cirnogodot/Scripts/Utils/ShuffleExtensions.cs

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 > 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;
        }
    }
}