package arp

import (
	"fmt"
	"log"
	"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"
)

func Scan(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")
	}

	arpChan := ps.OpenARP()
	defer func() {
		ps.CloseARP(arpChan)
	}()

	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 := <-arpChan:
				if !ok {
					// logging.Logger().Debugf("arp channel is closed")
					return
				}
				delay.Store(true)
				if h := handlePacketARP(zone, targetHosts, hosts, packet); nil != h {
					go discoverySession.AddHost(h)
				}
			case <-ticker.C:
				if false == delay.Load().(bool) {
					ticker.Stop()
					close(timerStopped)
					return
				}
				delay.Store(false)
			}
		}
	}()

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

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

func sendARP(ps pcap.PCapScanner, zone *omd.Zone, targetHosts []net.IP) error {
	hwAddr, err := net.ParseMAC(zone.Mac)
	if nil != err {
		return err
	}
	ip := net.ParseIP(zone.Address)
	if nil == ip {
		return fmt.Errorf("Discovery: IP(%s) of zone is not valid", zone.Address)
	}

	ethPacket := makePacketEthernet(hwAddr)
	arpPacket := makePacketARP(hwAddr, ip.To4())
	opts := gopacket.SerializeOptions{FixLengths: true, ComputeChecksums: true}
	buf := gopacket.NewSerializeBuffer()

	for _, targetHost := range targetHosts {
		arpPacket.DstProtAddress = []byte(targetHost)
		// log.Printf("ARP:%v", arpPacket)
		gopacket.SerializeLayers(buf, opts, &ethPacket, &arpPacket)
		if err := ps.WritePacketData(buf.Bytes()); err != nil {
			return err
		}

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

	}
	return nil
}

func handlePacketARP(zone *omd.Zone, targetHosts []net.IP, hosts map[string]*omd.Host, packet *layers.ARP) *omd.Host {
	if packet.Operation != layers.ARPReply {
		return nil
	}

	ip := net.IP(packet.SourceProtAddress)
	if _, ok := hosts[ip.String()]; ok {
		return nil
	}

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

	h := &omd.Host{
		MetaIPType:     omm.ToMetaIPType(omm.MetaIPTypeEnumV4),
		Address:        ip.String(),
		Mac:            net.HardwareAddr(packet.SourceHwAddress).String(),
		Zone:           zone,
		DiscoveredDate: omu.NowPtr(),
	}

	hosts[ip.String()] = h

	return h
}

func makePacketEthernet(hw net.HardwareAddr) layers.Ethernet {
	return layers.Ethernet{
		SrcMAC:       hw,
		DstMAC:       net.HardwareAddr{0xff, 0xff, 0xff, 0xff, 0xff, 0xff},
		EthernetType: layers.EthernetTypeARP,
	}
}

func makePacketARP(hw net.HardwareAddr, ip net.IP) layers.ARP {
	return layers.ARP{
		AddrType:          layers.LinkTypeEthernet,
		Protocol:          layers.EthernetTypeIPv4,
		HwAddressSize:     6,
		ProtAddressSize:   4,
		Operation:         layers.ARPRequest,
		SourceHwAddress:   []byte(hw),
		SourceProtAddress: []byte(ip),
		DstHwAddress:      []byte{0, 0, 0, 0, 0, 0},
	}
}