[Plot] Complete specs for plot updater

Complete specs for plot updater; particularly, address
case (and fix bug in case) where maximum buffer size
has been hit. WTD-751.

platform/features/plot/src/elements/PlotUpdater.js

@@ -21,7 +21,7 @@ define(
          * @param {string} domain the key to use when looking up domain values
          * @param {string} range the key to use when looking up range values
          */
-        function PlotUpdater(subscription, domain, range) {
+        function PlotUpdater(subscription, domain, range, maxPoints) {
             var max = [Number.NEGATIVE_INFINITY, Number.NEGATIVE_INFINITY],
                 min = [Number.POSITIVE_INFINITY, Number.POSITIVE_INFINITY],
                 x,
@@ -46,12 +46,12 @@ define(
                 // Check if we don't have enough room
                 if (index > (buffer.length / 2 - 1)) {
                     // If we don't, can we expand?
-                    if (index < MAX_POINTS) {
+                    if (index < maxPoints) {
                         // Double the buffer size
                         buffer = buffers[id] = doubleSize(buffer);
                     } else {
                         // Just shift the existing buffer
-                        buffer.copyWithin(0, 2);
+                        buffer.set(buffer.subarray(2));
                     }
                 }
 
@@ -82,12 +82,12 @@ define(
                     // Ensure there is space for the new buffer
                     buffer = ensureBufferSize(buffer, id, index);
                     // Account for shifting that may have occurred
-                    index = Math.min(index, MAX_POINTS - 2);
+                    index = Math.min(index, maxPoints - 1);
                     // Update the buffer
                     buffer[index * 2] = domainValue - domainOffset;
                     buffer[index * 2 + 1] = rangeValue;
                     // Update length
-                    lengths[id] = Math.min(index + 1, MAX_POINTS);
+                    lengths[id] = Math.min(index + 1, maxPoints);
                     // Observe max/min range values
                     max[1] = Math.max(max[1], rangeValue);
                     min[1] = Math.min(min[1], rangeValue);
@@ -130,6 +130,9 @@ define(
                 bufferArray.push(buffers[id]);
             }
 
+            // Use a default MAX_POINTS if none is provided
+            maxPoints = maxPoints || MAX_POINTS;
+
             // Initially prepare state for these objects.
             // Note that this may be an empty array at this time,
             // so we also need to check during update cycles.

platform/features/plot/test/elements/PlotUpdaterSpec.js

@@ -49,7 +49,8 @@ define(
                 updater = new PlotUpdater(
                     mockSubscription,
                     testDomain,
-                    testRange
+                    testRange,
+                    1350 // Smaller max size for easier testing
                 );
             });
 
@@ -66,7 +67,7 @@ define(
 
             it("maintains a buffer of received telemetry", function () {
                 // Count should be large enough to trigger a buffer resize
-                var count = 1000,
+                var count = 750,
                     i;
 
                 // Increment values exposed by subscription
@@ -107,6 +108,54 @@ define(
                 }
             });
 
+            it("can handle delayed telemetry object availability", function () {
+                // The case can occur where getTelemetryObjects() returns an
+                // empty array - specifically, while objects are still being
+                // loaded. The updater needs to be able to cope with that
+                // case.
+                var tmp = mockSubscription.getTelemetryObjects();
+                mockSubscription.getTelemetryObjects.andReturn([]);
+
+                // Reinstantiate with the empty subscription
+                updater = new PlotUpdater(
+                    mockSubscription,
+                    testDomain,
+                    testRange
+                );
+
+                // Should have 0 buffers for 0 objects
+                expect(updater.getBuffers().length).toEqual(0);
+
+                // Restore the three objects the test subscription would
+                // normally have.
+                mockSubscription.getTelemetryObjects.andReturn(tmp);
+                updater.update();
+
+                // Should have 3 buffers for 3 objects
+                expect(updater.getBuffers().length).toEqual(3);
+            });
+
+
+            it("shifts buffer upon expansion", function () {
+                // Count should be large enough to hit buffer's max size
+                var count = 1400,
+                    i;
+
+                // Initial update; should have 3 in first position
+                // (a's initial domain value)
+                updater.update();
+                expect(updater.getBuffers()[0][1]).toEqual(123);
+
+                // Simulate a lot of telemetry updates
+                for (i = 0; i < count; i += 1) {
+                    testDomainValues.a += 1;
+                    testRangeValues.a += 1;
+                    updater.update();
+                }
+
+                // Value at front of the buffer should have been pushed out
+                expect(updater.getBuffers()[0][1]).not.toEqual(123);
+            });
         });
     }
 );