import type { LiveEvent } from '@atm/shared/api';
import type { FastifyInstance } from 'fastify';
import type { LiveHub } from '../live/hub.ts';

export const HEARTBEAT_MS = 25_000;
const MAX_CLIENTS = 500;

const frame = (e: LiveEvent) => `id: ${e.id}\nevent: ${e.kind}\ndata: ${JSON.stringify(e.data)}\n\n`;

export async function liveRoutes(app: FastifyInstance, { hub }: { hub: LiveHub }) {
  let clients = 0;
  const open = new Set<{ end: () => void }>();
  // Hijacked streams are not tracked by Fastify; end them so shutdown does not hang.
  app.addHook('onClose', async () => {
    for (const res of open) res.end();
  });

  app.get<{ Headers: { 'last-event-id'?: string } }>('/api/live', async (req, reply) => {
    if (clients >= MAX_CLIENTS) return reply.code(503).send({ error: 'too_many_clients' });
    clients++;
    reply.hijack();
    const res = reply.raw;
    res.writeHead(200, {
      'content-type': 'text/event-stream; charset=utf-8',
      'cache-control': 'no-cache, no-transform',
      connection: 'keep-alive',
      'x-accel-buffering': 'no',
    });
    res.write(`retry: 5000\n: connected\n\n`);

    const lastId = Number(req.headers['last-event-id']);
    if (Number.isFinite(lastId) && lastId > 0) for (const e of hub.since(lastId)) res.write(frame(e));

    const unsubscribe = hub.subscribe((e) => res.write(frame(e)));
    const heartbeat = setInterval(() => res.write(': ping\n\n'), HEARTBEAT_MS);
    open.add(res);
    const close = () => {
      clearInterval(heartbeat);
      unsubscribe();
      open.delete(res);
      clients--;
    };
    req.raw.on('close', close);
  });
}