{-# language StandaloneKindSignatures #-}

module Rel8.Type.JSONEncoded ( JSONEncoded(..) ) where

-- aeson
import Data.Aeson ( FromJSON, ToJSON, parseJSON, toJSON )
import Data.Aeson.Types ( parseEither )

-- base
import Data.Kind ( Type )
import Prelude

-- rel8
import Rel8.Type ( DBType(..) )
import Rel8.Type.Information ( parseTypeInformation )


-- | A deriving-via helper type for column types that store a Haskell value
-- using a JSON encoding described by @aeson@'s 'ToJSON' and 'FromJSON' type
-- classes.
type JSONEncoded :: Type -> Type
newtype JSONEncoded a = JSONEncoded { fromJSONEncoded :: a }


instance (FromJSON a, ToJSON a) => DBType (JSONEncoded a) where
  typeInformation = parseTypeInformation f g typeInformation
    where
      f = fmap JSONEncoded . parseEither parseJSON
      g = toJSON . fromJSONEncoded