notif: On Android handle notification taps via Pigeon API

Instead of relying on Flutter's deeplinks implementation for
routing the notification URL, handle the Android Intents generated
by notification taps ourselves using Pigeon to pass those events
over to the Dart layer from the Java layer.

The upstream Flutter's deeplinks implementation has a bug where if
the deeplink is triggered after the app was killed by the OS when
it was in background, the app will get launched again but the
route/link will not reach the Flutter's navigation handlers. See:
  flutter/flutter#178305

In the failure case we seem to be receiving the Android Intent for
the notification tap from the OS via `MainActivity.onNewIntent`
without any problems. So, to workaround that upstream bug this
commit changes the implementation to handle these Android Intents
ourselves.

Fixes: #1567

Author: rajveermalviya

android/app/src/main/kotlin/com/zulip/flutter/MainActivity.kt

@@ -1,20 +1,27 @@
 package com.zulip.flutter
 
 import android.content.Intent
+import com.zulip.flutter.notifications.NotificationTapEventListener
+import com.zulip.flutter.notifications.NotificationTapEventsStreamHandler
 import io.flutter.embedding.android.FlutterActivity
 import io.flutter.embedding.engine.FlutterEngine
 
 class MainActivity : FlutterActivity() {
   private var androidIntentEventListener: AndroidIntentEventListener? = null
+  private var notificationTapEventListener: NotificationTapEventListener? = null
 
   override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
     super.configureFlutterEngine(flutterEngine)
 
     androidIntentEventListener = AndroidIntentEventListener()
     AndroidIntentEventsStreamHandler.register(
-      flutterEngine.dartExecutor.binaryMessenger,
-      androidIntentEventListener!!
+      flutterEngine.dartExecutor.binaryMessenger, androidIntentEventListener!!
     )
+    notificationTapEventListener = NotificationTapEventListener()
+    NotificationTapEventsStreamHandler.register(
+      flutterEngine.dartExecutor.binaryMessenger, notificationTapEventListener!!
+    )
+
     maybeHandleIntent(intent)
   }
 
@@ -35,6 +42,17 @@ class MainActivity : FlutterActivity() {
         return true
       }
 
+      Intent.ACTION_VIEW -> {
+        if (notificationTapEventListener!!.maybeHandleViewNotif(intent)) {
+          // Notification tapped
+          return true
+        }
+
+        // Let Flutter handle other intents, in particular the web-auth intents
+        // have ACTION_VIEW, scheme "zulip", and authority "login".
+        return false
+      }
+
       // For other intents, let Flutter handle it.
       else -> return false
     }

android/app/src/main/kotlin/com/zulip/flutter/notifications/NotificationTapEventListener.kt

@@ -0,0 +1,47 @@
+package com.zulip.flutter.notifications
+
+import android.content.Intent
+import android.net.Uri
+
+class NotificationTapEventListener : NotificationTapEventsStreamHandler() {
+  private var eventSink: PigeonEventSink<NotificationTapEvent>? = null
+  private val buffer = mutableListOf<NotificationTapEvent>()
+
+  override fun onListen(p0: Any?, sink: PigeonEventSink<NotificationTapEvent>) {
+    eventSink = sink
+    if (buffer.isNotEmpty()) {
+      buffer.forEach { sink.success(it) }
+      buffer.clear()
+    }
+  }
+
+  private fun onNotificationTapEvent(dataUrl: Uri) {
+    val event = AndroidNotificationTapEvent(dataUrl.toString())
+    if (eventSink != null) {
+      eventSink!!.success(event)
+    } else {
+      buffer.add(event)
+    }
+  }
+
+  /**
+   * Recognize if the ACTION_VIEW intent came from tapping a notification; handle it if so
+   *
+   * If the intent is recognized, sends a notification tap event via
+   * the Pigeon event stream to the Dart layer and returns true.
+   * Else does nothing and returns false.
+   *
+   * Do not call if `intent.action` is not ACTION_VIEW.
+   */
+  fun maybeHandleViewNotif(intent: Intent): Boolean {
+    assert(intent.action == Intent.ACTION_VIEW)
+
+    val url = intent.data
+    if (url?.scheme == "zulip" && url.authority == "notification") {
+      onNotificationTapEvent(url)
+      return true
+    }
+
+    return false
+  }
+}