wat.hs

data CharacteristicType = DiffPresent | DiffData
  deriving (Show, Eq)

type family DiffType (t :: CharacteristicType) where
  DiffType 'DiffPresent = Bool
  DiffType 'DiffData = Maybe LevelData

data LevelInfo t = (Show (DiffType t), Eq (DiffType t), FromJSON (DiffType t)) =>
  LevelInfo
    { _infoEasy       :: DiffType t
    , _infoNormal     :: DiffType t
    , _infoHard       :: DiffType t
    , _infoExpert     :: DiffType t
    , _infoExpertPlus :: DiffType t
    }

deriving instance Show (LevelInfo t)
deriving instance Eq (LevelInfo t)

instance FromJSON (LevelInfo 'DiffPresent) where
  parseJSON = withObject "difficulties" $ \o -> do
    LevelInfo <$> o .: "easy"
              <*> o .: "normal"
              <*> o .: "hard"
              <*> o .: "expert"
              <*> o .: "expertPlus"

instance FromJSON (LevelInfo 'DiffData) where
  parseJSON = withObject "difficulties" $ \o -> do
    LevelInfo <$> o .: "easy"
              <*> o .: "normal"
              <*> o .: "hard"
              <*> o .: "expert"
              <*> o .: "expertPlus"