package control

import (
	"bufio"
	"context"
	"errors"
	"io"
	"net"
	"net/http"
	"strconv"
	"strings"
	"sync"

	"github.com/k3s-io/k3s/pkg/daemons/config"
	"github.com/k3s-io/k3s/pkg/daemons/control/proxy"
	"github.com/k3s-io/k3s/pkg/nodeconfig"
	"github.com/k3s-io/k3s/pkg/util"
	"github.com/k3s-io/k3s/pkg/version"
	"github.com/rancher/remotedialer"
	"github.com/sirupsen/logrus"
	"github.com/yl2chen/cidranger"
	v1 "k8s.io/api/core/v1"
	"k8s.io/apimachinery/pkg/types"
	"k8s.io/apiserver/pkg/endpoints/request"
	"k8s.io/client-go/kubernetes"
)

var defaultDialer = net.Dialer{}

func loggingErrorWriter(rw http.ResponseWriter, req *http.Request, code int, err error) {
	logrus.Debugf("Tunnel server error: %d %v", code, err)
	util.SendError(err, rw, req, code)
}

func setupTunnel(ctx context.Context, cfg *config.Control) (http.Handler, error) {
	tunnel := &TunnelServer{
		cidrs:  cidranger.NewPCTrieRanger(),
		config: cfg,
		server: remotedialer.New(authorizer, loggingErrorWriter),
		egress: map[string]bool{},
	}
	cfg.Runtime.ClusterControllerStarts["tunnel-server"] = tunnel.watch
	return tunnel, nil
}

func authorizer(req *http.Request) (clientKey string, authed bool, err error) {
	user, ok := request.UserFrom(req.Context())
	if !ok {
		return "", false, nil
	}

	if strings.HasPrefix(user.GetName(), "system:node:") {
		return strings.TrimPrefix(user.GetName(), "system:node:"), true, nil
	}

	return "", false, nil
}

// explicit interface check
var _ http.Handler = &TunnelServer{}

type TunnelServer struct {
	sync.Mutex
	cidrs  cidranger.Ranger
	client kubernetes.Interface
	config *config.Control
	server *remotedialer.Server
	egress map[string]bool
}

// explicit interface check
var _ cidranger.RangerEntry = &tunnelEntry{}

type tunnelEntry struct {
	kubeletPort string
	nodeName    string
	podID       types.UID
	cidr        net.IPNet
}

func (n *tunnelEntry) Network() net.IPNet {
	return n.cidr
}

// Some ports can always be accessed via the tunnel server, at the loopback address.
// Other addresses and ports are only accessible via the tunnel on newer agents, when used by a pod.
func (n *tunnelEntry) IsReservedPort(port string) bool {
	return n.kubeletPort != "" && (port == n.kubeletPort || port == config.StreamServerPort)
}

// ServeHTTP handles either CONNECT requests, or websocket requests to the remotedialer server
func (t *TunnelServer) ServeHTTP(resp http.ResponseWriter, req *http.Request) {
	logrus.Debugf("Tunnel server handing %s %s request for %s from %s", req.Proto, req.Method, req.URL, req.RemoteAddr)
	if req.Method == http.MethodConnect {
		t.serveConnect(resp, req)
	} else {
		t.server.ServeHTTP(resp, req)
	}
}

// watch waits for the runtime core to become available,
// and registers OnChange handlers to observe changes to Nodes (and Endpoints if necessary).
func (t *TunnelServer) watch(ctx context.Context) {
	logrus.Infof("Tunnel server egress proxy mode: %s", t.config.EgressSelectorMode)

	if t.config.EgressSelectorMode == config.EgressSelectorModeDisabled {
		return
	}

	t.config.Runtime.Core.Core().V1().Node().OnChange(ctx, version.Program+"-tunnel-server", t.onChangeNode)
	switch t.config.EgressSelectorMode {
	case config.EgressSelectorModeCluster, config.EgressSelectorModePod:
		t.config.Runtime.Core.Core().V1().Pod().OnChange(ctx, version.Program+"-tunnel-server", t.onChangePod)
	}
}

// onChangeNode updates the node address mappings by observing changes to nodes.
func (t *TunnelServer) onChangeNode(nodeName string, node *v1.Node) (*v1.Node, error) {
	if node != nil {
		t.Lock()
		defer t.Unlock()
		_, t.egress[nodeName] = node.Labels[nodeconfig.ClusterEgressLabel]
		// Add all node IP addresses
		for _, addr := range node.Status.Addresses {
			if addr.Type == v1.NodeInternalIP || addr.Type == v1.NodeExternalIP {
				if n, err := util.IPStringToIPNet(addr.Address); err == nil {
					if node.DeletionTimestamp != nil {
						logrus.Debugf("Tunnel server egress proxy removing Node %s IP %v", nodeName, n)
						t.cidrs.Remove(*n)
					} else {
						logrus.Debugf("Tunnel server egress proxy updating Node %s IP %v", nodeName, n)
						kubeletPort := strconv.FormatInt(int64(node.Status.DaemonEndpoints.KubeletEndpoint.Port), 10)
						t.cidrs.Insert(&tunnelEntry{cidr: *n, nodeName: nodeName, kubeletPort: kubeletPort})
					}
				}
			}
		}
	}
	return node, nil
}

// onChangePod updates the pod address mappings by observing changes to pods.
func (t *TunnelServer) onChangePod(podName string, pod *v1.Pod) (*v1.Pod, error) {
	if pod != nil {
		t.Lock()
		defer t.Unlock()
		// Add all pod IPs, unless the pod uses host network
		if !pod.Spec.HostNetwork {
			nodeName := pod.Spec.NodeName
			for _, ip := range pod.Status.PodIPs {
				if cidr, err := util.IPStringToIPNet(ip.IP); err == nil {
					if pod.DeletionTimestamp != nil {
						if nets, err := t.cidrs.ContainingNetworks(cidr.IP); err != nil && len(nets) > 0 {
							if n, ok := nets[0].(*tunnelEntry); ok && n.podID == pod.UID {
								// only remove entry when the matching pod is deleted; some CNIs allow
								// IP reuse and the entry may have been replaced by a newer pod.
								logrus.Debugf("Tunnel server egress proxy removing Node %s Pod IP %v", nodeName, cidr)
								t.cidrs.Remove(*cidr)
							}
						}
					} else {
						logrus.Debugf("Tunnel server egress proxy updating Node %s Pod IP %s", nodeName, cidr)
						t.cidrs.Insert(&tunnelEntry{
							cidr:     *cidr,
							nodeName: nodeName,
							podID:    pod.UID,
						})
					}
				}
			}
		}
	}
	return pod, nil
}

// serveConnect attempts to handle the HTTP CONNECT request by dialing
// a connection, either locally or via the remotedialer tunnel.
func (t *TunnelServer) serveConnect(resp http.ResponseWriter, req *http.Request) {
	bconn, err := t.dialBackend(req.Context(), req.Host)
	if err != nil {
		util.SendError(err, resp, req, http.StatusBadGateway)
		return
	}

	hijacker, ok := resp.(http.Hijacker)
	if !ok {
		util.SendError(errors.New("hijacking not supported"), resp, req, http.StatusInternalServerError)
		return
	}
	resp.WriteHeader(http.StatusOK)

	rconn, bufrw, err := hijacker.Hijack()
	if err != nil {
		util.SendError(err, resp, req, http.StatusInternalServerError)
		return
	}

	proxy.Proxy(newConnReadWriteCloser(rconn, bufrw), bconn)
}

// dialBackend determines where to route the connection request to, and returns
// a dialed connection if possible. Note that in the case of a remotedialer
// tunnel connection, the agent may return an error if the agent's authorizer
// denies the connection, or if there is some other error in actually dialing
// the requested endpoint.
func (t *TunnelServer) dialBackend(ctx context.Context, addr string) (net.Conn, error) {
	host, port, err := net.SplitHostPort(addr)
	if err != nil {
		return nil, err
	}

	var nodeName string
	var toKubelet, useTunnel bool
	if ip := net.ParseIP(host); ip != nil {
		// Destination is an IP address, which could be either a pod, or node by IP.
		// We can only use the tunnel for egress to pods if the agent supports it.
		if nets, err := t.cidrs.ContainingNetworks(ip); err == nil && len(nets) > 0 {
			if n, ok := nets[0].(*tunnelEntry); ok {
				nodeName = n.nodeName
				if n.IsReservedPort(port) {
					toKubelet = true
					useTunnel = true
				} else {
					useTunnel = t.egress[nodeName]
				}
			} else {
				logrus.Debugf("Tunnel server egress proxy CIDR lookup returned unknown type for address %s", ip)
			}
		}
	} else {
		// Destination is a node by name, it is safe to use the tunnel.
		nodeName = host
		toKubelet = true
		useTunnel = true
	}

	// If connecting to something hosted by the local node, don't tunnel
	if nodeName == t.config.ServerNodeName {
		useTunnel = false
		if toKubelet {
			// Dial local kubelet at the configured bind address
			addr = net.JoinHostPort(t.config.BindAddress, port)
		}
	} else if toKubelet {
		// Dial remote kubelet via the loopback address, the remotedialer client
		// will ensure that it hits the right local address.
		addr = net.JoinHostPort(t.config.Loopback(false), port)
	}

	if useTunnel {
		// Dialer(nodeName) returns a dial function that calls getDialer internally, which does the same locked session search
		// as HasSession(nodeName). Rather than checking twice, just attempt the dial and handle the error if no session is found.
		dialContext := t.server.Dialer(nodeName)
		if conn, err := dialContext(ctx, "tcp", addr); err != nil {
			logrus.Debugf("Tunnel server egress proxy dial error: %v", err)
			if toKubelet && strings.HasPrefix(err.Error(), "failed to find Session for client") {
				// Don't have a session and we're trying to remote dial the kubelet via loopback, reject the connection.
				return conn, err
			}
			// any other error is ignored; fall back to to dialing directly.
		} else {
			// Have a session and it is safe to use for this destination, do so.
			logrus.Debugf("Tunnel server egress proxy dialing %s via Session to %s", addr, nodeName)
			return conn, err
		}
	}

	// Don't have a session, the agent doesn't support tunneling to this destination, or
	// the destination is local; fall back to direct connection.
	logrus.Debugf("Tunnel server egress proxy dialing %s directly", addr)
	return defaultDialer.DialContext(ctx, "tcp", addr)
}

// connReadWriteCloser bundles a net.Conn and a wrapping bufio.ReadWriter together into a type that
// meets the ReadWriteCloser interface. The http.Hijacker interface returns such a pair, and reads
// need to go through the buffered reader (because the http handler may have already read from the
// underlying connection), but writes and closes need to hit the connection directly.
type connReadWriteCloser struct {
	conn net.Conn
	once sync.Once
	rw   *bufio.ReadWriter
}

var _ io.ReadWriteCloser = &connReadWriteCloser{}

func newConnReadWriteCloser(conn net.Conn, rw *bufio.ReadWriter) *connReadWriteCloser {
	return &connReadWriteCloser{conn: conn, rw: rw}
}

func (crw *connReadWriteCloser) Read(p []byte) (n int, err error) {
	return crw.rw.Read(p)
}

func (crw *connReadWriteCloser) Write(b []byte) (n int, err error) {
	return crw.conn.Write(b)
}

func (crw *connReadWriteCloser) Close() (err error) {
	crw.once.Do(func() { err = crw.conn.Close() })
	return err
}