Scaffold out initial state management

lib/main.dart

@@ -4,6 +4,7 @@ import 'package:flutter/material.dart';
 import 'package:provider/provider.dart';
 import 'days_enum.dart';
 import 'day_page.dart';
+import "util.dart";
 
 void main() {
   runApp(MyApp());
@@ -28,7 +29,28 @@ class MyApp extends StatelessWidget {
   }
 }
 
+class DayPageState {
+  String? selectedFile;
+}
+
 class MyAppState extends ChangeNotifier {
+  Map<AdventOfCodeDays, DayPageState> dayPageState = {};
+
+  MyAppState() {
+    for (var day in AdventOfCodeDays.values) {
+      dayPageState[day] = DayPageState();
+    }
+  }
+
+  String? getSelectedFile(AdventOfCodeDays day) {
+    return dayPageState[day]?.selectedFile;
+  }
+
+  void setSelectedFile(AdventOfCodeDays day, String? file) {
+    debugLog("setSelectedFile called on $day");
+    dayPageState[day]?.selectedFile = file;
+    notifyListeners();
+  }
 }
 
 class MyHomePage extends StatefulWidget {
@@ -56,7 +78,7 @@ class _MyHomePageState extends State<MyHomePage> {
     }
     var colorScheme = Theme.of(context).colorScheme;
 
-    Widget page = DayPage();
+    Widget page = DayPage(AdventOfCodeDays.day1);
 
     // The container for the current page, with its background color
     // and subtle switching animation.