package syn

import (
	"encoding/json"
	"fmt"
	"log"
	"net"
	"strconv"
	"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"
)

func scanV4(discoverySession session.DiscoverySession, targetHost *omd.Host) error {
	ps := discoverySession.PCapScanner()
	if nil == ps {
		return fmt.Errorf("Cannot retain pcap instance")
	}

	tcpChan := ps.OpenTCP(targetHost.Address)
	defer func() {
		go ps.CloseTCP(targetHost.Address, tcpChan)
	}()

	timerStopped := make(chan struct{})
	stopChan := make(chan struct{})
	defer close(stopChan)

	go func() {
		ports := make(map[int]*omd.Port)

		var delay atomic.Value
		delay.Store(false)
		ticker := time.NewTicker(time.Millisecond * 1000)
		for {
			select {
			case packet, ok := <-tcpChan:
				if !ok {
					return
				}
				delay.Store(true)
				if p := handlePacketTCP4(discoverySession, targetHost, ports, packet); nil != p {
					go discoverySession.AddPort(p)
				}
			case <-ticker.C:
				if false == delay.Load().(bool) {
					ticker.Stop()
					timerStopped <- struct{}{}
					return
				}
				delay.Store(false)
			}
		}
	}()

	if err := sendTCP4(discoverySession, ps, targetHost, stopChan); nil != err {
		log.Printf("sendTCP %v", err)
		return nil
	}

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

func sendTCP4(discoverySession session.DiscoverySession, ps pcap.PCapScanner, host *omd.Host, stopChan chan struct{}) error {
	dp := discoverySession.DiscoverPort()

	tcpPacket, err := makePacketPortTCP4(host)
	if nil != err {
		return err
	}

	buf := gopacket.NewSerializeBuffer()

Loop:
	for portNumber := dp.FirstScanRange; portNumber < dp.LastScanRange; portNumber++ {
		if nil != dp.ExcludePorts {
			for _, exPortNumber := range dp.ExcludePorts {
				if portNumber == exPortNumber {
					continue Loop
				}
			}
		}
		tcpPacket.TCP.DstPort = layers.TCPPort(portNumber)
		if err := tcpPacket.TCP.SetNetworkLayerForChecksum(tcpPacket.IP); err != nil {
			return err
		}

		if err := gopacket.SerializeLayers(buf, tcpPacket.Opts, tcpPacket.Eth, tcpPacket.IP, tcpPacket.TCP); err != nil {
			return err
		}
		if err := ps.WritePacketData(buf.Bytes()); err != nil {
			return err
		}

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

	return nil
}

func handlePacketTCP4(discoverySession session.DiscoverySession, host *omd.Host, ports map[int]*omd.Port, packet *layers.TCP) *omd.Port {
	if nil == packet || packet.DstPort != 60000 {
		return nil
	}

	dp := discoverySession.DiscoverPort()

	if packet.SYN && packet.ACK {
		port := int(packet.SrcPort)

		if _, ok := ports[port]; ok || !dp.Contains(port) {
			return nil
		}
		// olog.Logger().Debug("Discovery", zap.String("ip", host.Address), zap.Int("port", port))

		p := &omd.Port{
			MetaPortType:   omm.ToMetaPortType(omm.MetaPortTypeEnumTCP),
			PortNumber:     json.Number(strconv.Itoa(port)),
			DiscoveredDate: omu.NowPtr(),
		}
		p.Host = host

		ports[port] = p

		return p
	}

	return nil

}

type PortPacketTCP4 struct {
	Eth  *layers.Ethernet
	IP   *layers.IPv4
	TCP  *layers.TCP
	Opts gopacket.SerializeOptions
	//PacketConn net.PacketConn
}

func makePacketPortTCP4(host *omd.Host) (*PortPacketTCP4, error) {
	packetTCP := &PortPacketTCP4{}

	srcIP := net.ParseIP(host.Zone.Address)
	if nil == srcIP {
		return nil, fmt.Errorf("IP(%s) of zone is not valid", host.Zone.Address)
	}
	dstIP := net.ParseIP(host.Address)
	if nil == dstIP {
		return nil, fmt.Errorf("IP(%s) of host is not valid", host.Address)
	}

	srcMac, err := net.ParseMAC(host.Zone.Mac)
	if nil != err {
		return nil, err
	}

	dstMac, err := net.ParseMAC(host.Mac)
	if nil != err {
		return nil, err
	}

	packetTCP.Eth = &layers.Ethernet{
		SrcMAC:       srcMac,
		DstMAC:       dstMac,
		EthernetType: layers.EthernetTypeIPv4,
	}

	packetTCP.IP = &layers.IPv4{
		SrcIP:    srcIP,
		DstIP:    dstIP,
		Version:  4,
		TTL:      64,
		Protocol: layers.IPProtocolTCP,
	}
	packetTCP.TCP = &layers.TCP{
		SrcPort: 60000,
		DstPort: 0, // will be incremented during the scan
		SYN:     true,
		Seq:     0,
	}
	packetTCP.Opts = gopacket.SerializeOptions{
		ComputeChecksums: true,
		FixLengths:       true,
	}

	return packetTCP, nil
}