{-# LANGUAGE DataKinds #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE KindSignatures #-}
{-# LANGUAGE StandaloneKindSignatures #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE StandaloneDeriving #-}
{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE LambdaCase #-}
{-# LANGUAGE RecordWildCards #-}
{-# LANGUAGE DeriveGeneric #-}
{-# LANGUAGE DeriveAnyClass #-}
{-# LANGUAGE DerivingStrategies #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}


module GTFS where


import qualified Data.ByteString.Lazy as LB
import qualified Data.ByteString as BS
import qualified Data.Csv as CSV
import Data.Csv ((.:))
import qualified Codec.Archive.Zip as Zip
import qualified Data.Vector as V
import Data.Vector (Vector)
import Text.Regex.TDFA ( (=~) )
import Data.Text (Text)
import Fmt ( (+|), (|+) )
import Data.Kind (Type)
import Data.Maybe (fromMaybe, fromJust)
import Data.Functor ((<&>))
import qualified Data.Time.Calendar.OrdinalDate as Day
import Data.Time.Calendar (Day, DayOfWeek(..))
import Data.Time.Calendar.MonthDay (monthAndDayToDayOfYearValid)
import Data.Time (getCurrentTime, UTCTime (utctDay), dayOfWeek)
import Data.Aeson (ToJSON, FromJSON)
import qualified Data.Aeson as A
import GHC.Generics (Generic)


newtype Time = Time { toSeconds :: Int }
  deriving newtype (ToJSON, FromJSON)

instance CSV.FromField Time where
  parseField f = do
    text :: String <- CSV.parseField f
    let (_,_,_,subs) = text =~ ("([0-9][0-9]?):([0-9][0-9]?):([0-9][0-9]?)" :: Text)
          :: (String, String, String, [String])
    case subs of
      [hh,mm,ss] -> pure $ Time $ read hh * 3600 + read mm * 60 + read ss
      _ -> fail $ "encountered an invalid date: " <> text

instance Show Time where
  show (Time seconds) = ""
    +|seconds `div` 3600|+":"
    +|(seconds `mod` 3600) `div` 60|+":"
    +|seconds `mod` 60|+""

instance CSV.FromField Day where
  parseField f = do
    text :: String <- CSV.parseField f
    let (_,_,_,subs) = text =~ ("([0-9][0-9][0-9][0-9])([0-9][0-9])([0-9][0-9])" :: Text)
          :: (String, String, String, [String])
    case subs of
      [yyyy,mm,dd] -> do
        let Just dayOfYear = monthAndDayToDayOfYearValid (Day.isLeapYear (read yyyy)) (read mm) (read dd)
        pure $ Day.fromOrdinalDate (read yyyy) dayOfYear
      _ -> fail $ "invalid date encountered: " <> show f



data Depth = Shallow | Deep
type Switch :: Depth -> Type -> Type -> Type
type family Switch c a b where
  Switch Deep a b = a
  Switch Shallow a b = b
type family Optional c a where
  Optional Deep a = a
  Optional Shallow _ = ()

type StationID = Text
type TripID = Text
type ServiceID = Text


-- | This is what's called a Stop in GTFS
data Station = Station
  { stationId :: StationID
  , stationName :: Text
  , stationLat :: Float
  , stationLon :: Float
  } deriving (Show, Generic, ToJSON)

-- | This is what's called a stop time in GTFS
data Stop (deep :: Depth) = Stop
  { stopTrip :: TripID
  , stopArrival :: Time
  , stopDeparture :: Time
  , stopStation:: Switch deep Station StationID
  , stopSequence :: Int
  } deriving Generic

deriving instance Show (Stop 'Shallow)
deriving instance Show (Stop 'Deep)
deriving instance ToJSON (Stop 'Deep)


data Calendar = Calendar
  { calServiceId :: Text
  , calMonday :: Bool
  , calTuesday :: Bool
  , calWednesday :: Bool
  , calThursday :: Bool
  , calFriday :: Bool
  , calSaturday :: Bool
  , calSunday :: Bool
  , calStartDate :: Day
  , calEndDate :: Day
  } deriving (Show, Generic, ToJSON)

data CalendarExceptionType = ServiceAdded | ServiceRemoved
  deriving (Show, Eq, Generic, ToJSON)

data CalendarDate = CalendarDate
  { caldateServiceId :: Text
  , caldateDate :: Day
  , caldateExceptionType :: CalendarExceptionType
  } deriving (Show, Generic, ToJSON)

data Trip (deep :: Depth) = Trip
  { tripRoute :: Text
  , tripTripID :: TripID
  , tripHeadsign :: Maybe Text
  , tripShortName :: Maybe Text
  , tripDirection :: Maybe Bool
  -- NOTE: there's also block_id, which we're unlikely to ever need
  , tripServiceId :: Text
  -- , tripWheelchairAccessible :: Bool
  -- , tripBikesAllowed :: Bool
  , tripShapeId :: Text
  , tripStops :: Optional deep (Vector (Stop deep))
  } deriving Generic

deriving instance Show (Trip Shallow)
deriving instance Show (Trip Deep)
deriving instance ToJSON (Trip Deep)

-- | helper function to find things in Vectors of things
tableLookup :: Eq key => (a -> key) -> key -> Vector a -> Maybe a
tableLookup proj key = V.find (\a -> proj a == key)

instance CSV.FromNamedRecord Station where
  parseNamedRecord r = Station
    <$> r .: "stop_id"
    <*> r .: "stop_name"
    <*> r .: "stop_lat"
    <*> r .: "stop_lon"

instance CSV.FromNamedRecord (Stop 'Shallow) where
  parseNamedRecord r = Stop
    <$> r .: "trip_id"
    <*> r .: "arrival_time"
    <*> r .: "departure_time"
    <*> r .: "stop_id"
    <*> r .: "stop_sequence"

instance CSV.FromNamedRecord Calendar where
  parseNamedRecord r = Calendar
    <$> r .: "service_id"
    <*> intAsBool' r "monday"
    <*> intAsBool' r "tuesday"
    <*> intAsBool' r "wednesday"
    <*> intAsBool' r "thursday"
    <*> intAsBool' r "friday"
    <*> intAsBool' r "saturday"
    <*> intAsBool' r "sunday"
    <*> r .: "start_date"
    <*> r .: "end_date"

intAsBool :: CSV.NamedRecord -> BS.ByteString -> CSV.Parser (Maybe Bool)
intAsBool r field = do
  int <- r .: field
  pure $ case int :: Int of
    1 -> Just True
    0 -> Just False
    _ -> Nothing

intAsBool' :: CSV.NamedRecord -> BS.ByteString -> CSV.Parser Bool
intAsBool' r field = intAsBool r field >>= maybe
  (fail "unexpected value for a boolean.")
  pure


instance CSV.FromNamedRecord CalendarDate where
  parseNamedRecord r = CalendarDate
    <$> r .: "service_id"
    <*> r .: "date"
    <*> do
      int <- r .: "exception_type"
      case int :: Int of
        1 -> pure ServiceAdded
        2 -> pure ServiceRemoved
        _ -> fail $ "unexpected value in exception_type: "+|int|+"."


instance CSV.FromNamedRecord (Trip Shallow) where
  parseNamedRecord r = Trip
    <$> r .: "route_id"
    <*> r .: "trip_id"
    <*> r .: "trip_headsign"
    <*> r .: "trip_short_name"
    <*> intAsBool r "direction_id"
    <*> r .: "service_id"
    -- NOTE: these aren't booleans but triple-values
    -- <*> intAsBool r "wheelchair_accessible"
    -- <*> intAsBool r "bikes_allowed"
    <*> r .: "shape_id"
    <*> pure ()

data GTFS (depth :: Depth) = GTFS
  { stations :: Vector Station
  , stops :: Vector (Stop depth)
  , trips :: Vector (Trip depth)
  , calendar :: Maybe (Vector Calendar)
  , calendarDates :: Maybe (Vector CalendarDate)
  }

deriving instance Show (GTFS Shallow)
deriving instance Show (GTFS Deep)

class Loadable depth where
  loadGtfs :: FilePath -> IO (GTFS depth)

instance Loadable Shallow where
  loadGtfs path = do
    zip <- Zip.toArchive <$> LB.readFile "./gtfs.zip"
    GTFS <$> decodeTable' "stops.txt" zip
         <*> decodeTable' "stop_times.txt" zip
         <*> decodeTable' "trips.txt" zip
         <*> decodeTable "calendar.txt" zip
         <*> decodeTable "calendar_dates.txt" zip
    where
      decodeTable :: CSV.FromNamedRecord a => FilePath -> Zip.Archive -> IO (Maybe (Vector a))
      decodeTable path zip = do
        case Zip.findEntryByPath path zip of
          Nothing -> pure Nothing
          Just csv -> case CSV.decodeByName (Zip.fromEntry csv) of
            Left err -> error $ "could not decode file "+|path|+": "+|err|+"."
            Right (_,v :: a) -> pure (Just v)
      decodeTable' path zip =
        decodeTable path zip >>= \case
          Nothing -> fail $ "required file "+|path|+" not found in gtfs.zip"
          Just a -> pure a

instance Loadable Deep where
  loadGtfs path = do
    shallow <- loadGtfs @Shallow path
    stops' <- V.mapM (pushStop (stations shallow)) (stops shallow)
    trips' <- V.mapM (pushTrip stops') (trips shallow)
    pure $ shallow { stops = stops', trips = trips' }
    where
      pushStop :: Vector Station -> Stop Shallow -> IO (Stop Deep)
      pushStop stations stop = do
        station <- case tableLookup stationId (stopStation stop) stations of
          Just a -> pure a
          Nothing -> fail $ "station with id "+|stopStation stop|+"is mentioned but not defined."
        pure $ stop { stopStation = station }
      pushTrip :: Vector (Stop Deep) -> Trip Shallow -> IO (Trip Deep)
      pushTrip stops trip = if V.length alongRoute < 2
          then fail $ "trip with id "+|tripTripID trip|+" has no stops"
          else pure $ trip { tripStops = alongRoute }
        where alongRoute = -- TODO: sort these according to stops
                V.filter (\s -> stopTrip s == tripTripID trip) stops



servicesOnDay :: GTFS Deep -> Day -> Vector ServiceID
servicesOnDay GTFS{..} day =
  fmap caldateServiceId added <> V.filter notCancelled regular
  where (added,removed) = case calendarDates of
          Nothing -> (mempty,mempty)
          Just exs ->
            V.partition (\cd -> caldateExceptionType cd == ServiceAdded)
            $ V.filter (\cd -> caldateDate cd == day) exs
        regular = case calendar of
          Nothing -> mempty
          Just cs -> V.mapMaybe (\cal -> if isRunning cal then Just (calServiceId cal) else Nothing) cs
          where isRunning Calendar{..} =
                  day >= calStartDate &&
                  day <= calEndDate &&
                  case weekday of
                    Monday -> calMonday
                    Tuesday -> calTuesday
                    Wednesday -> calWednesday
                    Thursday -> calThursday
                    Friday -> calFriday
                    Saturday -> calSaturday
                    Sunday -> calSunday
        weekday = dayOfWeek day
        notCancelled serviceID =
          null (tableLookup caldateServiceId serviceID removed)

tripsOfService :: GTFS Deep -> ServiceID -> Vector (Trip Deep)
tripsOfService GTFS{..} serviceId =
  V.filter (\trip -> tripServiceId trip == serviceId ) trips

-- TODO: this should filter out trips ending there
tripsAtStation :: GTFS Deep -> StationID -> Vector TripID
tripsAtStation GTFS{..} at = fmap stopTrip stops
  where
    stops = V.filter (\(stop :: Stop Deep) -> stationId (stopStation stop) == at) stops

tripsOnDay :: GTFS Deep -> Day -> Vector (Trip Deep)
tripsOnDay gtfs today = V.concatMap (tripsOfService gtfs) (servicesOnDay gtfs today)