import { mkdirSync, writeFileSync } from 'node:fs';
import { resolve } from 'node:path';
import type { Plugin } from 'vite';
import { defineConfig } from 'vite';

/**
 * Dev-only: lets the running game POST a rendered frame to disk.
 *
 * The game cannot always be looked at — a backgrounded or non-compositing tab
 * never fires requestAnimationFrame, so nothing draws and nothing can be
 * screenshotted from outside. With this, plus the `?debug=1` handle in
 * src/debug.ts, a script can step the simulation, render a frame, and drop the
 * image somewhere it can actually be opened.
 *
 * Never registered in a production build.
 */
function screenshotEndpoint(): Plugin {
  const directory = resolve(process.cwd(), 'shots');

  return {
    name: 'dbtl-screenshot',
    apply: 'serve',
    configureServer(server) {
      server.middlewares.use('/__shot', (req, res) => {
        if (req.method !== 'POST') {
          res.statusCode = 405;
          res.end('POST only');
          return;
        }
        const name = (new URL(req.url ?? '', 'http://x').searchParams.get('name') ?? 'frame')
          // Keep this from writing outside the shots directory.
          .replace(/[^a-z0-9_-]/gi, '');

        const chunks: Buffer[] = [];
        req.on('data', (chunk: Buffer) => chunks.push(chunk));
        req.on('end', () => {
          try {
            mkdirSync(directory, { recursive: true });
            const file = resolve(directory, `${name || 'frame'}.jpg`);
            writeFileSync(file, Buffer.concat(chunks));
            res.setHeader('content-type', 'application/json');
            res.end(JSON.stringify({ ok: true, file, bytes: Buffer.concat(chunks).length }));
          } catch (err) {
            res.statusCode = 500;
            res.end(String(err));
          }
        });
      });
    },
  };
}

export default defineConfig({
  plugins: [screenshotEndpoint()],
});