import type { MetadataRoute } from "next";
import { bff } from "@/lib/bff";

/**
 * Sitemap (index + sharded children) for the whole public corpus.
 *
 * How this stays cheap on the BFF:
 *   • One projection-only BFF call (`/sitemap/content`) returns every content
 *     leaf path in a single sweep — no per-document fan-out.
 *   • That fetch is cached for 24h (revalidate below) AND the rendered XML is
 *     ISR-cached, so crawlers hit Next's cache, not the BFF. The BFF sees
 *     ~one query/day regardless of crawl volume (tag "sitemap" allows
 *     on-demand revalidation after a re-seed).
 *   • generateSitemaps() shards into ≤40k-URL files (under the 50k/50MB
 *     limits) and Next serves a sitemap index at /sitemap.xml automatically.
 */

export const revalidate = 86400; // 24h

const SITE_URL =
  process.env.NEXT_PUBLIC_SITE_URL || "https://prabhupadasays.org";
const PER_SITEMAP = 40000;

// Top-level hubs that aren't content leaves but should be indexed.
const STATIC_PATHS = [
  "/",
  "/about",
  "/books",
  "/letters",
  "/transcriptions",
  "/disciples",
  "/glossary",
  "/essays",
  "/magazines",
  "/journals",
  "/other-documents",
];

/**
 * All indexable paths: static hubs + book/division landing pages (derived
 * from the content leaves) + every content leaf from the BFF. Resilient — if
 * the BFF call fails we still emit the static hubs so /sitemap.xml never 500s.
 */
async function fetchUrls(path: string): Promise<string[]> {
  try {
    const res = await bff<{ urls: string[] }>(path, {
      revalidate,
      tags: ["sitemap"],
    });
    return res?.urls ?? [];
  } catch {
    return [];
  }
}

async function allPaths(): Promise<string[]> {
  // Content (Mongo) and public profiles (Postgres) come from separate
  // projection-only endpoints. New signups appear automatically on the next
  // daily revalidation.
  const [content, users] = await Promise.all([
    fetchUrls("/sitemap/content"),
    fetchUrls("/sitemap/users"),
  ]);

  // Derive non-redirecting hub pages from the content leaves: every book's
  // landing page, and the SB canto / CC līlā division pages.
  const hubs = new Set<string>();
  for (const p of content) {
    const book = p.match(/^\/books\/([^/]+)/);
    if (book) hubs.add(`/books/${book[1]}`);
    const division = p.match(/^\/books\/(sb|cc)\/([^/]+)\/\d+\/\d+$/);
    if (division) hubs.add(`/books/${division[1]}/${division[2]}`);
  }

  // Dedupe across static + hubs + content + profiles.
  return [...new Set([...STATIC_PATHS, ...hubs, ...content, ...users])];
}

export async function generateSitemaps(): Promise<{ id: number }[]> {
  const paths = await allPaths();
  const count = Math.max(1, Math.ceil(paths.length / PER_SITEMAP));
  return Array.from({ length: count }, (_, id) => ({ id }));
}

export default async function sitemap({
  id,
}: {
  id: number;
}): Promise<MetadataRoute.Sitemap> {
  const paths = await allPaths();
  const slice = paths.slice(id * PER_SITEMAP, (id + 1) * PER_SITEMAP);
  return slice.map((path) => ({
    url: `${SITE_URL}${path}`,
    changeFrequency: "weekly",
    priority: path === "/" ? 1 : STATIC_PATHS.includes(path) ? 0.8 : 0.7,
  }));
}