Kavita/API/Extensions/ChapterListExtensions.cs

using System.Collections.Generic;
using System.Linq;
using API.Entities;
using API.Parser;

namespace API.Extensions
{
    public static class ChapterListExtensions
    {
        /// <summary>
        /// Returns first chapter in the list with at least one file
        /// </summary>
        /// <param name="chapters"></param>
        /// <returns></returns>
        public static Chapter GetFirstChapterWithFiles(this IList<Chapter> chapters)
        {
            return chapters.FirstOrDefault(c => c.Files.Any());
        }

        /// <summary>
        /// Gets a single chapter (or null if doesn't exist) where Range matches the info.Chapters property. If the info
        /// is <see cref="ParserInfo.IsSpecial"/> then, the filename is used to search against Range or if filename exists within Files of said Chapter.
        /// </summary>
        /// <param name="chapters"></param>
        /// <param name="info"></param>
        /// <returns></returns>
        public static Chapter GetChapterByRange(this IList<Chapter> chapters, ParserInfo info)
        {
            var specialTreatment = info.IsSpecialInfo();
            return specialTreatment
                ? chapters.SingleOrDefault(c => c.Range == info.Filename || (c.Files.Select(f => f.FilePath).Contains(info.FullFilePath)))
                : chapters.SingleOrDefault(c => c.Range == info.Chapters);
        }
    }
}