For #9100: Follow-up to fix memory leak in NotificationSessionObserver

The observer was moved and is now bound to the activity and its
context. If the activity is re-created we leak the observer and
therefore the activity itself.

With this we make sure to stop the observer and also don't use
the activity context to begin with.

app/src/main/java/org/mozilla/fenix/HomeActivity.kt

@@ -107,6 +107,7 @@ open class HomeActivity : LocaleAwareAppCompatActivity() {
     private var isVisuallyComplete = false
 
     private var visualCompletenessQueue: RunWhenReadyQueue? = null
+    private var privateNotificationObserver: NotificationSessionObserver? = null
 
     private var isToolbarInflated = false
 
@@ -156,8 +157,9 @@ open class HomeActivity : LocaleAwareAppCompatActivity() {
         sessionObserver = UriOpenedObserver(this)
 
         checkPrivateShortcutEntryPoint(intent)
-        val privateNotificationObserver = NotificationSessionObserver(this)
-        privateNotificationObserver.start()
+        privateNotificationObserver = NotificationSessionObserver(applicationContext).also {
+            it.start()
+        }
 
         if (isActivityColdStarted(intent, savedInstanceState)) {
             externalSourceIntentProcessors.any { it.process(intent, navHost.navController, this.intent) }
@@ -218,6 +220,11 @@ open class HomeActivity : LocaleAwareAppCompatActivity() {
         BrowsersCache.resetAll()
     }
 
+    override fun onDestroy() {
+        super.onDestroy()
+        privateNotificationObserver?.stop()
+    }
+
     /**
      * Handles intents received when the activity is open.
      */

app/src/main/java/org/mozilla/fenix/session/NotificationSessionObserver.kt

@@ -20,25 +20,22 @@ import org.mozilla.fenix.ext.components
  * indicating that a private tab is open.
  */
 class NotificationSessionObserver(
-    private val context: Context,
+    private val applicationContext: Context,
     private val notificationService: SessionNotificationService.Companion = SessionNotificationService
 ) {
 
     private var scope: CoroutineScope? = null
-    private var started = false
 
     @ExperimentalCoroutinesApi
     fun start() {
-        scope = context.components.core.store.flowScoped { flow ->
+        scope = applicationContext.components.core.store.flowScoped { flow ->
             flow.map { state -> state.privateTabs.isNotEmpty() }
                 .ifChanged()
                 .collect { hasPrivateTabs ->
                     if (hasPrivateTabs) {
-                        notificationService.start(context, isStartedFromPrivateShortcut)
-                        started = true
-                    } else if (started) {
-                        notificationService.stop(context)
-                        started = false
+                        notificationService.start(applicationContext, isStartedFromPrivateShortcut)
+                    } else if (SessionNotificationService.started) {
+                        notificationService.stop(applicationContext)
                     }
                 }
         }

app/src/main/java/org/mozilla/fenix/session/SessionNotificationService.kt

@@ -138,6 +138,7 @@ class SessionNotificationService : Service() {
 
         private const val ACTION_START = "start"
         private const val ACTION_ERASE = "erase"
+        internal var started = false
 
         internal fun start(
             context: Context,
@@ -154,6 +155,8 @@ class SessionNotificationService : Service() {
             ThreadUtils.postToMainThread(Runnable {
                 context.startService(intent)
             })
+
+            started = true
         }
 
         internal fun stop(context: Context) {
@@ -164,6 +167,8 @@ class SessionNotificationService : Service() {
             ThreadUtils.postToMainThread(Runnable {
                 context.stopService(intent)
             })
+
+            started = false
         }
     }
 }

app/src/test/java/org/mozilla/fenix/session/NotificationSessionObserverTest.kt

@@ -1,3 +1,7 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
 package org.mozilla.fenix.session
 
 import android.content.Context

app/src/test/java/org/mozilla/fenix/session/SessionNotificationServiceTest.kt

@@ -0,0 +1,27 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+package org.mozilla.fenix.session
+
+import mozilla.components.support.test.robolectric.testContext
+import org.junit.Assert.assertFalse
+import org.junit.Assert.assertTrue
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.mozilla.fenix.helpers.FenixRobolectricTestRunner
+
+@RunWith(FenixRobolectricTestRunner::class)
+class SessionNotificationServiceTest {
+
+    @Test
+    fun `Service keeps tracked of started state`() {
+        assertFalse(SessionNotificationService.started)
+
+        SessionNotificationService.start(testContext, false)
+        assertTrue(SessionNotificationService.started)
+
+        SessionNotificationService.stop(testContext)
+        assertFalse(SessionNotificationService.started)
+    }
+}