Update.hs

{-# LANGUAGE
    DeriveGeneric
  , OverloadedStrings
  #-}
module Vk.Update
  ( Update(..)
  )
where

import           Data.Aeson.Types               ( (.:)
                                                , FromJSON
                                                , Parser
                                                , parseJSON
                                                , withObject
                                                )
import           Data.Text                      ( Text )
import qualified Vk.Message                    as Message

data Update =
    NewMessage Message.Json
  | UnsupportedUpdate

instance FromJSON Update where
  parseJSON = withObject "" $ \upd -> do
    utype <- upd .: "type" :: Parser Text
    let obj = upd .: "object"
    case utype of
      "message_new" -> NewMessage <$> (obj >>= (.: "message"))
      _             -> return UnsupportedUpdate