using System.Xml.Linq;

namespace WordPressStaticExporter.Services;

public sealed class SiteMapService
{
    private readonly HttpClient _http = new();

    public async Task<IReadOnlyCollection<Uri>> DiscoverAsync(Uri siteUrl, CancellationToken cancellationToken)
    {
        var results = new HashSet<Uri>();
        var candidates = new[]
        {
            new Uri(siteUrl, "/sitemap.xml"),
            new Uri(siteUrl, "/sitemap_index.xml"),
            new Uri(siteUrl, "/wp-sitemap.xml")
        };

        foreach (var sitemap in candidates)
        {
            try
            {
                var xml = await _http.GetStringAsync(sitemap, cancellationToken);
                var doc = XDocument.Parse(xml);
                foreach (var value in doc.Descendants().Where(x => x.Name.LocalName == "loc").Select(x => x.Value.Trim()))
                {
                    if (Uri.TryCreate(value, UriKind.Absolute, out var uri) &&
                        string.Equals(uri.Host, siteUrl.Host, StringComparison.OrdinalIgnoreCase))
                        results.Add(uri);
                }
            }
            catch { }
        }

        return results;
    }
}