package dhcpv6

import (
	"crypto/rand"
	"encoding/binary"
	"errors"
	"fmt"
	"log"
	"net"
	"time"

	"github.com/insomniacslk/dhcp/iana"
)

const MessageHeaderSize = 4

type DHCPv6Message struct {
	messageType   MessageType
	transactionID uint32 // only 24 bits are used though
	options       []Option
}

func BytesToTransactionID(data []byte) (*uint32, error) {
	// return a uint32 from a  sequence of bytes, representing a transaction ID.
	// Transaction IDs are three-bytes long. If the provided data is shorter than
	// 3 bytes, it return an error. If longer, will use the first three bytes
	// only.
	if len(data) < 3 {
		return nil, fmt.Errorf("Invalid transaction ID: less than 3 bytes")
	}
	buf := make([]byte, 4)
	copy(buf[1:4], data[:3])
	tid := binary.BigEndian.Uint32(buf)
	return &tid, nil
}

func GenerateTransactionID() (*uint32, error) {
	var tid *uint32
	for {
		tidBytes := make([]byte, 4)
		n, err := rand.Read(tidBytes)
		if n != 4 {
			return nil, fmt.Errorf("Invalid random sequence: shorter than 4 bytes")
		}
		tid, err = BytesToTransactionID(tidBytes)
		if err != nil {
			return nil, err
		}
		if tid == nil {
			return nil, fmt.Errorf("Error: got a nil Transaction ID")
		}
		// retry until != 0
		// TODO add retry limit
		if *tid != 0 {
			break
		}
	}
	return tid, nil
}

// GetTime returns a time integer suitable for DUID-LLT, i.e. the current time counted
// in seconds since January 1st, 2000, midnight UTC, modulo 2^32
func GetTime() uint32 {
	now := time.Since(time.Date(2000, time.January, 1, 0, 0, 0, 0, time.UTC))
	return uint32((now.Nanoseconds() / 1000000000) % 0xffffffff)
}

// NewSolicitWithCID creates a new SOLICIT message with CID.
func NewSolicitWithCID(duid Duid, modifiers ...Modifier) (DHCPv6, error) {
	d, err := NewMessage()
	if err != nil {
		return nil, err
	}
	d.(*DHCPv6Message).SetMessage(MessageTypeSolicit)
	d.AddOption(&OptClientId{Cid: duid})
	oro := new(OptRequestedOption)
	oro.SetRequestedOptions([]OptionCode{
		OptionDNSRecursiveNameServer,
		OptionDomainSearchList,
	})
	d.AddOption(oro)
	d.AddOption(&OptElapsedTime{})
	// FIXME use real values for IA_NA
	iaNa := &OptIANA{}
	iaNa.IaId = [4]byte{0xfa, 0xce, 0xb0, 0x0c}
	iaNa.T1 = 0xe10
	iaNa.T2 = 0x1518
	d.AddOption(iaNa)
	// Apply modifiers
	for _, mod := range modifiers {
		d = mod(d)
	}
	return d, nil
}

// NewSolicitForInterface creates a new SOLICIT message with DUID-LLT, using the
// given network interface's hardware address and current time
func NewSolicitForInterface(ifname string, modifiers ...Modifier) (DHCPv6, error) {
	iface, err := net.InterfaceByName(ifname)
	if err != nil {
		return nil, err
	}
	duid := Duid{
		Type:          DUID_LLT,
		HwType:        iana.HwTypeEthernet,
		Time:          GetTime(),
		LinkLayerAddr: iface.HardwareAddr,
	}
	return NewSolicitWithCID(duid, modifiers...)
}

// NewAdvertiseFromSolicit creates a new ADVERTISE packet based on an SOLICIT packet.
func NewAdvertiseFromSolicit(solicit DHCPv6, modifiers ...Modifier) (DHCPv6, error) {
	if solicit == nil {
		return nil, errors.New("SOLICIT cannot be nil")
	}
	if solicit.Type() != MessageTypeSolicit {
		return nil, errors.New("The passed SOLICIT must have SOLICIT type set")
	}
	sol, ok := solicit.(*DHCPv6Message)
	if !ok {
		return nil, errors.New("The passed SOLICIT must be of DHCPv6Message type")
	}
	// build ADVERTISE from SOLICIT
	adv := DHCPv6Message{}
	adv.SetMessage(MessageTypeAdvertise)
	adv.SetTransactionID(sol.TransactionID())
	// add Client ID
	cid := sol.GetOneOption(OptionClientID)
	if cid == nil {
		return nil, errors.New("Client ID cannot be nil in SOLICIT when building ADVERTISE")
	}
	adv.AddOption(cid)

	// apply modifiers
	d := DHCPv6(&adv)
	for _, mod := range modifiers {
		d = mod(d)
	}
	return d, nil
}

// NewRequestFromAdvertise creates a new REQUEST packet based on an ADVERTISE
// packet options.
func NewRequestFromAdvertise(advertise DHCPv6, modifiers ...Modifier) (DHCPv6, error) {
	if advertise == nil {
		return nil, fmt.Errorf("ADVERTISE cannot be nil")
	}
	if advertise.Type() != MessageTypeAdvertise {
		return nil, fmt.Errorf("The passed ADVERTISE must have ADVERTISE type set")
	}
	adv, ok := advertise.(*DHCPv6Message)
	if !ok {
		return nil, fmt.Errorf("The passed ADVERTISE must be of DHCPv6Message type")
	}
	// build REQUEST from ADVERTISE
	req := DHCPv6Message{}
	req.SetMessage(MessageTypeRequest)
	req.SetTransactionID(adv.TransactionID())
	// add Client ID
	cid := adv.GetOneOption(OptionClientID)
	if cid == nil {
		return nil, fmt.Errorf("Client ID cannot be nil in ADVERTISE when building REQUEST")
	}
	req.AddOption(cid)
	// add Server ID
	sid := adv.GetOneOption(OptionServerID)
	if sid == nil {
		return nil, fmt.Errorf("Server ID cannot be nil in ADVERTISE when building REQUEST")
	}
	req.AddOption(sid)
	// add Elapsed Time
	req.AddOption(&OptElapsedTime{})
	// add IA_NA
	iaNa := adv.GetOneOption(OptionIANA)
	if iaNa == nil {
		return nil, fmt.Errorf("IA_NA cannot be nil in ADVERTISE when building REQUEST")
	}
	req.AddOption(iaNa)
	// add OptRequestedOption
	oro := OptRequestedOption{}
	oro.SetRequestedOptions([]OptionCode{
		OptionDNSRecursiveNameServer,
		OptionDomainSearchList,
	})
	req.AddOption(&oro)
	// add OPTION_VENDOR_CLASS, only if present in the original request
	// TODO implement OptionVendorClass
	vClass := adv.GetOneOption(OptionVendorClass)
	if vClass != nil {
		req.AddOption(vClass)
	}

	// apply modifiers
	d := DHCPv6(&req)
	for _, mod := range modifiers {
		d = mod(d)
	}
	return d, nil
}

// NewReplyFromDHCPv6Message creates a new REPLY packet based on a
// DHCPv6Message. The function is to be used when generating a reply to
// REQUEST, CONFIRM, RENEW, REBIND and RELEASE packets.
func NewReplyFromDHCPv6Message(message DHCPv6, modifiers ...Modifier) (DHCPv6, error) {
	if message == nil {
		return nil, errors.New("DHCPv6Message cannot be nil")
	}
	switch message.Type() {
	case MessageTypeRequest, MessageTypeConfirm, MessageTypeRenew, MessageTypeRebind, MessageTypeRelease:
	default:
		return nil, errors.New("Cannot create REPLY from the passed message type set")
	}
	msg, ok := message.(*DHCPv6Message)
	if !ok {
		return nil, errors.New("The passed MESSAGE must be of DHCPv6Message type")
	}
	// build REPLY from MESSAGE
	rep := DHCPv6Message{}
	rep.SetMessage(MessageTypeReply)
	rep.SetTransactionID(msg.TransactionID())
	// add Client ID
	cid := message.GetOneOption(OptionClientID)
	if cid == nil {
		return nil, errors.New("Client ID cannot be nil when building REPLY")
	}
	rep.AddOption(cid)

	// apply modifiers
	d := DHCPv6(&rep)
	for _, mod := range modifiers {
		d = mod(d)
	}
	return d, nil
}

func (d *DHCPv6Message) Type() MessageType {
	return d.messageType
}

func (d *DHCPv6Message) SetMessage(messageType MessageType) {
	msgString := MessageTypeToString(messageType)
	if msgString == "" {
		log.Printf("Warning: unknown DHCPv6 message type: %v", messageType)
	}
	if messageType == MessageTypeRelayForward || messageType == MessageTypeRelayReply {
		log.Printf("Warning: using a RELAY message type with a non-relay message: %v (%v)",
			msgString, messageType)
	}
	d.messageType = messageType
}

func (d *DHCPv6Message) MessageTypeToString() string {
	return MessageTypeToString(d.messageType)
}

func (d *DHCPv6Message) TransactionID() uint32 {
	return d.transactionID
}

func (d *DHCPv6Message) SetTransactionID(tid uint32) {
	ttid := tid & 0x00ffffff
	if ttid != tid {
		log.Printf("Warning: truncating transaction ID that is longer than 24 bits: %v", tid)
	}
	d.transactionID = ttid
}

func (d *DHCPv6Message) SetOptions(options []Option) {
	d.options = options
}

func (d *DHCPv6Message) AddOption(option Option) {
	d.options = append(d.options, option)
}

func (d *DHCPv6Message) UpdateOption(option Option) {
	for idx, opt := range d.options {
		if opt.Code() == option.Code() {
			d.options[idx] = option
			// don't look further
			return
		}
	}
	// if not found, add it
	d.AddOption(option)
}

func (d *DHCPv6Message) String() string {
	return fmt.Sprintf("DHCPv6Message(messageType=%v transactionID=0x%06x, %d options)",
		d.MessageTypeToString(), d.TransactionID(), len(d.options),
	)
}

func (d *DHCPv6Message) Summary() string {
	ret := fmt.Sprintf(
		"DHCPv6Message\n"+
			"  messageType=%v\n"+
			"  transactionid=0x%06x\n",
		d.MessageTypeToString(),
		d.TransactionID(),
	)
	ret += "  options=["
	if len(d.options) > 0 {
		ret += "\n"
	}
	for _, opt := range d.options {
		ret += fmt.Sprintf("    %v\n", opt.String())
	}
	ret += "  ]\n"
	return ret
}

// Convert a DHCPv6Message structure into its binary representation, suitable for being
// sent over the network
func (d *DHCPv6Message) ToBytes() []byte {
	var ret []byte
	ret = append(ret, byte(d.messageType))
	tidBytes := make([]byte, 4)
	binary.BigEndian.PutUint32(tidBytes, d.transactionID)
	ret = append(ret, tidBytes[1:4]...) // discard the first byte
	for _, opt := range d.options {
		ret = append(ret, opt.ToBytes()...)
	}
	return ret
}

func (d *DHCPv6Message) Length() int {
	mLen := 4
	for _, opt := range d.options {
		mLen += opt.Length() + 4 // +4 for opt code and opt len
	}
	return mLen
}

func (d *DHCPv6Message) Options() []Option {
	return d.options
}

func (d *DHCPv6Message) GetOption(code OptionCode) []Option {
	return getOptions(d.options, code, false)
}

func (d *DHCPv6Message) GetOneOption(code OptionCode) Option {
	return getOption(d.options, code)
}

func (d *DHCPv6Message) IsRelay() bool {
	return false
}