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{-# LANGUAGE AllowAmbiguousTypes #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE MultiWayIf #-}
{-# LANGUAGE RecordWildCards #-}
module Extrapolation (Extrapolator(..), LinearExtrapolator(..), linearDelay, distanceAlongLine, euclid) where
import Data.Foldable (maximumBy, minimumBy)
import Data.Function (on)
import Data.List.NonEmpty (NonEmpty)
import qualified Data.List.NonEmpty as NE
import qualified Data.Map as M
import Data.Time (Day,
UTCTime (UTCTime, utctDay),
diffUTCTime,
getCurrentTime,
nominalDiffTimeToSeconds)
import qualified Data.Vector as V
import GHC.Float (int2Double)
import GHC.IO (unsafePerformIO)
import API (SentPing (..))
import Conduit (MonadIO (liftIO))
import Data.List (sortBy, sortOn)
import Data.Ord (Down (..))
import Data.Time.LocalTime.TimeZone.Series (TimeZoneSeries)
import GTFS (Seconds (..),
seconds2Double, toSeconds)
import Persist (Geopos (..),
ShapePoint (shapePointGeopos),
Station (..), Stop (..),
Ticket (..), TicketId,
Token (..), Tracker (..),
TrainAnchor (..))
import Server.Util (utcToSeconds)
-- | Determines how to extrapolate delays (and potentially other things) from the real-time
-- data sent in by the OBU. Potentially useful to swap out the algorithm, or give it options.
-- TODO: maybe split into two classes?
class Extrapolator strategy where
-- | here's a position ping, guess things from that!
extrapolateAnchorFromPing
:: strategy
-> TicketId
-> Ticket
-> V.Vector (Stop, Station, TimeZoneSeries)
-> V.Vector ShapePoint
-> SentPing
-> TrainAnchor
-- | extrapolate status at some time (i.e. "how much delay does the train have *now*?")
extrapolateAtSeconds :: strategy -> NonEmpty TrainAnchor -> Seconds -> Maybe TrainAnchor
-- | extrapolate status at some places (i.e. "how much delay will it have at the next station?")
extrapolateAtPosition :: strategy -> NonEmpty TrainAnchor -> Double -> Maybe TrainAnchor
data LinearExtrapolator = LinearExtrapolator
instance Extrapolator LinearExtrapolator where
extrapolateAtSeconds _ history secondsNow =
fmap (minimumBy (compare `on` difference))
$ NE.nonEmpty $ NE.filter (\a -> trainAnchorWhen a < secondsNow) history
where difference status = secondsNow - trainAnchorWhen status
-- note that this sorts (descending) for time first as a tie-breaker
-- (in case the train just stands still for a while, take the most recent update)
extrapolateAtPosition _ history positionNow =
fmap (minimumBy (compare `on` difference))
$ NE.nonEmpty $ sortOn (Down . trainAnchorCreated)
$ NE.filter (\a -> trainAnchorSequence a < positionNow) history
where difference status = positionNow - trainAnchorSequence status
extrapolateAnchorFromPing _ ticketId Ticket{..} stops shape ping@SentPing{..} = TrainAnchor
{ trainAnchorCreated = sentPingTimestamp
, trainAnchorTicket = ticketId
, trainAnchorWhen = utcToSeconds sentPingTimestamp ticketDay
, trainAnchorSequence
, trainAnchorDelay
, trainAnchorMsg = Nothing
}
where
(trainAnchorDelay, trainAnchorSequence) = linearDelay stops shape ping ticketDay
tzseries = undefined
linearDelay :: V.Vector (Stop, Station, TimeZoneSeries) -> V.Vector ShapePoint -> SentPing -> Day -> (Seconds, Double)
linearDelay tripStops shape SentPing{..} runningDay = (observedDelay, observedSequence)
where -- at which (fractional) sequence number is the ping?
observedSequence = int2Double (stopSequence lastStop)
+ observedProgress * int2Double (stopSequence nextStop - stopSequence lastStop)
-- how much later/earlier is the ping than would be expected?
observedDelay = Seconds $ round $
(expectedProgress - observedProgress) * int2Double (unSeconds expectedTravelTime)
+ if expectedProgress == 1
-- if the hypothetical on-time train is already at (or past) the next station,
-- just add the time distance we're behind
then seconds2Double (utcToSeconds sentPingTimestamp runningDay - nextSeconds)
-- otherwise the above is sufficient
else 0
-- how far along towards the next station is the ping (between 0 and 1)?
observedProgress =
distanceAlongLine line (stationGeopos lastStation) closestPoint
/ distanceAlongLine line (stationGeopos lastStation) (stationGeopos nextStation)
-- to compare: where would a linearly-moving train be (between 0 and 1)?
expectedProgress = if
| p < 0 -> 0
| p > 1 -> 1
| otherwise -> p
where p = seconds2Double (utcToSeconds sentPingTimestamp runningDay - lastSeconds)
/ seconds2Double expectedTravelTime
-- scheduled duration between last and next stops
expectedTravelTime = nextSeconds - lastSeconds
-- closest point on the shape; this is where we assume the train to be
closestPoint = minimumBy (compare `on` euclid sentPingGeopos) line
-- scheduled departure at last & arrival at next stop
lastSeconds = toSeconds (stopDeparture lastStop) lastTzSeries runningDay
nextSeconds = toSeconds (stopArrival nextStop) nextTzSeries runningDay
(lastStop, lastStation, lastTzSeries) = tripStops V.! (nextIndex - 1)
(nextStop, nextStation, nextTzSeries) = tripStops V.! nextIndex
line = fmap shapePointGeopos shape
-- index of the /next/ stop in the list, except when we're already at the last stop
-- (in which case it stays the same)
nextIndex = if
| null remaining -> length tripStops - 1
| idx' == 0 -> 1
| otherwise -> idx'
where idx' = fst $ V.minimumBy (compare `on` snd) remaining
remaining = V.filter (\(_,dist) -> dist > 0) $ V.indexed
$ fmap (distanceAlongLine line closestPoint . stationGeopos . \(_,stop,_) -> stop) tripStops
-- | approximate (but euclidean) distance along a geoline
distanceAlongLine :: V.Vector Geopos -> Geopos -> Geopos -> Double
distanceAlongLine line p1 p2 = along2 - along1
where along1 = along p1
along2 = along p2
along p@(Geopos (x,y)) =
sumSegments
$ V.take (index + 1) line
where index = V.minIndexBy (compare `on` euclid p) line
sumSegments :: V.Vector Geopos -> Double
sumSegments line = snd
$ foldl (\(p,a) p' -> (p', a + euclid p p')) (V.head line,0) line
-- | euclidean distance. Notably not applicable when you're on a sphere
-- (but good enough when the sphere is the earth)
euclid :: Geopos -> Geopos -> Double
euclid (Geopos (x1,y1)) (Geopos (x2,y2)) = sqrt (x*x + y*y)
where x = x1 - x2
y = y1 - y2
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