set Model start/duration from points

frontend/src/Main.elm

@@ -158,7 +158,7 @@ init _ url navKey =
                 Just (Timeline (Just s) (Just d)) -> (s, d)
                 _ -> (10,10)
     in
-        ((Model (toCoord 51.60 -0.01) (FineZoomLevel (13*8)) None None start duration Empty),
+        ((Model (toCoord 51.60 -0.01) (FineZoomLevel (13*8)) None None 0 0 Empty),
              (fetchTrack start duration))
 
 -- SUBSCRIPTIONS
@@ -234,7 +234,15 @@ updateModel msg model =
             }
         Loaded result ->
             case result of
-                Ok trk -> { model | track = Present trk }
+                Ok trk ->
+                    let start = Maybe.withDefault 0 (Point.startTime trk)
+                        duration = Point.duration trk
+                    in
+                    { model
+                        | track = Present trk
+                        , startTime = floor start
+                        , duration = ceiling duration
+                    }
                 Err (Http.BadBody e) -> { model | track = Debug.log e (Failure "e") }
                 Err e -> { model | track = Debug.log "unknown error" (Failure "e") }
         NewUrlRequest -> model

frontend/src/Point.elm

@@ -1,4 +1,4 @@
-module Point exposing(Pos, Point, decoder, downsample, duration, subseq)
+module Point exposing(Pos, Point, decoder, downsample, duration, subseq, startTime)
 
 import Json.Decode as D
 
@@ -63,6 +63,11 @@ duration points =
         (p::ps) -> (last p ps).time - p.time
         _ -> 0
 
+startTime points =
+    case points of
+        (p::ps) -> Just p.time
+        _ -> Nothing
+
 subseq points start dur =
     case points of
         [] -> []