emby-toolbox/EmbyToolbox/Services/NaturalStringComparer.cs

using System.Collections;
using System.Globalization;

namespace EmbyToolbox.Services;

public sealed class NaturalStringComparer : IComparer<string>, IComparer
{
    public static readonly NaturalStringComparer Instance = new();

    public int Compare(string? x, string? y)
    {
        if (ReferenceEquals(x, y))
        {
            return 0;
        }

        if (x is null)
        {
            return -1;
        }

        if (y is null)
        {
            return 1;
        }

        var ix = 0;
        var iy = 0;
        while (ix < x.Length && iy < y.Length)
        {
            var cx = x[ix];
            var cy = y[iy];

            if (char.IsDigit(cx) && char.IsDigit(cy))
            {
                var startX = ix;
                var startY = iy;
                while (ix < x.Length && char.IsDigit(x[ix])) ix++;
                while (iy < y.Length && char.IsDigit(y[iy])) iy++;

                var partX = x[startX..ix].TrimStart('0');
                var partY = y[startY..iy].TrimStart('0');
                if (partX.Length != partY.Length)
                {
                    return partX.Length.CompareTo(partY.Length);
                }

                var compareNumeric = string.Compare(partX, partY, StringComparison.Ordinal);
                if (compareNumeric != 0)
                {
                    return compareNumeric;
                }

                var rawX = x[startX..ix];
                var rawY = y[startY..iy];
                if (rawX.Length != rawY.Length)
                {
                    return rawX.Length.CompareTo(rawY.Length);
                }
            }
            else
            {
                var cmp = char.ToUpper(cx, CultureInfo.InvariantCulture).CompareTo(char.ToUpper(cy, CultureInfo.InvariantCulture));
                if (cmp != 0)
                {
                    return cmp;
                }

                ix++;
                iy++;
            }
        }

        return x.Length.CompareTo(y.Length);
    }

    int IComparer.Compare(object? x, object? y) => Compare(x as string, y as string);
}