[mob][photos] Send pair req after getting receiver status

mobile/plugins/ente_cast_normal/lib/src/service.dart

@@ -1,29 +1,49 @@
+import "dart:developer" as dev;
+
 import "package:cast/cast.dart";
 import "package:ente_cast/ente_cast.dart";
 import "package:flutter/material.dart";
 
 class CastServiceImpl extends CastService {
+  final String _appId = 'F5BCEC64';
+  final String _pairRequestNamespace = 'urn:x-cast:pair-request';
+  final Map<String, CastDevice> sessionIDToDeviceID = {};
+
   @override
   Future<void> connectDevice(BuildContext context, Object device) async {
     final CastDevice castDevice = device as CastDevice;
     final session = await CastSessionManager().startSession(castDevice);
+    session.messageStream.listen((message) {
+      if (message['type'] == "RECEIVER_STATUS") {
+        dev.log(
+          "got RECEIVER_STATUS, Send request to pair",
+          name: "CastServiceImpl",
+        );
+        session.sendMessage(_pairRequestNamespace, {});
+      } else {
+        print('receive message: $message');
+      }
+    });
 
     session.stateStream.listen((state) {
       if (state == CastSessionState.connected) {
         const snackBar = SnackBar(content: Text('Connected'));
         ScaffoldMessenger.of(context).showSnackBar(snackBar);
-        session.sendMessage('urn:x-cast:pair-request', {});
+        sessionIDToDeviceID[session.sessionId] = castDevice;
+        debugPrint("Send request to pair");
+        session.sendMessage(_pairRequestNamespace, {});
+      } else if (state == CastSessionState.closed) {
+        dev.log('Session closed', name: 'CastServiceImpl');
+        sessionIDToDeviceID.remove(session.sessionId);
       }
     });
-    session.messageStream.listen((message) {
-      print('receive message: $message');
-    });
 
+    debugPrint("Send request to launch");
     session.sendMessage(CastSession.kNamespaceReceiver, {
       'type': 'LAUNCH',
-      'appId': 'F5BCEC64', // set the appId of your app here
+      'appId': _appId, // set the appId of your app here
     });
-    session.sendMessage('urn:x-cast:pair-request', {});
+    // session.sendMessage('urn:x-cast:pair-request', {});
   }
 
   @override