package privileged

import (
	"fmt"
	"log"
	"math/rand"
	"net"
	"sync/atomic"
	"time"

	omd "git.loafle.net/overflow/model/discovery"
	omm "git.loafle.net/overflow/model/meta"
	omu "git.loafle.net/overflow/model/util"
	"git.loafle.net/overflow_scanner/probe/discovery/session"
	"git.loafle.net/overflow_scanner/probe/internal/pcap"
	"github.com/google/gopacket"
	"github.com/google/gopacket/layers"
	"golang.org/x/net/icmp"
	"golang.org/x/net/ipv6"
)

func scanV6(discoverySession session.DiscoverySession) error {
	targetHosts := discoverySession.TargetHosts()
	if nil == targetHosts || 0 == len(targetHosts) {
		return nil
	}

	zone := discoverySession.Zone()

	ps, err := pcap.RetainScanner(zone)
	if nil != err {
		return fmt.Errorf("Cannot retain pcap instance %v", err)
	}

	defer func() {
		pcap.ReleaseScanner(zone)
	}()

	icmpChan := ps.OpenICMP6()
	defer func() {
		ps.CloseICMP6(icmpChan)
	}()

	timerStopped := make(chan struct{})
	go func() {
		hosts := make(map[string]*omd.Host)

		var delay atomic.Value
		delay.Store(false)
		ticker := time.NewTicker(time.Millisecond * 500)

		for {
			select {
			case packet, ok := <-icmpChan:
				if !ok {
					// logging.Logger().Debugf("icmp channel is closed")
					return
				}
				delay.Store(true)
				if h := handlePacketICMP6(zone, targetHosts, hosts, packet); nil != h {
					if h != nil {
						discoverySession.AddHost(h)
					}

					// resultChan <- h
				}
			case <-ticker.C:
				if false == delay.Load().(bool) {
					ticker.Stop()
					timerStopped <- struct{}{}
					return
				}
				delay.Store(false)
			}
		}
	}()

	if err := sendICMP6(ps, zone, targetHosts); nil != err {
		log.Printf("sendICMP %v", err)
		return nil
	}

	select {
	case <-timerStopped:
		return nil
	}
}

func sendICMP6(ps pcap.PCapScanner, zone *omd.Zone, targetHosts []net.IP) error {
	conn, err := icmp.ListenPacket("ip6:ipv6-icmp", "")
	if nil != err {
		return err
	}
	defer conn.Close()

	msg, err := makeMessageICMP6()
	if nil != err {
		return err
	}

	var dst net.IPAddr
LOOP:
	for _, targetHost := range targetHosts {
		dst.IP = targetHost
		if _, err := conn.WriteTo(msg, &dst); nil != err {
			continue LOOP
		}

		timer := time.NewTimer(time.Microsecond * 100)

		select {
		case <-timer.C:
		}

	}
	return nil
}

func handlePacketICMP6(zone *omd.Zone, targetHosts []net.IP, hosts map[string]*omd.Host, packet gopacket.Packet) *omd.Host {
	_ethLayer := packet.Layer(layers.LayerTypeEthernet)
	ethLayer := _ethLayer.(*layers.Ethernet)

	_ip6Layer := packet.Layer(layers.LayerTypeIPv6)
	ip6Layer := _ip6Layer.(*layers.IPv6)

	_icmp6Layer := packet.Layer(layers.LayerTypeICMPv6)
	icmp6Layer := _icmp6Layer.(*layers.ICMPv6)

	if icmp6Layer.TypeCode != layers.ICMPv6TypeEchoReply {
		return nil
	}

	ip := ip6Layer.SrcIP
	if _, ok := hosts[ip.String()]; ok {
		return nil
	}

	isTarget := false
	for _, h := range targetHosts {
		if h.Equal(ip) {
			isTarget = true
			break
		}
	}
	if !isTarget {
		return nil
	}

	h := &omd.Host{
		MetaIPType:     omm.ToMetaIPType(omm.MetaIPTypeEnumV6),
		Address:        ip.String(),
		Mac:            net.HardwareAddr(ethLayer.SrcMAC).String(),
		Zone:           zone,
		DiscoveredDate: omu.NowPtr(),
	}

	hosts[ip.String()] = h

	return h
}

func makeMessageICMP6() ([]byte, error) {
	id := rand.Intn(0xffff)
	seq := rand.Intn(0xffff)

	return (&icmp.Message{
		Type: ipv6.ICMPTypeEchoRequest,
		Code: 0,
		Body: &icmp.Echo{
			ID:   id,
			Seq:  seq,
			Data: []byte("PING by overFlow"),
		},
	}).Marshal(nil)
}