import {
  AngularNodeAppEngine,
  createNodeRequestHandler,
  isMainModule,
  writeResponseToNodeResponse,
} from '@angular/ssr/node';
import * as fs from 'node:fs';
import * as http from 'node:http';
import * as path from 'node:path';
import { isSpider, getUserAgent } from './spider_detection';

/**
 * Manually import and register the Angular app engine manifest.
 * The Angular 21 builder generates angular-app-engine-manifest.mjs at build time
 * but does NOT automatically inject the import into server.mjs.
 * Without this, AngularNodeAppEngine fails with "Angular app engine manifest is not set"
 * and every SSR request returns 404.
 */
// @ts-ignore — generated at build time by @angular/build
import engineManifest from './angular-app-engine-manifest.mjs';
import { ɵsetAngularAppEngineManifest } from '@angular/ssr';
ɵsetAngularAppEngineManifest(engineManifest);

const appEngine = new AngularNodeAppEngine();

/**
 * Resolve the static browser index.html path.
 * In the built output the browser files live in the `browser/` subdirectory.
 */
function browserIndexPath(): string {
  // __dirname in ESM resolves to this file's directory
  const dir = typeof __dirname !== 'undefined' ? __dirname : path.dirname(new URL(import.meta.url).pathname);
  return path.join(dir, 'browser', 'index.html');
}

/**
 * Serve the static CSR app shell from disk.
 *
 * Regular browser users get the prerendered HTML shell — Angular hydrates
 * client-side and fetches fresh config via the API. This avoids the SSR
 * overhead for every human request while still delivering a fast first paint.
 */
function serveStaticShell(res: http.ServerResponse): void {
  const indexPath = browserIndexPath();
  try {
    const content = fs.readFileSync(indexPath, 'utf-8');
    res.setHeader('Content-Type', 'text/html; charset=utf-8');
    res.setHeader('X-Render-Mode', 'CSR');
    res.end(content);
  } catch {
    res.statusCode = 500;
    res.end('Internal server error — index.html not found');
  }
}

const requestHandler = createNodeRequestHandler(async (req, res, next) => {
  try {
    const response = await appEngine.handle(req);

    if (response) {
      await writeResponseToNodeResponse(response, res);
    } else {
      next();
    }
  } catch (error) {
    next(error);
  }
});

if (isMainModule(import.meta.url)) {
  console.log('Node.js SSR server ready');
  const server = http.createServer();
  server.on('request', async (req, res) => {
    try {
      // ── Spider detection gate ──────────────────────────
      // Only search engine spiders get full SSR rendering.
      // Regular users receive the static CSR app shell from disk,
      // which hydrates client-side and fetches fresh data from the API.
      const userAgent = getUserAgent(req.headers);
      if (!isSpider(userAgent)) {
        serveStaticShell(res);
        return;
      }

      // Spider — render full HTML via Angular SSR with live API data
      await requestHandler(req, res, () => {
        res.statusCode = 404;
        res.end('Not Found');
      });
    } catch (error) {
      console.error('SSR error:', error);
      res.statusCode = 500;
      res.end('Internal server error');
    }
  });
  server.listen(4200, () => {
    console.log('SSR server listening on http://localhost:4200');
  });
}

export { requestHandler };