import type { APIRoute } from 'astro';

/**
 * `/robots.txt` (D49, phase 10).
 *
 * The site had a sitemap covering all fifty URLs — Starlight bundles `@astrojs/sitemap`, so
 * it has been written on every build since phase 1 — and nothing that pointed at it. A
 * crawler finds a sitemap two ways: submitted by hand in a search console, or named here.
 * There is no search console for this project (D9's no-analytics posture extends to not
 * having accounts with anyone), so this file is the only way it is ever found.
 *
 * **Everything is allowed.** The site has no authenticated surface at all (§6), so there is
 * no private area to keep out of an index, and the two exclusions worth arguing about were
 * both rejected:
 *
 *  - `/brand/*` is derived images and a stylesheet. Nothing links them as pages and they
 *    carry no text; disallowing them would only stop an image crawler fetching the OG card
 *    that exists to be fetched.
 *  - `/beta/` is a live page a person is meant to find. It is the closed test's front door
 *    and the nearest real deadline this project has — hiding it from search to keep the
 *    signup list small would be solving a problem nobody has.
 *
 * The 404 page is excluded from the *search index* instead (`data-pagefind-ignore`), which
 * is the right layer for it: it is never a URL a crawler is given.
 *
 * Written as a route rather than a file in `public/` so the sitemap URL is derived from
 * `site` in `astro.config.mjs`. A hand-written copy would be one more place the domain is
 * spelled out, and the first thing to go stale if it ever changes.
 */
export const GET: APIRoute = ({ site }) =>
  new Response(
    [
      'User-agent: *',
      'Allow: /',
      '',
      `Sitemap: ${new URL('sitemap-index.xml', site)}`,
      '',
    ].join('\n'),
    { headers: { 'Content-Type': 'text/plain; charset=utf-8' } }
  );