using System.ServiceModel.Syndication;
using System.Xml;
using FinlyticCore.Dtos.News;

namespace FinlyticNews.Adapters.Discovery;

/// <summary>
/// Discovery adapter targeting standard RSS/Atom syndication feeds.
/// </summary>
public class RssDiscoveryAdapter : ArticleDiscoveryAdapter
{
    /// <inheritdoc />
    public override string Name => "rss";

    /// <inheritdoc />
    public override List<DiscoveredArticle> ExtractUrls(string content, string sourceUrl)
    {
        if (string.IsNullOrWhiteSpace(content)) return [];

        var articles = new List<DiscoveredArticle>();
        if (!Uri.TryCreate(sourceUrl, UriKind.Absolute, out var baseUri)) return articles;

        try
        {
            using var stringReader = new StringReader(content);
            using var xmlReader = XmlReader.Create(stringReader, new XmlReaderSettings 
            { 
                DtdProcessing = DtdProcessing.Ignore,
                IgnoreWhitespace = true 
            });

            var feed = SyndicationFeed.Load(xmlReader);
            var feedLanguage = feed?.Language;
            var feedTitle = feed?.Title?.Text;

            if (feed?.Items != null)
            {
                foreach (var item in feed.Items)
                {
                    var link = item.Links.FirstOrDefault()?.Uri?.ToString() ?? item.Id;

                    if (!string.IsNullOrWhiteSpace(link) && Uri.TryCreate(baseUri, link, out var absoluteUri))
                    {
                        var title = item.Title?.Text?.Trim();
                        var summary = item.Summary?.Text?.Trim();
                        
                        DateTime? pubDate = item.PublishDate != DateTimeOffset.MinValue 
                            ? item.PublishDate.UtcDateTime 
                            : (item.LastUpdatedTime != DateTimeOffset.MinValue ? item.LastUpdatedTime.UtcDateTime : null);

                        articles.Add(new DiscoveredArticle(
                            Url: absoluteUri.ToString(),
                            Isins: null,
                            Title: title,
                            Summary: summary,
                            PublishedAt: pubDate,
                            Language: feedLanguage,
                            SourceName: feedTitle
                        ));
                    }
                }
            }
        }
        catch
        {
            // Graceful handling fehlerhafter Feeds
        }

        return articles.GroupBy(u => u.Url, StringComparer.OrdinalIgnoreCase)
                       .Select(g => g.First())
                       .ToList();
    }
}