package inet

import (
	"encoding/binary"
	"fmt"
	"strconv"
	"syscall"
	"unsafe"
)

func reverse(b []byte) {
	var (
		mid  uint8
		blen = len(b)
	)
	if blen > 1 {
		for i := 0; i < blen/2; i++ {
			mid = b[i]
			b[i] = b[blen-i-1]
			b[blen-i-1] = mid
		}
	}
}
//主機字節(jié)序變網(wǎng)絡(luò)字節(jié)序
func Htons[T uint | uint16 | uint32 | uint64](t T) T {
	var (
		b   []byte = make([]byte, unsafe.Sizeof(t))
		ptr *T     = (*T)(unsafe.Pointer(&b[0]))
	)
	*ptr = t
	reverse(b)
	return *ptr
}

//ip包必選，ip6自行根據(jù)wireshark進行編寫，此處ip4為例
type IPHeader struct {
	Version_And_Len        uint8//前4個bit為version(4 ip4,6 ip6)，后bit個字節(jié)為首部length xxxx xxxx
	DiffernetialtedService uint8
	Tot_Len                uint16
	Id                     uint16
	Flag_And_Seek          uint16//前3bit 為flag后面13bit為seek
	TTL                    uint8
	Protocol               uint8
	CheckSum               uint16
	Source                 uint32
	Dest                   uint32
}
type PortInfo struct {
	Source uint16
	Dest   uint16
}

var (
	__IP_DEFAULT  IPHeader
	IPHEADER_SIZE = int(unsafe.Sizeof(__IP_DEFAULT))
)

func Watch(watcher func([]byte, int)) error {
  //socket af_packet 會抓取全部網(wǎng)卡的IP數(shù)據(jù)包，如需監(jiān)聽特定的網(wǎng)卡請自行判斷
	fd, _, err_ := syscall.Syscall(syscall.SYS_SOCKET, syscall.AF_PACKET, syscall.SOCK_DGRAM, uintptr(Htons[uint16](syscall.ETH_P_IP)))
	if int(fd) < 0 {
		return err_
	}
	ifd := int(fd)
	var (
		buff []byte = make([]byte, 512)
		lang int
		err error
	)
	defer syscall.Close(ifd)
	fmt.Println("start watch raw stream", ifd)
	for {
		lang, _, err = syscall.Recvfrom(ifd, buff, 0)
		if lang <= 0 {
			break
		}
		watcher(buff, lang)
	}
	return err
}
//輸出所有來源去向
func print_info(info []byte, size int) {
	if size <= IPHEADER_SIZE {
		return
	}
	var (
		ipheader *IPHeader = (*IPHeader)(unsafe.Pointer(&info[0]))
		portinfo *PortInfo
	)
	if size > IPHEADER_SIZE+4 {
		portinfo = (*PortInfo)(unsafe.Pointer(&info[IPHEADER_SIZE]))
		fmt.Printf("src %s:%d dst %s:%d\n", Raw2String(ipheader.Source), portinfo.Source, Raw2String(ipheader.Dest), portinfo.Dest)
	} else {
		fmt.Printf("src %s dst %s\n", Raw2String(ipheader.Source), Raw2String(ipheader.Dest))
	}

}
func Raw2String(src uint32) string {
	raw := make([]byte, 4)
	binary.LittleEndian.PutUint32(raw, src)
	return strconv.FormatUint(uint64(raw[0]), 10) + "." + strconv.FormatUint(uint64(raw[1]), 10) + "." + strconv.FormatUint(uint64(raw[2]), 10) + "." + strconv.FormatUint(uint64(raw[3]), 10)
}
func Print_Info() func([]byte, int) {
	return print_info
}

func main() {
	fmt.Fprintln(os.Stderr, inet.Watch(inet.Print_Info()))
}