package main

import (
	"context"
	"errors"
	"flag"
	"fmt"
	"net"
	"os"
	"os/signal"
	"strings"

	"github.com/golang/glog"
	v1 "k8s.io/apimachinery/pkg/apis/meta/v1"

	"code.hackerspace.pl/hscloud/cluster/identd/ident"
	"code.hackerspace.pl/hscloud/cluster/identd/kubenat"
	"code.hackerspace.pl/hscloud/go/mirko"
)

func init() {
	flag.Set("logtostderr", "true")
}

var (
	flagIdentdListen     = "127.0.0.1:8113"
	flagContainerdSocket = "/var/run/containerd/containerd.sock"
	flagConntrackProc    = "/proc/net/nf_conntrack"
	flagPodName          = ""
	flagPodNamespace     = ""
)

func main() {
	flag.StringVar(&flagIdentdListen, "identd_listen", flagIdentdListen, "Address at which to listen for incoming ident protocol connections")
	flag.StringVar(&flagContainerdSocket, "identd_containerd_socket", flagContainerdSocket, "Containerd gRPC socket path")
	flag.StringVar(&flagConntrackProc, "identd_conntrack_proc", flagConntrackProc, "Conntrack procfs file")
	flag.StringVar(&flagPodName, "identd_pod_name", flagPodName, "Name of this pod, if on k8s. Needed for public IP resolution.")
	flag.StringVar(&flagPodNamespace, "identd_pod_namespace", flagPodNamespace, "Namespace where this pod is running, if on k8s. Needed for public IP resolution.")
	flag.Parse()

	ctx, ctxC := context.WithCancel(context.Background())

	resolver, err := kubenat.NewResolver(ctx, flagConntrackProc, flagContainerdSocket)
	if err != nil {
		glog.Exitf("Could not start kubenet resolver: %v", err)
	}

	var localIP net.IP

	localIPStr, _, err := net.SplitHostPort(flagIdentdListen)
	if err != nil {
		glog.Warningf("Could not parse identd listen flag %q", flagIdentdListen)
	} else {
		localIP = net.ParseIP(localIPStr)
		if localIP == nil || !localIP.IsGlobalUnicast() {
			glog.Warningf("Could not parse unicast IP from identd flag %q", localIPStr)
			localIP = nil
		}
	}

	if localIP == nil {
		glog.Infof("Could not figure out public IP address for identd, attempting to retrieve from k8s...")
		cs := mirko.KubernetesClient()
		if cs == nil {
			glog.Exitf("Not in k8s and identd_listen set to invalid public IP address - exiting.")
		}
		if flagPodName == "" {
			glog.Exitf("identd_pod_name must be set")
		}
		if flagPodNamespace == "" {
			glog.Exitf("identd_pod_namespace must be set")
		}
		pod, err := cs.CoreV1().Pods(flagPodNamespace).Get(ctx, flagPodName, v1.GetOptions{})
		if err != nil {
			glog.Exitf("Could not find pod %q in namespace %q: %v", flagPodName, flagPodNamespace, err)
		}
		ipStr := pod.Status.HostIP
		if ipStr == "" {
			glog.Exitf("HostIP in status of pod %q is empty", flagPodName)
		}
		glog.Infof("Resolved k8s node IP to %s", ipStr)

		localIP = net.ParseIP(ipStr)
		if localIP == nil {
			glog.Exitf("HostIP in status of pod %q is unparseable", flagPodName, ipStr)
		}
	}

	glog.Infof("Will respond to identd queries on %s...", localIP)
	s := &service{
		resolver: resolver,
		localIP:  localIP,
	}

	lis, err := net.Listen("tcp", flagIdentdListen)
	if err != nil {
		glog.Exitf("Could not listen for identd: %v", err)
	}
	isrv := ident.NewServer()
	isrv.HandleFunc(s.handleIdent)
	go func() {
		glog.Infof("Starting identd on %s...", flagIdentdListen)
		err := isrv.Serve(lis)
		if err != nil {
			glog.Exitf("identd Serve: %v", err)
		}
	}()

	signalChan := make(chan os.Signal, 1)
	signal.Notify(signalChan, os.Interrupt)
	go func() {
		<-signalChan
		ctxC()
	}()

	<-ctx.Done()
	glog.Infof("Stopping identd...")
	isrv.Stop()
	lis.Close()
}

type service struct {
	resolver *kubenat.Resolver
	localIP  net.IP
}

func (s *service) handleIdent(ctx context.Context, w ident.ResponseWriter, r *ident.Request) {
	clientIPStr, _, err := net.SplitHostPort(r.ClientAddress.String())
	if err != nil {
		glog.Errorf("Unparseable ClientAddres %q", r.ClientAddress)
		w.SendError(ident.UnknownError)
		return
	}
	clientIP := net.ParseIP(clientIPStr)
	if clientIP == nil {
		glog.Errorf("Unparseable ClientAddres IP %q", r.ClientAddress)
		w.SendError(ident.UnknownError)
		return
	}

	t4 := kubenat.Tuple4{
		RemoteIP:   clientIP,
		RemotePort: r.ClientPort,
		LocalIP:    s.localIP,
		LocalPort:  r.ServerPort,
	}
	glog.Infof("Running query for %s...", t4.String())
	info, err := s.resolver.ResolvePod(ctx, &t4)
	if err != nil {
		glog.Errorf("ResolvePod(%q): %v", t4.String(), err)
		w.SendError(ident.NoUser)
		return
	}

	ns := info.KubernetesNamespace
	pod := info.Name

	if ns == "matrix" && strings.HasPrefix(pod, "appservice-irc-") {
		target := net.JoinHostPort(info.PodIP.String(), "1113")
		clientPort := r.ClientPort
		serverPort := info.PodTranslatedPort
		glog.Infof("Forwarding to appservice-irc at %q, clientPort: %d, serverPort: %d", target, clientPort, serverPort)
		res, err := ident.Query(ctx, target, clientPort, serverPort)
		if err != nil {
			var identErr *ident.IdentError
			if errors.As(err, &identErr) {
				glog.Infof("appservice-irc: %s", identErr.Inner)
				w.SendError(identErr.Inner)
			} else {
				glog.Infof("appservice-irc: error: %v", err)
				w.SendError(ident.UnknownError)
			}
		} else {
			glog.Infof("Response from appservice-irc: %q", res.UserID)
			w.SendIdent(&ident.IdentResponse{
				UserID: res.UserID,
			})
		}
		return
	}
	// default to kns-*
	user := fmt.Sprintf("kns-%s", ns)
	// q3k's old personal namespace.
	if ns == "q3k" {
		user = "q3k"
	}
	// personal-* namespaces.
	if strings.HasPrefix(ns, "personal-") {
		user = strings.TrimPrefix(ns, "personal-")
	}
	glog.Infof("Returning %q (from %q) for %q", user, ns, t4.String())
	w.SendIdent(&ident.IdentResponse{
		UserID: user,
	})
}