/*
   Copyright 2024 Josh Deprez

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
*/

package main

import (
	"bufio"
	"cmp"
	"context"
	"errors"
	"flag"
	"fmt"
	"log"
	"math/rand/v2"
	"net"
	"net/http"
	"os"
	"os/signal"
	"regexp"
	"runtime/debug"
	"slices"
	"strings"
	"sync"
	"time"

	"gitea.drjosh.dev/josh/jrouter/aurp"
	"gitea.drjosh.dev/josh/jrouter/router"
	"gitea.drjosh.dev/josh/jrouter/status"

	"github.com/google/gopacket/pcap"
	"github.com/sfiera/multitalk/pkg/ddp"
	"github.com/sfiera/multitalk/pkg/ethernet"
)

const routingTableTemplate = `
<table>
	<thead><tr>
		<th>Network range</th>
		<th>Extended?</th>
		<th>Zone names</th>
		<th>Distance</th>
		<th>Last seen</th>
		<th>Port</th>
	</tr></thead>
	<tbody>
{{range $route := . }}
	<tr>
		<td>{{$route.NetStart}}{{if not (eq $route.NetStart $route.NetEnd)}} - {{$route.NetEnd}}{{end}}</td>
		<td>{{if $route.Extended}}✅{{else}}-{{end}}</td>
		<td>{{range $route.ZoneNames.ToSlice}}{{.}}<br>{{end}}</td>
		<td>{{$route.Distance}}</td>
		<td>{{$route.LastSeenAgo}}</td>
		<td>
			{{- with $route.AURPPeer -}}
				[redacted]
			{{- end -}}
			{{- with $route.EtherTalkPeer -}}
				{{.Port.Device}} {{.PeerAddr.Network}}.{{.PeerAddr.Node}}
			{{- end -}}
			{{- with $route.EtherTalkDirect -}}
				{{.Device}}
			{{- end -}}
		</td>
	</tr>
{{end}}
	</tbody>
</table>
`

const peerTableTemplate = `
<table>
	<thead><tr>
		<th>Configured addr</th>
		<th>Remote addr</th>
		<th>Receiver state</th>
		<th>Sender state</th>
	</tr></thead>
	<tbody>
{{range $peer := . }}
	<tr>
		<td>[redacted]</td>
		<td>[redacted]</td>
		<td>{{$peer.ReceiverState}}</td>
		<td>{{$peer.SenderState}}</td>
	</tr>
{{end}}
	</tbody>
</table>
`

var hasPortRE = regexp.MustCompile(`:\d+$`)

var configFilePath = flag.String("config", "jrouter.yaml", "Path to configuration file to use")

func main() {
	// For some reason it occasionally panics and the panics have no traceback?
	debug.SetTraceback("all")

	flag.Parse()
	log.Println("jrouter")

	cfg, err := router.LoadConfig(*configFilePath)
	if err != nil {
		log.Fatalf("Couldn't load configuration file: %v", err)
	}

	localIP := net.ParseIP(cfg.LocalIP).To4()
	if localIP == nil {
		iaddrs, err := net.InterfaceAddrs()
		if err != nil {
			log.Fatalf("Couldn't read network interface addresses: %v", err)
		}
		for _, iaddr := range iaddrs {
			inet, ok := iaddr.(*net.IPNet)
			if !ok {
				continue
			}
			if !inet.IP.IsGlobalUnicast() {
				continue
			}
			localIP = inet.IP.To4()
			if localIP != nil {
				break
			}
		}
		if localIP == nil {
			log.Fatalf("No global unicast IPv4 addresses on any network interfaces, and no valid local_ip address in configuration")
		}
	}
	localDI := aurp.IPDomainIdentifier(localIP)

	// log.Printf("Using %v as local domain identifier", localIP)

	// log.Printf("EtherTalk configuration: %+v", cfg.EtherTalk)

	ln, err := net.ListenUDP("udp4", &net.UDPAddr{Port: int(cfg.ListenPort)})
	if err != nil {
		log.Fatalf("AURP: Couldn't listen on udp4:387: %v", err)
	}
	defer ln.Close()
	log.Printf("AURP: Listening on %v", ln.LocalAddr())

	log.Println("Press ^C or send SIGINT to stop the router gracefully")
	cctx, cancel := context.WithCancel(context.Background())
	defer cancel()
	ctx, _ := signal.NotifyContext(cctx, os.Interrupt)

	// --------------------------------- HTTP ---------------------------------
	http.HandleFunc("/status", status.Handle)
	go func() {
		log.Print(http.ListenAndServe(":9459", nil))
	}()

	// --------------------------------- Pcap ---------------------------------
	// First check the interface
	iface, err := net.InterfaceByName(cfg.EtherTalk.Device)
	if err != nil {
		log.Fatalf("Couldn't find interface named %q: %v", cfg.EtherTalk.Device, err)
	}
	myHWAddr := ethernet.Addr(iface.HardwareAddr)
	if cfg.EtherTalk.EthAddr != "" {
		// Override myHWAddr with the configured address
		netHWAddr, err := net.ParseMAC(cfg.EtherTalk.EthAddr)
		if err != nil {
			log.Fatalf("Couldn't parse ethertalk.ethernet_addr value %q: %v", cfg.EtherTalk.EthAddr, err)
		}
		myHWAddr = ethernet.Addr(netHWAddr)
	}

	pcapHandle, err := pcap.OpenLive(cfg.EtherTalk.Device, 4096, true, 100*time.Millisecond)
	if err != nil {
		log.Fatalf("Couldn't open %q for packet capture: %v", cfg.EtherTalk.Device, err)
	}
	bpfFilter := fmt.Sprintf("(atalk or aarp) and (ether multicast or ether dst %s)", myHWAddr)
	if err := pcapHandle.SetBPFFilter(bpfFilter); err != nil {
		pcapHandle.Close()
		log.Fatalf("Couldn't set BPF filter on packet capture: %v", err)
	}
	defer pcapHandle.Close()

	// -------------------------------- Tables --------------------------------
	routes := router.NewRouteTable()
	status.AddItem(ctx, "Routing table", routingTableTemplate, func(context.Context) (any, error) {
		rs := routes.Dump()
		slices.SortFunc(rs, func(ra, rb router.Route) int {
			return cmp.Compare(ra.NetStart, rb.NetStart)
		})
		return rs, nil
	})

	// -------------------------------- Peers ---------------------------------
	var peersMu sync.Mutex
	peers := make(map[udpAddr]*router.AURPPeer)
	status.AddItem(ctx, "AURP Peers", peerTableTemplate, func(context.Context) (any, error) {
		var peerInfo []*router.AURPPeer
		func() {
			peersMu.Lock()
			defer peersMu.Unlock()
			peerInfo = make([]*router.AURPPeer, 0, len(peers))
			for _, p := range peers {
				peerInfo = append(peerInfo, p)
			}
		}()
		slices.SortFunc(peerInfo, func(pa, pb *router.AURPPeer) int {
			return cmp.Or(
				-cmp.Compare(
					bool2Int(pa.ReceiverState() == router.ReceiverConnected),
					bool2Int(pb.ReceiverState() == router.ReceiverConnected),
				),
				-cmp.Compare(
					bool2Int(pa.SenderState() == router.SenderConnected),
					bool2Int(pb.SenderState() == router.SenderConnected),
				),
				cmp.Compare(pa.ConfiguredAddr, pb.ConfiguredAddr),
			)
		})
		return peerInfo, nil
	})

	var nextConnID uint16
	for nextConnID == 0 {
		nextConnID = uint16(rand.IntN(0x10000))
	}

	var wg sync.WaitGroup
	goPeerHandler := func(p *router.AURPPeer) {
		wg.Add(1)
		go func() {
			defer wg.Done()
			p.Handle(ctx)
		}()
	}

	// ------------------------- Configured peer setup ------------------------
	if cfg.PeerListURL != "" {
		log.Print("Fetching peer list...")
		existing := len(cfg.Peers)
		func() {
			resp, err := http.Get(cfg.PeerListURL)
			if err != nil {
				log.Fatalf("Couldn't fetch peer list!")
			}
			defer resp.Body.Close()

			sc := bufio.NewScanner(resp.Body)
			for sc.Scan() {
				p := strings.TrimSpace(sc.Text())
				if p == "" {
					continue
				}
				cfg.Peers = append(cfg.Peers, p)
			}
			if err := sc.Err(); err != nil {
				log.Fatalf("Couldn't scan peer list response: %v", err)
			}
		}()
		log.Printf("Fetched list containing %d peers", len(cfg.Peers)-existing)
	}

	for _, peerStr := range cfg.Peers {
		if !hasPortRE.MatchString(peerStr) {
			peerStr += ":387"
		}

		raddr, err := net.ResolveUDPAddr("udp4", peerStr)
		if err != nil {
			log.Print("couldn't resolve UDP address, skipping peer")
			continue
		}
		//log.Printf("resolved %q to %v", peerStr, raddr)

		if raddr.IP.Equal(localIP) {
			//log.Print("peer == me, skipping")
			continue
		}

		peer := &router.AURPPeer{
			Transport: &aurp.Transport{
				LocalDI:     localDI,
				RemoteDI:    aurp.IPDomainIdentifier(raddr.IP),
				LocalConnID: nextConnID,
			},
			UDPConn:        ln,
			ConfiguredAddr: peerStr,
			RemoteAddr:     raddr,
			ReceiveCh:      make(chan aurp.Packet, 1024),
			RouteTable:     routes,
		}
		aurp.Inc(&nextConnID)
		peersMu.Lock()
		peers[udpAddrFromNet(raddr)] = peer
		peersMu.Unlock()
		goPeerHandler(peer)
	}

	// --------------------------------- AARP ---------------------------------
	aarpMachine := router.NewAARPMachine(cfg, pcapHandle, myHWAddr)
	go aarpMachine.Run(ctx)

	// -------------------------------- Router --------------------------------
	rooter := &router.Router{
		Config:     cfg,
		RouteTable: routes,
		// ZoneTable:  zones,
	}

	etherTalkPort := &router.EtherTalkPort{
		Device:          cfg.EtherTalk.Device,
		EthernetAddr:    myHWAddr,
		NetStart:        cfg.EtherTalk.NetStart,
		NetEnd:          cfg.EtherTalk.NetEnd,
		DefaultZoneName: cfg.EtherTalk.ZoneName,
		AvailableZones:  router.SetFromSlice([]string{cfg.EtherTalk.ZoneName}),
		PcapHandle:      pcapHandle,
		AARPMachine:     aarpMachine,
		Router:          rooter,
	}
	rooter.Ports = append(rooter.Ports, etherTalkPort)
	routes.InsertEtherTalkDirect(etherTalkPort)

	// --------------------------------- RTMP ---------------------------------
	go etherTalkPort.RunRTMP(ctx)

	// ---------------------- Raw AppleTalk/AARP inbound ----------------------
	wg.Add(1)
	go func() {
		defer wg.Done()

		ctx, setStatus, _ := status.AddSimpleItem(ctx, "EtherTalk inbound")
		defer setStatus("EtherTalk Serve goroutine exited!")

		setStatus(fmt.Sprintf("Listening on %s", cfg.EtherTalk.Device))

		etherTalkPort.Serve(ctx)
	}()

	// ----------------------------- AURP inbound -----------------------------
	wg.Add(1)
	go func() {
		defer wg.Done()

		ctx, setStatus, done := status.AddSimpleItem(ctx, "AURP inbound")
		defer done()
		setStatus(fmt.Sprintf("Listening on UDP port %d", cfg.ListenPort))

		for {
			if ctx.Err() != nil {
				return
			}
			ln.SetReadDeadline(time.Now().Add(100 * time.Millisecond))
			pktbuf := make([]byte, 4096)
			pktlen, raddr, readErr := ln.ReadFromUDP(pktbuf)

			var operr *net.OpError
			if errors.As(readErr, &operr) && operr.Timeout() {
				continue
			}

			// log.Printf("AURP: Received packet of length %d from %v", pktlen, raddr)

			dh, pkt, parseErr := aurp.ParsePacket(pktbuf[:pktlen])
			if parseErr != nil {
				log.Printf("AURP: Failed to parse packet: %v", parseErr)
				continue
			}
			if readErr != nil {
				log.Printf("AURP: Failed to read packet: %v", readErr)
				return
			}

			// log.Printf("AURP: Got %T from %v (%v)", pkt, raddr, dh.SourceDI)

			// Existing peer?
			ra := udpAddrFromNet(raddr)
			peersMu.Lock()
			pr := peers[ra]
			if pr == nil {
				if !cfg.OpenPeering {
					log.Print("AURP: Got packet but it's not in my config and open peering is disabled; dropping the packet")
					peersMu.Unlock()
					continue
				}
				// New peer!
				pr = &router.AURPPeer{
					Transport: &aurp.Transport{
						LocalDI:     localDI,
						RemoteDI:    dh.SourceDI, // platinum rule
						LocalConnID: nextConnID,
					},
					UDPConn:    ln,
					RemoteAddr: raddr,
					ReceiveCh:  make(chan aurp.Packet, 1024),
					RouteTable: routes,
				}
				aurp.Inc(&nextConnID)
				peers[ra] = pr
				goPeerHandler(pr)
			}
			peersMu.Unlock()

			switch dh.PacketType {
			case aurp.PacketTypeRouting:
				// It's AURP routing data.
				// Pass the packet to the goroutine in charge of this peer.
				select {
				case pr.ReceiveCh <- pkt:
					// That's it for us.

				case <-ctx.Done():
					return
				}
				continue

			case aurp.PacketTypeAppleTalk:
				apkt, ok := pkt.(*aurp.AppleTalkPacket)
				if !ok {
					log.Printf("AURP: Got %T but domain header packet type was %v ?", pkt, dh.PacketType)
					continue
				}

				// Route or otherwise handle the encapsulated AppleTalk traffic
				ddpkt := new(ddp.ExtPacket)
				if err := ddp.ExtUnmarshal(apkt.Data, ddpkt); err != nil {
					log.Printf("AURP: Couldn't unmarshal encapsulated DDP packet: %v", err)
					continue
				}
				// log.Printf("DDP/AURP: Got %d.%d.%d -> %d.%d.%d proto %d data len %d",
				// 	ddpkt.SrcNet, ddpkt.SrcNode, ddpkt.SrcSocket,
				// 	ddpkt.DstNet, ddpkt.DstNode, ddpkt.DstSocket,
				// 	ddpkt.Proto, len(ddpkt.Data))

				// Is it addressed to me?
				var localPort *router.EtherTalkPort
				for _, port := range rooter.Ports {
					if ddpkt.DstNet >= port.NetStart && ddpkt.DstNet <= port.NetEnd {
						localPort = port
						break
					}
				}
				if ddpkt.DstNode == 0 && localPort != nil { // Node 0 = any router for the network = me
					// Is it NBP? FwdReq needs translating.
					if ddpkt.DstSocket != 2 {
						// Something else?? TODO
						log.Printf("DDP/AURP: I don't have anything 'listening' on socket %d", ddpkt.DstSocket)
						continue
					}
					// It's NBP, specifically it should be a FwdReq
					if err := rooter.HandleNBPFromAURP(ctx, ddpkt); err != nil {
						log.Printf("NBP/DDP/AURP: %v", err)
					}
					continue
				}

				// Route the packet!
				if err := rooter.Forward(ctx, ddpkt); err != nil {
					log.Printf("DDP/AURP: Couldn't route packet: %v", err)
				}

			default:
				log.Printf("AURP: Got unknown packet type %v", dh.PacketType)
			}
		}
	}()

	// -------------------------------- Close ---------------------------------
	wg.Wait()
}

// Hashable net.UDPAddr
type udpAddr struct {
	ipv4 [4]byte
	port uint16
}

func udpAddrFromNet(a *net.UDPAddr) udpAddr {
	return udpAddr{
		ipv4: [4]byte(a.IP.To4()),
		port: uint16(a.Port),
	}
}

func (u udpAddr) toNet() *net.UDPAddr {
	return &net.UDPAddr{
		IP:   u.ipv4[:],
		Port: int(u.port),
	}
}

func bool2Int(b bool) int {
	if b {
		return 1
	}
	return 0
}