import 'server-only';
import { api, safe } from '@/lib/api';
import { SITE_URL, routes } from '@/lib/site';

/**
 * Sharded sitemap data. Shard 0 = static pages + non-satellite entities; shards 1..N = on-orbit satellites,
 * SATELLITES_PER_SHARD per shard (N from the API total). Served by `app/sitemap.xml/route.ts` (index) and
 * `app/sitemap/[id]/route.ts` (shards) — Next 16's `generateSitemaps` cannot emit an index at /sitemap.xml, which robots.txt requires.
 * If the API is unreachable a shard degrades to static pages only; URLs are never fabricated.
 */
export const SATELLITES_PER_SHARD = 5000;

type ChangeFreq = 'always' | 'hourly' | 'daily' | 'weekly' | 'monthly' | 'yearly' | 'never';
export interface SitemapEntry {
  url: string;
  lastModified?: Date;
  changeFrequency?: ChangeFreq;
  priority?: number;
}

const STATIC: { path: string; priority: number; changeFrequency: ChangeFreq }[] = [
  { path: routes.home(), priority: 1, changeFrequency: 'hourly' },
  { path: routes.explore(), priority: 0.9, changeFrequency: 'hourly' },
  { path: routes.satellites(), priority: 0.9, changeFrequency: 'hourly' },
  { path: routes.constellations(), priority: 0.8, changeFrequency: 'daily' },
  { path: routes.operators(), priority: 0.8, changeFrequency: 'daily' },
  { path: routes.countries(), priority: 0.8, changeFrequency: 'daily' },
  { path: routes.launches(), priority: 0.8, changeFrequency: 'daily' },
  { path: routes.launchSites(), priority: 0.6, changeFrequency: 'weekly' },
  { path: routes.debris(), priority: 0.7, changeFrequency: 'daily' },
  { path: routes.reentries(), priority: 0.7, changeFrequency: 'daily' },
  { path: routes.events(), priority: 0.7, changeFrequency: 'hourly' },
  { path: routes.stats(), priority: 0.7, changeFrequency: 'daily' },
  { path: routes.rankings(), priority: 0.6, changeFrequency: 'daily' },
  { path: routes.sources(), priority: 0.5, changeFrequency: 'weekly' },
  { path: routes.methodology(), priority: 0.5, changeFrequency: 'monthly' },
  { path: routes.status(), priority: 0.3, changeFrequency: 'hourly' },
  { path: routes.developers(), priority: 0.5, changeFrequency: 'monthly' },
  { path: routes.about(), priority: 0.4, changeFrequency: 'monthly' },
  { path: routes.privacy(), priority: 0.2, changeFrequency: 'yearly' },
  { path: routes.terms(), priority: 0.2, changeFrequency: 'yearly' },
];

const abs = (path: string) => `${SITE_URL}${path}`;
const date = (v: string | null | undefined) => (v && !Number.isNaN(new Date(v).getTime()) ? new Date(v) : undefined);

/** Number of satellite shards (≥ 1 even when the API is down, so /sitemap/1.xml always exists). */
export async function satelliteShardCount(): Promise<number> {
  const first = await safe(api.sitemapSatellites(1, SATELLITES_PER_SHARD));
  const total = first?.data.total ?? 0;
  return Math.max(1, Math.ceil(total / SATELLITES_PER_SHARD));
}

export async function shardEntries(shard: number): Promise<SitemapEntry[]> {
  if (shard === 0) {
    const out: SitemapEntry[] = STATIC.map((s) => ({ url: abs(s.path), changeFrequency: s.changeFrequency, priority: s.priority }));
    const ents = await safe(api.sitemapEntities());
    if (ents) {
      const d = ents.data;
      out.push(...d.constellations.map((c) => ({ url: abs(routes.constellation(c.slug)), lastModified: date(c.updated_at), changeFrequency: 'daily' as const, priority: 0.8 })));
      out.push(...d.operators.map((o) => ({ url: abs(routes.operator(o.slug)), lastModified: date(o.updated_at), changeFrequency: 'weekly' as const, priority: 0.7 })));
      out.push(...d.countries.map((c) => ({ url: abs(routes.country(c.slug)), changeFrequency: 'weekly' as const, priority: 0.7 })));
      out.push(...d.launches.map((l) => ({ url: abs(routes.launch(l.slug)), lastModified: date(l.updated_at), changeFrequency: 'weekly' as const, priority: 0.5 })));
      out.push(...d.launch_sites.map((s) => ({ url: abs(routes.launchSite(s.slug)), changeFrequency: 'monthly' as const, priority: 0.5 })));
    }
    return out;
  }
  const page = await safe(api.sitemapSatellites(shard, SATELLITES_PER_SHARD));
  if (!page) return [];
  return page.data.items.map((s) => ({
    url: abs(routes.satellite(s.slug)),
    lastModified: date(s.updated_at),
    changeFrequency: s.status === 'ACTIVE' ? 'daily' : 'weekly',
    priority: s.status === 'ACTIVE' ? 0.6 : 0.4,
  }));
}

const esc = (s: string) => s.replace(/&/g, '&amp;').replace(/</g, '&lt;').replace(/>/g, '&gt;').replace(/"/g, '&quot;').replace(/'/g, '&apos;');

export function toUrlset(entries: SitemapEntry[]): string {
  const body = entries
    .map((e) => {
      const parts = [`<loc>${esc(e.url)}</loc>`];
      if (e.lastModified) parts.push(`<lastmod>${e.lastModified.toISOString()}</lastmod>`);
      if (e.changeFrequency) parts.push(`<changefreq>${e.changeFrequency}</changefreq>`);
      if (e.priority !== undefined) parts.push(`<priority>${e.priority}</priority>`);
      return `<url>${parts.join('')}</url>`;
    })
    .join('\n');
  return `<?xml version="1.0" encoding="UTF-8"?>\n<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">\n${body}\n</urlset>\n`;
}

export function toIndex(shardIds: number[], lastmod: Date = new Date()): string {
  const body = shardIds.map((id) => `<sitemap><loc>${esc(`${SITE_URL}/sitemap/${id}.xml`)}</loc><lastmod>${lastmod.toISOString()}</lastmod></sitemap>`).join('\n');
  return `<?xml version="1.0" encoding="UTF-8"?>\n<sitemapindex xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">\n${body}\n</sitemapindex>\n`;
}

export const SITEMAP_HEADERS = { 'content-type': 'application/xml; charset=utf-8', 'cache-control': 'public, max-age=0, s-maxage=3600, stale-while-revalidate=86400' };