{-# LANGUAGE AllowAmbiguousTypes     #-}
{-# LANGUAGE ConstrainedClassMethods #-}
{-# LANGUAGE ConstraintKinds         #-}
{-# LANGUAGE DataKinds               #-}
{-# LANGUAGE RecordWildCards         #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}

module Extrapolation (Extrapolator(..), LinearExtrapolator, linearDelay) where
import           Data.Foldable (maximumBy, minimumBy)
import           Data.Function (on)
import qualified Data.Map      as M
import           Data.Time     (Day, UTCTime (UTCTime, utctDay), diffUTCTime,
                                nominalDiffTimeToSeconds)
import qualified Data.Vector   as V
import           GHC.Float     (int2Double)
import           GHC.IO        (unsafePerformIO)
import Data.List.NonEmpty (NonEmpty)
import qualified Data.List.NonEmpty as NE

import           Persist       (Running (..), TrainAnchor (..), TrainPing (..))
import           GTFS          (Depth (Deep), GTFS (..), Shape (..), Stop (..),
                                Time, Trip (..), stationGeopos, toSeconds, Seconds(..), seconds2Double)

class Extrapolator a where
  -- | here's a position ping, guess things from that!
  extrapolateAnchorFromPing :: GTFS -> Running -> TrainPing -> TrainAnchor

  -- | extrapolate status at some time (i.e. "how much delay does the train have *now*?")
  extrapolateAtSeconds :: NonEmpty TrainAnchor -> Seconds -> Maybe TrainAnchor
  -- | extrapolate status at some places (i.e. "how much delay will it have at the next station?")
  extrapolateAtPosition :: NonEmpty TrainAnchor -> Double -> Maybe TrainAnchor

data LinearExtrapolator

instance Extrapolator LinearExtrapolator where
  -- TODO: this kind of sorting is bullshit; should look up depending on position,
  -- not time (else there's glitches)
  extrapolateAtSeconds history secondsNow =
    fmap (minimumBy (compare `on` difference))
    $ NE.nonEmpty $ NE.filter (\a -> trainAnchorWhen a < secondsNow) history
    where difference status = secondsNow - (trainAnchorWhen status)

  extrapolateAtPosition = error "todo!"

  extrapolateAnchorFromPing gtfs@GTFS{..} Running{..} ping@TrainPing{..} = TrainAnchor
    { trainAnchorCreated = trainPingTimestamp
    , trainAnchorTrip = runningTrip
    , trainAnchorDay = runningDay
    , trainAnchorWhen = utcToSeconds trainPingTimestamp runningDay
    -- either do this ^ as a "time when the train *should* be here" or
    -- replace it with a trainAnchorWhere; this isn't very useful to get
    -- delays at stations
    , trainAnchorDelay = Just (linearDelay gtfs trip ping runningDay)
    , trainAnchorMsg = Nothing
    }
    where Just trip = M.lookup runningTrip trips

linearDelay :: GTFS -> Trip Deep Deep -> TrainPing -> Day -> Seconds
linearDelay GTFS{..} trip@Trip{..} TrainPing{..} runningDay = unsafePerformIO $ do
  -- print (nextStop, lastStop)
  -- print expectedTravelTime
  -- -- print (((utcToSeconds trainPingTimestamp runningDay),  toSeconds (stopDeparture lastStop)))
  -- print (observedProgress, expectedProgress)

  -- these convoluted conversions necessary to get rounding in the right place
  pure $ Seconds $ round $ (expectedProgress - observedProgress) * int2Double (unSeconds expectedTravelTime)
  where closestPoint =
            minimumBy (compare `on` euclid (trainPingLat, trainPingLong)) line
        nextStop = snd $
            minimumBy (compare `on` fst)
            $ V.filter (\(dist,_) -> dist > 0)
            $ fmap (\stop -> (distanceAlongLine line closestPoint (stationGeopos $ stopStation stop), stop)) tripStops
        lastStop = snd $
            maximumBy (compare `on` fst)
            $ V.filter (\(dist,_) -> dist < 0)
            $ fmap (\stop -> (distanceAlongLine line closestPoint (stationGeopos $ stopStation stop), stop)) tripStops
        line = shapePoints tripShape
        expectedTravelTime =
            toSeconds (stopArrival nextStop) tzseries runningDay
            - toSeconds (stopDeparture lastStop) tzseries runningDay
        expectedProgress =
            seconds2Double (utcToSeconds trainPingTimestamp runningDay
                         - toSeconds (stopDeparture lastStop) tzseries runningDay)
            / seconds2Double expectedTravelTime
            -- where crop a
            --         | a < 0 = 0
            --         | a > 1 = 1
            --         | otherwise = a
        observedProgress =
            distanceAlongLine line (stationGeopos $ stopStation lastStop) closestPoint
            / distanceAlongLine line (stationGeopos $ stopStation lastStop) (stationGeopos $ stopStation nextStop)

distanceAlongLine :: V.Vector (Double, Double) -> (Double, Double) -> (Double, Double) -> Double
distanceAlongLine line p1 p2 = along2 - along1
  where along1 = along p1
        along2 = along p2
        along p@(x,y) = snd
          $ foldl (\(p,a) p' -> (p', a + euclid p p')) (V.head line,0)
          $ V.take (index + 1) line
          where index = fst $ minimumBy (compare `on` (euclid p . snd))
                  $ V.indexed line

-- | 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)

euclid :: Fractional f => (f,f) -> (f,f) -> f
euclid (x1,y1) (x2,y2) = x*x + y*y
  where x = x1 - x2
        y = y1 - y2