namespace DeepDrftPublic.Seo;

/// <summary>
/// Pure composition of the <c>robots.txt</c> body (Phase 23 wave 23.1). The environment gate is the
/// caller's: the endpoint reads <see cref="Microsoft.AspNetCore.Hosting.IWebHostEnvironment.IsProduction"/>
/// server-side and passes the boolean here, so the production-vs-beta branch lives in one testable place.
/// Fail-safe is closed — anything that is not Production yields <c>Disallow: /</c> (Invariant E1).
/// </summary>
public static class RobotsTxt
{
    /// <summary>
    /// Builds the directive body. In Production: allow everything except the embed shell and the proxy API
    /// paths, plus a <c>Sitemap:</c> pointer (OQ-R2). In any non-production environment: a closed door
    /// (<c>Disallow: /</c>) with no sitemap pointer, so a crawl of beta sees nothing and the sitemap is
    /// never advertised.
    /// </summary>
    /// <param name="isProduction">The server-side <c>IsProduction()</c> result — the single gate.</param>
    /// <param name="baseUrl">Canonical origin (no trailing slash) for the <c>Sitemap:</c> line; Production only.</param>
    public static string Build(bool isProduction, string baseUrl)
    {
        if (!isProduction)
        {
            return "User-agent: *\n" +
                   "Disallow: /\n";
        }

        var origin = baseUrl.TrimEnd('/');
        return "User-agent: *\n" +
               "Allow: /\n" +
               "Disallow: /FramePlayer\n" +
               "Disallow: /api/\n" +
               $"Sitemap: {origin}/sitemap.xml\n";
    }
}