{-# LANGUAGE NamedFieldPuns    #-}
{-# LANGUAGE OverloadedLists   #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE RecordWildCards   #-}
{-# LANGUAGE TypeApplications  #-}

module Server.GTFSRT (gtfsRealtimeServer) where

import qualified Data.Sequence                              as Seq
import           Data.Time.Clock.POSIX                      (getPOSIXTime)
import           Data.Time.Clock.System                     (SystemTime (systemSeconds),
                                                             getSystemTime)
import           GTFS.Realtime.Alert                        as AL (Alert (..))
import           GTFS.Realtime.Alert.Cause                  (Cause (CONSTRUCTION))
import           GTFS.Realtime.Alert.Effect                 (Effect (DETOUR))
import           GTFS.Realtime.Alert.SeverityLevel          (SeverityLevel (WARNING))
import           GTFS.Realtime.EntitySelector               as ES (EntitySelector (..))
import           GTFS.Realtime.FeedEntity                   as FE (FeedEntity (..))
import           GTFS.Realtime.FeedHeader                   (FeedHeader (FeedHeader))
import           GTFS.Realtime.FeedHeader.Incrementality    (Incrementality (FULL_DATASET))
import           GTFS.Realtime.FeedMessage                  as FM (FeedMessage (..))
import           GTFS.Realtime.TimeRange                    (TimeRange (TimeRange))
import           GTFS.Realtime.TranslatedString             (TranslatedString (TranslatedString))
import           GTFS.Realtime.TranslatedString.Translation (Translation (Translation))
import           GTFS.Realtime.TripDescriptor               as TD (TripDescriptor (..))
import           Prelude                                    hiding (id)
import           Text.ProtocolBuffers                       (Utf8 (Utf8),
                                                             defaultValue)
import           Text.ProtocolBuffers.WireMessage           (zzEncode64)

import           API                                        (GtfsRealtimeAPI)
import           Control.Monad.IO.Class                     (MonadIO (..))
import           Data.ByteString.Lazy                       (fromStrict)
import           Data.Functor                               ((<&>))
import           Data.Pool                                  (Pool)
import           Data.Sequence                              (Seq)
import           Data.Text                                  (Text)
import qualified Data.Text                                  as T
import           Data.Text.Encoding                         (encodeUtf8)
import           Data.Time                                  (Day)
import           Data.Time.Calendar                         (Day, toGregorian)
import qualified Data.UUID                                  as UUID
import           Database.Persist                           (Entity (Entity),
                                                             selectList)
import           Database.Persist.Postgresql                (SqlBackend)
import           GTFS                                       (GTFS)
import           Persist                                    (Announcement (..),
                                                             Key (..),
                                                             RunningTrip,
                                                             runSql)
import           Servant.API                                ((:<|>) (..))
import           Servant.Server                             (Handler (Handler),
                                                             Server)


uuidUtf8 :: UUID.UUID -> Utf8
uuidUtf8 = Utf8 . fromStrict . UUID.toASCIIBytes

toUtf8 :: Text -> Utf8
toUtf8 = Utf8 . fromStrict . encodeUtf8

-- | formats a day in the "stupid" format used by gtfs realtime
toStupidDate :: Day -> Utf8
toStupidDate date = toUtf8
  $ pad 4 year <> pad 2 month <> pad 2 day
  where (year, month, day) = toGregorian date
        pad len num = T.pack $ if ndigits < len
          then replicate (len - ndigits) '0' <> show num
          else show num
          where ndigits = length (show num)


gtfsRealtimeServer :: GTFS -> Pool SqlBackend -> Server GtfsRealtimeAPI
gtfsRealtimeServer gtfs dbpool = handleServiceAlerts :<|> handleTripUpdates :<|> handleVehiclePositions
  where handleServiceAlerts = runSql dbpool $ do
            -- TODO filter: only select current & future days
            announcements <- selectList [] []
            dFeedMessage $ Seq.fromList $ fmap mkAlert announcements
            where mkAlert (Entity (AnnouncementKey uuid) Announcement{..}) =
                    (dFeedEntity (uuidUtf8 uuid))
                    { alert =
                      (Just $ Alert
                        { active_period = [TimeRange Nothing Nothing defaultValue]
                        -- TODO: is this time range reasonable, needed, etc.?
                        , informed_entity =
                          [dEntitySelector
                           { trip =
                             Just (TripDescriptor
                             { trip_id = Just (toUtf8 announcementTrip)
                             , route_id = Nothing
                             , direction_id = Nothing
                             , start_time = Nothing
                             , start_date = Just (toStupidDate announcementDay)
                             , schedule_relationship = Nothing
                             , TD.ext'field = defaultValue
                             })
                           }
                          ]
                        , cause = Nothing
                        , effect = Nothing
                        , url = fmap (lang "de" . toUtf8) announcementUrl
                        , header_text = Just $ lang "de" (toUtf8 announcementHeader)
                        , description_text = Just $ lang "de" (toUtf8 announcementMessage)
                        , tts_header_text = Nothing
                        , tts_description_text = Nothing
                        , severity_level = Nothing
                        , image = Nothing
                        , image_alternative_text = Nothing
                        , AL.ext'field = defaultValue
                        }) }
        handleTripUpdates = runSql dbpool $ do
          -- TODO: how to propagate delay values to next stops?
          pure undefined
        handleVehiclePositions = runSql dbpool $ do
          -- TODO: how to know which trips are currently running?
          pure undefined


lang :: Utf8 -> Utf8 -> TranslatedString
lang code msg = TranslatedString [Translation msg (Just code) defaultValue] defaultValue

-- | a default FeedMessage, issued at the current system time
-- TODO: do we ever need incremental updates?
-- TODO: maybe instead use last update time?
dFeedMessage :: MonadIO m => Seq FeedEntity -> m FeedMessage
dFeedMessage entities = do
  now <- liftIO getSystemTime <&> systemSeconds
  pure $ FeedMessage
    { header = FeedHeader "2.0" (Just FULL_DATASET) (Just $ fromIntegral now) defaultValue
    , entity = entities
    , FM.ext'field = defaultValue
    }

-- | a dummy FeedEntity (use record updates to add meaningful values to this)
dFeedEntity :: Utf8 -> FeedEntity
dFeedEntity id = FeedEntity
  { id
  , is_deleted = Nothing
  , trip_update = Nothing
  , vehicle = Nothing
  , alert = Nothing
  , shape = Nothing
  , FE.ext'field = defaultValue
  }

dEntitySelector :: EntitySelector
dEntitySelector = EntitySelector
  { agency_id = Nothing
  , route_id = Nothing
  , route_type = Nothing
  , trip = Nothing
  , stop_id = Nothing
  , direction_id = Nothing
  , ES.ext'field = defaultValue
  }