Frontend first draft

frontend/pweb/lib/utils/snackbar.dart

@@ -0,0 +1,29 @@
+import 'dart:async';
+
+import 'package:flutter/material.dart';
+
+
+ScaffoldFeatureController<SnackBar, SnackBarClosedReason> notifyUserX(
+  ScaffoldMessengerState sm, 
+  String message, 
+  { int delaySeconds = 3 }
+) => sm.showSnackBar(SnackBar(content: Text(message), duration: Duration(seconds: delaySeconds)));
+
+ScaffoldFeatureController<SnackBar, SnackBarClosedReason> notifyUser(
+  BuildContext context, 
+  String message, 
+  { int delaySeconds = 3 }
+) => notifyUserX(ScaffoldMessenger.of(context), message, delaySeconds: delaySeconds);
+
+Future<ScaffoldFeatureController<SnackBar, SnackBarClosedReason>> postNotifyUser(
+  BuildContext context, String message, {int delaySeconds = 3}) {
+
+  final completer = Completer<ScaffoldFeatureController<SnackBar, SnackBarClosedReason>>();
+
+  WidgetsBinding.instance.addPostFrameCallback((_) {
+    final controller = notifyUser(context, message, delaySeconds: delaySeconds);
+    completer.complete(controller);
+  });
+
+  return completer.future;
+}