package middleware

import (
	"errors"
	"net"
	"net/http"
	"strings"
)

// GetRealIP 提取客户端真实 IP 地址
func GetRealIP(r *http.Request) string {
	headers := []string{"x-forwarded-for", "X-Forwarded-For", "Proxy-Client-IP", "WL-Proxy-Client-IP", "X-Real-IP"}

	// 遍历头信息，找到第一个有效 IP
	for _, header := range headers {
		ip := extractIP(r.Header.Get(header))
		if ip != "" {
			return ip
		}
	}

	// 获取 RemoteAddr，如果经过代理则是代理 IP
	ip, _, err := net.SplitHostPort(r.RemoteAddr)
	if err == nil && ip != "" {
		return ip
	}

	// 检查是否是本地地址
	if strings.HasPrefix(ip, "127.0.0.1") || strings.HasPrefix(ip, "[::1]") {
		if externalIP, err := getExternalIP(); err == nil {
			return externalIP.String()
		}
	}
	return ""
}

// 提取 IP 地址并返回第一个非空部分
func extractIP(ips string) string {
	if ips == "" || strings.EqualFold(ips, "unknown") {
		return ""
	}
	// 返回第一个有效 IP
	return strings.TrimSpace(strings.Split(ips, ",")[0])
}

// 获取非 127.0.0.1 的局域网 IP
func getExternalIP() (net.IP, error) {
	ifaces, err := net.Interfaces()
	if err != nil {
		return nil, err
	}
	for _, iface := range ifaces {
		if iface.Flags&net.FlagUp == 0 || iface.Flags&net.FlagLoopback != 0 {
			continue
		}
		addrs, err := iface.Addrs()
		if err != nil {
			return nil, err
		}
		for _, addr := range addrs {
			ip := getIPFromAddr(addr)
			if ip != nil {
				return ip, nil
			}
		}
	}
	return nil, errors.New("not connected to the network")
}

func getIPFromAddr(addr net.Addr) net.IP {
	var ip net.IP
	switch v := addr.(type) {
	case *net.IPNet:
		ip = v.IP
	case *net.IPAddr:
		ip = v.IP
	}
	if ip != nil && !ip.IsLoopback() {
		return ip.To4()
	}
	return nil
}