// sse-server.js  (CommonJS)
const http = require('http');
const express = require('express');
const cors = require('cors');


function startSSE({
    port = 3312,
    path = '/events',
    corsOrigin = '*',      // 也可填 'http://localhost:8080' 或你的前端地址
    heartbeatMs = 15000,
} = {}) {
    const app = express();
    if (corsOrigin) app.use(cors({ origin: corsOrigin, credentials: true }));

    const clients = new Map(); // id -> res

    app.get(path, (req, res) => {
        res.set({
            'Content-Type': 'text/event-stream; charset=utf-8',
            'Cache-Control': 'no-cache, no-transform',
            'Connection': 'keep-alive',
            'X-Accel-Buffering': 'no'
        });
        if (corsOrigin) res.set('Access-Control-Allow-Origin', corsOrigin);
        res.flushHeaders?.();

        const id = `${Date.now()}-${Math.random().toString(36).slice(2)}`;
        clients.set(id, res);

        // // 初次握手
        // res.write(`event: hello\n`);
        // res.write(`data: ${JSON.stringify({ connected: true, t: Date.now() })}\n\n`);
        console.log("sse连接成功")
        const timer = setInterval(() => {
            if (!res.writableEnded) res.write(`: keep-alive ${Date.now()}\n\n`);
        }, heartbeatMs);

        req.on('close', () => {
            clearInterval(timer);
            clients.delete(id);
            try { res.end(); } catch { }
        });
    });

    // 简单健康检查
    app.get('/health', (_req, res) => res.json({ ok: true, clients: clients.size }));

    const server = http.createServer(app);
    server.listen(port, () => {
        console.log(`[SSE] listening at http://127.0.0.1:${port}${path}`);
    });

    // 广播：event 自定义；data 可传对象/字符串/Buffer
    function broadcast(eventOrData, maybeData) {
        const hasEventName = typeof maybeData !== 'undefined'; // 两种调用方式
        const eventName = hasEventName ? eventOrData : null;
        const data = hasEventName ? maybeData : eventOrData;

        const payload = Buffer.isBuffer(data)
            ? data.toString()
            : (typeof data === 'string' ? data : JSON.stringify(data));

        for (const [id, res] of clients.entries()) {
            try {
                if (eventName && eventName !== 'message') {
                    res.write(`event: ${eventName}\n`);
                } // 否则省略 event 行 => 触发前端 onmessage
                res.write(`data: ${payload}\n\n`);
            } catch {
                clients.delete(id);
                try { res.end(); } catch { }
            }
        }
    }

    async function close() {
        for (const [, res] of clients.entries()) {
            try { res.end(); } catch { }
        }
        clients.clear();
        await new Promise(r => server.close(r));
    }

    return { app, server, broadcast, close, clientsCount: () => clients.size };
}

module.exports = { startSSE };