import { useState, useEffect } from 'react';
import mqtt from 'mqtt';
import { getMqttUrl, getMqttCredentials, MQTT_TOPIC_COMMAND, MQTT_TOPIC_TICK } from '../config';

/* =========================================================
   MQTT 客户端（mqtt.js）—— 后端控制通道
   订阅 opc/display/command（页面/媒体/卡片控制）与 opc/dashboard/tick（数据快照）
   断线自动重连；未连接时静默降级（页面仍可本地操作）
   ========================================================= */

let client = null;
let status = 'connecting'; // connecting | connected | offline
let clientId = null;
const listeners = new Set();

function notifyStatus() {
  window.dispatchEvent(new CustomEvent('dpm:mqtt-status', { detail: { status } }));
}

/* 每个连接生成全局唯一 client_id（独立客户端 ID 铁律）：
   优先 crypto.randomUUID（WebView2/现代浏览器），回退时间戳+双段高熵随机 */
function makeClientId() {
  try {
    if (window.crypto && typeof window.crypto.randomUUID === 'function') {
      return `dpm-screen-${crypto.randomUUID().replace(/-/g, '')}`;
    }
  } catch { /* 继续回退 */ }
  return `dpm-screen-${Date.now().toString(36)}-${Math.random().toString(16).slice(2, 12)}-${Math.random().toString(16).slice(2, 10)}`;
}

export function connectMqtt() {
  if (client) return;
  try {
    // 独立客户端 ID：避免多屏/多实例/多标签页同 ID 被 broker 互相踢下线
    clientId = makeClientId();
    // 连接时惰性读取 MQTT 地址/账号：打包部署时 main.jsx 引导已从后端 /api/config 覆盖
    const { username, password } = getMqttCredentials();
    client = mqtt.connect(getMqttUrl(), {
      reconnectPeriod: 3000,
      connectTimeout: 8000,
      clientId,
      clean: true,
      username: username || undefined,
      password: password || undefined,
    });
    client.on('connect', () => {
      status = 'connected';
      notifyStatus();
      client.subscribe([MQTT_TOPIC_COMMAND, MQTT_TOPIC_TICK], { qos: 1 });
    });
    client.on('reconnect', () => {
      status = 'connecting';
      notifyStatus();
    });
    client.on('close', () => {
      status = 'offline';
      notifyStatus();
    });
    client.on('error', () => {
      status = 'offline';
      notifyStatus();
    });
    client.on('message', (topic, payload) => {
      let data = null;
      try {
        data = JSON.parse(payload.toString());
      } catch {
        return;
      }
      listeners.forEach((fn) => fn(topic, data));
    });
  } catch (e) {
    status = 'offline';
    notifyStatus();
  }
}

export function getMqttStatus() {
  return status;
}

/** 当前连接的稳定 client_id */
export function getClientId() {
  return clientId;
}

/** 发布消息（大屏心跳等） */
export function publishMqtt(topic, payload) {
  if (!client || status !== 'connected') return false;
  try {
    client.publish(topic, JSON.stringify(payload), { qos: 1 });
    return true;
  } catch (e) {
    return false;
  }
}

/** 订阅 MQTT 消息，返回取消订阅函数 */
export function onMqttMessage(fn) {
  listeners.add(fn);
  return () => listeners.delete(fn);
}

/** React Hook：MQTT 连接状态 */
export function useMqttStatus() {
  const [s, setS] = useState(status);
  useEffect(() => {
    connectMqtt();
    const on = (e) => setS(e.detail.status);
    window.addEventListener('dpm:mqtt-status', on);
    return () => window.removeEventListener('dpm:mqtt-status', on);
  }, []);
  return s;
}