set viewBox for graphs to show full time range

todo: also scale the y axis correctly

frontend/src/Main.elm

@@ -235,7 +235,9 @@ measureView fn allPoints =
         string = String.concat (List.map coords filteredPoints)
     in
         svg
-        [ ]
+        [ H.style "width" (px portalWidth)
+        , viewBox ("0 0 " ++ (String.fromFloat (Point.duration allPoints)) ++ " 150")
+        ]
         [ g
           [ fill "none"
           , stroke "red"

frontend/src/Point.elm

@@ -1,4 +1,4 @@
-module Point exposing(Pos, Point, decoder, downsample)
+module Point exposing(Pos, Point, decoder, downsample, duration)
 
 import Json.Decode as D
 
@@ -33,10 +33,10 @@ decoder = D.map5 Point
           (D.field "heartRate" (D.maybe D.int))
 
 
-llast x xs =
+last x xs =
     case xs of
         [] -> x
-        (x_::xs_) -> llast x_ xs_
+        (x_::xs_) -> last x_ xs_
 
 tracef x = Debug.log (String.fromFloat x) x
 
@@ -54,8 +54,11 @@ downsample n points =
     in
         case points of
             (first::rest) ->
-                let last = llast first rest
-                    duration = last.time - first.time
-                    step = duration / (toFloat n)
+                let step = (duration points) / (toFloat n)
                 in nextpoint step first rest
             [] -> []
+
+duration points =
+    case points of
+        (p::ps) -> (last p ps).time - p.time
+        _ -> 0