Utils.hs

{-# LANGUAGE ScopedTypeVariables #-}

module Test.Aeson.Internal.Utils where

import           Control.Exception

import           Data.Aeson
import           Data.ByteString.Lazy (ByteString)
import           Data.Proxy

import           Prelude

import           Test.Hspec
import           Test.QuickCheck

-- | put brackets around a String.
addBrackets :: String -> String
addBrackets s =
  if ' ' `elem` s
    then "(" ++ s ++ ")"
    else s

-- | [hspec](http://hspec.github.io/) style combinator to easily write tests
-- that check the a given operation returns the same value it was given, e.g.
-- roundtrip tests.
shouldBeIdentity :: (Eq a, Show a, Arbitrary a) =>
  Proxy a -> (a -> IO a) -> Property
shouldBeIdentity Proxy function =
  property $ \ (a :: a) -> function a `shouldReturn` a

-- | run decode in IO, if it returns Left then throw an error.
aesonDecodeIO :: FromJSON a => ByteString -> IO a
aesonDecodeIO bs = case eitherDecode bs of
  Right a -> return a
  Left msg -> throwIO $ ErrorCall
    ("aeson couldn't parse value: " ++ msg)