/**
 * llms.txt — GET /llms.txt
 *
 * A machine-readable site summary for AI answer engines (ChatGPT, Perplexity,
 * Claude, AI Overviews): a concise markdown map of what the site is and where
 * its key content lives, so AI crawlers ground answers in (and cite) the
 * right pages. /agents.md is the richer agent-facing companion (the newer
 * convention) — keep the two consistent.
 */
import { getServerClient } from '@/core/lib/brainerce.server';
import { getCanonicalSiteUrl } from '@/core/lib/site-url';

export const revalidate = 3600;

interface CategoryNodeLike {
  name: string;
  slug?: string | null;
  children?: CategoryNodeLike[];
}

export async function GET() {
  const baseUrl = await getCanonicalSiteUrl();
  const client = await getServerClient();

  const [info, posts, categoriesRes] = await Promise.all([
    client.getStoreInfo().catch(() => null),
    client.blog.getPosts({ limit: 20 }).catch(() => null),
    client.getCategories().catch(() => null),
  ]);

  const topCategories: CategoryNodeLike[] = (
    (categoriesRes?.categories as CategoryNodeLike[] | undefined) ?? []
  ).filter((c) => c.slug);

  const lines: string[] = [
    `# ${info?.name ?? 'Store'}`,
    '',
    ...(info?.metaDescription ? [`> ${info.metaDescription}`, ''] : []),
    '## Key pages',
    '',
    `- [Products](${baseUrl}/products): full catalog`,
    ...topCategories
      .slice(0, 20)
      .map((c) => `- [${c.name}](${baseUrl}/category/${c.slug}): category`),
    `- [Blog](${baseUrl}/blog): guides and articles`,
    `- [FAQ](${baseUrl}/faq)`,
    `- [Contact](${baseUrl}/contact)`,
    ...(info?.contactEmail ? [`- Contact email: ${info.contactEmail}`] : []),
    '',
    '## Machine-readable surfaces',
    '',
    `- [Agent guide](${baseUrl}/agents.md)`,
    `- [Sitemap](${baseUrl}/sitemap.xml)`,
    `- [Blog RSS](${baseUrl}/blog/rss.xml)`,
  ];

  if (posts && posts.data.length > 0) {
    lines.push('', '## Recent articles', '');
    for (const post of posts.data) {
      const summary = post.seoDescription ?? post.excerpt ?? '';
      lines.push(`- [${post.title}](${baseUrl}/blog/${post.slug})${summary ? `: ${summary}` : ''}`);
    }
  }

  return new Response(lines.join('\n') + '\n', {
    headers: { 'Content-Type': 'text/plain; charset=utf-8' },
  });
}