import { getCachedPayload } from '@/lib/payload';
import { absoluteUrl } from '@/lib/site';
import { getFlags } from '@/lib/flags';

/*
 * Dynamic, not ISR.
 *
 * This route has no dynamic params, so Next prerenders it at build time — and
 * CI builds the image with no database reachable, which fails the build. It is
 * a single indexed query against Postgres on the same Docker network, so
 * rendering per request is cheap, and it means a newly published post appears
 * here immediately rather than waiting on a revalidation.
 */
export const dynamic = 'force-dynamic';

function escapeXml(value: string): string {
  return value.replace(/[<>&'"]/g, (char) =>
    ({ '<': '&lt;', '>': '&gt;', '&': '&amp;', "'": '&apos;', '"': '&quot;' }[char]!));
}

export async function GET() {
  // A dark blog has no feed. 404 rather than an empty channel: an empty feed
  // is a live feed with nothing in it, which a reader would keep polling.
  const flags = await getFlags();
  if (flags.blog !== true) return new Response('Not found', { status: 404 });

  const payload = await getCachedPayload();
  const { docs } = await payload.find({
    collection: 'posts',
    where: { _status: { equals: 'published' } },
    sort: '-publishedAt',
    limit: 50,
    depth: 0,
  });

  const items = docs.map((post) => `
    <item>
      <title>${escapeXml(String(post.title))}</title>
      <link>${absoluteUrl(`/blog/${post.slug}`)}</link>
      <guid isPermaLink="true">${absoluteUrl(`/blog/${post.slug}`)}</guid>
      <description>${escapeXml(String(post.excerpt))}</description>
      <pubDate>${new Date(String(post.publishedAt)).toUTCString()}</pubDate>
    </item>`).join('');

  const xml = `<?xml version="1.0" encoding="UTF-8"?>
<rss version="2.0">
  <channel>
    <title>schoolcompare blog</title>
    <link>${absoluteUrl('/blog')}</link>
    <description>What school performance data shows, and what it does not.</description>
    <language>en-GB</language>${items}
  </channel>
</rss>`;

  return new Response(xml, {
    headers: { 'Content-Type': 'application/rss+xml; charset=utf-8' },
  });
}