namespace WordPressStaticExporter.Services;

public sealed class RobotsService
{
    private readonly HttpClient _http = new();
    private readonly List<string> _disallow = [];
    private bool _loaded;

    public async Task LoadAsync(Uri siteUrl, CancellationToken cancellationToken)
    {
        if (_loaded) return;
        _loaded = true;

        try
        {
            var robots = new Uri(siteUrl, "/robots.txt");
            var text = await _http.GetStringAsync(robots, cancellationToken);

            var applies = false;
            foreach (var raw in text.Split('\n'))
            {
                var line = raw.Split('#')[0].Trim();
                if (line.StartsWith("User-agent:", StringComparison.OrdinalIgnoreCase))
                {
                    var agent = line["User-agent:".Length..].Trim();
                    applies = agent == "*" || agent.Contains("WordPressStaticExporter", StringComparison.OrdinalIgnoreCase);
                }
                else if (applies && line.StartsWith("Disallow:", StringComparison.OrdinalIgnoreCase))
                {
                    var path = line["Disallow:".Length..].Trim();
                    if (!string.IsNullOrWhiteSpace(path))
                        _disallow.Add(path);
                }
            }
        }
        catch
        {
            // Missing or unreachable robots.txt does not block the export.
        }
    }

    public bool IsAllowed(Uri uri)
    {
        var path = uri.AbsolutePath;
        return !_disallow.Any(rule => rule == "/" || path.StartsWith(rule, StringComparison.OrdinalIgnoreCase));
    }
}