// Copyright 2018-present the CoreDHCP Authors. All rights reserved
// This source code is licensed under the MIT license found in the
// LICENSE file in the root directory of this source tree.

package serverid

import (
	"errors"
	"net"
	"strings"

	"github.com/coredhcp/coredhcp/handler"
	"github.com/coredhcp/coredhcp/logger"
	"github.com/coredhcp/coredhcp/plugins"
	"github.com/insomniacslk/dhcp/dhcpv4"
	"github.com/insomniacslk/dhcp/dhcpv6"
	"github.com/insomniacslk/dhcp/iana"
)

var log = logger.GetLogger("plugins/server_id")

func init() {
	plugins.RegisterPlugin("server_id", setupServerID6, setupServerID4)
}

// v6ServerID is the DUID of the v6 server
var (
	v6ServerID *dhcpv6.Duid
	v4ServerID net.IP
)

// Handler6 handles DHCPv6 packets for the server_id plugin.
func Handler6(req, resp dhcpv6.DHCPv6) (dhcpv6.DHCPv6, bool) {
	if v6ServerID == nil {
		log.Fatal("BUG: Plugin is running uninitialized!")
		return nil, true
	}

	msg, err := req.GetInnerMessage()
	if err != nil {
		// BUG: this should already have failed in the main handler. Abort
		log.Error(err)
		return nil, true
	}

	if opt := msg.GetOneOption(dhcpv6.OptionServerID); opt != nil {
		// RFC8415 §16.{2,5,7}
		// These message types MUST be discarded if they contain *any* ServerID option
		if msg.Type() == dhcpv6.MessageTypeSolicit ||
			msg.Type() == dhcpv6.MessageTypeConfirm ||
			msg.Type() == dhcpv6.MessageTypeRebind {
			return nil, true
		}

		// Approximately all others MUST be discarded if the ServerID doesn't match
		sid := opt.(*dhcpv6.OptServerId)
		if !sid.Sid.Equal(*v6ServerID) {
			log.Infof("requested server ID does not match this server's ID. Got %v, want %v", sid.Sid, *v6ServerID)
			return nil, true
		}
	} else {
		// RFC8415 §16.{6,8,10,11}
		// These message types MUST be discarded if they *don't* contain a ServerID option
		if msg.Type() == dhcpv6.MessageTypeRequest ||
			msg.Type() == dhcpv6.MessageTypeRenew ||
			msg.Type() == dhcpv6.MessageTypeDecline ||
			msg.Type() == dhcpv6.MessageTypeRelease {
			return nil, true
		}
	}
	dhcpv6.WithServerID(*v6ServerID)(resp)
	return resp, false
}

// Handler4 handles DHCPv4 packets for the server_id plugin.
func Handler4(req, resp *dhcpv4.DHCPv4) (*dhcpv4.DHCPv4, bool) {
	if v4ServerID == nil {
		log.Fatal("BUG: Plugin is running uninitialized!")
		return nil, true
	}
	if req.OpCode != dhcpv4.OpcodeBootRequest {
		log.Warningf("not a BootRequest, ignoring")
		return resp, false
	}
	if req.ServerIPAddr != nil &&
		!req.ServerIPAddr.Equal(net.IPv4zero) &&
		!req.ServerIPAddr.Equal(v4ServerID) {
		// This request is not for us, drop it.
		log.Infof("requested server ID does not match this server's ID. Got %v, want %v", req.ServerIPAddr, v4ServerID)
		return nil, true
	}
	resp.ServerIPAddr = make(net.IP, net.IPv4len)
	copy(resp.ServerIPAddr[:], v4ServerID)
	resp.UpdateOption(dhcpv4.OptServerIdentifier(v4ServerID))
	return resp, false
}

func setupServerID4(args ...string) (handler.Handler4, error) {
	log.Print("loading `server_id` plugin for DHCPv4")
	if len(args) < 1 {
		return nil, errors.New("need an argument")
	}
	serverID := net.ParseIP(args[0])
	if serverID == nil {
		return nil, errors.New("invalid or empty IP address")
	}
	if serverID.To4() == nil {
		return nil, errors.New("not a valid IPv4 address")
	}
	v4ServerID = serverID
	return Handler4, nil
}

func setupServerID6(args ...string) (handler.Handler6, error) {
	log.Print("loading `server_id` plugin for DHCPv6")
	if len(args) < 2 {
		return nil, errors.New("need a DUID type and value")
	}
	duidType := args[0]
	if duidType == "" {
		return nil, errors.New("got empty DUID type")
	}
	duidValue := args[1]
	if duidValue == "" {
		return nil, errors.New("got empty DUID value")
	}
	duidType = strings.ToLower(duidType)
	hwaddr, err := net.ParseMAC(duidValue)
	if err != nil {
		return nil, err
	}
	switch duidType {
	case "ll", "duid-ll", "duid_ll":
		v6ServerID = &dhcpv6.Duid{
			Type: dhcpv6.DUID_LL,
			// sorry, only ethernet for now
			HwType:        iana.HWTypeEthernet,
			LinkLayerAddr: hwaddr,
		}
	case "llt", "duid-llt", "duid_llt":
		v6ServerID = &dhcpv6.Duid{
			Type: dhcpv6.DUID_LLT,
			// sorry, zero-time for now
			Time: 0,
			// sorry, only ethernet for now
			HwType:        iana.HWTypeEthernet,
			LinkLayerAddr: hwaddr,
		}
	case "en", "uuid":
		return nil, errors.New("EN/UUID DUID type not supported yet")
	default:
		return nil, errors.New("Opaque DUID type not supported yet")
	}
	log.Printf("using %s %s", duidType, duidValue)

	return Handler6, nil
}