{-# LANGUAGE FlexibleContexts #-}

-- | mostly the monad the service runs in
module Server.Util (Service, ServiceM, runService, sendErrorMsg, secondsNow, utcToSeconds) where

import           Control.Monad.IO.Class (MonadIO (liftIO))
import           Control.Monad.Logger   (LoggingT, runStderrLoggingT)
import qualified Data.Aeson             as A
import           Data.ByteString        (ByteString)
import           Data.Text              (Text)
import           Data.Time              (Day, UTCTime (..), diffUTCTime,
                                         getCurrentTime,
                                         nominalDiffTimeToSeconds)
import           GTFS                   (Seconds (..))
import           Servant                (Handler, ServerError, ServerT, err404,
                                         errBody, errHeaders, throwError)

type ServiceM  = LoggingT Handler
type Service api = ServerT api ServiceM

runService :: ServiceM a -> Handler a
runService = runStderrLoggingT

sendErrorMsg :: Text -> ServiceM a
sendErrorMsg msg = throwError err404
  { errBody = A.encode $ A.object ["error" A..= (404 :: Int), "msg" A..= msg] }

secondsNow :: MonadIO m => Day -> m Seconds
secondsNow runningDay = do
  now <- liftIO getCurrentTime
  pure $ utcToSeconds now runningDay

-- | convert utc time to seconds on a day, with wrap-around
-- for trains that cross midnight.
utcToSeconds :: UTCTime -> Day -> Seconds
utcToSeconds time day =
  Seconds $ round $ nominalDiffTimeToSeconds $ diffUTCTime time (UTCTime day 0)