ext1R` mapText
             `ext1R` mapLazyText
             `ext1R` mapString
             -- 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 Float)
             `extR` (value :: F Rational)
             `extR` (value :: F Char)
             `extR` (value :: F Text)
             `extR` (value :: F L.Text)
             `extR` (value :: F String)
             `extR` (value :: F B.ByteString)
             `extR` (value :: F L.ByteString)
             `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
    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
               _        -> modFail "parseJSON" $ "bad data: " ++ show j
    mapText :: (Data a) => Parser (Map.Map Text a)
    mapText = case j of
                Object js -> T.mapM parseJSON js
                _         -> modFail "parseJSON" $ "bad data: " ++ show j
    mapLazyText :: (Data a) => Parser (Map.Map L.Text a)
    mapLazyText = Map.mapKeysMonotonic L.fromStrict <$> parseJSON j
    mapString :: (Data a) => Parser (Map.Map String a)
    mapString = Map.mapKeysMonotonic unpack <$> parseJSON 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 (error "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 []   -- nullary constructor
          go 1 c []       jd         = construct c [jd] -- unary constructor
          go n c []       (Array js)
              | n > 1 = 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) . Map.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 sel
          where sel f = maybe (modFail "parseJSON" $ "field does not exist " ++
                               f) return $ Map.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 _ = error "resType"

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