using System.Text.RegularExpressions;
using System.Xml.Linq;
using FinlyticCore.Dtos.News;

namespace FinlyticNews.Adapters.Discovery;

/// <summary>
/// Specialized RSS discovery adapter for Finanznachrichten.de, capable of parsing custom fn:isin elements and standard RSS metadata.
/// </summary>
public partial class FinanznachrichtenRssDiscoveryAdapter : ArticleDiscoveryAdapter
{
    private static readonly XNamespace FnNamespace = "http://www.finanznachrichten.de/service/rss";

    /// <inheritdoc />
    public override string Name => "finanznachrichten_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
        {
            var doc = XDocument.Parse(content);
            var channel = doc.Root?.Element("channel");
            var channelTitle = channel?.Element("title")?.Value?.Trim();
            var channelLanguage = channel?.Element("language")?.Value?.Trim();

            var items = doc.Descendants("item");

            foreach (var item in items)
            {
                var link = item.Element("link")?.Value?.Trim() ?? item.Element("guid")?.Value?.Trim();
                if (string.IsNullOrWhiteSpace(link)) continue;

                // ISIN Extraktion
                var isins = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
                foreach (var isinEl in item.Elements(FnNamespace + "isin"))
                {
                    if (string.IsNullOrWhiteSpace(isinEl.Value)) continue;

                    var parts = isinEl.Value.Split(new[] { ',', ';', ' ' }, StringSplitOptions.RemoveEmptyEntries);
                    foreach (var part in parts)
                    {
                        var trimmed = part.Trim().ToUpperInvariant();
                        if (IsValidIsin(trimmed))
                        {
                            isins.Add(trimmed);
                        }
                    }
                }

                var title = item.Element("title")?.Value?.Trim();
                var description = item.Element("description")?.Value?.Trim();

                DateTime? pubDate = null;
                var pubDateValue = item.Element("pubDate")?.Value;
                if (!string.IsNullOrWhiteSpace(pubDateValue) && DateTime.TryParse(pubDateValue, out var parsedDate))
                {
                    pubDate = parsedDate.ToUniversalTime();
                }

                if (Uri.TryCreate(baseUri, link, out var absoluteUri))
                {
                    articles.Add(new DiscoveredArticle(
                        Url: absoluteUri.ToString(),
                        Isins: isins.Count > 0 ? isins.ToList() : null,
                        Title: title,
                        Summary: description,
                        PublishedAt: pubDate,
                        Language: channelLanguage,
                        SourceName: channelTitle
                    ));
                }
            }
        }
        catch
        {
            // XML Malformed / Parsing Errors ignorieren
        }

        // Deduplizierung nach URL
        return articles.GroupBy(a => a.Url, StringComparer.OrdinalIgnoreCase)
                       .Select(g => g.First())
                       .ToList();
    }

    private static bool IsValidIsin(string input) 
        => input.Length == 12 && char.IsLetter(input[0]) && char.IsLetter(input[1]);
}