using DynamicData.Binding;

namespace PLib.Desktop.ViewModels;

/// <summary>
/// A sort order, its label, and the comparer DynamicData keeps the bound collection in.
/// </summary>
/// <remarks>
/// Every comparer ends with the identifier so the order is total. Ties would otherwise let
/// DynamicData move equal items around on each refresh, which the user sees as cards
/// twitching while a scan streams in.
/// </remarks>
public sealed record SortOption(string Label, IComparer<VideoCardViewModel> Comparer)
{
    public static IReadOnlyList<SortOption> All { get; } =
    [
        new("Недавно добавленные", SortExpressionComparer<VideoCardViewModel>
            .Descending(x => x.AddedAt)
            .ThenByAscending(x => x.Id)),

        new("По названию", new TitleComparer()),

        new("Сначала длинные", SortExpressionComparer<VideoCardViewModel>
            .Descending(x => x.RawDuration ?? TimeSpan.Zero)
            .ThenByAscending(x => x.Id)),

        new("Сначала большие", SortExpressionComparer<VideoCardViewModel>
            .Descending(x => x.RawSizeInBytes)
            .ThenByAscending(x => x.Id)),
    ];

    /// <summary>
    /// Culture-aware, case-insensitive title order. <see cref="SortExpressionComparer{T}"/>
    /// would fall back to ordinal comparison, which puts Cyrillic and Latin titles in an
    /// order no reader expects.
    /// </summary>
    private sealed class TitleComparer : IComparer<VideoCardViewModel>
    {
        public int Compare(VideoCardViewModel? x, VideoCardViewModel? y)
        {
            var byTitle = string.Compare(x?.Title, y?.Title, StringComparison.CurrentCultureIgnoreCase);
            return byTitle != 0 ? byTitle : Comparer<Guid>.Default.Compare(x?.Id ?? Guid.Empty, y?.Id ?? Guid.Empty);
        }
    }
}