Disable the activity lifecycle callbacks on app delete

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

@@ -57,11 +57,11 @@ constructor(
             Log.d(TAG, "Sessions SDK disabled. Not listening to lifecycle events.")
           } else {
             firebaseApp.addLifecycleEventListener { _, _ ->
-              // Log.w(
-              //   TAG,
-              //   "FirebaseApp instance deleted. Sessions library will stop collecting data.",
-              // )
-              // TODO(mrober): Clean up on firebase app delete
+              Log.w(
+                TAG,
+                "FirebaseApp instance deleted. Sessions library will stop collecting data.",
+              )
+              sessionsActivityLifecycleCallbacks.onAppDelete()
             }
           }
         }

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

@@ -31,10 +31,23 @@ internal class SessionsActivityLifecycleCallbacks
 @Inject
 constructor(private val sharedSessionRepository: SharedSessionRepository) :
   ActivityLifecycleCallbacks {
-
-  override fun onActivityResumed(activity: Activity) = sharedSessionRepository.appForeground()
-
-  override fun onActivityPaused(activity: Activity) = sharedSessionRepository.appBackground()
+  private var enabled = true
+
+  fun onAppDelete() {
+    enabled = false
+  }
+
+  override fun onActivityResumed(activity: Activity) {
+    if (enabled) {
+      sharedSessionRepository.appForeground()
+    }
+  }
+
+  override fun onActivityPaused(activity: Activity) {
+    if (enabled) {
+      sharedSessionRepository.appBackground()
+    }
+  }
 
   override fun onActivityCreated(activity: Activity, savedInstanceState: Bundle?) = Unit