dpot-backend/Infrastructure/YouTube/YouTubeLiveChatService.cs

using System.Collections.Concurrent;
using System.Text.Json;
using Application.Abstractions.YouTube;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;

namespace Infrastructure.YouTube;

/// <summary>
/// YouTube 라이브 채팅 수집 서비스
///
/// 동작 흐름:
/// 1. StartAsync(videoId) 호출 → videos.list로 liveChatId 획득 (1 unit)
/// 2. liveChatMessages.list 폴링 시작 (pollingIntervalMillis 준수)
/// 3. 새 메시지 → OnMessageReceived 이벤트 발행 → ChatHub에서 브로드캐스트
/// 4. 방송 종료 감지 → 자동 정리
///
/// 향후 gRPC streamList로 전환 시 이 클래스 내부만 교체하면 됨
/// (인터페이스 IYouTubeLiveChatService는 동일하게 유지)
/// </summary>
internal sealed class YouTubeLiveChatService(
    IYouTubeApiService youTubeApiService,
    IHttpClientFactory httpClientFactory,
    ILogger<YouTubeLiveChatService> logger
) : BackgroundService, IYouTubeLiveChatService
{
    private const string BaseUrl = "https://www.googleapis.com/youtube/v3";
    private const int DefaultPollingMs = 10_000; // 10초 (API 응답 없으면 기본값)
    private const int MaxPollingMs = 30_000;     // 최대 30초

    // liveChatId → CancellationTokenSource
    private readonly ConcurrentDictionary<string, ChatMonitorContext> _monitors = new();

    public event Func<YouTubeChatMessage, Task>? OnMessageReceived;

    // ── IYouTubeLiveChatService ──────────────────────────────────────

    public async Task<bool> StartAsync(string videoId, CancellationToken ct)
    {
        // videos.list로 liveChatId 획득 (~1 unit)
        var liveInfo = await youTubeApiService.GetLiveStreamInfoAsync(videoId, ct);

        if (liveInfo is null)
        {
            logger.LogWarning("[LiveChat] 영상 정보를 가져올 수 없음: videoId={VideoId}", videoId);
            return false;
        }

        if (!liveInfo.IsLive || string.IsNullOrEmpty(liveInfo.ActiveLiveChatId))
        {
            logger.LogWarning("[LiveChat] 라이브 방송이 아니거나 채팅이 비활성: videoId={VideoId}, status={Status}",
                videoId, liveInfo.LiveBroadcastContent);
            return false;
        }

        var liveChatId = liveInfo.ActiveLiveChatId;

        if (_monitors.ContainsKey(liveChatId))
        {
            logger.LogInformation("[LiveChat] 이미 모니터링 중: liveChatId={LiveChatId}", liveChatId);
            return true;
        }

        var cts = new CancellationTokenSource();
        var context = new ChatMonitorContext(videoId, liveChatId, liveInfo.ChannelId, cts);

        if (_monitors.TryAdd(liveChatId, context))
        {
            // 백그라운드에서 폴링 시작
            _ = Task.Run(() => PollChatMessagesAsync(context), CancellationToken.None);
            logger.LogInformation("[LiveChat] 모니터링 시작: videoId={VideoId}, liveChatId={LiveChatId}", videoId, liveChatId);
            return true;
        }

        return false;
    }

    public Task StopAsync(string liveChatId)
    {
        if (_monitors.TryRemove(liveChatId, out var context))
        {
            context.Cts.Cancel();
            context.Cts.Dispose();
            logger.LogInformation("[LiveChat] 모니터링 중지: liveChatId={LiveChatId}", liveChatId);
        }

        return Task.CompletedTask;
    }

    public bool IsMonitoring(string liveChatId) => _monitors.ContainsKey(liveChatId);

    public IReadOnlyList<string> GetActiveChatIds() => _monitors.Keys.ToList().AsReadOnly();

    // ── BackgroundService ────────────────────────────────────────────

    protected override Task ExecuteAsync(CancellationToken stoppingToken)
    {
        // 서비스 시작만 해둠 — 실제 폴링은 StartAsync 호출 시 개별 Task로 실행
        logger.LogInformation("[LiveChat] YouTubeLiveChatService 준비 완료");
        return Task.CompletedTask;
    }

    public override async Task StopAsync(CancellationToken cancellationToken)
    {
        logger.LogInformation("[LiveChat] 서비스 종료 — 모든 모니터 중지");

        foreach (var (liveChatId, context) in _monitors)
        {
            context.Cts.Cancel();
            context.Cts.Dispose();
        }

        _monitors.Clear();
        await base.StopAsync(cancellationToken);
    }

    // ── 폴링 루프 ───────────────────────────────────────────────────

    private async Task PollChatMessagesAsync(ChatMonitorContext context)
    {
        var ct = context.Cts.Token;
        string? pageToken = null;
        var seenMessageIds = new HashSet<string>();

        try
        {
            while (!ct.IsCancellationRequested)
            {
                var (messages, nextPageToken, pollingIntervalMs) = await FetchMessagesAsync(context.LiveChatId, pageToken, ct);

                if (messages is not null)
                {
                    foreach (var msg in messages)
                    {
                        // 중복 제거
                        if (!seenMessageIds.Add(msg.MessageId))
                        {
                            continue;
                        }

                        // 메모리 절약: 최근 2000개만 유지
                        if (seenMessageIds.Count > 2000)
                        {
                            seenMessageIds.Clear();
                            seenMessageIds.Add(msg.MessageId);
                        }

                        try
                        {
                            if (OnMessageReceived is not null)
                            {
                                await OnMessageReceived.Invoke(msg);
                            }
                        }
                        catch (Exception ex)
                        {
                            logger.LogError(ex, "[LiveChat] OnMessageReceived handler error");
                        }
                    }
                }

                pageToken = nextPageToken;

                // pollingIntervalMillis 준수 (할당량 절약 핵심)
                var delay = Math.Clamp(pollingIntervalMs, 1000, MaxPollingMs);
                await Task.Delay(delay, ct);
            }
        }
        catch (OperationCanceledException)
        {
            // 정상 종료
        }
        catch (Exception ex)
        {
            logger.LogError(ex, "[LiveChat] 폴링 루프 오류: liveChatId={LiveChatId}", context.LiveChatId);
        }
        finally
        {
            _monitors.TryRemove(context.LiveChatId, out _);
            logger.LogInformation("[LiveChat] 폴링 종료: liveChatId={LiveChatId}", context.LiveChatId);
        }
    }

    private async Task<(List<YouTubeChatMessage>? Messages, string? NextPageToken, int PollingIntervalMs)>
        FetchMessagesAsync(string liveChatId, string? pageToken, CancellationToken ct)
    {
        try
        {
            var client = httpClientFactory.CreateClient("YouTubeApi");
            var url = $"{BaseUrl}/liveChat/messages?liveChatId={Uri.EscapeDataString(liveChatId)}&part=snippet,authorDetails&maxResults=500";

            if (!string.IsNullOrEmpty(pageToken))
            {
                url += $"&pageToken={Uri.EscapeDataString(pageToken)}";
            }

            var response = await client.GetAsync(url, ct);

            if (!response.IsSuccessStatusCode)
            {
                var statusCode = (int)response.StatusCode;

                // 403: 채팅 종료 또는 권한 없음
                if (statusCode is 403 or 404)
                {
                    logger.LogInformation("[LiveChat] 채팅 종료 또는 접근 불가 ({StatusCode}): liveChatId={LiveChatId}",
                        statusCode, liveChatId);

                    // 모니터링 자동 중지
                    if (_monitors.TryRemove(liveChatId, out var ctx))
                    {
                        ctx.Cts.Cancel();
                    }

                    return (null, null, MaxPollingMs);
                }

                logger.LogWarning("[LiveChat] API 오류: {StatusCode}", statusCode);
                return (null, pageToken, DefaultPollingMs);
            }

            var json = await response.Content.ReadAsStringAsync(ct);
            var doc = JsonSerializer.Deserialize<JsonElement>(json);

            var nextPageToken = doc.TryGetProperty("nextPageToken", out var nptProp) ? nptProp.GetString() : null;
            var pollingIntervalMs = doc.TryGetProperty("pollingIntervalMillis", out var piProp) ? piProp.GetInt32() : DefaultPollingMs;

            // offlineAt → 방송 종료
            if (doc.TryGetProperty("offlineAt", out _))
            {
                logger.LogInformation("[LiveChat] 방송 종료 감지: liveChatId={LiveChatId}", liveChatId);
                if (_monitors.TryRemove(liveChatId, out var ctx))
                {
                    ctx.Cts.Cancel();
                }

                return (null, null, MaxPollingMs);
            }

            var items = doc.GetProperty("items");
            var messages = new List<YouTubeChatMessage>();

            foreach (var item in items.EnumerateArray())
            {
                var msg = ParseChatMessage(item, liveChatId);
                if (msg is not null)
                {
                    messages.Add(msg);
                }
            }

            return (messages, nextPageToken, pollingIntervalMs);
        }
        catch (OperationCanceledException)
        {
            throw;
        }
        catch (Exception ex)
        {
            logger.LogError(ex, "[LiveChat] FetchMessages 오류: liveChatId={LiveChatId}", liveChatId);
            return (null, pageToken, DefaultPollingMs);
        }
    }

    private static YouTubeChatMessage? ParseChatMessage(JsonElement item, string liveChatId)
    {
        try
        {
            var id = item.GetProperty("id").GetString()!;
            var snippet = item.GetProperty("snippet");
            var author = item.GetProperty("authorDetails");

            var typeStr = snippet.GetProperty("type").GetString() ?? "textMessageEvent";
            var messageType = typeStr switch
            {
                "textMessageEvent" => YouTubeChatMessageType.TextMessage,
                "superChatEvent" => YouTubeChatMessageType.SuperChat,
                "superStickerEvent" => YouTubeChatMessageType.SuperSticker,
                "newSponsorEvent" => YouTubeChatMessageType.NewSponsor,
                "memberMilestoneChatEvent" => YouTubeChatMessageType.MemberMilestone,
                "giftMembershipEvent" => YouTubeChatMessageType.GiftMembership,
                _ => YouTubeChatMessageType.TextMessage
            };

            var displayMessage = snippet.TryGetProperty("displayMessage", out var dmProp)
                ? dmProp.GetString() ?? ""
                : "";

            // textMessageEvent의 경우 textMessageDetails에서 메시지 추출
            if (messageType == YouTubeChatMessageType.TextMessage
                && snippet.TryGetProperty("textMessageDetails", out var tmd)
                && tmd.TryGetProperty("messageText", out var mtProp))
            {
                displayMessage = mtProp.GetString() ?? displayMessage;
            }

            var publishedAt = snippet.TryGetProperty("publishedAt", out var paProp)
                && DateTime.TryParse(paProp.GetString(), out var pa)
                    ? pa
                    : DateTime.UtcNow;

            // SuperChat 금액
            decimal? superChatAmount = null;
            string? superChatCurrency = null;
            if (messageType == YouTubeChatMessageType.SuperChat
                && snippet.TryGetProperty("superChatDetails", out var scd))
            {
                superChatAmount = scd.TryGetProperty("amountMicros", out var amProp)
                    && long.TryParse(amProp.GetString(), out var micros)
                        ? micros / 1_000_000m
                        : null;
                superChatCurrency = scd.TryGetProperty("currency", out var curProp) ? curProp.GetString() : null;
            }

            return new YouTubeChatMessage(
                id,
                liveChatId,
                author.GetProperty("channelId").GetString() ?? "",
                author.GetProperty("displayName").GetString() ?? "",
                author.TryGetProperty("profileImageUrl", out var imgProp) ? imgProp.GetString() ?? "" : "",
                displayMessage,
                publishedAt,
                messageType,
                superChatAmount,
                superChatCurrency
            );
        }
        catch
        {
            return null;
        }
    }

    // ── 내부 모니터 컨텍스트 ─────────────────────────────────────────

    private sealed record ChatMonitorContext(
        string VideoId,
        string LiveChatId,
        string ChannelId,
        CancellationTokenSource Cts
    );
}