[Plot] Separate out positioning

Separate out pixel-to-plot-coordinate conversion into its
own script, to simplify PlotController for testing and
maintainability. WTD-533.

platform/features/plot/src/PlotController.js

@@ -8,9 +8,10 @@ define(
         "./PlotPreparer",
         "./PlotPalette",
         "./PlotPanZoomStack",
+        "./PlotPosition",
         "../lib/moment.min.js"
     ],
-    function (PlotPreparer, PlotPalette, PlotPanZoomStack) {
+    function (PlotPreparer, PlotPalette, PlotPanZoomStack, PlotPosition) {
         "use strict";
 
         var AXIS_DEFAULTS = [
@@ -44,30 +45,15 @@ define(
                 return (i ? formatRangeValue : formatDomainValue)(v);
             }
 
-
-            function pixelToDomainRange(x, y, width, height, domainOffset) {
-                var panZoom = panZoomStack.getPanZoom(),
-                    offset = [ domainOffset || 0, 0 ],
-                    origin = panZoom.origin,
-                    dimensions = panZoom.dimensions;
-
-                if (!dimensions || !origin) {
-                    return [];
-                }
-
-                return [ x / width, (height - y) / height ].map(function (v, i) {
-                    return v * dimensions[i] + origin[i] + offset[i];
-                });
-            }
-
             function mousePositionToDomainRange(mousePosition, domainOffset) {
-                return pixelToDomainRange(
+                return new PlotPosition(
                     mousePosition.x,
                     mousePosition.y,
                     mousePosition.width,
                     mousePosition.height,
+                    panZoomStack,
                     domainOffset
-                );
+                ).getPosition();
             }
 
             function generateTicks(start, span, count, format) {

platform/features/plot/src/PlotPosition.js

@@ -0,0 +1,39 @@
+/*global define*/
+
+define(
+    [],
+    function () {
+        "use strict";
+
+        function PlotPosition(x, y, width, height, panZoomStack, domainOffset) {
+            var panZoom = panZoomStack.getPanZoom(),
+                offset = [ domainOffset || 0, 0 ],
+                origin = panZoom.origin,
+                dimensions = panZoom.dimensions,
+                position;
+
+            if (!dimensions || !origin) {
+                position = [];
+            } else {
+                position = [ x / width, (height - y) / height ].map(function (v, i) {
+                    return v * dimensions[i] + origin[i] + offset[i];
+                });
+            }
+
+            return {
+                getDomain: function () {
+                    return position[0];
+                },
+                getRange: function () {
+                    return position[1];
+                },
+                getPosition: function () {
+                    return position;
+                }
+            };
+
+        }
+
+        return PlotPosition;
+    }
+);