package netTest

//原文链接：https://blog.csdn.net/qq_38858546/article/details/119873424
//【golang】syscall 获取本机网卡IP、网关，可以通过IP地址来进行路由选择（多网卡）
import (
	"fmt"
	"net"
	"sort"
	"syscall"
	"testing"
	"unsafe"
)

type rtInfo struct {
	Dst              net.IPNet
	Gateway, PrefSrc net.IP
	OutputIface      uint32
	Priority         uint32
}

type routeSlice []*rtInfo

type router struct {
	ifaces []net.Interface
	addrs  []net.IP
	v4     routeSlice
}

func getRouteInfo() (*router, error) {
	rtr := &router{}

	tab, err := syscall.NetlinkRIB(syscall.RTM_GETROUTE, syscall.AF_INET)
	if err != nil {
		return nil, err
	}

	msgs, err := syscall.ParseNetlinkMessage(tab)
	if err != nil {
		return nil, err
	}

	for _, m := range msgs {
		switch m.Header.Type {
		case syscall.NLMSG_DONE:
			break
		case syscall.RTM_NEWROUTE:
			rtmsg := (*syscall.RtMsg)(unsafe.Pointer(&m.Data[0]))
			attrs, err := syscall.ParseNetlinkRouteAttr(&m)
			if err != nil {
				return nil, err
			}
			routeInfo := rtInfo{}
			rtr.v4 = append(rtr.v4, &routeInfo)
			for _, attr := range attrs {
				switch attr.Attr.Type {
				case syscall.RTA_DST:
					routeInfo.Dst.IP = net.IP(attr.Value)
					routeInfo.Dst.Mask = net.CIDRMask(int(rtmsg.Dst_len), len(attr.Value)*8)
				case syscall.RTA_GATEWAY:
					routeInfo.Gateway = net.IPv4(attr.Value[0], attr.Value[1], attr.Value[2], attr.Value[3])
				case syscall.RTA_OIF:
					routeInfo.OutputIface = *(*uint32)(unsafe.Pointer(&attr.Value[0]))
				case syscall.RTA_PRIORITY:
					routeInfo.Priority = *(*uint32)(unsafe.Pointer(&attr.Value[0]))
				case syscall.RTA_PREFSRC:
					routeInfo.PrefSrc = net.IPv4(attr.Value[0], attr.Value[1], attr.Value[2], attr.Value[3])
				}
			}
		}
	}

	sort.Slice(rtr.v4, func(i, j int) bool {
		return rtr.v4[i].Priority < rtr.v4[j].Priority
	})

	ifaces, err := net.Interfaces()
	if err != nil {
		return nil, err
	}

	for i, iface := range ifaces {

		if i != iface.Index-1 {
			break
		}

		if iface.Flags&net.FlagUp == 0 {
			continue
		}
		rtr.ifaces = append(rtr.ifaces, iface)
		ifaceAddrs, err := iface.Addrs()
		if err != nil {
			return nil, err
		}
		var addrs net.IP
		for _, addr := range ifaceAddrs {
			if inet, ok := addr.(*net.IPNet); ok {
				if v4 := inet.IP.To4(); v4 != nil {
					if addrs == nil {
						addrs = v4
					}
				}
			}
		}
		rtr.addrs = append(rtr.addrs, addrs)
	}
	return rtr, nil
}

func TestRoute(tt *testing.T) {
	newRoute, err := getRouteInfo()
	if err != nil {
		fmt.Println(err)
		return
	}

	fmt.Println("**************************************")
	fmt.Printf("%-15v %-15v %-15v\n", "interfaceName", "gateway", "ip")
	for _, rt := range newRoute.v4 {
		if rt.Gateway != nil {
			fmt.Printf("%-15v %-15v %-15v\n", newRoute.ifaces[rt.OutputIface-1].Name, rt.Gateway.String(), newRoute.addrs[rt.OutputIface-1])
		}
	}
	fmt.Println("**************************************")

	newRoute.getRoute(net.ParseIP("192.168.2.100"))
	newRoute.getRoute(net.ParseIP("10.10.100.100"))
	newRoute.getRoute(net.ParseIP("172.1.2.100"))
}

func (r *router) getRoute(dst net.IP) {
	for _, rt := range r.v4 {
		if rt.Dst.IP != nil && !rt.Dst.Contains(dst) {
			continue
		}
		fmt.Printf("%-15v : ", dst.String())
		if rt.PrefSrc == nil {
			fmt.Println(r.ifaces[rt.OutputIface-1].Name, rt.Gateway.String(), r.addrs[rt.OutputIface-1].String())
		} else {
			fmt.Println(r.ifaces[rt.OutputIface-1].Name, rt.Gateway.String(), rt.PrefSrc.String())
		}
		return
	}
}