render cadence graph

in the wrong place and size but it's on the screen which is a start

elm.json

@@ -1,7 +1,8 @@
 {
     "type": "application",
     "source-directories": [
-        "frontend/src"
+        "frontend/src",
+	"frontend/tests"
     ],
     "elm-version": "0.19.1",
     "dependencies": {

frontend/src/Main.elm

@@ -220,8 +220,41 @@ tileImg zoom tilenumber = img [ width 256,
                                 height 256,
                                 src (tileUrl tilenumber zoom) ] []
 
-trackView : List Point -> Int -> Int -> Zoom -> Svg Msg
-trackView points leftedge topedge zoom =
+
+cadenceView : List Point -> Svg Msg
+cadenceView allPoints =
+    let filteredPoints = Point.downsample 100 allPoints
+        startTime = case allPoints of
+                        (p::_) -> p.time
+                        _ -> 0
+        coords p = case p.cadence of
+                       Just c ->
+                           (String.fromFloat (p.time - startTime)) ++ "," ++
+                           (String.fromInt c) ++ ", "
+                       Nothing -> ""
+        string = String.concat (List.map coords filteredPoints)
+    in
+        svg
+        [ H.style "width" "100%"
+        , H.style "height" "100%"
+        , H.style "position" "absolute"
+        ]
+        [ g
+          [ fill "none"
+          , stroke "red"
+          , strokeWidth "3"
+          ]
+          [
+           polyline
+               [ fill "none"
+               , S.points string
+               ] []
+          ]
+        ]
+
+
+trackView : Int -> Int -> Zoom -> List Point -> Svg Msg
+trackView leftedge topedge zoom points =
     let plot p =
             let (x, y) = pixelFromCoord (toCoord p.pos.lat p.pos.lon) zoom
                 x_ = x - leftedge
@@ -257,6 +290,13 @@ tiles xs ys zoom =
              (List.map (\ x -> tileImg zoom (TileNumber x y)) xs))
         ys
 
+ifTrack track content =
+    case track of
+        Present t -> content t
+        Failure f -> Debug.log f (div [] [ text "failure", text f])
+        Loading -> div [] [text "loading"]
+        Empty -> div [] [text "no points"]
+
 
 canvas centre zoom width height track =
     let (mintile, maxtile) = boundingTiles centre zoom width height
@@ -272,11 +312,7 @@ canvas centre zoom width height track =
         xs = List.range mintile.x maxtile.x
         ys = List.range mintile.y maxtile.y
         epos e = Tuple.mapBoth floor floor e.pointer.clientPos
-        tv = case track of
-                 Present t -> trackView t leftedge topedge zoom
-                 Failure f -> Debug.log f (div [] [ text "failure", text f])
-                 Loading -> div [] [text "loading"]
-                 Empty -> div [] [text "no points"]
+        tv = ifTrack track (trackView leftedge topedge zoom)
     in  div [style "position" "absolute"
             ,style "width" (px pixWidth)
             ,style "height" (px pixHeight)
@@ -295,13 +331,15 @@ viewDiv : Model -> Html Msg
 viewDiv model =
     let coord = translate model.centre (pixelsToCoord model.zoom (dragDelta model.drag))
         canvasV = canvas coord model.zoom portalWidth portalHeight model.track
-    in div []
+    in div [ style "display" "inline-block" ]
         [ (div [ style "width" (px portalWidth)
                , style "height" (px portalHeight)
                , style "display" "inline-block"
                , style "position" "relative"
                , style "overflow" "hidden"]
                [canvasV])
+        , div [ style "width" (px portalWidth), style "height" "150"]
+            [ ifTrack model.track cadenceView ]
         , div [] [ text (String.fromInt model.zoom ) ]
         , div [] [ case model.track of
                        -- Present tk -> text (String.fromInt (List.length tk))

frontend/src/Point.elm

@@ -1,4 +1,4 @@
-module Point exposing(Pos, Point, decoder)
+module Point exposing(Pos, Point, decoder, downsample)
 
 import Json.Decode as D
 
@@ -31,3 +31,31 @@ decoder = D.map5 Point
           (D.field "cadence" (D.maybe D.int))
           (D.field "power" (D.maybe D.int))
           (D.field "heartRate" (D.maybe D.int))
+
+
+llast x xs =
+    case xs of
+        [] -> x
+        (x_::xs_) -> llast x_ xs_
+
+tracef x = Debug.log (String.fromFloat x) x
+
+-- divide the points into n equal time buckets and return the first
+-- point in each
+downsample n points =
+    let
+        nextpoint step prev points_ =
+            case points_ of
+                (next::rest) ->
+                    if next.time - prev.time > step
+                    then prev :: (nextpoint step next rest)
+                    else nextpoint step prev rest
+                _ -> [prev]
+    in
+        case points of
+            (first::rest) ->
+                let last = llast first rest
+                    duration = last.time - first.time
+                    step = duration / (toFloat n)
+                in nextpoint step first rest
+            [] -> []

frontend/tests/PointTest.elm

@@ -0,0 +1,35 @@
+module PointTest exposing (specs)
+
+import Point exposing (Point, Pos, downsample)
+import Test exposing (..)
+import Expect exposing (Expectation)
+
+newPoint i = Point
+             (1731437067 + (toFloat i)*1.2)
+             (Pos 52 1 (Just 10))
+             (Just (round(sin((toFloat i)/10)*10))) (Just i) Nothing
+
+
+points n = List.map newPoint (List.range 0 n)
+
+maybe default val =
+    case val of
+        Just v -> v
+        Nothing -> default
+
+specs: Test
+specs =
+    describe "downsample"
+        [ test "it returns no more points than requested" <|
+              \_ ->
+              let orig = (points 10)
+                  sampled = Point.downsample 5 orig
+              in Expect.equal 5 (List.length sampled)
+        , test "it drops points which are too close together" <|
+              \_ ->
+              let orig = List.map newPoint [ 0, 1, 2, 3, 4, 10, 500, 1000 ]
+                  sampled = Point.downsample 10 orig
+                  idx p = maybe 0 p.power
+              in Expect.equalLists [0, 500, 1000] (List.map idx sampled)
+
+        ]