From fe822e0a4568b04ae85c7d4c756939fb8c117651 Mon Sep 17 00:00:00 2001
From: Najib Boutaib <104867447+N-Boutaib@users.noreply.github.com>
Date: Thu, 5 Sep 2024 11:26:42 +0200
Subject: [PATCH] :sparkles: Discard loading time when page is hidden (#2965)

---
 .../domain/view/viewMetrics/trackLoadingTime.spec.ts | 10 +++++++++-
 .../src/domain/view/viewMetrics/trackLoadingTime.ts  | 12 ++++++++++--
 2 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/packages/rum-core/src/domain/view/viewMetrics/trackLoadingTime.spec.ts b/packages/rum-core/src/domain/view/viewMetrics/trackLoadingTime.spec.ts
index 7baf8f22b8..0c71a38f50 100644
--- a/packages/rum-core/src/domain/view/viewMetrics/trackLoadingTime.spec.ts
+++ b/packages/rum-core/src/domain/view/viewMetrics/trackLoadingTime.spec.ts
@@ -1,7 +1,7 @@
 import type { RelativeTime, Duration } from '@datadog/browser-core'
 import { addDuration, clocksOrigin, Observable } from '@datadog/browser-core'
 import type { Clock } from '@datadog/browser-core/test'
-import { mockClock } from '@datadog/browser-core/test'
+import { mockClock, setPageVisibility, restorePageVisibility } from '@datadog/browser-core/test'
 import { ViewLoadingType } from '../../../rawRumEvent.types'
 import { createPerformanceEntry } from '../../../../test'
 import { PAGE_ACTIVITY_END_DELAY, PAGE_ACTIVITY_VALIDATION_DELAY } from '../../waitPageActivityEnd'
@@ -47,6 +47,7 @@ describe('trackLoadingTime', () => {
 
   afterEach(() => {
     stopLoadingTimeTracking()
+    restorePageVisibility()
     clock.cleanup()
   })
 
@@ -125,4 +126,11 @@ describe('trackLoadingTime', () => {
 
     expect(loadingTimeCallback).toHaveBeenCalledOnceWith(addDuration(BEFORE_PAGE_ACTIVITY_VALIDATION_DELAY, CLOCK_GAP))
   })
+
+  it('should discard loading time if page is hidden before activity', () => {
+    setPageVisibility('hidden')
+    startLoadingTimeTracking()
+
+    expect(loadingTimeCallback).not.toHaveBeenCalled()
+  })
 })
diff --git a/packages/rum-core/src/domain/view/viewMetrics/trackLoadingTime.ts b/packages/rum-core/src/domain/view/viewMetrics/trackLoadingTime.ts
index d34ed787eb..60de33a4d8 100644
--- a/packages/rum-core/src/domain/view/viewMetrics/trackLoadingTime.ts
+++ b/packages/rum-core/src/domain/view/viewMetrics/trackLoadingTime.ts
@@ -4,6 +4,7 @@ import { waitPageActivityEnd } from '../../waitPageActivityEnd'
 import type { RumConfiguration } from '../../configuration'
 import type { LifeCycle } from '../../lifeCycle'
 import { ViewLoadingType } from '../../../rawRumEvent.types'
+import { trackFirstHidden } from './trackFirstHidden'
 
 export function trackLoadingTime(
   lifeCycle: LifeCycle,
@@ -16,10 +17,14 @@ export function trackLoadingTime(
   let isWaitingForLoadEvent = loadType === ViewLoadingType.INITIAL_LOAD
   let isWaitingForActivityLoadingTime = true
   const loadingTimeCandidates: Duration[] = []
+  const firstHidden = trackFirstHidden(configuration)
 
   function invokeCallbackIfAllCandidatesAreReceived() {
     if (!isWaitingForActivityLoadingTime && !isWaitingForLoadEvent && loadingTimeCandidates.length > 0) {
-      callback(Math.max(...loadingTimeCandidates) as Duration)
+      const loadingTime = Math.max(...loadingTimeCandidates)
+      if (loadingTime < firstHidden.timeStamp) {
+        callback(loadingTime as Duration)
+      }
     }
   }
 
@@ -34,7 +39,10 @@ export function trackLoadingTime(
   })
 
   return {
-    stop,
+    stop: () => {
+      stop()
+      firstHidden.stop()
+    },
     setLoadEvent: (loadEvent: Duration) => {
       if (isWaitingForLoadEvent) {
         isWaitingForLoadEvent = false