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 Point =
    { lat : Float
    , lon : Float
    , ele : Maybe Float
    , time : Maybe Time.Posix
    }

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

pointDecoder = XD.map4 Point
               (floatAttr "lat")
               (floatAttr "lon")
               (XD.maybe (path ["ele"] (single XD.float)))
               (XD.maybe (path ["time"] (single timeDecoder)))


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


parse str = XD.run gpxDecoder str