notif android: Migrate to cross-platform Pigeon API for navigation

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

@@ -1,6 +1,79 @@
 package com.zulip.flutter
 
+import android.content.Intent
 import io.flutter.embedding.android.FlutterActivity
+import io.flutter.embedding.engine.FlutterEngine
 
-class MainActivity: FlutterActivity() {
+class MainActivity : FlutterActivity() {
+  private var notificationTapEventListener: NotificationTapEventListener? = null
+
+  override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
+    super.configureFlutterEngine(flutterEngine)
+
+    val maybeNotifPayload = maybeIntentExtrasData(intent)
+    val api = NotificationHostApiImpl(maybeNotifPayload?.let { NotificationDataFromLaunch(it) })
+    NotificationHostApi.setUp(flutterEngine.dartExecutor.binaryMessenger, api)
+
+    notificationTapEventListener = NotificationTapEventListener()
+    NotificationTapEventsStreamHandler.register(
+      flutterEngine.dartExecutor.binaryMessenger, notificationTapEventListener!!
+    )
+  }
+
+  override fun onNewIntent(intent: Intent) {
+    val maybeExtrasData = maybeIntentExtrasData(intent)
+    if (notificationTapEventListener != null && maybeExtrasData != null) {
+      notificationTapEventListener!!.onNotificationTapEvent(NotificationTapEvent(payload = maybeExtrasData))
+      return
+    }
+
+    super.onNewIntent(intent)
+  }
+
+  override fun cleanUpFlutterEngine(flutterEngine: FlutterEngine) {
+    notificationTapEventListener?.onEventsDone()
+    notificationTapEventListener = null
+
+    super.cleanUpFlutterEngine(flutterEngine)
+  }
+
+  private fun maybeIntentExtrasData(intent: Intent): Map<Any?, Any?>? {
+    var extrasData: Map<Any?, Any?>? = null
+    if (intent.action == Intent.ACTION_VIEW) {
+      val intentUrl = intent.data
+      if (intentUrl?.scheme == "zulip" && intentUrl.authority == "notification") {
+        val bundle = intent.getBundleExtra("data")
+        if (bundle != null) {
+          extrasData =
+            bundle.keySet().mapNotNull { key -> bundle.getString(key)?.let { key to it } }
+              .toMap<Any?, Any?>()
+        }
+      }
+    }
+    return extrasData
+  }
+}
+
+private class NotificationHostApiImpl(val maybeDataFromLaunch: NotificationDataFromLaunch?) :
+  NotificationHostApi {
+  override fun getNotificationDataFromLaunch(): NotificationDataFromLaunch? {
+    return maybeDataFromLaunch
+  }
+}
+
+private class NotificationTapEventListener : NotificationTapEventsStreamHandler() {
+  private var eventSink: PigeonEventSink<NotificationTapEvent>? = null
+
+  override fun onListen(p0: Any?, sink: PigeonEventSink<NotificationTapEvent>) {
+    eventSink = sink
+  }
+
+  fun onNotificationTapEvent(data: NotificationTapEvent) {
+    eventSink?.success(data)
+  }
+
+  fun onEventsDone() {
+    eventSink?.endOfStream()
+    eventSink = null
+  }
 }