newtype EventId =
  EventId
    { getEventId :: ByteString
    }
  deriving (Eq)

instance FromJSON EventId where
    parseJSON = withObject "EventId" $ \i -> do
        i' <- i .: "id"
        return $ fromJust $ eventId' i'

eventId' :: Text -> Maybe EventId
eventId' t = do
    bs <- Schnorr.decodeHex t
    case BS.length bs of
        32 -> Just $ EventId bs
        _  -> Nothing