package main

import (
	"bufio"
	"fmt"
	"log"
	"net"
	"sync"
)

var (
	clients   = make(map[net.Conn]string) // 连接映射：连接对象到用户名
	clientsMu sync.Mutex                  // 保护clients的互斥锁
)

func main() {
	listener, err := net.Listen("tcp", ":8888")
	if err != nil {
		log.Fatalf("监听端口失败: %v", err)
	}
	defer listener.Close()
	fmt.Println("服务器已启动，监听端口 8888")

	for {
		conn, err := listener.Accept()
		if err != nil {
			log.Printf("接受连接失败: %v", err)
			continue
		}
		go handleConnection(conn)
	}
}

func handleConnection(conn net.Conn) {
	defer func() {
		// 连接关闭时，移除客户端
		clientsMu.Lock()
		delete(clients, conn)
		clientsMu.Unlock()
		conn.Close()
		broadcast(fmt.Sprintf("用户退出：%s", conn.RemoteAddr().String()), "系统")
		fmt.Printf("客户端断开：%s\n", conn.RemoteAddr().String())
	}()

	// 添加新连接
	clientsMu.Lock()
	clients[conn] = conn.RemoteAddr().String()
	clientsMu.Unlock()

	// 通知所有客户端有新用户加入
	broadcast(fmt.Sprintf("新用户加入：%s", conn.RemoteAddr().String()), "系统")

	scanner := bufio.NewScanner(conn)
	for scanner.Scan() {
		msg := scanner.Text()
		sender := clients[conn]
		broadcast(msg, sender)
	}
	if err := scanner.Err(); err != nil {
		log.Printf("读取消息错误: %v", err)
	}
}

func broadcast(message, sender string) {
	clientsMu.Lock()
	defer clientsMu.Unlock()
	for c := range clients {
		if c != nil {
			_, err := fmt.Fprintf(c, "[%s] %s\n", sender, message)
			if err != nil {
				log.Printf("广播失败: %v", err)
			}
		}
	}
}