Fisher-Yates shuffle

Scripts/Utils/ShuffleExtensions.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using Godot;
+
+namespace Cirno.Scripts.Utils;
+
+public static class ShuffleExtensions
+{
+    //private static Random rng = new Random();
+
+    public static IEnumerable<T> Shuffle<T>(this IEnumerable<T> source, int? desiredLength = null)
+    {
+        if (source == null) throw new ArgumentNullException(nameof(source));
+
+        var list = source.ToList();
+        int originalCount = list.Count;
+
+        if (originalCount == 0) yield break;
+
+        // Repeat elements to meet the desired length
+        if (desiredLength.HasValue && desiredLength > originalCount)
+        {
+            int countToAdd = desiredLength.Value - originalCount;
+            for (int i = 0; i < countToAdd; i++)
+            {
+                list.Add(list[i % originalCount]);
+            }
+        }
+
+        // Fisher-Yates shuffle
+        for (int i = list.Count - 1; i > 0; i--)
+        {
+            //int j = rng.Next(i + 1);
+            int j = GD.RandRange(0, i);
+            (list[i], list[j]) = (list[j], list[i]);
+        }
+
+        // Return only up to desired length if specified
+        foreach (var item in list.Take(desiredLength ?? list.Count))
+        {
+            yield return item;
+        }
+    }
+}