ANTOOZA-BACKEND/Application/Features/Api/Channel/GetLiveList/Handler.cs

using Application.Abstractions.Cache;
using Application.Abstractions.Data;
using Application.Abstractions.Messaging;
using Application.Abstractions.YouTube;
using Microsoft.EntityFrameworkCore;
using SharedKernel.Results;

namespace Application.Features.Api.Channel.GetLiveList;

public sealed class Handler(
    IAppDbContext db,
    IYouTubeLiveStateStore liveStateStore,
    IYouTubeChannelCache channelCache,
    ICacheService cache
) : IQueryHandler<Query, Result<Response>>
{
    private const string CacheKey = "channel:live:list:main";
    private const int MaxLimit = 100;
    private const int DefaultLimit = 24;
    private static readonly TimeSpan CacheTtl = TimeSpan.FromSeconds(30);

    public async Task<Result<Response>> Handle(Query request, CancellationToken ct)
    {
        var limit = request.Limit <= 0 ? DefaultLimit : Math.Min(request.Limit, MaxLimit);
        var offset = Math.Max(request.Offset, 0);

        var fullList = await cache.GetAsync<List<LiveChannelItem>>(CacheKey, ct);
        if (fullList is null)
        {
            fullList = await BuildFullLiveListAsync(ct);
            await cache.SetAsync(CacheKey, fullList, CacheTtl, ct);
        }

        IEnumerable<LiveChannelItem> filtered = fullList;

        if (!string.IsNullOrWhiteSpace(request.Keyword))
        {
            var keyword = request.Keyword.Trim();
            filtered = filtered.Where(c => c.ChannelName.Contains(keyword, StringComparison.OrdinalIgnoreCase) || (c.Handle is not null && c.Handle.Contains(keyword, StringComparison.OrdinalIgnoreCase)));
        }

        filtered = request.Sort switch
        {
            "newest" => filtered.OrderByDescending(c => c.StartedAt ?? DateTime.MinValue),
            "name" => filtered.OrderBy(c => c.ChannelName),
            _ => filtered.OrderByDescending(c => c.ViewerCount)
        };

        var ordered = filtered.ToList();
        var total = ordered.Count;
        var page = ordered.Skip(offset).Take(limit).ToList();

        return new Response(page, total);
    }

    private async Task<List<LiveChannelItem>> BuildFullLiveListAsync(CancellationToken ct)
    {
        var channels = await db.Channel.AsNoTracking().Where(c => c.IsActive).Select(c => new { c.SID, c.Name, c.Handle }).ToListAsync(ct);

        if (channels.Count == 0)
        {
            return [];
        }

        var allLive = await liveStateStore.GetAllLiveAsync();
        var liveMap = allLive.Where(l => l.IsLive).ToDictionary(l => l.ChannelId);

        if (liveMap.Count == 0)
        {
            return [];
        }

        var liveChannels = channels.Where(c => liveMap.ContainsKey(c.SID)).ToList();

        if (liveChannels.Count == 0)
        {
            return [];
        }

        var ytCache = await channelCache.GetManyAsync(liveChannels.Select(c => c.SID));

        // ViewerCount 는 YouTube concurrentViewers 를 poller 가 30초 주기로 Redis 에 갱신한 값
        // (과거 IChatConnectionTracker 는 "사이트 접속자 수" 였음 — YouTube 시청자 수가 아니라서 제거)
        var items = liveChannels.Select(ch => {
            var liveInfo = liveMap[ch.SID];
            var ytInfo = ytCache.GetValueOrDefault(ch.SID);

            return new LiveChannelItem(
                ch.SID,
                ch.Name,
                ch.Handle,
                ytInfo?.ThumbnailUrl,
                liveInfo.VideoId,
                $"https://img.youtube.com/vi/{liveInfo.VideoId}/mqdefault.jpg",
                liveInfo.Title,
                liveInfo.ViewerCount,
                liveInfo.ActualStartTime
            );
        }).ToList();

        items.Sort((a, b) => b.ViewerCount.CompareTo(a.ViewerCount));

        return items;
    }
}