{-# LANGUAGE OverloadedStrings, DataKinds#-}
module Requester(request) where
  
import qualified Network.Wreq as N
import Network.HTTP.Client (HttpException)
import qualified Control.Exception as E
import Control.Lens.Getter ((^.))
import qualified Data.ByteString.Lazy as LBS
import Monad

url :: String
url = "https://md.darmstadt.ccc.de/mathechor-probenplanung/download"

eitherToFail :: (Show a, MonadFail m) => Either a b -> m b
eitherToFail (Right a) = return a
eitherToFail (Left b)  = fail $ show b

request :: (MonadIO m, MonadFail m) => m LBS.ByteString
request = do
  -- catch might seem to be more convenient instead of catch. But the handler in catch forces
  -- IO and not MonadIO, so we can't call fail. We use try to escape so we can escape IO first
  -- and then handle the error (with fail in scope)
  responseWithError <- liftIO (E.try (N.get url) :: IO (Either HttpException (N.Response LBS.ByteString)))
  response <- eitherToFail responseWithError
  return $ response ^. N.responseBody