Fireperf: fix incorrect sessionIds for _fs and _bs traces (#3122)

* simple fix by changing order of methods

* add test

* comments

* rewording

Author: leotianlizhan

firebase-perf/src/main/java/com/google/firebase/perf/application/AppStateMonitor.java

@@ -340,8 +340,9 @@ public synchronized void onActivityStopped(Activity activity) {
       if (activityToResumedMap.isEmpty()) {
         // no more activity in foreground, app goes to background.
         stopTime = clock.getTime();
-        updateAppState(ApplicationProcessState.BACKGROUND);
         sendSessionLog(Constants.TraceNames.FOREGROUND_TRACE_NAME.toString(), resumeTime, stopTime);
+        // order is important to complete _fs before triggering a sessionId change b/204362742
+        updateAppState(ApplicationProcessState.BACKGROUND);
       }
     }
   }
@@ -356,14 +357,16 @@ public synchronized void onActivityResumed(Activity activity) {
       // The first resumed activity means app comes to foreground.
       resumeTime = clock.getTime();
       activityToResumedMap.put(activity, true);
-      updateAppState(ApplicationProcessState.FOREGROUND);
       if (isColdStart) {
         // case 1: app startup.
+        updateAppState(ApplicationProcessState.FOREGROUND);
         sendAppColdStartUpdate();
         isColdStart = false;
       } else {
         // case 2: app switch from background to foreground.
         sendSessionLog(Constants.TraceNames.BACKGROUND_TRACE_NAME.toString(), stopTime, resumeTime);
+        // order is important to complete _bs before triggering a sessionId change b/204362742
+        updateAppState(ApplicationProcessState.FOREGROUND);
       }
     } else {
       // case 3: app already in foreground, current activity is replaced by another activity.
@@ -626,6 +629,11 @@ Timer getPauseTime() {
     return stopTime;
   }
 
+  @VisibleForTesting
+  void setStopTime(Timer timer) {
+    stopTime = timer;
+  }
+
   @VisibleForTesting
   Timer getResumeTime() {
     return resumeTime;

firebase-perf/src/main/java/com/google/firebase/perf/application/AppStateUpdateHandler.java

@@ -15,6 +15,7 @@
 package com.google.firebase.perf.application;
 
 import androidx.annotation.NonNull;
+import com.google.android.gms.common.util.VisibleForTesting;
 import com.google.firebase.perf.application.AppStateMonitor.AppStateCallback;
 import com.google.firebase.perf.v1.ApplicationProcessState;
 import java.lang.ref.WeakReference;
@@ -102,4 +103,9 @@ public void onUpdateAppState(ApplicationProcessState newState) {
   public ApplicationProcessState getAppState() {
     return currentAppState;
   }
+
+  @VisibleForTesting
+  public WeakReference<AppStateCallback> getAppStateCallback() {
+    return appStateCallback;
+  }
 }

firebase-perf/src/test/java/com/google/firebase/perf/application/AppStateMonitorTest.java

@@ -38,13 +38,15 @@
 import com.google.firebase.perf.config.DeviceCacheManager;
 import com.google.firebase.perf.metrics.NetworkRequestMetricBuilder;
 import com.google.firebase.perf.metrics.Trace;
+import com.google.firebase.perf.session.SessionManager;
 import com.google.firebase.perf.session.gauges.GaugeManager;
 import com.google.firebase.perf.transport.TransportManager;
 import com.google.firebase.perf.util.Clock;
 import com.google.firebase.perf.util.Constants;
 import com.google.firebase.perf.util.ImmutableBundle;
 import com.google.firebase.perf.util.Timer;
 import com.google.firebase.perf.v1.ApplicationProcessState;
+import com.google.firebase.perf.v1.PerfSession;
 import com.google.firebase.perf.v1.TraceMetric;
 import com.google.testing.timing.FakeDirectExecutorService;
 import java.lang.ref.WeakReference;
@@ -766,6 +768,32 @@ public void appColdStart_singleSubscriberRegistersForMultipleTimes_oneCallbackIs
     verify(mockInitializer1, times(1)).onAppColdStart();
   }
 
+  @Test
+  public void updatePerfSession_isAfterSendingForegroundOrBackgroundSession() {
+    AppStateMonitor monitor = new AppStateMonitor(transportManager, clock);
+    monitor.registerForAppState(SessionManager.getInstance().getAppStateCallback());
+    monitor.setStopTime(new Timer(currentTime));
+    monitor.setIsColdStart(false);
+    // Mandatory due to circular dependencies of singletons AppStateMonitor and SessionManager
+    AppStateMonitor.getInstance().setIsColdStart(false);
+
+    // Foreground -> Background, sends _fs
+    PerfSession currentSession = SessionManager.getInstance().perfSession().build();
+    monitor.onActivityResumed(activity1);
+
+    verify(transportManager, times(1)).log(argTraceMetric.capture(), eq(FOREGROUND_BACKGROUND));
+    PerfSession sentSession = argTraceMetric.getValue().getPerfSessions(0);
+    Assert.assertEquals(currentSession, sentSession);
+
+    // Background -> Foreground, sends _bs
+    currentSession = SessionManager.getInstance().perfSession().build();
+    monitor.onActivityStopped(activity1);
+
+    verify(transportManager, times(2)).log(argTraceMetric.capture(), eq(FOREGROUND_BACKGROUND));
+    sentSession = argTraceMetric.getValue().getPerfSessions(0);
+    Assert.assertEquals(currentSession, sentSession);
+  }
+
   private static Activity createFakeActivity(boolean isHardwareAccelerated) {
     ActivityController<Activity> fakeActivityController = Robolectric.buildActivity(Activity.class);