From 4ed0168c0524a7a855ace169e833157343922df2 Mon Sep 17 00:00:00 2001
From: Jeremy Press <jpress@box.com>
Date: Thu, 22 Feb 2018 13:00:54 -0800
Subject: [PATCH] Chore: Allow viewers to emit metrics (#679)

---
 src/lib/Preview.js                | 18 ++++++++++++++++++
 src/lib/__tests__/Preview-test.js | 19 +++++++++++++++++++
 src/lib/events.js                 |  5 +++--
 src/lib/viewers/BaseViewer.js     | 16 ++++++++++++++++
 4 files changed, 56 insertions(+), 2 deletions(-)

diff --git a/src/lib/Preview.js b/src/lib/Preview.js
index 2d212516a..e0402f42e 100644
--- a/src/lib/Preview.js
+++ b/src/lib/Preview.js
@@ -1054,6 +1054,7 @@ class Preview extends EventEmitter {
         // Node requires listener attached to 'error'
         this.viewer.addListener('error', this.triggerError);
         this.viewer.addListener(VIEWER_EVENT.default, this.handleViewerEvents);
+        this.viewer.addListener(VIEWER_EVENT.metric, this.handleViewerMetrics);
     }
 
     /**
@@ -1101,6 +1102,23 @@ class Preview extends EventEmitter {
         }
     }
 
+    /**
+     * Handle metrics emitted by the viewer
+     *
+     * @private
+     * @param {Object} [data] - Viewer metric data
+     * @return {void}
+     */
+    handleViewerMetrics(data) {
+        const formattedEvent = {
+            event_name: data.event,
+            value: data.data,
+            ...this.createLogEvent()
+        };
+
+        this.emit(PREVIEW_METRIC, formattedEvent);
+    }
+
     /**
      * Finish loading a viewer - display the appropriate control buttons, re-emit the 'load' event, log
      * the preview, and prefetch the next few files.
diff --git a/src/lib/__tests__/Preview-test.js b/src/lib/__tests__/Preview-test.js
index 3edff480f..36ad3cc1c 100644
--- a/src/lib/__tests__/Preview-test.js
+++ b/src/lib/__tests__/Preview-test.js
@@ -1511,6 +1511,7 @@ describe('lib/Preview', () => {
             preview.attachViewerListeners();
             expect(preview.viewer.addListener).to.be.calledWith('error', sinon.match.func);
             expect(preview.viewer.addListener).to.be.calledWith(VIEWER_EVENT.default, sinon.match.func);
+            expect(preview.viewer.addListener).to.be.calledWith(VIEWER_EVENT.metric, sinon.match.func);
         });
     });
 
@@ -1591,6 +1592,24 @@ describe('lib/Preview', () => {
         });
     });
 
+    describe('handleViewerMetrics()', () => {
+        it('should create a formatted event and emit a preview_metric', () => {
+            sandbox.stub(preview, 'createLogEvent');
+            sandbox.stub(preview, 'emit');
+            const fakeEvent = {
+                event: 'test',
+                data: 7
+            }
+
+            const fakeLog = {
+                event_name: fakeEvent.event,
+                value: fakeEvent.data
+            }
+            preview.handleViewerMetrics(fakeEvent);
+            expect(preview.emit).to.be.calledWith(PREVIEW_METRIC, fakeLog);
+        });
+    });
+
     describe('finishLoading()', () => {
         beforeEach(() => {
             stubs.checkPermission = sandbox.stub(file, 'checkPermission');
diff --git a/src/lib/events.js b/src/lib/events.js
index 5eb67ec4e..695e156ca 100644
--- a/src/lib/events.js
+++ b/src/lib/events.js
@@ -8,8 +8,9 @@ export const VIEWER_EVENT = {
     notificationShow: 'notificationshow', // Show notification modal.
     notificationHide: 'notificationhide', // Hide notification modal.
     mediaEndAutoplay: 'mediaendautoplay', // Media playback has completed, with autoplay enabled.
-    error: 'error', // When an error occurs
-    default: 'viewerevent' // The default viewer event
+    error: 'error', // When an error occurs.
+    default: 'viewerevent', // The default viewer event.
+    metric: 'viewermetric' // A viewer metric.
 };
 
 // Error codes logged by preview with "preview_error" events
diff --git a/src/lib/viewers/BaseViewer.js b/src/lib/viewers/BaseViewer.js
index 4afedf816..9f2a20a8f 100644
--- a/src/lib/viewers/BaseViewer.js
+++ b/src/lib/viewers/BaseViewer.js
@@ -499,6 +499,22 @@ class BaseViewer extends EventEmitter {
         });
     }
 
+    /**
+     * Emits a viewer metric
+     *
+     * @protected
+     * @emits metric
+     * @param {string} event - Event name
+     * @param {Object} data - Event data
+     * @return {void}
+     */
+    emitMetric(event, data) {
+        super.emit(VIEWER_EVENT.metric, {
+            event,
+            data
+        });
+    }
+
     /**
      * Handles the beginning of a pinch to zoom event on mobile.
      * Although W3 strongly discourages the prevention of pinch to zoom,