package handshake

import (
	"crypto"
	"crypto/cipher"
	"crypto/tls"
	"encoding/binary"
	"fmt"
	"time"

	"github.com/lucas-clemente/quic-go/internal/protocol"
	"github.com/lucas-clemente/quic-go/internal/qerr"
	"github.com/lucas-clemente/quic-go/internal/qtls"
	"github.com/lucas-clemente/quic-go/internal/utils"
	"github.com/lucas-clemente/quic-go/logging"
)

// KeyUpdateInterval is the maximum number of packets we send or receive before initiating a key update.
// It's a package-level variable to allow modifying it for testing purposes.
var KeyUpdateInterval uint64 = protocol.KeyUpdateInterval

type updatableAEAD struct {
	suite *qtls.CipherSuiteTLS13

	keyPhase           protocol.KeyPhase
	largestAcked       protocol.PacketNumber
	firstPacketNumber  protocol.PacketNumber
	handshakeConfirmed bool

	keyUpdateInterval  uint64
	invalidPacketLimit uint64
	invalidPacketCount uint64

	// Time when the keys should be dropped. Keys are dropped on the next call to Open().
	prevRcvAEADExpiry time.Time
	prevRcvAEAD       cipher.AEAD

	firstRcvdWithCurrentKey protocol.PacketNumber
	firstSentWithCurrentKey protocol.PacketNumber
	numRcvdWithCurrentKey   uint64
	numSentWithCurrentKey   uint64
	rcvAEAD                 cipher.AEAD
	sendAEAD                cipher.AEAD
	// caches cipher.AEAD.Overhead(). This speeds up calls to Overhead().
	aeadOverhead int

	nextRcvAEAD           cipher.AEAD
	nextSendAEAD          cipher.AEAD
	nextRcvTrafficSecret  []byte
	nextSendTrafficSecret []byte

	headerDecrypter headerProtector
	headerEncrypter headerProtector

	rttStats *utils.RTTStats

	tracer logging.ConnectionTracer
	logger utils.Logger

	// use a single slice to avoid allocations
	nonceBuf []byte
}

var _ ShortHeaderOpener = &updatableAEAD{}
var _ ShortHeaderSealer = &updatableAEAD{}

func newUpdatableAEAD(rttStats *utils.RTTStats, tracer logging.ConnectionTracer, logger utils.Logger) *updatableAEAD {
	return &updatableAEAD{
		firstPacketNumber:       protocol.InvalidPacketNumber,
		largestAcked:            protocol.InvalidPacketNumber,
		firstRcvdWithCurrentKey: protocol.InvalidPacketNumber,
		firstSentWithCurrentKey: protocol.InvalidPacketNumber,
		keyUpdateInterval:       KeyUpdateInterval,
		rttStats:                rttStats,
		tracer:                  tracer,
		logger:                  logger,
	}
}

func (a *updatableAEAD) rollKeys() {
	if a.prevRcvAEAD != nil {
		a.logger.Debugf("Dropping key phase %d ahead of scheduled time. Drop time was: %s", a.keyPhase-1, a.prevRcvAEADExpiry)
		if a.tracer != nil {
			a.tracer.DroppedKey(a.keyPhase - 1)
		}
		a.prevRcvAEADExpiry = time.Time{}
	}

	a.keyPhase++
	a.firstRcvdWithCurrentKey = protocol.InvalidPacketNumber
	a.firstSentWithCurrentKey = protocol.InvalidPacketNumber
	a.numRcvdWithCurrentKey = 0
	a.numSentWithCurrentKey = 0
	a.prevRcvAEAD = a.rcvAEAD
	a.rcvAEAD = a.nextRcvAEAD
	a.sendAEAD = a.nextSendAEAD

	a.nextRcvTrafficSecret = a.getNextTrafficSecret(a.suite.Hash, a.nextRcvTrafficSecret)
	a.nextSendTrafficSecret = a.getNextTrafficSecret(a.suite.Hash, a.nextSendTrafficSecret)
	a.nextRcvAEAD = createAEAD(a.suite, a.nextRcvTrafficSecret)
	a.nextSendAEAD = createAEAD(a.suite, a.nextSendTrafficSecret)
}

func (a *updatableAEAD) startKeyDropTimer(now time.Time) {
	d := 3 * a.rttStats.PTO(true)
	a.logger.Debugf("Starting key drop timer to drop key phase %d (in %s)", a.keyPhase-1, d)
	a.prevRcvAEADExpiry = now.Add(d)
}

func (a *updatableAEAD) getNextTrafficSecret(hash crypto.Hash, ts []byte) []byte {
	return hkdfExpandLabel(hash, ts, []byte{}, "quic ku", hash.Size())
}

// For the client, this function is called before SetWriteKey.
// For the server, this function is called after SetWriteKey.
func (a *updatableAEAD) SetReadKey(suite *qtls.CipherSuiteTLS13, trafficSecret []byte) {
	a.rcvAEAD = createAEAD(suite, trafficSecret)
	a.headerDecrypter = newHeaderProtector(suite, trafficSecret, false)
	if a.suite == nil {
		a.setAEADParameters(a.rcvAEAD, suite)
	}

	a.nextRcvTrafficSecret = a.getNextTrafficSecret(suite.Hash, trafficSecret)
	a.nextRcvAEAD = createAEAD(suite, a.nextRcvTrafficSecret)
}

// For the client, this function is called after SetReadKey.
// For the server, this function is called before SetWriteKey.
func (a *updatableAEAD) SetWriteKey(suite *qtls.CipherSuiteTLS13, trafficSecret []byte) {
	a.sendAEAD = createAEAD(suite, trafficSecret)
	a.headerEncrypter = newHeaderProtector(suite, trafficSecret, false)
	if a.suite == nil {
		a.setAEADParameters(a.sendAEAD, suite)
	}

	a.nextSendTrafficSecret = a.getNextTrafficSecret(suite.Hash, trafficSecret)
	a.nextSendAEAD = createAEAD(suite, a.nextSendTrafficSecret)
}

func (a *updatableAEAD) setAEADParameters(aead cipher.AEAD, suite *qtls.CipherSuiteTLS13) {
	a.nonceBuf = make([]byte, aead.NonceSize())
	a.aeadOverhead = aead.Overhead()
	a.suite = suite
	switch suite.ID {
	case tls.TLS_AES_128_GCM_SHA256, tls.TLS_AES_256_GCM_SHA384:
		a.invalidPacketLimit = protocol.InvalidPacketLimitAES
	case tls.TLS_CHACHA20_POLY1305_SHA256:
		a.invalidPacketLimit = protocol.InvalidPacketLimitChaCha
	default:
		panic(fmt.Sprintf("unknown cipher suite %d", suite.ID))
	}
}

func (a *updatableAEAD) Open(dst, src []byte, rcvTime time.Time, pn protocol.PacketNumber, kp protocol.KeyPhaseBit, ad []byte) ([]byte, error) {
	dec, err := a.open(dst, src, rcvTime, pn, kp, ad)
	if err == ErrDecryptionFailed {
		a.invalidPacketCount++
		if a.invalidPacketCount >= a.invalidPacketLimit {
			return nil, qerr.AEADLimitReached
		}
	}
	return dec, err
}

func (a *updatableAEAD) open(dst, src []byte, rcvTime time.Time, pn protocol.PacketNumber, kp protocol.KeyPhaseBit, ad []byte) ([]byte, error) {
	if a.prevRcvAEAD != nil && !a.prevRcvAEADExpiry.IsZero() && rcvTime.After(a.prevRcvAEADExpiry) {
		a.prevRcvAEAD = nil
		a.logger.Debugf("Dropping key phase %d", a.keyPhase-1)
		a.prevRcvAEADExpiry = time.Time{}
		if a.tracer != nil {
			a.tracer.DroppedKey(a.keyPhase - 1)
		}
	}
	binary.BigEndian.PutUint64(a.nonceBuf[len(a.nonceBuf)-8:], uint64(pn))
	if kp != a.keyPhase.Bit() {
		if a.keyPhase > 0 && a.firstRcvdWithCurrentKey == protocol.InvalidPacketNumber || pn < a.firstRcvdWithCurrentKey {
			if a.prevRcvAEAD == nil {
				return nil, ErrKeysDropped
			}
			// we updated the key, but the peer hasn't updated yet
			dec, err := a.prevRcvAEAD.Open(dst, a.nonceBuf, src, ad)
			if err != nil {
				err = ErrDecryptionFailed
			}
			return dec, err
		}
		// try opening the packet with the next key phase
		dec, err := a.nextRcvAEAD.Open(dst, a.nonceBuf, src, ad)
		if err != nil {
			return nil, ErrDecryptionFailed
		}
		// Opening succeeded. Check if the peer was allowed to update.
		if a.keyPhase > 0 && a.firstSentWithCurrentKey == protocol.InvalidPacketNumber {
			return nil, qerr.NewError(qerr.KeyUpdateError, "keys updated too quickly")
		}
		a.rollKeys()
		a.logger.Debugf("Peer updated keys to %d", a.keyPhase)
		// The peer initiated this key update. It's safe to drop the keys for the previous generation now.
		// Start a timer to drop the previous key generation.
		a.startKeyDropTimer(rcvTime)
		if a.tracer != nil {
			a.tracer.UpdatedKey(a.keyPhase, true)
		}
		a.firstRcvdWithCurrentKey = pn
		return dec, err
	}
	// The AEAD we're using here will be the qtls.aeadAESGCM13.
	// It uses the nonce provided here and XOR it with the IV.
	dec, err := a.rcvAEAD.Open(dst, a.nonceBuf, src, ad)
	if err != nil {
		return dec, ErrDecryptionFailed
	}
	a.numRcvdWithCurrentKey++
	if a.firstRcvdWithCurrentKey == protocol.InvalidPacketNumber {
		// We initiated the key updated, and now we received the first packet protected with the new key phase.
		// Therefore, we are certain that the peer rolled its keys as well. Start a timer to drop the old keys.
		if a.keyPhase > 0 {
			a.logger.Debugf("Peer confirmed key update to phase %d", a.keyPhase)
			a.startKeyDropTimer(rcvTime)
		}
		a.firstRcvdWithCurrentKey = pn
	}
	return dec, err
}

func (a *updatableAEAD) Seal(dst, src []byte, pn protocol.PacketNumber, ad []byte) []byte {
	if a.firstSentWithCurrentKey == protocol.InvalidPacketNumber {
		a.firstSentWithCurrentKey = pn
	}
	if a.firstPacketNumber == protocol.InvalidPacketNumber {
		a.firstPacketNumber = pn
	}
	a.numSentWithCurrentKey++
	binary.BigEndian.PutUint64(a.nonceBuf[len(a.nonceBuf)-8:], uint64(pn))
	// The AEAD we're using here will be the qtls.aeadAESGCM13.
	// It uses the nonce provided here and XOR it with the IV.
	return a.sendAEAD.Seal(dst, a.nonceBuf, src, ad)
}

func (a *updatableAEAD) SetLargestAcked(pn protocol.PacketNumber) error {
	if a.firstSentWithCurrentKey != protocol.InvalidPacketNumber &&
		pn >= a.firstSentWithCurrentKey && a.numRcvdWithCurrentKey == 0 {
		return qerr.NewError(qerr.KeyUpdateError, fmt.Sprintf("received ACK for key phase %d, but peer didn't update keys", a.keyPhase))
	}
	a.largestAcked = pn
	return nil
}

func (a *updatableAEAD) SetHandshakeConfirmed() {
	a.handshakeConfirmed = true
}

func (a *updatableAEAD) updateAllowed() bool {
	if !a.handshakeConfirmed {
		return false
	}
	// the first key update is allowed as soon as the handshake is confirmed
	return a.keyPhase == 0 ||
		// subsequent key updates as soon as a packet sent with that key phase has been acknowledged
		(a.firstSentWithCurrentKey != protocol.InvalidPacketNumber &&
			a.largestAcked != protocol.InvalidPacketNumber &&
			a.largestAcked >= a.firstSentWithCurrentKey)
}

func (a *updatableAEAD) shouldInitiateKeyUpdate() bool {
	if !a.updateAllowed() {
		return false
	}
	if a.numRcvdWithCurrentKey >= a.keyUpdateInterval {
		a.logger.Debugf("Received %d packets with current key phase. Initiating key update to the next key phase: %d", a.numRcvdWithCurrentKey, a.keyPhase+1)
		return true
	}
	if a.numSentWithCurrentKey >= a.keyUpdateInterval {
		a.logger.Debugf("Sent %d packets with current key phase. Initiating key update to the next key phase: %d", a.numSentWithCurrentKey, a.keyPhase+1)
		return true
	}
	return false
}

func (a *updatableAEAD) KeyPhase() protocol.KeyPhaseBit {
	if a.shouldInitiateKeyUpdate() {
		a.rollKeys()
		a.logger.Debugf("Initiating key update to key phase %d", a.keyPhase)
		if a.tracer != nil {
			a.tracer.UpdatedKey(a.keyPhase, false)
		}
	}
	return a.keyPhase.Bit()
}

func (a *updatableAEAD) Overhead() int {
	return a.aeadOverhead
}

func (a *updatableAEAD) EncryptHeader(sample []byte, firstByte *byte, hdrBytes []byte) {
	a.headerEncrypter.EncryptHeader(sample, firstByte, hdrBytes)
}

func (a *updatableAEAD) DecryptHeader(sample []byte, firstByte *byte, hdrBytes []byte) {
	a.headerDecrypter.DecryptHeader(sample, firstByte, hdrBytes)
}

func (a *updatableAEAD) FirstPacketNumber() protocol.PacketNumber {
	return a.firstPacketNumber
}