{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE UndecidableInstances #-}


module Servant.GTFS.Realtime (Proto) where

import Servant
    ( MimeRender(..),
      MimeUnrender(mimeUnrender),
      Accept(contentType),
      Proxy(Proxy) )
import Text.ProtocolBuffers
    ( Wire, ReflectDescriptor, messagePut, messageGet )
import Network.HTTP.Media ((//))
import Data.Either.Combinators (mapRight)
import Data.Swagger (ToSchema(..))


-- | A servant encoding for protobuf-encoded messages
data Proto

instance Accept Proto where
  contentType _ = "application" // "octet-stream"

instance (Wire msg, ReflectDescriptor msg) => MimeUnrender Proto msg where
  mimeUnrender _ = mapRight fst . messageGet @msg

instance (Wire msg, ReflectDescriptor msg) => MimeRender Proto msg where
  mimeRender _ = messagePut

-- TODO: this instance is horrible; ideally it should at least include
-- the name of the message type (if at all possible)
instance {-# OVERLAPPABLE #-} Wire msg => ToSchema msg where
  declareNamedSchema _ = declareNamedSchema (Proxy @String)