using System.Xml.Linq;
using Application.Abstractions.YouTube;
using Microsoft.Extensions.Logging;

namespace Infrastructure.YouTube;

/// <summary>
/// YouTube 공개 Atom Feed 폴링 (할당량 0 unit).
/// 비용 없는 라이브 감지 — PubSub의 라이브 푸시 누락을 보완.
/// </summary>
internal sealed class YouTubeFeedPoller(
    IHttpClientFactory httpClientFactory,
    ILogger<YouTubeFeedPoller> logger
) : IYouTubeFeedPoller
{
    private const string FeedBase = "https://www.youtube.com/feeds/videos.xml?channel_id=";

    public async Task<string?> GetLatestVideoIdAsync(string youtubeChannelID, CancellationToken ct)
    {
        if (string.IsNullOrWhiteSpace(youtubeChannelID))
        {
            return null;
        }

        try
        {
            var client = httpClientFactory.CreateClient("YouTubeFeed");
            var url = FeedBase + Uri.EscapeDataString(youtubeChannelID);

            var response = await client.GetAsync(url, ct);
            if (!response.IsSuccessStatusCode)
            {
                logger.LogWarning("[FeedPoller] GET failed: channelId={ChannelId}, status={Status}",
                    youtubeChannelID, response.StatusCode);
                return null;
            }

            var xml = await response.Content.ReadAsStringAsync(ct);
            var doc = XDocument.Parse(xml);
            XNamespace atom = "http://www.w3.org/2005/Atom";
            XNamespace yt = "http://www.youtube.com/xml/schemas/2015";

            var entry = doc.Descendants(atom + "entry").FirstOrDefault();
            if (entry is null)
            {
                return null;
            }

            return entry.Element(yt + "videoId")?.Value;
        }
        catch (OperationCanceledException)
        {
            throw;
        }
        catch (Exception ex)
        {
            logger.LogError(ex, "[FeedPoller] Unexpected error: channelId={ChannelId}", youtubeChannelID);
            return null;
        }
    }
}