// Copyright Safing ICS Technologies GmbH. Use of this source code is governed by the AGPL license that can be found in the LICENSE file.

package firewall

import (
	"net"
	"os"
	"sync/atomic"
	"time"

	"github.com/Safing/safing-core/configuration"
	"github.com/Safing/safing-core/firewall/inspection"
	"github.com/Safing/safing-core/firewall/interception"
	"github.com/Safing/safing-core/log"
	"github.com/Safing/safing-core/modules"
	"github.com/Safing/safing-core/network"
	"github.com/Safing/safing-core/network/packet"
	"github.com/Safing/safing-core/port17/entry"
	"github.com/Safing/safing-core/port17/mode"
	"github.com/Safing/safing-core/portmaster"
	"github.com/Safing/safing-core/process"
)

var (
	firewallModule *modules.Module
	// localNet        net.IPNet
	localhost       net.IP
	dnsServer       net.IPNet
	packetsAccepted *uint64
	packetsBlocked  *uint64
	packetsDropped  *uint64

	config = configuration.Get()

	localNet4 *net.IPNet
	// Yes, this would normally be 127.0.0.0/8
	// TODO: figure out any side effects

	localhost4 = net.IPv4(127, 0, 0, 1)
	localhost6 = net.IPv6loopback

	tunnelNet4   *net.IPNet
	tunnelNet6   *net.IPNet
	tunnelEntry4 = net.IPv4(127, 0, 0, 17)
	tunnelEntry6 = net.ParseIP("fd17::17")
)

func init() {

	var err error

	_, localNet4, err = net.ParseCIDR("127.0.0.0/24")
	// Yes, this would normally be 127.0.0.0/8
	// TODO: figure out any side effects
	if err != nil {
		log.Criticalf("firewall: failed to parse cidr 127.0.0.0/24: %s", err)
	}

	_, tunnelNet4, err = net.ParseCIDR("127.17.0.0/16")
	if err != nil {
		log.Criticalf("firewall: failed to parse cidr 127.17.0.0/16: %s", err)
	}
	_, tunnelNet6, err = net.ParseCIDR("fd17::/64")
	if err != nil {
		log.Criticalf("firewall: failed to parse cidr fd17::/64: %s", err)
	}

	var pA uint64
	packetsAccepted = &pA
	var pB uint64
	packetsBlocked = &pB
	var pD uint64
	packetsDropped = &pD
}

func Start() {
	firewallModule = modules.Register("Firewall", 128)
	defer firewallModule.StopComplete()

	// start interceptor
	go interception.Start()
	go statLogger()

	// go run()
	// go run()
	// go run()
	run()
}

func handlePacket(pkt packet.Packet) {

	// log.Tracef("handling packet: %s", pkt)

	// allow anything local, that is not dns
	if pkt.MatchesIP(packet.Remote, localNet4) && !(pkt.GetTCPUDPHeader() != nil && pkt.GetTCPUDPHeader().DstPort == 53) {
		pkt.PermanentAccept()
		return
	}

	// allow ICMP and IGMP
	// TODO: actually handle these
	switch pkt.GetIPHeader().Protocol {
	case packet.ICMP:
		pkt.PermanentAccept()
		return
	case packet.ICMPv6:
		pkt.PermanentAccept()
		return
	case packet.IGMP:
		pkt.PermanentAccept()
		return
	}

	// allow anything that goes to a tunnel entrypoint
	if pkt.IsOutbound() && (pkt.GetIPHeader().Dst.Equal(tunnelEntry4) || pkt.GetIPHeader().Dst.Equal(tunnelEntry6)) {
		pkt.PermanentAccept()
		return
	}

	// log.Debugf("firewall: pkt %s has ID %s", pkt, pkt.GetConnectionID())

	// use this to time how long it takes process packet
	// timed := time.Now()
	// defer log.Tracef("firewall: took %s to process packet %s", time.Now().Sub(timed).String(), pkt)

	// check if packet is destined for tunnel
	switch pkt.IPVersion() {
	case packet.IPv4:
		if portmaster.TunnelNet4 != nil && portmaster.TunnelNet4.Contains(pkt.GetIPHeader().Dst) {
			tunnelHandler(pkt)
		}
	case packet.IPv6:
		if portmaster.TunnelNet6 != nil && portmaster.TunnelNet6.Contains(pkt.GetIPHeader().Dst) {
			tunnelHandler(pkt)
		}
	}

	// associate packet to link and handle
	link, created := network.GetOrCreateLinkByPacket(pkt)
	if created {
		link.SetFirewallHandler(initialHandler)
		link.HandlePacket(pkt)
		return
	}
	if link.FirewallHandlerIsSet() {
		link.HandlePacket(pkt)
		return
	}
	verdict(pkt, link.Verdict)

}

func initialHandler(pkt packet.Packet, link *network.Link) {

	// get Connection
	connection, err := network.GetConnectionByFirstPacket(pkt)
	if err != nil {
		if err != process.ErrConnectionNotFound {
			log.Warningf("firewall: could not find process of packet (dropping link %s): %s", pkt.String(), err)
		}
		link.UpdateVerdict(network.DROP)
		verdict(pkt, network.DROP)
		return
	}

	// reroute dns requests to nameserver
	if connection.Process().Pid != os.Getpid() && pkt.IsOutbound() && pkt.GetTCPUDPHeader() != nil && !pkt.GetIPHeader().Dst.Equal(localhost) && pkt.GetTCPUDPHeader().DstPort == 53 {
		pkt.RerouteToNameserver()
		return
	}

	// persist connection
	connection.CreateInProcessNamespace()

	// add new Link to Connection
	connection.AddLink(link, pkt)

	// make a decision if not made already
	if connection.Verdict == network.UNDECIDED {
		portmaster.DecideOnConnection(connection, pkt)
	}
	if connection.Verdict != network.CANTSAY {
		link.UpdateVerdict(connection.Verdict)
	} else {
		portmaster.DecideOnLink(connection, link, pkt)
	}

	// log decision
	logInitialVerdict(link)

	// TODO: link this to real status
	port17Active := mode.Client()

	switch {
	case port17Active && link.Inspect:
		// tunnel link, but also inspect (after reroute)
		link.Tunneled = true
		link.SetFirewallHandler(inspectThenVerdict)
		verdict(pkt, link.Verdict)
	case port17Active:
		// tunnel link, don't inspect
		link.Tunneled = true
		link.StopFirewallHandler()
		permanentVerdict(pkt, network.ACCEPT)
	case link.Inspect:
		link.SetFirewallHandler(inspectThenVerdict)
		inspectThenVerdict(pkt, link)
	default:
		link.StopFirewallHandler()
		verdict(pkt, link.Verdict)
	}

}

func inspectThenVerdict(pkt packet.Packet, link *network.Link) {
	pktVerdict, continueInspection := inspection.RunInspectors(pkt, link)
	if continueInspection {
		// do not allow to circumvent link decision: e.g. to ACCEPT packets from a DROP-ed link
		if pktVerdict > link.Verdict {
			verdict(pkt, pktVerdict)
		} else {
			verdict(pkt, link.Verdict)
		}
		return
	}

	// we are done with inspecting
	link.StopFirewallHandler()

	config.Changed()
	config.RLock()
	link.VerdictPermanent = config.PermanentVerdicts
	config.RUnlock()

	if link.VerdictPermanent {
		link.Save()
		permanentVerdict(pkt, link.Verdict)
	} else {
		verdict(pkt, link.Verdict)
	}
}

func permanentVerdict(pkt packet.Packet, action network.Verdict) {
	switch action {
	case network.ACCEPT:
		atomic.AddUint64(packetsAccepted, 1)
		pkt.PermanentAccept()
		return
	case network.BLOCK:
		atomic.AddUint64(packetsBlocked, 1)
		pkt.PermanentBlock()
		return
	case network.DROP:
		atomic.AddUint64(packetsDropped, 1)
		pkt.PermanentDrop()
		return
	}
	pkt.Drop()
}

func verdict(pkt packet.Packet, action network.Verdict) {
	switch action {
	case network.ACCEPT:
		atomic.AddUint64(packetsAccepted, 1)
		pkt.Accept()
		return
	case network.BLOCK:
		atomic.AddUint64(packetsBlocked, 1)
		pkt.Block()
		return
	case network.DROP:
		atomic.AddUint64(packetsDropped, 1)
		pkt.Drop()
		return
	}
	pkt.Drop()
}

func tunnelHandler(pkt packet.Packet) {
	tunnelInfo := portmaster.GetTunnelInfo(pkt.GetIPHeader().Dst)
	if tunnelInfo == nil {
		pkt.Block()
		return
	}

	entry.CreateTunnel(pkt, tunnelInfo.Domain, tunnelInfo.RRCache.ExportAllARecords())
	log.Tracef("firewall: rerouting %s to tunnel entry point", pkt)
	pkt.RerouteToTunnel()
	return
}

func logInitialVerdict(link *network.Link) {
	// switch link.Verdict {
	// case network.ACCEPT:
	// 	log.Infof("firewall: accepting new link: %s", link.String())
	// case network.BLOCK:
	// 	log.Infof("firewall: blocking new link: %s", link.String())
	// case network.DROP:
	// 	log.Infof("firewall: dropping new link: %s", link.String())
	// }
}

func logChangedVerdict(link *network.Link) {
	// switch link.Verdict {
	// case network.ACCEPT:
	// 	log.Infof("firewall: change! - now accepting link: %s", link.String())
	// case network.BLOCK:
	// 	log.Infof("firewall: change! - now blocking link: %s", link.String())
	// case network.DROP:
	// 	log.Infof("firewall: change! - now dropping link: %s", link.String())
	// }
}

func run() {

packetProcessingLoop:
	for {
		select {
		case <-firewallModule.Stop:
			break packetProcessingLoop
		case pkt := <-interception.Packets:
			handlePacket(pkt)
		}
	}

}

func statLogger() {
	for {
		time.Sleep(10 * time.Second)
		log.Tracef("firewall: packets accepted %d, blocked %d, dropped %d", atomic.LoadUint64(packetsAccepted), atomic.LoadUint64(packetsBlocked), atomic.LoadUint64(packetsDropped))
		atomic.StoreUint64(packetsAccepted, 0)
		atomic.StoreUint64(packetsBlocked, 0)
		atomic.StoreUint64(packetsDropped, 0)
	}
}