{-# LANGUAGE LambdaCase      #-}
{-# LANGUAGE RecordWildCards #-}

module Server.Ingest (handleTrackerRegister, handleTrainPing, handleWS) where
import           API                                 (Metrics (..),
                                                      RegisterJson (..))
import           Control.Concurrent.STM              (atomically, readTVar,
                                                      writeTQueue)
import           Control.Monad                       (forever, void, when)
import           Control.Monad.Catch                 (handle)
import           Control.Monad.Extra                 (ifM, mapMaybeM, whenJust)
import           Control.Monad.IO.Class              (MonadIO (liftIO))
import           Control.Monad.Logger                (LoggingT, logInfoN,
                                                      logWarnN)
import           Control.Monad.Reader                (ReaderT)
import qualified Data.Aeson                          as A
import qualified Data.ByteString.Char8               as C8
import           Data.Coerce                         (coerce)
import           Data.Functor                        ((<&>))
import qualified Data.Map                            as M
import           Data.Pool                           (Pool)
import           Data.Text                           (Text)
import           Data.Text.Encoding                  (decodeASCII, decodeUtf8)
import           Data.Time                           (NominalDiffTime,
                                                      UTCTime (..), addUTCTime,
                                                      getCurrentTime,
                                                      nominalDay)
import qualified Data.Vector                         as V
import           Database.Persist
import           Database.Persist.Postgresql         (SqlBackend)
import           Fmt                                 ((+|), (|+))
import qualified GTFS
import qualified Network.WebSockets                  as WS
import           Persist
import           Servant                             (err400, throwError)
import           Servant.Server                      (Handler)
import           Server.Util                         (ServiceM, getTzseries,
                                                      utcToSeconds)

import           Config                              (LoggingConfig,
                                                      ServerConfig)
import           Data.ByteString                     (ByteString)
import           Data.ByteString.Lazy                (toStrict)
import           Data.Foldable                       (minimumBy)
import           Data.Function                       (on, (&))
import qualified Data.Text                           as T
import           Data.Time.LocalTime.TimeZone.Series (TimeZoneSeries)
import qualified Data.UUID                           as UUID
import           Extrapolation                       (Extrapolator (..),
                                                      LinearExtrapolator (..),
                                                      euclid)
import           GTFS                                (seconds2Double)
import           Prometheus                          (decGauge, incGauge)
import           Server.Base                         (ServerState)



handleTrackerRegister
  :: Pool SqlBackend
  -> RegisterJson
  -> ServiceM Token
handleTrackerRegister dbpool RegisterJson{..} = do
  today <- liftIO getCurrentTime <&> utctDay
  expires <- liftIO $ getCurrentTime <&> addUTCTime validityPeriod
  runSql dbpool $ do
    TrackerKey tracker <- insert (Tracker expires False registerAgent Nothing)
    pure tracker
  where
    validityPeriod :: NominalDiffTime
    validityPeriod = nominalDay

handleTrainPing
  :: Pool SqlBackend
  -> ServerState
  -> ServerConfig
  -> LoggingT (ReaderT LoggingConfig Handler) a
  -> TrainPing
  -> LoggingT (ReaderT LoggingConfig Handler) (Maybe TrainAnchor)
handleTrainPing dbpool subscribers cfg onError ping@TrainPing{..} =
  isTokenValid dbpool trainPingToken >>= \case
  Nothing -> onError >> pure Nothing
  Just tracker@Tracker{..} -> do

    -- if the tracker is not associated with a ticket, it is probably
    -- just starting out on a new trip, or has finished an old one.
    maybeTicketId <- case trackerCurrentTicket of
      Just ticketId -> pure (Just ticketId)
      Nothing -> runSql dbpool $ do
        now <- liftIO getCurrentTime
        tickets <- selectList [ TicketDay ==. utctDay now, TicketCompleted ==. False ] []
        ticketsWithFirstStation <- flip mapMaybeM tickets
            (\ticket@(Entity ticketId _) -> do
              selectFirst [StopTicket ==. ticketId] [Asc StopSequence] >>= \case
                Nothing -> pure Nothing
                Just (Entity _ stop) -> do
                  station <- getJust (stopStation stop)
                  tzseries <- liftIO $ getTzseries cfg (GTFS.tzname (stopDeparture stop))
                  pure (Just (ticket, station, stop, tzseries)))

        if null ticketsWithFirstStation then pure Nothing else do
          let (closestTicket, _, _, _) = minimumBy
                -- (compare `on` euclid trainPingGeopos . stationGeopos . snd)
                (compare `on`
                 (\(Entity _ ticket, station, stop, tzseries) ->
                     let
                       runningDay = ticketDay ticket
                       spaceDistance = euclid trainPingGeopos (stationGeopos station)
                       timeDiff =
                         GTFS.toSeconds (stopDeparture stop) tzseries runningDay
                         - utcToSeconds now runningDay
                     in
                       euclid trainPingGeopos (stationGeopos station)
                       + abs (seconds2Double timeDiff / 3600)))
                ticketsWithFirstStation
          logInfoN
            $ "Tracker "+|UUID.toString (coerce trainPingToken)|+
            " is now handling ticket "+|UUID.toString (coerce (entityKey closestTicket))|+
            " (trip "+|ticketTripName (entityVal closestTicket)|+")."

          update trainPingToken
            [TrackerCurrentTicket =. Just (entityKey closestTicket)]

          pure (Just (entityKey closestTicket))

    ticketId <- case maybeTicketId of
      Just ticketId -> pure ticketId
      Nothing -> do
        logWarnN $ "Tracker "+|UUID.toString (coerce trainPingToken)|+
          " sent a ping, but no trips are running today."
        throwError err400

    runSql dbpool $ do
      ticket@Ticket{..} <- getJust ticketId

      stations <- selectList [ StopTicket ==. ticketId ] [Asc StopArrival]
         >>= mapM (\stop -> do
           station <- getJust (stopStation (entityVal stop))
           tzseries <- liftIO $ getTzseries cfg (GTFS.tzname (stopArrival (entityVal stop)))
           pure (entityVal stop, station, tzseries))
         <&> V.fromList

      shapePoints <- selectList [ShapePointShape ==. ticketShape] [Asc ShapePointIndex]
        <&> (V.fromList . fmap entityVal)

      let anchor = extrapolateAnchorFromPing LinearExtrapolator
                      ticketId ticket stations shapePoints ping

      insert ping

      last <- selectFirst [TrainAnchorTicket ==. ticketId] [Desc TrainAnchorWhen]
      -- only insert new estimates if they've actually changed anything
      when (fmap (trainAnchorDelay . entityVal) last /= Just (trainAnchorDelay anchor))
        $ void $ insert anchor

      -- are we at the final stop? if so, mark this ticket as done
      -- & the tracker as free
      let maxSequence = V.last stations
            & (\(stop, _, _) -> stopSequence stop)
            & fromIntegral
      when (trainAnchorSequence anchor + 0.1 >= maxSequence) $ do
        update trainPingToken
          [TrackerCurrentTicket =. Nothing]
        update ticketId
          [TicketCompleted =. True]
        logInfoN $ "Tracker "+|UUID.toString (coerce trainPingToken)|+
          " has completed ticket "+|UUID.toString (coerce ticketId)|+
          " (trip "+|ticketTripName|+")"

      queues <- liftIO $ atomically $ do
        queues <- readTVar subscribers <&> M.lookup (coerce ticketId)
        whenJust queues $
          mapM_ (\q -> writeTQueue q (Just ping))
        pure queues
      pure (Just anchor)

handleWS
  :: Pool SqlBackend
  -> ServerState
  -> ServerConfig
  -> Metrics
  -> WS.Connection -> ServiceM ()
handleWS dbpool subscribers cfg Metrics{..} conn = do
  liftIO $ WS.forkPingThread conn 30
  incGauge metricsWSGauge
  handle (\(e :: WS.ConnectionException) -> decGauge metricsWSGauge) $ forever $ do
    msg <- liftIO $ WS.receiveData conn
    case A.eitherDecode msg of
      Left err -> do
        logWarnN ("stray websocket message: "+|decodeASCII (toStrict msg)|+" (could not decode: "+|err|+")")
        liftIO $ WS.sendClose conn (C8.pack err)
        -- TODO: send a close msg (Nothing) to the subscribed queues?               decGauge metricsWSGauge
      Right ping -> do
        -- if invalid token, send a "polite" close request. Note that the client may
        -- ignore this and continue sending messages, which will continue to be handled.
        handleTrainPing dbpool subscribers cfg (liftIO $ WS.sendClose conn ("" :: ByteString)) ping >>= \case
          Just anchor -> liftIO $ WS.sendTextData conn (A.encode anchor)
          Nothing     -> pure ()

-- TODO: proper debug logging for expired tokens
isTokenValid :: Pool SqlBackend -> TrackerId -> ServiceM (Maybe Tracker)
isTokenValid dbpool token = runSql dbpool $ get token >>= \case
  Just tracker | not (trackerBlocked tracker) -> do
    ifM (hasExpired (trackerExpires tracker))
      (pure Nothing)
      (pure (Just tracker))
  _ -> pure Nothing

hasExpired :: MonadIO m => UTCTime -> m Bool
hasExpired limit = do
  now <- liftIO getCurrentTime
  pure (now > limit)