module Track exposing (Track, Point, parse)

import Result
import Xml.Decode as XD exposing (path, list, single, floatAttr, stringAttr)
import Time
import Iso8601

type alias Position = (Float, Float, Maybe Float) -- lat, lon, ele

type alias Point =
    { loc : Position
    , time : Maybe Time.Posix
    , power : Maybe Int
    , cadence : Maybe Int
    , hr : Maybe Int
    }

type alias Track =  List Point

timeDecoder : XD.Decoder Time.Posix
timeDecoder = XD.andThen (\ts ->
                          case Iso8601.toTime ts of
                              Result.Ok time -> XD.succeed time
                              Result.Err f -> XD.fail "err"
                         )
              XD.string

triple x y z = (x,y,z)

pointDecoder = XD.map5 Point
               (XD.map3 triple (floatAttr "lat") (floatAttr "lon")
                        (XD.maybe (path ["ele"] (single XD.float))))
               (XD.maybe (path ["time"] (single timeDecoder)))
               (XD.maybe (path ["extensions", "gpxtpx:TrackPointExtension", "pwr:PowerInWatts"] (single XD.int)))
               (XD.maybe (path ["extensions", "gpxtpx:TrackPointExtension", "gpxtpx:cad"] (single XD.int)))
               (XD.maybe (path ["extensions", "gpxtpx:TrackPointExtension", "gpxtpx:hr"] (single XD.int)))


gpxDecoder =
             (path [ "trk", "trkseg", "trkpt" ] (list pointDecoder))


parse str = XD.run gpxDecoder str