server/src/Data.hs

{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE DeriveGeneric #-}
module Data (
      Key(..)
    , RW(..)
  ) where

import Data.Aeson (FromJSON(..), ToJSON(..), ToJSONKey(..), genericToEncoding)
import Data.Aeson.Types (toJSONKeyText)
import Data.Text (pack)
import GHC.Generics
import qualified JSON (defaultOptions)

class RW a b where
  get :: b -> a
  set :: a -> b -> b
  update :: (a ->  a) -> b -> b
  update f v =
    set (f (get v)) v

newtype Key a = Key Int deriving (Eq, Ord, Enum, Read, Show, Generic)

instance FromJSON (Key a)
instance ToJSON (Key a) where
  toEncoding = genericToEncoding JSON.defaultOptions

instance ToJSONKey (Key a) where
  toJSONKey = toJSONKeyText (pack . \(Key n) -> show n)