package nebula

import (
	"encoding/binary"
	"fmt"
	"net"
	"os"
	"os/signal"
	"syscall"

	"github.com/sirupsen/logrus"
	"github.com/slackhq/nebula/cert"
	"golang.org/x/net/ipv4"
)

// Every interaction here needs to take extra care to copy memory and not return or use arguments "as is" when touching
// core. This means copying IP objects, slices, de-referencing pointers and taking the actual value, etc

type Control struct {
	f *Interface
	l *logrus.Logger
}

type ControlHostInfo struct {
	VpnIP          net.IP                  `json:"vpnIp"`
	LocalIndex     uint32                  `json:"localIndex"`
	RemoteIndex    uint32                  `json:"remoteIndex"`
	RemoteAddrs    []udpAddr               `json:"remoteAddrs"`
	CachedPackets  int                     `json:"cachedPackets"`
	Cert           *cert.NebulaCertificate `json:"cert"`
	MessageCounter uint64                  `json:"messageCounter"`
	CurrentRemote  udpAddr                 `json:"currentRemote"`
}

// Start actually runs nebula, this is a nonblocking call. To block use Control.ShutdownBlock()
func (c *Control) Start() {
	c.f.run()
}

// Stop signals nebula to shutdown, returns after the shutdown is complete
func (c *Control) Stop() {
	//TODO: stop tun and udp routines, the lock on hostMap effectively does that though
	//TODO: this is probably better as a function in ConnectionManager or HostMap directly
	c.f.hostMap.Lock()
	for _, h := range c.f.hostMap.Hosts {
		if h.ConnectionState.ready {
			c.f.send(closeTunnel, 0, h.ConnectionState, h, h.remote, []byte{}, make([]byte, 12, 12), make([]byte, mtu))
			c.l.WithField("vpnIp", IntIp(h.hostId)).WithField("udpAddr", h.remote).
				Debug("Sending close tunnel message")
		}
	}
	c.f.hostMap.Unlock()
	c.l.Info("Goodbye")
}

// ShutdownBlock will listen for and block on term and interrupt signals, calling Control.Stop() once signalled
func (c *Control) ShutdownBlock() {
	sigChan := make(chan os.Signal)
	signal.Notify(sigChan, syscall.SIGTERM)
	signal.Notify(sigChan, syscall.SIGINT)

	rawSig := <-sigChan
	sig := rawSig.String()
	c.l.WithField("signal", sig).Info("Caught signal, shutting down")
	c.Stop()
}

// RebindUDPServer asks the UDP listener to rebind it's listener. Mainly used on mobile clients when interfaces change
func (c *Control) RebindUDPServer() {
	_ = c.f.outside.Rebind()
}

// ListHostmap returns details about the actual or pending (handshaking) hostmap
func (c *Control) ListHostmap(pendingMap bool) []ControlHostInfo {
	var hm *HostMap
	if pendingMap {
		hm = c.f.handshakeManager.pendingHostMap
	} else {
		hm = c.f.hostMap
	}

	hm.RLock()
	hosts := make([]ControlHostInfo, len(hm.Hosts))
	i := 0
	for _, v := range hm.Hosts {
		hosts[i] = copyHostInfo(v)
		i++
	}
	hm.RUnlock()

	return hosts
}

// GetHostInfoByVpnIP returns a single tunnels hostInfo, or nil if not found
func (c *Control) GetHostInfoByVpnIP(vpnIP uint32, pending bool) *ControlHostInfo {
	var hm *HostMap
	if pending {
		hm = c.f.handshakeManager.pendingHostMap
	} else {
		hm = c.f.hostMap
	}

	h, err := hm.QueryVpnIP(vpnIP)
	if err != nil {
		return nil
	}

	ch := copyHostInfo(h)
	return &ch
}

// SetRemoteForTunnel forces a tunnel to use a specific remote
func (c *Control) SetRemoteForTunnel(vpnIP uint32, addr udpAddr) *ControlHostInfo {
	hostInfo, err := c.f.hostMap.QueryVpnIP(vpnIP)
	if err != nil {
		return nil
	}

	hostInfo.SetRemote(addr.Copy())
	ch := copyHostInfo(hostInfo)
	return &ch
}

// CloseTunnel closes a fully established tunnel. If localOnly is false it will notify the remote end as well.
func (c *Control) CloseTunnel(vpnIP uint32, localOnly bool) bool {
	hostInfo, err := c.f.hostMap.QueryVpnIP(vpnIP)
	if err != nil {
		return false
	}

	if !localOnly {
		c.f.send(
			closeTunnel,
			0,
			hostInfo.ConnectionState,
			hostInfo,
			hostInfo.remote,
			[]byte{},
			make([]byte, 12, 12),
			make([]byte, mtu),
		)
	}

	c.f.closeTunnel(hostInfo)
	return true
}

func copyHostInfo(h *HostInfo) ControlHostInfo {
	addrs := h.RemoteUDPAddrs()
	chi := ControlHostInfo{
		VpnIP:          int2ip(h.hostId),
		LocalIndex:     h.localIndexId,
		RemoteIndex:    h.remoteIndexId,
		RemoteAddrs:    make([]udpAddr, len(addrs), len(addrs)),
		CachedPackets:  len(h.packetStore),
		MessageCounter: *h.ConnectionState.messageCounter,
	}

	if c := h.GetCert(); c != nil {
		chi.Cert = c.Copy()
	}

	if h.remote != nil {
		chi.CurrentRemote = *h.remote
	}

	for i, addr := range addrs {
		chi.RemoteAddrs[i] = addr.Copy()
	}

	return chi
}

// Hook provides the ability to hook into the network path for a particular
// message sub type. Any received message of that subtype that is allowed by
// the firewall will be written to the provided write func instead of the
// inside interface.
// TODO: make this an io.Writer
func (c *Control) Hook(t NebulaMessageSubType, w func([]byte) error) error {
	if t == 0 {
		return fmt.Errorf("non-default message subtype must be specified")
	}
	if _, ok := c.f.handlers[Version][message][t]; ok {
		return fmt.Errorf("message subtype %d already hooked", t)
	}

	c.f.handlers[Version][message][t] = c.f.newHook(w)
	return nil
}

// Send provides the ability to send arbitrary message packets to peer nodes.
// The provided payload will be encapsulated in a Nebula Firewall packet
// (IPv4 plus ports) from the node IP to the provided destination nebula IP.
// Any protocol handling above layer 3 (IP) must be managed by the caller.
func (c *Control) Send(ip uint32, port uint16, st NebulaMessageSubType, payload []byte) {
	headerLen := ipv4.HeaderLen + minFwPacketLen
	length := headerLen + len(payload)
	packet := make([]byte, length)
	packet[0] = 0x45 // IPv4 HL=20
	packet[9] = 114  // Declare as arbitrary 0-hop protocol
	binary.BigEndian.PutUint16(packet[2:4], uint16(length))
	binary.BigEndian.PutUint32(packet[12:16], ip2int(c.f.inside.CidrNet().IP.To4()))
	binary.BigEndian.PutUint32(packet[16:20], ip)

	// Set identical values for src and dst port as they're only
	// used for nebula firewall rule/conntrack matching.
	binary.BigEndian.PutUint16(packet[20:22], port)
	binary.BigEndian.PutUint16(packet[22:24], port)

	copy(packet[headerLen:], payload)

	fp := &FirewallPacket{}
	nb := make([]byte, 12)
	out := make([]byte, mtu)
	c.f.consumeInsidePacket(st, packet, fp, nb, out)
}