fallback module

Author: themiswang

firebase-sessions/src/main/kotlin/com/google/firebase/sessions/FirebaseSessions.kt

@@ -24,6 +24,7 @@ import com.google.firebase.annotations.concurrent.Background
 import com.google.firebase.app
 import com.google.firebase.sessions.api.FirebaseSessionsDependencies
 import com.google.firebase.sessions.settings.SessionsSettings
+import dagger.Lazy
 import javax.inject.Inject
 import javax.inject.Singleton
 import kotlin.coroutines.CoroutineContext
@@ -38,14 +39,13 @@ constructor(
   private val firebaseApp: FirebaseApp,
   private val settings: SessionsSettings,
   @Background backgroundDispatcher: CoroutineContext,
-  sessionsActivityLifecycleCallbacks: SessionsActivityLifecycleCallbacks,
+  sessionsActivityLifecycleCallbacks: Lazy<SessionsActivityLifecycleCallbacks>,
+  sessionsFallbackActivityLifecycleCallbacks: Lazy<SessionsFallbackActivityLifecycleCallbacks>,
 ) {
-
   init {
     Log.d(TAG, "Initializing Firebase Sessions SDK.")
     val appContext = firebaseApp.applicationContext.applicationContext
     if (appContext is Application) {
-      appContext.registerActivityLifecycleCallbacks(sessionsActivityLifecycleCallbacks)
 
       CoroutineScope(backgroundDispatcher).launch {
         val subscribers = FirebaseSessionsDependencies.getRegisteredSubscribers()
@@ -55,14 +55,18 @@ constructor(
           settings.updateSettings()
           if (!settings.sessionsEnabled) {
             Log.d(TAG, "Sessions SDK disabled. Not listening to lifecycle events.")
+            appContext.registerActivityLifecycleCallbacks(
+              sessionsFallbackActivityLifecycleCallbacks.get().activityLifecycleCallbacks
+            )
           } else {
-            firebaseApp.addLifecycleEventListener { _, _ ->
-              // Log.w(
-              //   TAG,
-              //   "FirebaseApp instance deleted. Sessions library will stop collecting data.",
-              // )
-              // TODO(mrober): Clean up on firebase app delete
-            }
+            appContext.registerActivityLifecycleCallbacks(sessionsActivityLifecycleCallbacks.get())
+          }
+          firebaseApp.addLifecycleEventListener { _, _ ->
+            // Log.w(
+            //   TAG,
+            //   "FirebaseApp instance deleted. Sessions library will stop collecting data.",
+            // )
+            // TODO(mrober): Clean up on firebase app delete
           }
         }
       }

firebase-sessions/src/main/kotlin/com/google/firebase/sessions/SessionsFallbackActivityLifecycleCallbacks.kt

@@ -0,0 +1,111 @@
+/*
+ * Copyright 2025 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.firebase.sessions
+
+import android.app.Activity
+import android.app.Application.ActivityLifecycleCallbacks
+import android.os.Bundle
+import android.util.Log
+import com.google.firebase.annotations.concurrent.Background
+import com.google.firebase.sessions.api.FirebaseSessionsDependencies
+import com.google.firebase.sessions.api.SessionSubscriber
+import com.google.firebase.sessions.settings.SessionsSettings
+import javax.inject.Inject
+import javax.inject.Singleton
+import kotlin.coroutines.CoroutineContext
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.launch
+
+@Singleton
+internal class SessionsFallbackActivityLifecycleCallbacks
+@Inject
+constructor(
+  private val sessionsSettings: SessionsSettings,
+  private val sessionGenerator: SessionGenerator,
+  private val timeProvider: TimeProvider,
+  @Background private val backgroundDispatcher: CoroutineContext,
+) {
+  private var localSessionData: SessionData
+  init {
+    localSessionData =
+      SessionData(
+        sessionDetails = sessionGenerator.generateNewSession(null),
+        backgroundTime = timeProvider.currentTime()
+      )
+
+    CoroutineScope(backgroundDispatcher).launch {
+      // Only notify subscriber for session change, not send to event to firelog
+      FirebaseSessionsDependencies.getRegisteredSubscribers().values.forEach { subscriber ->
+        subscriber.onSessionChanged(
+          SessionSubscriber.SessionDetails(localSessionData.sessionDetails.sessionId)
+        )
+        Log.d(
+          TAG,
+          "Notified ${subscriber.sessionSubscriberName} of new session $localSessionData.sessionId with fallback mode"
+        )
+      }
+    }
+  }
+
+  fun appBackground() {
+    localSessionData.copy(backgroundTime = timeProvider.currentTime())
+  }
+
+  fun appForeground() {
+    // Fallback mode, not using datastore, pre multi-process support stage
+    if (shouldInitiateNewSession(localSessionData)) {
+      val newSessionDetails = sessionGenerator.generateNewSession(localSessionData.sessionDetails)
+      localSessionData.copy(sessionDetails = newSessionDetails)
+      CoroutineScope(backgroundDispatcher).launch {
+        // Only notify subscriber for session change, not send to event to firelog
+        FirebaseSessionsDependencies.getRegisteredSubscribers().values.forEach { subscriber ->
+          subscriber.onSessionChanged(SessionSubscriber.SessionDetails(newSessionDetails.sessionId))
+          Log.d(
+            TAG,
+            "Notified ${subscriber.sessionSubscriberName} of new session $newSessionDetails.sessionId with fallback mode"
+          )
+        }
+      }
+    }
+  }
+
+  internal val activityLifecycleCallbacks =
+    object : ActivityLifecycleCallbacks {
+      override fun onActivityResumed(activity: Activity) = appForeground()
+
+      override fun onActivityPaused(activity: Activity) = appBackground()
+
+      override fun onActivityCreated(activity: Activity, savedInstanceState: Bundle?) = Unit
+
+      override fun onActivityStarted(activity: Activity) = Unit
+
+      override fun onActivityStopped(activity: Activity) = Unit
+
+      override fun onActivityDestroyed(activity: Activity) = Unit
+
+      override fun onActivitySaveInstanceState(activity: Activity, outState: Bundle) = Unit
+    }
+
+  private fun shouldInitiateNewSession(sessionData: SessionData): Boolean {
+    val interval = timeProvider.currentTime() - sessionData.backgroundTime
+    return interval > sessionsSettings.sessionRestartTimeout
+  }
+
+  private companion object {
+    const val TAG = "SessionsFallbackALC"
+  }
+}