using Application.Abstractions.Data;
using Application.Abstractions.Messaging;
using Microsoft.EntityFrameworkCore;

namespace Application.Features.Api.ChannelTitle.GetMyTitles;

internal sealed class Handler(IAppDbContext db) : IQueryHandler<Query, Response>
{
    public async Task<Response> Handle(Query request, CancellationToken ct)
    {
        var stats = await db.DonorChannelStats.AsNoTracking()
            .Where(s => s.DonorMemberID == request.MemberID && s.CumulativeAmount > 0)
            .Join(db.Channel.AsNoTracking(), s => s.ChannelID, c => c.ID, (s, c) => new
            {
                s.ChannelID,
                ChannelName = c.Name,
                ChannelThumb = c.ThumbnailUrl,
                s.CumulativeAmount,
                s.DonationCount
            })
            .ToListAsync(ct);

        if (stats.Count == 0)
        {
            return new Response([]);
        }

        var channelIds = stats.Select(s => s.ChannelID).ToList();

        var titles = await db.ChannelTitle.AsNoTracking()
            .Where(t => t.IsActive && channelIds.Contains(t.ChannelID))
            .OrderBy(t => t.ChannelID).ThenBy(t => t.MinAmount)
            .ToListAsync(ct);

        var selections = await db.DonorTitleSelection.AsNoTracking()
            .Where(s => s.DonorMemberID == request.MemberID && channelIds.Contains(s.ChannelID))
            .ToListAsync(ct);

        var groups = stats.Select(stat => {
            var selected = selections.FirstOrDefault(s => s.ChannelID == stat.ChannelID);
            var channelTitles = titles.Where(t => t.ChannelID == stat.ChannelID).ToList();

            var items = channelTitles.Select(t => {
                var acquired = stat.CumulativeAmount >= t.MinAmount;
                var remaining = Math.Max(0, t.MinAmount - stat.CumulativeAmount);
                var isSelected = selected?.SelectedTitleID == t.ID;

                return new MyTitleItem(
                    t.ID,
                    t.Name,
                    t.Description,
                    t.MinAmount,
                    t.Color,
                    t.IconUrl,
                    acquired,
                    isSelected,
                    remaining
                );
            }).ToList();

            return new ChannelTitleGroup(
                stat.ChannelID,
                stat.ChannelName,
                stat.ChannelThumb,
                stat.CumulativeAmount,
                stat.DonationCount,
                selected?.SelectedTitleID,
                items
            );
        }).ToList();

        return new Response(groups);
    }
}