{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE AllowAmbiguousTypes #-}

-- | Standard test `Spec`s and raw `Property`s for `FromJSON` and `ToJSON` instances.
--
-- You will need @TypeApplications@ to use these.
module Test.Validity.Aeson
    ( jsonSpecOnValid
    , jsonSpec
    , jsonSpecOnArbitrary
    , jsonSpecOnGen
    , neverFailsToEncodeOnGen
    , encodeAndDecodeAreInversesOnGen
    ) where

import Data.GenValidity

import Control.DeepSeq (deepseq)
import Control.Exception (evaluate)
import Control.Monad
import Data.Aeson (FromJSON, ToJSON)
import qualified Data.Aeson as JSON
import Data.Typeable
import Test.Hspec
import Test.QuickCheck
import Test.Validity.Utils

-- | Standard test spec for properties of JSON-related functions for valid values
--
-- Example usage:
--
-- > jsonSpecOnValid @Rational
jsonSpecOnValid ::
       forall a. (Show a, Eq a, Typeable a, GenValid a, FromJSON a, ToJSON a)
    => Spec
jsonSpecOnValid = jsonSpecOnGen (genValid @a) "valid" shrinkValid

-- | Standard test spec for properties of JSON-related functions for unchecked values
--
-- Example usage:
--
-- > jsonSpec @Int
jsonSpec ::
       forall a.
       (Show a, Eq a, Typeable a, GenUnchecked a, FromJSON a, ToJSON a)
    => Spec
jsonSpec = jsonSpecOnGen (genUnchecked @a) "unchecked" shrinkUnchecked

-- | Standard test spec for properties of JSON-related functions for arbitrary values
--
-- Example usage:
--
-- > jsonSpecOnArbitrary @Int
jsonSpecOnArbitrary ::
       forall a. (Show a, Eq a, Typeable a, Arbitrary a, FromJSON a, ToJSON a)
    => Spec
jsonSpecOnArbitrary = jsonSpecOnGen (arbitrary @a) "arbitrary" shrink

-- | Standard test spec for properties of JSON-related functions for a given generator (and a name for that generator).
--
-- Example usage:
--
-- > jsonSpecOnGen (genListOf $ pure 'a') "sequence of 'a's"
jsonSpecOnGen ::
       forall a. (Show a, Eq a, Typeable a, FromJSON a, ToJSON a)
    => Gen a
    -> String
    -> (a -> [a])
    -> Spec
jsonSpecOnGen gen genname s =
    parallel $ do
        let name = nameOf @a
        describe ("JSON " ++ name ++ " (" ++ genname ++ ")") $ do
            describe
                ("encode :: " ++ name ++ " -> Data.ByteString.Lazy.ByteString") $
                it
                    (unwords
                         [ "never fails to encode a"
                         , "\"" ++ genname
                         , name ++ "\""
                         ]) $
                neverFailsToEncodeOnGen gen s
            describe
                ("decode :: Data.ByteString.Lazy.ByteString -> Either String " ++
                 name) $
                it
                    (unwords
                         [ "ensures that encode and decode are inverses for"
                         , "\"" ++ genname
                         , name ++ "\"" ++ "'s"
                         ]) $
                encodeAndDecodeAreInversesOnGen gen s

-- |
--
-- prop> neverFailsToEncodeOnGen @Bool arbitrary shrink
-- prop> neverFailsToEncodeOnGen @Bool genUnchecked shrinkUnchecked
-- prop> neverFailsToEncodeOnGen @Bool genValid shrinkValid
-- prop> neverFailsToEncodeOnGen @Int arbitrary shrink
-- prop> neverFailsToEncodeOnGen @Int genUnchecked shrinkUnchecked
-- prop> neverFailsToEncodeOnGen @Int genValid shrinkValid
neverFailsToEncodeOnGen :: (Show a, ToJSON a) => Gen a -> (a -> [a]) -> Property
neverFailsToEncodeOnGen gen s =
    forAllShrink gen s $ \(a :: a) ->
        evaluate (deepseq (JSON.encode a) ()) `shouldReturn` ()

-- |
--
-- prop> encodeAndDecodeAreInversesOnGen @Bool arbitrary shrink
-- prop> encodeAndDecodeAreInversesOnGen @Bool genUnchecked shrinkUnchecked
-- prop> encodeAndDecodeAreInversesOnGen @Bool genValid shrinkValid
-- prop> encodeAndDecodeAreInversesOnGen @Int arbitrary shrink
-- prop> encodeAndDecodeAreInversesOnGen @Int genUnchecked shrinkUnchecked
-- prop> encodeAndDecodeAreInversesOnGen @Int genValid shrinkValid
encodeAndDecodeAreInversesOnGen ::
       (Show a, Eq a, FromJSON a, ToJSON a) => Gen a -> (a -> [a]) -> Property
encodeAndDecodeAreInversesOnGen gen s =
    forAllShrink gen s $ \(a :: a) ->
        let encoded = JSON.encode a
            errOrDecoded = JSON.eitherDecode encoded
         in case errOrDecoded of
                Left err ->
                    expectationFailure $
                    unlines
                        [ "Decoding failed with error"
                        , err
                        , "instead of decoding to"
                        , show a
                        , "'encode' encoded it to the json"
                        , show encoded
                        ]
                Right decoded ->
                    unless (decoded == a) $
                    expectationFailure $
                    unlines
                        [ "Decoding succeeded, but the decoded value"
                        , show decoded
                        , "differs from expected decoded value"
                        , show a
                        , "'encode' encoded it to the json"
                        , show encoded
                        ]