using Application.Abstractions.Data;
using Application.Abstractions.YouTube;
using Domain.Entities.Members;
using Domain.Entities.Members.ValueObject;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;

namespace Infrastructure.YouTube;

/// <summary>
/// 매일 자정 00:00(KST) 1회 실행 — YouTube 방송 지표 집계.
/// - 각 활성 채널의 uploads 플레이리스트에서 최근 50개 videoId 조회
/// - IsFinalized=false 세션 또는 최근 7일 내 업로드 videoId만 대상
/// - videos.list 로 liveStreamingDetails + statistics 배치 조회
/// - BroadcastSession 생성/갱신, End+24h 경과 시 IsFinalized=true
/// - ChannelBroadcastStats 누적 재계산
///
/// API quota: 채널당 1(playlistItems) + 3(videos.list) = 4 units/일
/// 1,000채널까지 안전 (기본 10,000 quota).
/// </summary>
internal sealed class YouTubeDailyAggregatorService(
    IServiceScopeFactory scopeFactory,
    IYouTubeApiService youTubeApi,
    ILogger<YouTubeDailyAggregatorService> logger
) : BackgroundService
{
    private const int BatchSize = 50; // YouTube API 최대 50개/요청
    private const int UploadsLookback = 50; // 채널당 조회할 최근 업로드 수
    private static readonly TimeSpan InitialDelay = TimeSpan.FromMinutes(2);

    // 한국 표준시(KST) 자정 기준으로 실행
    private static readonly TimeZoneInfo Kst = TimeZoneInfo.FindSystemTimeZoneById("Korea Standard Time");

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        await Task.Delay(InitialDelay, stoppingToken);
        logger.LogInformation("[YouTubeDailyAggregator] 서비스 시작 — 매일 KST 00:00 실행");

        while (!stoppingToken.IsCancellationRequested)
        {
            var delay = CalculateDelayUntilNextMidnight();
            logger.LogInformation("[YouTubeDailyAggregator] 다음 실행까지 대기: {Hours}시간 {Minutes}분", delay.Hours, delay.Minutes);

            try
            {
                await Task.Delay(delay, stoppingToken);
            }
            catch (TaskCanceledException)
            {
                break;
            }

            try
            {
                await AggregateAllAsync(stoppingToken);
            }
            catch (Exception ex)
            {
                logger.LogError(ex, "[YouTubeDailyAggregator] 집계 실행 중 오류");
            }
        }
    }

    private static TimeSpan CalculateDelayUntilNextMidnight()
    {
        var nowKst = TimeZoneInfo.ConvertTimeFromUtc(DateTime.UtcNow, Kst);
        var nextMidnightKst = nowKst.Date.AddDays(1);
        var delay = nextMidnightKst - nowKst;

        if (delay <= TimeSpan.Zero)
        {
            delay = TimeSpan.FromMinutes(1);
        }

        return delay;
    }

    private async Task AggregateAllAsync(CancellationToken ct)
    {
        logger.LogInformation("[YouTubeDailyAggregator] 집계 시작");

        using var scope = scopeFactory.CreateScope();
        var db = scope.ServiceProvider.GetRequiredService<IAppDbContext>();

        // YouTubeChannelID 가 설정된 활성 채널만 대상
        var channels = await db.Channel.AsNoTracking()
            .Where(c => c.IsActive && c.YouTubeChannelID != null && c.YouTubeChannelID != "")
            .Select(c => new { c.ID, c.YouTubeChannelID })
            .ToListAsync(ct);

        if (channels.Count == 0)
        {
            logger.LogInformation("[YouTubeDailyAggregator] 대상 채널 없음");
            return;
        }

        var processed = 0;
        var failed = 0;

        foreach (var channel in channels)
        {
            if (ct.IsCancellationRequested)
            {
                break;
            }

            try
            {
                await AggregateChannelAsync(channel.ID, channel.YouTubeChannelID!, ct);
                processed++;
            }
            catch (Exception ex)
            {
                failed++;
                logger.LogError(ex, "[YouTubeDailyAggregator] 채널 {ChannelID} 집계 실패", channel.ID);
            }

            // API rate limit 방어
            await Task.Delay(TimeSpan.FromMilliseconds(500), ct);
        }

        logger.LogInformation("[YouTubeDailyAggregator] 집계 완료 — 성공: {Processed}, 실패: {Failed}", processed, failed);
    }

    private async Task AggregateChannelAsync(int channelID, string youtubeChannelID, CancellationToken ct)
    {
        // 1. 최근 업로드 videoId 조회 (1 unit)
        var recentVideoIds = await youTubeApi.GetRecentUploadsAsync(youtubeChannelID, UploadsLookback, ct);
        if (recentVideoIds.Count == 0)
        {
            return;
        }

        using var scope = scopeFactory.CreateScope();
        var db = scope.ServiceProvider.GetRequiredService<IAppDbContext>();

        // 2. 기존 세션 중 IsFinalized=false 또는 최근 7일 내 세션 videoId 추가
        var now = DateTime.UtcNow;
        var lookbackStart = now.AddDays(-7);

        var pendingSessions = await db.BroadcastSession
            .Where(s => s.ChannelID == channelID && (!s.IsFinalized || (s.EndAt != null && s.EndAt > lookbackStart)))
            .ToListAsync(ct);

        var targetVideoIds = new HashSet<string>(recentVideoIds);
        foreach (var session in pendingSessions)
        {
            targetVideoIds.Add(session.VideoID);
        }

        // 3. videos.list 배치 조회 (50개씩, 3 units/배치)
        var targetList = targetVideoIds.ToList();
        var allStats = new List<YouTubeVideoStats>();

        for (var i = 0; i < targetList.Count; i += BatchSize)
        {
            var batch = targetList.Skip(i).Take(BatchSize).ToList();
            var stats = await youTubeApi.GetVideoStatsBatchAsync(batch, ct);
            allStats.AddRange(stats);

            if (i + BatchSize < targetList.Count)
            {
                await Task.Delay(TimeSpan.FromMilliseconds(250), ct);
            }
        }

        // 4. 세션 upsert
        var existingByVideoId = pendingSessions.ToDictionary(s => s.VideoID, s => s);
        var sessionsToAdd = new List<BroadcastSession>();

        foreach (var stat in allStats)
        {
            // 라이브 방송이 아닌 일반 업로드는 제외
            if (!stat.IsLiveStream || stat.ActualStartTime == null)
            {
                continue;
            }

            if (existingByVideoId.TryGetValue(stat.VideoID, out var existing))
            {
                existing.UpdateStats(stat.Title, stat.ActualStartTime, stat.ActualEndTime, stat.ViewCount, stat.LikeCount);

                // End + 24h 경과 시 finalize
                if (stat.ActualEndTime.HasValue && stat.ActualEndTime.Value.AddHours(24) < now)
                {
                    existing.MarkFinalized();
                }
            }
            else
            {
                var session = BroadcastSession.Create(channelID, BroadcastPlatform.YouTube, stat.VideoID);
                session.UpdateStats(stat.Title, stat.ActualStartTime, stat.ActualEndTime, stat.ViewCount, stat.LikeCount);

                if (stat.ActualEndTime.HasValue && stat.ActualEndTime.Value.AddHours(24) < now)
                {
                    session.MarkFinalized();
                }

                sessionsToAdd.Add(session);
            }
        }

        if (sessionsToAdd.Count > 0)
        {
            await db.BroadcastSession.AddRangeAsync(sessionsToAdd, ct);
        }

        await db.SaveChangesAsync(ct);

        // 5. ChannelBroadcastStats 누적 재계산 (모든 세션 스캔)
        await RecalculateChannelStatsAsync(db, channelID, ct);
    }

    private static async Task RecalculateChannelStatsAsync(IAppDbContext db, int channelID, CancellationToken ct)
    {
        var aggregate = await db.BroadcastSession
            .Where(s => s.ChannelID == channelID && s.StartAt != null && s.EndAt != null)
            .GroupBy(s => 1)
            .Select(g => new
            {
                TotalDurationSec = g.Sum(s => (long)s.DurationSec),
                CumulativeViews = g.Sum(s => s.FinalViews),
                TotalLikes = g.Sum(s => s.FinalLikes),
                SessionCount = g.Count(),
                LastBroadcastAt = g.Max(s => s.EndAt)
            })
            .FirstOrDefaultAsync(ct);

        var stats = await db.ChannelBroadcastStats.FirstOrDefaultAsync(s => s.ChannelID == channelID, ct);

        if (aggregate == null)
        {
            return;
        }

        if (stats == null)
        {
            stats = ChannelBroadcastStats.Create(channelID);
            stats.Update(aggregate.TotalDurationSec, aggregate.CumulativeViews, aggregate.TotalLikes, aggregate.SessionCount, aggregate.LastBroadcastAt);
            await db.ChannelBroadcastStats.AddAsync(stats, ct);
        }
        else
        {
            stats.Update(aggregate.TotalDurationSec, aggregate.CumulativeViews, aggregate.TotalLikes, aggregate.SessionCount, aggregate.LastBroadcastAt);
        }

        await db.SaveChangesAsync(ct);
    }
}