Kavita/API/Extensions/EnumerableExtensions.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;
using API.Data.Misc;
using API.Entities.Enums;

namespace API.Extensions;
#nullable enable

public static class EnumerableExtensions
{
    private static readonly Regex Regex = new Regex(@"\d+", RegexOptions.Compiled, TimeSpan.FromMilliseconds(500));

    /// <summary>
    /// A natural sort implementation
    /// </summary>
    /// <param name="items">IEnumerable to process</param>
    /// <param name="selector">Function that produces a string. Does not support null values</param>
    /// <param name="stringComparer">Defaults to CurrentCulture</param>
    /// <typeparam name="T"></typeparam>
    /// <returns>Sorted Enumerable</returns>
    public static IEnumerable<T> OrderByNatural<T>(this IEnumerable<T> items, Func<T, string> selector, StringComparer? stringComparer = null)
    {
        var list = items.ToList();
        var maxDigits = list
            .SelectMany(i => Regex.Matches(selector(i))
                .Select(digitChunk => (int?)digitChunk.Value.Length))
            .Max() ?? 0;

        return list.OrderBy(i => Regex.Replace(selector(i), match => match.Value.PadLeft(maxDigits, '0')), stringComparer ?? StringComparer.CurrentCulture);
    }

    public static IEnumerable<RecentlyAddedSeries> RestrictAgainstAgeRestriction(this IEnumerable<RecentlyAddedSeries> items, AgeRestriction restriction)
    {
        if (restriction.AgeRating == AgeRating.NotApplicable) return items;
        var q = items.Where(s => s.AgeRating <= restriction.AgeRating);
        if (!restriction.IncludeUnknowns)
        {
            return q.Where(s => s.AgeRating != AgeRating.Unknown);
        }

        return q;
    }
}