feat(in_app_messaging): expose the message lifecycle events

Adds `onMessageClicked`, `onMessageImpression`, `onMessageDismissed` and
`onMessageDisplayError` to `FirebaseInAppMessaging`, so apps can react to
what happens to a campaign message - most importantly read the action URL
of the button a user tapped, together with the campaign metadata.

The native listeners are attached the first time one of the streams is
read, so apps that never listen keep the current behavior and, on iOS,
keep ownership of the `InAppMessaging` display delegate.

Android reports no dismiss type, so `InAppMessagingDismissType.unknown`
is always used there.

Closes #12984

Author: Lyokone

packages/firebase_in_app_messaging/firebase_in_app_messaging/README.md

@@ -14,6 +14,20 @@ To get started with Firebase In-App Messaging for Flutter, please [see the docum
 
 To use this plugin, please visit the [Firebase In-App Messaging Usage documentation](https://firebase.google.com/docs/in-app-messaging/get-started?platform=flutter)
 
+### Message lifecycle events
+
+Listen to the streams below to react to what happens to the messages of your
+campaigns, for example to handle the URL of the button a user tapped yourself:
+
+```dart
+FirebaseInAppMessaging.instance.onMessageClicked.listen((event) {
+  print('${event.campaignMetadata.campaignName} -> ${event.action.actionUrl}');
+});
+```
+
+`onMessageImpression`, `onMessageDismissed` and `onMessageDisplayError` report
+the rest of the message lifecycle.
+
 ## Issues and feedback
 
 Please file FlutterFire specific issues, bugs, or feature requests in our [issue tracker](https://github.com/firebase/flutterfire/issues/new).

packages/firebase_in_app_messaging/firebase_in_app_messaging/android/src/main/kotlin/io/flutter/plugins/firebase/inappmessaging/FirebaseInAppMessagingPlugin.kt

@@ -3,24 +3,61 @@
 // found in the LICENSE file.
 package io.flutter.plugins.firebase.inappmessaging
 
+import android.os.Handler
+import android.os.Looper
 import com.google.android.gms.tasks.Task
 import com.google.android.gms.tasks.TaskCompletionSource
 import com.google.firebase.FirebaseApp
 import com.google.firebase.inappmessaging.FirebaseInAppMessaging
+import com.google.firebase.inappmessaging.FirebaseInAppMessagingClickListener
+import com.google.firebase.inappmessaging.FirebaseInAppMessagingDismissListener
+import com.google.firebase.inappmessaging.FirebaseInAppMessagingDisplayErrorListener
+import com.google.firebase.inappmessaging.FirebaseInAppMessagingImpressionListener
+import com.google.firebase.inappmessaging.model.InAppMessage
 import io.flutter.embedding.engine.plugins.FlutterPlugin
 import io.flutter.embedding.engine.plugins.FlutterPlugin.FlutterPluginBinding
 import io.flutter.plugin.common.BinaryMessenger
 import io.flutter.plugins.firebase.core.FlutterFirebasePlugin
 import io.flutter.plugins.firebase.core.FlutterFirebasePluginRegistry
+import java.util.concurrent.Executor
 
 /** FirebaseInAppMessagingPlugin */
 class FirebaseInAppMessagingPlugin :
     FlutterFirebasePlugin, FlutterPlugin, FirebaseInAppMessagingHostApi {
   private var binaryMessenger: BinaryMessenger? = null
+  private var flutterApi: FirebaseInAppMessagingFlutterApi? = null
+
+  // The listeners below forward events to Dart, which has to happen on the main
+  // thread, so they are registered with a main thread executor.
+  private val mainThreadExecutor = Executor { command ->
+    Handler(Looper.getMainLooper()).post(command)
+  }
+
+  private val clickListener = FirebaseInAppMessagingClickListener { inAppMessage, action ->
+    flutterApi?.onMessageClicked(
+        campaignMetadata(inAppMessage), FiamAction(action.actionUrl, action.button?.text?.text)) {}
+  }
+
+  private val impressionListener = FirebaseInAppMessagingImpressionListener { inAppMessage ->
+    flutterApi?.onMessageImpression(campaignMetadata(inAppMessage)) {}
+  }
+
+  private val dismissListener = FirebaseInAppMessagingDismissListener { inAppMessage ->
+    // The Android SDK does not report how a message was dismissed.
+    flutterApi?.onMessageDismissed(campaignMetadata(inAppMessage), FiamDismissType.UNKNOWN) {}
+  }
+
+  private val displayErrorListener =
+      FirebaseInAppMessagingDisplayErrorListener { inAppMessage, errorReason ->
+        flutterApi?.onMessageDisplayError(campaignMetadata(inAppMessage), errorReason.name) {}
+      }
+
+  private var eventListenersAdded = false
 
   private fun initInstance(messenger: BinaryMessenger) {
     FlutterFirebasePluginRegistry.registerPlugin(METHOD_CHANNEL_NAME, this)
     binaryMessenger = messenger
+    flutterApi = FirebaseInAppMessagingFlutterApi(messenger)
     FirebaseInAppMessagingHostApi.setUp(messenger, this)
   }
 
@@ -29,10 +66,49 @@ class FirebaseInAppMessagingPlugin :
   }
 
   override fun onDetachedFromEngine(binding: FlutterPluginBinding) {
+    removeEventListeners()
     binaryMessenger = null
+    flutterApi = null
     FirebaseInAppMessagingHostApi.setUp(binding.binaryMessenger, null)
   }
 
+  private fun campaignMetadata(inAppMessage: InAppMessage): FiamCampaignMetadata {
+    val metadata = inAppMessage.campaignMetadata
+    return FiamCampaignMetadata(
+        metadata?.campaignId ?: "", metadata?.campaignName ?: "", metadata?.isTestMessage ?: false)
+  }
+
+  private fun removeEventListeners() {
+    if (!eventListenersAdded) return
+    eventListenersAdded = false
+
+    FirebaseInAppMessaging.getInstance().apply {
+      removeClickListener(clickListener)
+      removeImpressionListener(impressionListener)
+      removeDismissListener(dismissListener)
+      removeDisplayErrorListener(displayErrorListener)
+    }
+  }
+
+  override fun addEventListeners(appName: String, callback: (Result<Unit>) -> Unit) {
+    FlutterFirebasePlugin.cachedThreadPool.execute {
+      try {
+        if (!eventListenersAdded) {
+          FirebaseInAppMessaging.getInstance().apply {
+            addClickListener(clickListener, mainThreadExecutor)
+            addImpressionListener(impressionListener, mainThreadExecutor)
+            addDismissListener(dismissListener, mainThreadExecutor)
+            addDisplayErrorListener(displayErrorListener, mainThreadExecutor)
+          }
+          eventListenersAdded = true
+        }
+        callback(Result.success(Unit))
+      } catch (exception: Exception) {
+        handleFailure(callback, exception)
+      }
+    }
+  }
+
   override fun triggerEvent(appName: String, eventName: String, callback: (Result<Unit>) -> Unit) {
     FlutterFirebasePlugin.cachedThreadPool.execute {
       try {