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/ipv4"
)

func scanV4(discoverySession session.DiscoverySession) error {
	targetHosts := discoverySession.TargetHosts()
	if nil == targetHosts || 0 == len(targetHosts) {
		return nil
	}

	zone := discoverySession.Zone()

	ps := discoverySession.PCapScanner()
	if nil == ps {
		return fmt.Errorf("Cannot retain pcap instance")
	}

	icmpChan := ps.OpenICMP4()
	defer func() {
		ps.CloseICMP4(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 := handlePacketICMP4(zone, targetHosts, hosts, packet); nil != h {
					go discoverySession.AddHost(h)
				}
			case <-ticker.C:
				if false == delay.Load().(bool) {
					ticker.Stop()
					timerStopped <- struct{}{}
					return
				}
				delay.Store(false)
			}
		}
	}()

	if err := sendICMP4(ps, zone, targetHosts); nil != err {
		log.Printf("sendICMP %v", err)
		return nil
	}

	select {
	case <-timerStopped:
		return nil
	case <-discoverySession.StopChan():
		return nil
	}
}

func sendICMP4(ps pcap.PCapScanner, zone *omd.Zone, targetHosts []net.IP) error {
	conn, err := icmp.ListenPacket("ip4:icmp", "")
	if nil != err {
		return err
	}
	defer conn.Close()

	msg, err := makeMessageICMP4()
	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
		}

		select {
		case <-time.After(time.Microsecond * 100):
		}

	}
	return nil
}

func handlePacketICMP4(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)

	_ip4Layer := packet.Layer(layers.LayerTypeIPv4)
	ip4Layer := _ip4Layer.(*layers.IPv4)

	_icmp4Layer := packet.Layer(layers.LayerTypeICMPv4)
	icmp4Layer := _icmp4Layer.(*layers.ICMPv4)

	if icmp4Layer.TypeCode != layers.ICMPv4TypeEchoReply {
		return nil
	}

	ip := ip4Layer.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.MetaIPTypeEnumV4),
		Address:        ip.String(),
		Mac:            net.HardwareAddr(ethLayer.SrcMAC).String(),
		Zone:           zone,
		DiscoveredBy:   "ICMP",
		DiscoveredDate: omu.NowPtr(),
	}

	hosts[ip.String()] = h

	return h
}

func makeMessageICMP4() ([]byte, error) {
	id := rand.Intn(0xffff)
	seq := rand.Intn(0xffff)

	return (&icmp.Message{
		Type: ipv4.ICMPTypeEcho,
		Code: 0,
		Body: &icmp.Echo{
			ID:   id,
			Seq:  seq,
			Data: []byte("PING by overFlow"),
		},
	}).Marshal(nil)
}