package discovery

import (
	"fmt"
	"net"
	"os"
	"os/exec"
	"runtime"
	"strings"
	"sync"
	"time"
)

// Host 存活主机信息
type Host struct {
	IP       net.IP
	MAC      string // 物理地址（设备唯一标识）
	Alive    bool
	OpenPort int
}

// Scanner 网段扫描器
type Scanner struct {
	CIDR        string
	Port        int
	Timeout     time.Duration
	Concurrency int
}

// NewScanner 创建扫描器
func NewScanner(cidr string, port int, timeout time.Duration, concurrency int) *Scanner {
	return &Scanner{
		CIDR:        cidr,
		Port:        port,
		Timeout:     timeout,
		Concurrency: concurrency,
	}
}

// Scan 扫描网段，返回存活主机列表
func (s *Scanner) Scan() []Host {
	ip, ipnet, err := net.ParseCIDR(s.CIDR)
	if err != nil {
		fmt.Printf("[扫描] 网段解析失败: %v\n", err)
		return nil
	}

	var ips []net.IP
	for ip := ip.Mask(ipnet.Mask); ipnet.Contains(ip); inc(ip) {
		dst := make(net.IP, len(ip))
		copy(dst, ip)
		ips = append(ips, dst)
	}
	// 排除网络地址和广播地址
	if len(ips) > 2 {
		ips = ips[1 : len(ips)-1]
	}

	fmt.Printf("[扫描] 网段 %s，共 %d 个IP，开始探测...\n", s.CIDR, len(ips))

	// 并发探测
	var mu sync.Mutex
	var wg sync.WaitGroup
	var results []Host

	sem := make(chan struct{}, s.Concurrency)
	for _, ip := range ips {
		wg.Add(1)
		sem <- struct{}{}
		go func(target net.IP) {
			defer wg.Done()
			defer func() { <-sem }()

			h := s.probe(target)
			if h.Alive {
				// 获取 MAC 地址（TCP 探测已触发 ARP 解析）
				h.MAC = getMAC(target.String())
				mu.Lock()
				results = append(results, h)
				mu.Unlock()
				desc := "无MAC"
				if h.MAC != "" {
					desc = h.MAC
				}
				fmt.Printf("  [+] %s 存活 (MAC: %s, 端口 %d 开放)\n", target, desc, h.OpenPort)
			}
		}(ip)
	}
	wg.Wait()

	fmt.Printf("[扫描] 完成，发现 %d 台存活主机\n", len(results))
	return results
}

// probe 探测单个 IP
func (s *Scanner) probe(ip net.IP) Host {
	h := Host{IP: ip}

	// TCP 端口探测（连接成功会触发本地 ARP 解析）
	addr := net.JoinHostPort(ip.String(), fmt.Sprintf("%d", s.Port))
	conn, err := net.DialTimeout("tcp", addr, s.Timeout)
	if err == nil {
		conn.Close()
		h.Alive = true
		h.OpenPort = s.Port
		return h
	}

	// 备选：尝试常见端口
	for _, p := range []int{22, 80, 443, 8080, 3306} {
		addr = net.JoinHostPort(ip.String(), fmt.Sprintf("%d", p))
		conn, err = net.DialTimeout("tcp", addr, s.Timeout)
		if err == nil {
			conn.Close()
			h.Alive = true
			h.OpenPort = p
			return h
		}
	}

	return h
}

// getMAC 从 ARP 表获取 IP 对应的 MAC 地址（跨平台）
// 返回空字符串表示无法获取
func getMAC(ip string) string {
	switch runtime.GOOS {
	case "linux":
		return macFromProcNetArp(ip)
	case "windows":
		return macFromWindowsArp(ip)
	case "darwin":
		return macFromUnixArp(ip)
	default:
		return macFromUnixArp(ip)
	}
}

// macFromProcNetArp 解析 Linux /proc/net/arp
func macFromProcNetArp(ip string) string {
	data, err := os.ReadFile("/proc/net/arp")
	if err != nil {
		return ""
	}
	for _, line := range strings.Split(string(data), "\n")[1:] {
		fields := strings.Fields(line)
		if len(fields) >= 4 && fields[0] == ip {
			mac := fields[3]
			if mac != "" && mac != "00:00:00:00:00:00" {
				return mac
			}
		}
	}
	return ""
}

// macFromWindowsArp 解析 Windows `arp -a` 输出
func macFromWindowsArp(ip string) string {
	out, err := exec.Command("arp", "-a").Output()
	if err != nil {
		return ""
	}
	for _, line := range strings.Split(string(out), "\n") {
		fields := strings.Fields(line)
		// Windows 格式: IP  MAC  Type
		if len(fields) >= 2 && fields[0] == ip {
			mac := strings.ReplaceAll(fields[1], "-", ":")
			if mac != "" && mac != "00:00:00:00:00:00" {
				return strings.ToLower(mac)
			}
		}
	}
	return ""
}

// macFromUnixArp 解析 macOS/Linux `arp -n` 输出
func macFromUnixArp(ip string) string {
	out, err := exec.Command("arp", "-n", ip).Output()
	if err != nil {
		return ""
	}
	for _, line := range strings.Split(string(out), "\n") {
		fields := strings.Fields(line)
		// macOS 格式: ? (IP) at MAC on en0 ifscope [ethernet]
		for i, f := range fields {
			if f == "("+ip+")" && i+2 < len(fields) {
				mac := fields[i+2]
				if mac != "" && mac != "ff:ff:ff:ff:ff:ff" {
					return strings.ToLower(mac)
				}
			}
		}
	}
	return ""
}

// inc IP 递增
func inc(ip net.IP) {
	for j := len(ip) - 1; j >= 0; j-- {
		ip[j]++
		if ip[j] > 0 {
			break
		}
	}
}