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

module Server.Ingest (handleTrackerRegister, handleTrainPing, handleWS) where
import           API                                 (Metrics (..),
                                                      RegisterJson (..),
                                                      SentPing (..))
import           Control.Concurrent.STM              (atomically, readTVar,
                                                      writeTQueue)
import           Control.Monad                       (forM, forever, unless,
                                                      void, when)
import           Control.Monad.Catch                 (handle)
import           Control.Monad.Extra                 (ifM, mapMaybeM, whenJust,
                                                      whenJustM)
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,
                                                      diffUTCTime,
                                                      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           Control.Exception                   (throw)
import           Control.Monad.Logger.CallStack      (logErrorN)
import           Data.ByteString                     (ByteString)
import           Data.ByteString.Lazy                (toStrict)
import           Data.Foldable                       (find, 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           GHC.Generics                        (Generic)
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
  -> SentPing
  -> LoggingT (ReaderT LoggingConfig Handler) (Maybe TrainAnchor)
handleTrainPing dbpool subscribers cfg onError ping@SentPing{..} =
  isTokenValid dbpool sentPingToken >>= \case
  Nothing -> onError >> pure Nothing
  Just tracker@Tracker{..} -> do

    -- unless (serverConfigDebugMode cfg) $ do
      -- now <- liftIO getCurrentTime
      -- let timeDiff = sentPingTimestamp `diffUTCTime` now
      -- when (utctDay sentPingTimestamp /= utctDay now) $ do
        -- logErrorN "received ping for wrong day"
        -- throw err400
      -- when (timeDiff < 10) $ do
        -- logWarnN "received ping more than 10 seconds out of date"
        -- throw err400
      -- when (timeDiff > 10) $ do
        -- logWarnN "received ping from more than 10 seconds in the future"
        -- throw err400

    ticketId <- case trackerCurrentTicket of
      Just ticketId -> pure ticketId
      -- if the tracker is not associated with a ticket, it is probably new
      -- & should be auto-associated with the most fitting current ticket
      Nothing -> runSql dbpool (guessTicketFromPing cfg ping) >>= \case
        Just ticketId -> pure ticketId
        Nothing -> do
          logWarnN $ "Tracker "+|UUID.toString (coerce sentPingToken)|+
            " sent a ping, but no trips are running today."
          throwError err400


    runSql dbpool $ insertSentPing subscribers cfg ping tracker ticketId

insertSentPing
  :: ServerState
  -> ServerConfig
  -> SentPing
  -> Tracker
  -> TicketId
  -> InSql (Maybe TrainAnchor)
insertSentPing subscribers cfg ping@SentPing{..} tracker@Tracker{..} ticketId = 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


  maybeReassign <- selectFirst
      [ TrainPingTicket ==. ticketId ]
      [ Desc TrainPingTimestamp ]
    <&> find (\ping -> trainPingSequence (entityVal ping) > trainAnchorSequence anchor)
    >> guessTicketFromPing cfg ping
    <&> find (/= ticketId)


      -- mapM (\newTicketId -> if ticketId /= newTicketId then Just newTicketId else Nothing))
    -- >>= (\ping -> guessTicketFromPing cfg ping >>= \case
    --   Just newTicketId | ticketId /= newTicketId -> pure (Just newTicketId)
    --   _ -> pure Nothing)

  case maybeReassign of
    Just newTicketId -> do
      update sentPingToken
        [TrackerCurrentTicket =. Just newTicketId ]
      logInfoN $ "tracker "+|UUID.toText (coerce sentPingToken)|+
        "has switched direction, and was reassigned to ticket "
        +|UUID.toText (coerce newTicketId)|+"."
      insertSentPing subscribers cfg ping tracker newTicketId
    Nothing -> do
      let trackedPing = TrainPing
           { trainPingToken = sentPingToken
           , trainPingGeopos = sentPingGeopos
           , trainPingTimestamp = sentPingTimestamp
           , trainPingSequence = trainAnchorSequence anchor
           , trainPingTicket = ticketId
           }

      insert trackedPing

      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 sentPingToken
          [TrackerCurrentTicket =. Nothing]
        update ticketId
          [TicketCompleted =. True]
        logInfoN $ "Tracker "+|UUID.toString (coerce sentPingToken)|+
          " 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 trackedPing))
        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 ()


guessTicketFromPing :: ServerConfig -> SentPing -> InSql (Maybe (Key Ticket))
guessTicketFromPing cfg SentPing{..} = do
  tickets <- selectList [ TicketDay ==. utctDay sentPingTimestamp, TicketCompleted ==. False ] []

  ticketsWithStation <- forM tickets (\ticket@(Entity ticketId _) -> do
    stops <- selectList [StopTicket ==. ticketId] [Asc StopSequence] >>= mapM (\(Entity _ stop) -> do
      station <- getJust (stopStation stop)
      tzseries <- liftIO $ getTzseries cfg (GTFS.tzname (stopDeparture stop))
      pure (station, stop, tzseries))
    pure (ticket, stops))

  if null ticketsWithStation then pure Nothing else do
    let (closestTicket, _) = ticketsWithStation
         & minimumBy (compare `on` (\(Entity _ ticket, stations) ->
            let
              runningDay = ticketDay ticket
              smallestDistance = stations
                <&> (\(station, stop, tzseries) -> spaceAndTimeDiff
                      (sentPingGeopos, utcToSeconds sentPingTimestamp runningDay)
                      (stationGeopos station, GTFS.toSeconds (stopDeparture stop) tzseries runningDay))
                & minimum
            in smallestDistance))

    logInfoN
      $ "Tracker "+|UUID.toString (coerce sentPingToken)|+
      " is now handling ticket "+|UUID.toString (coerce (entityKey closestTicket))|+
      " (trip "+|ticketTripName (entityVal closestTicket)|+")."

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

    pure (Just (entityKey closestTicket))

spaceAndTimeDiff :: (Geopos, GTFS.Seconds) -> (Geopos, GTFS.Seconds) -> Double
spaceAndTimeDiff (pos1, time1) (pos2, time2) =
  spaceDistance + abs (seconds2Double timeDiff / 3600)
  where spaceDistance = euclid pos1 pos2
        timeDiff = time1 - time2

-- 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)