module Frontend.Tracklets
  ( TrackletSOA
  , trackletSOA
  , unTrackletSOA
  ) where

import Prelude

import Data.Argonaut.Core (Json)
import Data.Argonaut.Decode (class DecodeJson, JsonDecodeError(..), decodeJson, (.:))
import Data.Array (length, (!!))
import Data.DateTime (DateTime)
import Data.Either (Either, note)
import Data.Maybe (Maybe(..))
import Frontend.Util (secondsToDateTime)


type TrackletSOAData =
  { id :: Int
  , t :: Array Number
  , x :: Array Number
  , y :: Array Number
  , t0 :: DateTime
  }

newtype TrackletSOA = TrackletSOA TrackletSOAData


trackletSOA :: TrackletSOAData -> Maybe TrackletSOA
trackletSOA {id, t, x, y, t0}
  | length t == length x && length x == length y = Just $ TrackletSOA {id, t, x, y, t0}
  | otherwise = Nothing


unTrackletSOA :: TrackletSOA -> TrackletSOAData
unTrackletSOA (TrackletSOA d) = d


instance showTrackletSOA :: Show TrackletSOA where
  show (TrackletSOA {t0, t, x, y}) = "Tracklet with " <> show (length t) <> " points starting at " <> show t0


instance decodeJsonTracklets :: DecodeJson TrackletSOA where
  decodeJson :: Json -> Either JsonDecodeError TrackletSOA
  decodeJson json = do
    tracklet <- decodeJson json
    id <- tracklet .: "id"
    t <- tracklet .: "t"
    x <- tracklet .: "x"
    y <- tracklet .: "y"
    t0s <- note (TypeMismatch "Empty tracklet.") $ t !! 0
    t0 <- note (TypeMismatch "Invalid timestamp.") $ secondsToDateTime t0s
    note (TypeMismatch "Lengths of {t, x, y} arrays are not equal.") $ trackletSOA
      {id, t: (_ - t0s) <$> t, x, y, t0}