ANTOOZA-BACKEND/Application/Features/Admin/Channel/YouTubePubSub/Get/Handler.cs

using Application.Abstractions.Data;
using Application.Abstractions.Messaging;
using Application.Abstractions.YouTube;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Options;
using SharedKernel;

namespace Application.Features.Admin.Channel.YouTubePubSub.Get;

internal sealed class Handler(
    IAppDbContext db,
    IYouTubePubSubService pubSubService,
    IOptions<AppSettings> settings
) : IQueryHandler<Query, Response>
{
    public async Task<Response> Handle(Query request, CancellationToken ct)
    {
        var subscribedIds = (await pubSubService.GetSubscribedChannelIdsAsync(ct)).ToHashSet();

        // DB의 YouTube 연동 채널 전체 (활성/비활성 모두)
        var channels = await db.Channel.AsNoTracking()
            .Where(c => c.YouTubeChannelID != null && c.YouTubeChannelID != "")
            .OrderByDescending(c => c.IsActive)
            .ThenBy(c => c.Name)
            .Select(c => new
            {
                c.ID,
                c.YouTubeChannelID,
                c.Name,
                c.Handle,
                c.ThumbnailUrl,
                c.IsActive
            })
            .ToListAsync(ct);

        var items = new List<SubscriptionItem>(channels.Count + subscribedIds.Count);
        var coveredIds = new HashSet<string>();

        // DB 채널 기준 표시 (구독 여부 표시)
        foreach (var c in channels)
        {
            var ytId = c.YouTubeChannelID!;
            items.Add(new SubscriptionItem(
                ytId,
                c.ID,
                c.Name,
                c.Handle,
                c.ThumbnailUrl,
                true,
                c.IsActive,
                subscribedIds.Contains(ytId)
            ));
            coveredIds.Add(ytId);
        }

        // DB에 없는데 Redis Set에 남아있는 "고아 구독" 표시
        foreach (var ytId in subscribedIds.Where(id => !coveredIds.Contains(id)))
        {
            items.Add(new SubscriptionItem(ytId, null, null, null, null, false, false, true));
        }

        var subscribedCount = items.Count(x => x.IsSubscribed);

        return new Response(items, items.Count, subscribedCount, settings.Value.YouTube.CallbackUrl);
    }
}