migrated Marianum Message module to the Marianum-Connect API and implemented push notification deep linking

lib/push/push_tap_router.dart

@@ -16,6 +16,10 @@ class PushTapRouter {
   /// listens to this and opens the chat, then resets it to null.
   static final ValueNotifier<String?> pendingChatToken = ValueNotifier(null);
 
+  /// Newsletter id of the most recently tapped Marianum-Message notification,
+  /// or null. [App] listens to this and opens the message, then resets it.
+  static final ValueNotifier<String?> pendingNewsletterId = ValueNotifier(null);
+
   static void handleResponse(NotificationResponse response) {
     final actionId = response.actionId;
     if (actionId == kTalkReplyActionId || actionId == kTalkMarkReadActionId) {
@@ -23,18 +27,28 @@ class PushTapRouter {
       PushActions.handleBackgroundResponse(response);
       return;
     }
-    final token = _chatTokenFrom(response.payload);
+    final map = _payloadMap(response.payload);
+    if (map == null) return;
+    final newsletterId = _stringValue(map, 'newsletterId');
+    if (newsletterId != null) {
+      pendingNewsletterId.value = newsletterId;
+      return;
+    }
+    final token = _stringValue(map, 'chatToken');
     if (token != null) pendingChatToken.value = token;
   }
 
-  static String? _chatTokenFrom(String? payload) {
+  static Map<String, dynamic>? _payloadMap(String? payload) {
     if (payload == null || payload.isEmpty) return null;
     try {
-      final map = jsonDecode(payload) as Map<String, dynamic>;
-      final token = map['chatToken'];
-      return token is String && token.isNotEmpty ? token : null;
+      return jsonDecode(payload) as Map<String, dynamic>;
     } on Object {
       return null;
     }
   }
+
+  static String? _stringValue(Map<String, dynamic> map, String key) {
+    final value = map[key];
+    return value is String && value.isNotEmpty ? value : null;
+  }
 }