Lens.hs

{-# LANGUAGE CPP #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE Trustworthy #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE DeriveDataTypeable #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE DefaultSignatures #-}
{-# OPTIONS_GHC -fno-warn-orphans #-}
--------------------------------------------------------------------
-- |
-- Copyright :  (c) Edward Kmett 2013-2014, (c) Paul Wilson 2012
-- License   :  BSD3
-- Maintainer:  Edward Kmett <ekmett@gmail.com>
-- Stability :  experimental
-- Portability: non-portable
--
--------------------------------------------------------------------
module Data.Aeson.Lens
  (
  -- * Numbers
    AsNumber(..)
  , _Integral
  , nonNull
  -- * Primitive
  , Primitive(..)
  , AsPrimitive(..)
  -- * Objects and Arrays
  , AsValue(..)
  , key, members
  , nth, values
  -- * Decoding
  , AsJSON(..)
  ) where

import Control.Lens
import Data.Aeson
import Data.Aeson.Parser (value)
import Data.Attoparsec.ByteString.Lazy (maybeResult, parse)
import Data.Scientific (Scientific)
import qualified Data.Scientific as Scientific
import qualified Data.ByteString as Strict
import Data.ByteString.Lazy.Char8 as Lazy hiding (putStrLn)
import Data.Data
import Data.HashMap.Strict (HashMap)
import Data.Text as Text
import Data.Text.Encoding
import Data.Vector (Vector)
import Prelude hiding (null)

-- $setup
-- >>> import Data.ByteString.Char8 as Strict.Char8
-- >>> :set -XOverloadedStrings

------------------------------------------------------------------------------
-- Scientific prisms
------------------------------------------------------------------------------

class AsNumber t where
  -- |
  -- >>> "[1, \"x\"]" ^? nth 0 . _Number
  -- Just 1.0
  --
  -- >>> "[1, \"x\"]" ^? nth 1 . _Number
  -- Nothing
  _Number :: Prism' t Scientific
#ifndef HLINT
  default _Number :: AsPrimitive t => Prism' t Scientific
  _Number = _Primitive._Number
  {-# INLINE _Number #-}
#endif

  -- |
  -- Prism into an 'Double' over a 'Value', 'Primitive' or 'Scientific'
  --
  -- >>> "[10.2]" ^? nth 0 . _Double
  -- Just 10.2
  _Double :: Prism' t Double
  _Double = _Number.iso Scientific.toRealFloat realToFrac
  {-# INLINE _Double #-}

  -- |
  -- Prism into an 'Integer' over a 'Value', 'Primitive' or 'Scientific'
  --
  -- >>> "[10]" ^? nth 0 . _Integer
  -- Just 10
  --
  -- >>> "[10.5]" ^? nth 0 . _Integer
  -- Just 10
  --
  -- >>> "42" ^? _Integer
  -- Just 42
  _Integer :: Prism' t Integer
  _Integer = _Number.iso floor fromIntegral
  {-# INLINE _Integer #-}

instance AsNumber Value where
  _Number = prism Number $ \v -> case v of Number n -> Right n; _ -> Left v
  {-# INLINE _Number #-}

instance AsNumber Scientific where
  _Number = id
  {-# INLINE _Number #-}

instance AsNumber Strict.ByteString
instance AsNumber Lazy.ByteString
instance AsNumber String

------------------------------------------------------------------------------
-- Conversion Prisms
------------------------------------------------------------------------------

-- | Access Integer 'Value's as Integrals.
--
-- >>> "[10]" ^? nth 0 . _Integral
-- Just 10
--
-- >>> "[10.5]" ^? nth 0 . _Integral
-- Just 10
_Integral :: (AsNumber t, Integral a) => Prism' t a
_Integral = _Number . iso floor fromIntegral
{-# INLINE _Integral #-}

------------------------------------------------------------------------------
-- Null values and primitives
------------------------------------------------------------------------------

-- | Primitives of 'Value'
data Primitive
  = StringPrim !Text
  | NumberPrim !Scientific
  | BoolPrim !Bool
  | NullPrim
  deriving (Eq,Ord,Show,Data,Typeable)

instance AsNumber Primitive where
  _Number = prism NumberPrim $ \v -> case v of NumberPrim s -> Right s; _ -> Left v
  {-# INLINE _Number #-}

class AsNumber t => AsPrimitive t where
  -- |
  -- >>> "[1, \"x\", null, true, false]" ^? nth 0 . _Primitive
  -- Just (NumberPrim 1.0)
  --
  -- >>> "[1, \"x\", null, true, false]" ^? nth 1 . _Primitive
  -- Just (StringPrim "x")
  --
  -- >>> "[1, \"x\", null, true, false]" ^? nth 2 . _Primitive
  -- Just NullPrim
  --
  -- >>> "[1, \"x\", null, true, false]" ^? nth 3 . _Primitive
  -- Just (BoolPrim True)
  --
  -- >>> "[1, \"x\", null, true, false]" ^? nth 4 . _Primitive
  -- Just (BoolPrim False)
  _Primitive :: Prism' t Primitive
#ifndef HLINT
  default _Primitive :: AsValue t => Prism' t Primitive
  _Primitive = _Value._Primitive
  {-# INLINE _Primitive #-}
#endif

  -- "{\"a\": \"xyz\", \"b\": true}" ^? key "a" . _String
  -- Just "xyz"
  --
  -- >>> "{\"a\": \"xyz\", \"b\": true}" ^? key "b" . _String
  -- Nothing
  --
  -- >>> _Object._Wrapped # [("key" :: Text, _String # "value")]
  -- "{\"key\":\"value\"}"
  _String :: Prism' t Text
  _String = _Primitive.prism StringPrim (\v -> case v of StringPrim s -> Right s; _ -> Left v)
  {-# INLINE _String #-}

  -- >>> "{\"a\": \"xyz\", \"b\": true}" ^? key "b" . _Bool
  -- Just True
  --
  -- "{\"a\": \"xyz\", \"b\": true}" ^? key "a" . _Bool
  -- Nothing
  --
  -- >>> _Bool # True
  -- "true"
  --
  -- >>> _Bool # False
  -- "false"
  _Bool :: Prism' t Bool
  _Bool = _Primitive.prism BoolPrim (\v -> case v of BoolPrim b -> Right b; _ -> Left v)
  {-# INLINE _Bool #-}

  -- >>> "{\"a\": \"xyz\", \"b\": null}" ^? key "b" . _Null
  -- Just ()
  --
  -- >>> "{\"a\": \"xyz\", \"b\": null}" ^? key "a" . _Null
  -- Nothing
  --
  -- >>> _Null # ()
  -- "null"
  _Null :: Prism' t ()
  _Null = _Primitive.prism (const NullPrim) (\v -> case v of NullPrim -> Right (); _ -> Left v)
  {-# INLINE _Null #-}


instance AsPrimitive Value where
  _Primitive = prism fromPrim toPrim
    where
      toPrim (String s) = Right $ StringPrim s
      toPrim (Number n) = Right $ NumberPrim n
      toPrim (Bool b)   = Right $ BoolPrim b
      toPrim Null       = Right NullPrim
      toPrim v          = Left v
      {-# INLINE toPrim #-}
      fromPrim (StringPrim s) = String s
      fromPrim (NumberPrim n) = Number n
      fromPrim (BoolPrim b)   = Bool b
      fromPrim NullPrim       = Null
      {-# INLINE fromPrim #-}
  {-# INLINE _Primitive #-}
  _String = prism String $ \v -> case v of String s -> Right s; _ -> Left v
  {-# INLINE _String #-}
  _Bool = prism Bool (\v -> case v of Bool b -> Right b; _ -> Left v)
  {-# INLINE _Bool #-}
  _Null = prism (const Null) (\v -> case v of Null -> Right (); _ -> Left v)
  {-# INLINE _Null #-}

instance AsPrimitive Strict.ByteString
instance AsPrimitive Lazy.ByteString
instance AsPrimitive String

instance AsPrimitive Primitive where
  _Primitive = id
  {-# INLINE _Primitive #-}

-- | Prism into non-'Null' values
--
-- >>> "{\"a\": \"xyz\", \"b\": null}" ^? key "a" . nonNull
-- Just (String "xyz")
--
-- >>> "{\"a\": {}, \"b\": null}" ^? key "a" . nonNull
-- Just (Object (fromList []))
--
-- >>> "{\"a\": \"xyz\", \"b\": null}" ^? key "b" . nonNull
-- Nothing
nonNull :: Prism' Value Value
nonNull = prism id (\v -> if isn't _Null v then Right v else Left v)
{-# INLINE nonNull #-}

------------------------------------------------------------------------------
-- Non-primitive traversals
------------------------------------------------------------------------------

class AsPrimitive t => AsValue t where
  -- |
  -- >>> "[1,2,3]" ^? _Value
  -- Just (Array (fromList [Number 1.0,Number 2.0,Number 3.0]))
  _Value :: Prism' t Value

  -- |
  -- >>> "{\"a\": {}, \"b\": null}" ^? key "a" . _Object
  -- Just (fromList [])
  --
  -- >>> "{\"a\": {}, \"b\": null}" ^? key "b" . _Object
  -- Nothing
  --
  -- >>> _Object._Wrapped # [("key" :: Text, _String # "value")] :: String
  -- "{\"key\":\"value\"}"
  _Object :: Prism' t (HashMap Text Value)
  _Object = _Value.prism Object (\v -> case v of Object o -> Right o; _ -> Left v)
  {-# INLINE _Object #-}

  -- |
  -- >>> "[1,2,3]" ^? _Array
  -- Just (fromList [Number 1.0,Number 2.0,Number 3.0])
  _Array :: Prism' t (Vector Value)
  _Array = _Value.prism Array (\v -> case v of Array a -> Right a; _ -> Left v)
  {-# INLINE _Array #-}

instance AsValue Value where
  _Value = id
  {-# INLINE _Value #-}

instance AsValue Strict.ByteString where
  _Value = _JSON
  {-# INLINE _Value #-}

instance AsValue Lazy.ByteString where
  _Value = _JSON
  {-# INLINE _Value #-}

instance AsValue String where
  _Value = utf8._JSON
  {-# INLINE _Value #-}

-- |
-- Like 'ix', but for 'Object' with Text indices. This often has better
-- inference than 'ix' when used with OverloadedStrings.
--
-- >>> "{\"a\": 100, \"b\": 200}" ^? key "a"
-- Just (Number 100.0)
--
-- >>> "[1,2,3]" ^? key "a"
-- Nothing
key :: AsValue t => Text -> Traversal' t Value
key i = _Object . ix i
{-# INLINE key #-}

-- | An indexed Traversal into Object properties
--
-- > "{\"a\": 4, \"b\": 7}" ^@.. members
-- [("a",Number 4.0),("b",Number 7.0)]
--
-- > "{\"a\": 4, \"b\": 7}" & members . _Number *~ 10
-- "{\"a\":40,\"b\":70}"
members :: AsValue t => IndexedTraversal' Text t Value
members = _Object . itraversed
{-# INLINE members #-}

-- | Like 'ix', but for Arrays with Int indexes
--
-- >>> "[1,2,3]" ^? nth 1
-- Just (Number 2.0)
--
-- >>> "\"a\": 100, \"b\": 200}" ^? nth 1
-- Nothing
--
-- >>> "[1,2,3]" & nth 1 .~ Number 20
-- "[1,20,3]"
nth :: AsValue t => Int -> Traversal' t Value
nth i = _Array . ix i
{-# INLINE nth #-}

-- | An indexed Traversal into Array elements
--
-- >>> "[1,2,3]" ^.. values
-- [Number 1.0,Number 2.0,Number 3.0]
--
-- >>> "[1,2,3]" & values . _Number *~ 10
-- "[10,20,30]"
values :: AsValue t => IndexedTraversal' Int t Value
values = _Array . traversed
{-# INLINE values #-}

utf8 :: Iso' String Strict.ByteString
utf8 = iso (encodeUtf8 . Text.pack) (Text.unpack . decodeUtf8)

class AsJSON t where
  -- | '_JSON' is a 'Prism' from something containing JSON to something encoded in that structure
  _JSON :: (FromJSON a, ToJSON a) => Prism' t a

instance AsJSON Strict.ByteString where
  _JSON = lazy._JSON
  {-# INLINE _JSON #-}

instance AsJSON Lazy.ByteString where
  _JSON = prism' encode decodeValue
    where
      decodeValue :: (FromJSON a) => Lazy.ByteString -> Maybe a
      decodeValue s = maybeResult (parse value s) >>= \x -> case fromJSON x of
        Success v -> Just v
        _         -> Nothing
  {-# INLINE _JSON #-}

instance AsJSON String where
  _JSON = utf8._JSON
  {-# INLINE _JSON #-}

instance AsJSON Value where
  _JSON = prism toJSON $ \x -> case fromJSON x of
    Success y -> Right y;
    _         -> Left x
  {-# INLINE _JSON #-}

------------------------------------------------------------------------------
-- Some additional tests for prismhood; see https://github.com/ekmett/lens/issues/439.
------------------------------------------------------------------------------

-- $LazyByteStringTests
-- >>> "42" ^? (_JSON :: Prism' Lazy.ByteString Value)
-- Just (Number 42.0)
--
-- >>> preview (_Integer :: Prism' Lazy.ByteString Integer) "42"
-- Just 42
--
-- >>> Lazy.unpack (review (_Integer :: Prism' Lazy.ByteString Integer) 42)
-- "42"

-- $StrictByteStringTests
-- >>> "42" ^? (_JSON :: Prism' Strict.ByteString Value)
-- Just (Number 42.0)
--
-- >>> preview (_Integer :: Prism' Strict.ByteString Integer) "42"
-- Just 42
--
-- >>> Strict.Char8.unpack (review (_Integer :: Prism' Strict.ByteString Integer) 42)
-- "42"

-- $StringTests
-- >>> "42" ^? (_JSON :: Prism' String Value)
-- Just (Number 42.0)
--
-- >>> preview (_Integer :: Prism' String Integer) "42"
-- Just 42
--
-- >>> review (_Integer :: Prism' String Integer) 42
-- "42"