Initial commit

Helpers/ChangeNotifier.cs

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+using System;
+using System.Collections.Generic;
+using System.ComponentModel;
+using System.Runtime.CompilerServices;
+using System.Text;
+
+namespace ReceiptPDFBuilder.Helpers
+{
+
+    // https://docs.microsoft.com/en-us/dotnet/api/system.componentmodel.inotifypropertychanged?view=netframework-4.7.2
+    class ChangeNotifier : INotifyPropertyChanged
+    {
+        public event PropertyChangedEventHandler? PropertyChanged;
+        protected void NotifyPropertyChanged([CallerMemberName] string propertyName = "")
+        {
+            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
+        }
+    }
+}

Helpers/ListExtensions.cs

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+using System;
+using System.Collections.Generic;
+using System.Threading;
+
+namespace ReceiptPDFBuilders.Helpers;
+
+public static class ThreadSafeRandom
+{
+    [ThreadStatic] private static Random? Local;
+
+    public static Random ThisThreadsRandom
+    {
+        get { return Local ?? (Local = new Random(unchecked(Environment.TickCount * 31 + Thread.CurrentThread.ManagedThreadId))); }
+    }
+}
+
+// https://stackoverflow.com/a/1262619/3938401
+static class ListExtensions
+{
+    public static void Shuffle<T>(this IList<T> list)
+    {
+        int n = list.Count;
+        while (n > 1)
+        {
+            n--;
+            int k = ThreadSafeRandom.ThisThreadsRandom.Next(n + 1);
+            T value = list[k];
+            list[k] = list[n];
+            list[n] = value;
+        }
+    }
+}