ANTOOZA-BACKEND/Web.Api/Endpoints/YouTube/PubSubCallback.cs

using System.Text;
using Application.Abstractions.YouTube;
using MediatR;

namespace Web.Api.Endpoints.YouTube;

/// <summary>
/// YouTube PubSubHubbub(WebSub) 콜백 엔드포인트
/// - GET: hub.challenge 검증 (구독 확인)
/// - POST: ATOM Feed 알림 수신 (새 영상/라이브)
/// </summary>
internal sealed class PubSubCallback : IEndpoint
{
    public void MapEndpoint(IEndpointRouteBuilder app)
    {
        var group = app.MapGroup("api/youtube/pubsub/callback").WithTags("YouTube").AllowAnonymous();

        group.MapGet("", HandleVerifyAsync);
        group.MapPost("", HandleNotifyAsync);
    }

    // ── GET: 구독 검증 ─────────────────────────────────────────────

    private static async Task<IResult> HandleVerifyAsync(
        HttpContext context,
        IYouTubePubSubService pubSubService,
        ILogger<PubSubCallback> logger,
        CancellationToken ct
    ) {
        var query = context.Request.Query;
        var mode = query["hub.mode"].ToString();
        var topic = query["hub.topic"].ToString();
        var challenge = query["hub.challenge"].ToString();
        var lease = query["hub.lease_seconds"].ToString();

        if (string.IsNullOrEmpty(mode) || string.IsNullOrEmpty(topic) || string.IsNullOrEmpty(challenge))
        {
            logger.LogWarning("[PubSub] Invalid verify request: mode={Mode}, topic={Topic}", mode, topic);
            return Results.BadRequest();
        }

        if (mode is not ("subscribe" or "unsubscribe"))
        {
            logger.LogWarning("[PubSub] Unsupported hub.mode: {Mode}", mode);
            return Results.BadRequest();
        }

        // subscribe 시 lease_seconds 기반 만료 시각 Redis에 저장 (관리자 대시보드용)
        if (mode is "subscribe" && int.TryParse(lease, out var leaseSeconds) && leaseSeconds > 0)
        {
            var channelId = ExtractChannelIdFromTopic(topic);
            if (!string.IsNullOrEmpty(channelId))
            {
                try
                {
                    var expiresAt = DateTime.UtcNow.AddSeconds(leaseSeconds);
                    await pubSubService.SetLeaseExpiryAsync(channelId, expiresAt, ct);
                }
                catch (Exception ex)
                {
                    logger.LogWarning(ex, "[PubSub] Failed to persist lease expiry — channelId={ChannelId}", channelId);
                }
            }
        }

        logger.LogInformation(
            "[PubSub] Verify {Mode}: topic={Topic}, lease={Lease}s",
            mode, topic, lease
        );

        // hub.challenge 평문 에코 (200 OK + text/plain)
        return Results.Text(challenge, "text/plain");
    }

    // hub.topic 예: https://www.youtube.com/feeds/videos.xml?channel_id=UCxxx
    private static string? ExtractChannelIdFromTopic(string topic)
    {
        if (string.IsNullOrWhiteSpace(topic))
        {
            return null;
        }

        const string marker = "channel_id=";
        var idx = topic.IndexOf(marker, StringComparison.OrdinalIgnoreCase);
        if (idx < 0)
        {
            return null;
        }

        var value = topic[(idx + marker.Length)..];
        var amp = value.IndexOf('&');
        return amp >= 0 ? value[..amp] : value;
    }

    // ── POST: Atom Feed 알림 수신 ──────────────────────────────────

    private static async Task<IResult> HandleNotifyAsync(
        HttpContext context,
        IYouTubePubSubService pubSubService,
        ISender sender,
        ILogger<PubSubCallback> logger,
        CancellationToken ct
    ) {
        using var reader = new StreamReader(context.Request.Body, Encoding.UTF8);
        var body = await reader.ReadToEndAsync(ct);

        if (string.IsNullOrWhiteSpace(body))
        {
            logger.LogWarning("[PubSub] Empty notify body");
            return Results.BadRequest();
        }

        // HMAC 서명 검증
        var signature = context.Request.Headers["X-Hub-Signature"].ToString();
        if (string.IsNullOrEmpty(signature))
        {
            logger.LogWarning("[PubSub] Missing X-Hub-Signature header");
            return Results.Unauthorized();
        }

        if (!pubSubService.VerifySignature(body, signature))
        {
            logger.LogWarning("[PubSub] Signature verification failed");
            return Results.Unauthorized();
        }

        // Atom Feed 파싱
        var notification = pubSubService.ParseNotification(body);
        if (notification is null)
        {
            logger.LogWarning("[PubSub] Failed to parse Atom feed");
            return Results.Ok(); // 파싱 실패해도 200 반환 (재전송 방지)
        }

        // MediatR 커맨드로 라이브 판별 & BroadcastSession 생성 위임
        try
        {
            await sender.Send(new Application.Features.Api.YouTube.PubSubNotify.Command(
                notification.VideoId,
                notification.ChannelId,
                notification.Title,
                notification.Published,
                notification.Updated
            ), ct);
        }
        catch (Exception ex)
        {
            logger.LogError(ex, "[PubSub] Notify handler error: videoId={VideoId}", notification.VideoId);
            // 예외 발생해도 200 반환 — 재전송은 dedupe로 막힘
        }

        return Results.Ok();
    }
}