{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE OverloadedStrings #-}
module Servant.API.Get where

import Control.Monad
import Control.Monad.IO.Class
import Control.Monad.Trans.Either
import Data.Aeson
import Data.Proxy
import Data.String.Conversions
import Network.HTTP.Types
import Network.URI
import Network.Wai
import Servant.Client
import Servant.Server

import qualified Network.HTTP.Client as Client

-- | Endpoint for simple GET requests. The server doesn't receive any arguments
-- and serves the contained type as JSON.
data Get a

instance ToJSON result => HasServer (Get result) where
  type Server (Get result) = EitherT (Int, String) IO result
  route Proxy action request
    | null (pathInfo request) && requestMethod request == methodGet = do
        e <- runEitherT action
        return $ Just $ case e of
          Right output ->
            responseLBS ok200 [("Content-Type", "application/json")] (encode output)
          Left (status, message) ->
            responseLBS (mkStatus status (cs message)) [] (cs message)
    | otherwise = return Nothing

instance FromJSON result => HasClient (Get result) where
  type Client (Get result) = URI -> EitherT String IO result
  clientWithRoute Proxy req uri = do
    innerRequest <- liftIO $ reqToRequest req uri

    innerResponse <- liftIO $ __withGlobalManager $ \ manager ->
      Client.httpLbs innerRequest manager
    when (Client.responseStatus innerResponse /= ok200) $
      left ("HTTP GET request failed with status: " ++ show (Client.responseStatus innerResponse))
    maybe (left "HTTP GET request returned invalid json") return $
      decode' (Client.responseBody innerResponse)