#nullable enable
using System.Collections.Generic;
using System.Linq;
using API.Comparators;
using API.Entities;

namespace API.Extensions;

public static class SeriesExtensions
{
    /// <summary>
    /// Calculates the Cover Image for the Series
    /// </summary>
    /// <param name="series"></param>
    /// <returns></returns>
    /// <remarks>This is under the assumption that the Volume already has a Cover Image calculated and set</remarks>
    public static string? GetCoverImage(this Series series)
    {
        var volumes = series.Volumes ?? new List<Volume>();
        var firstVolume = volumes.GetCoverImage(series.Format);
        if (firstVolume == null) return null;
        string? coverImage = null;

        var chapters = firstVolume.Chapters
            .OrderBy(c => double.Parse(c.Number), ChapterSortComparerZeroFirst.Default).ToList();
        if (chapters.Count > 1 && chapters.Any(c => c.IsSpecial))
        {
            coverImage = chapters.FirstOrDefault(c => !c.IsSpecial)?.CoverImage ?? chapters.First().CoverImage;
            firstVolume = null;
        }
        else
        {
            var allChapters = volumes
                .SelectMany(v => v.Chapters)
                .OrderBy(c => double.Parse(c.Number), ChapterSortComparerZeroFirst.Default)
                .Where(c => !c.IsSpecial)
                .ToList();

            var num = allChapters.FirstOrDefault()?.Number ?? $"{int.MaxValue}";

            if (double.Parse(num) < firstVolume.Number && double.Parse(num) < double.Parse(chapters.First().Number))
            {
                coverImage = allChapters.First().CoverImage;
            }
        }


        return coverImage ?? firstVolume?.CoverImage;
    }
}