/* SPDX-License-Identifier: MIT
 *
 * Copyright (C) 2017-2023 WireGuard LLC. All Rights Reserved.
 */

package device

import (
	"encoding/binary"
	"errors"
	"fmt"
	"net"
	"net/netip"
	"sync"
	"time"

	"github.com/tailscale/wireguard-go/conn"
	"golang.org/x/crypto/chacha20poly1305"
	"golang.org/x/net/ipv4"
	"golang.org/x/net/ipv6"
)

type QueueHandshakeElement struct {
	msgType    uint32
	packet     []byte
	packetMeta conn.ReceivedPacket
	buffer     *packetBuf
}

type QueueInboundElement struct {
	buffer     *packetBuf
	packet     []byte
	packetMeta conn.ReceivedPacket
	counter    uint64
	keypair    *Keypair
}

type QueueInboundElementsContainer struct {
	// filling is a one-shot barrier signaling decryption→receive
	// handoff. RoutineReceiveIncoming calls Add(1) before sending the
	// container down the decryption and inbound queues; RoutineDecryption
	// calls Done after decrypting; RoutineSequentialReceiver calls Wait
	// before reading the decrypted packets.
	filling sync.WaitGroup
	elems   []*QueueInboundElement
}

// clearPointers clears elem fields that contain pointers.
// This makes the garbage collector's life easier and
// avoids accidentally keeping other objects around unnecessarily.
// It also reduces the possible collateral damage from use-after-free bugs.
func (elem *QueueInboundElement) clearPointers() {
	elem.buffer = nil
	elem.packet = nil
	elem.packetMeta = conn.ReceivedPacket{}
	elem.keypair = nil
}

/* Called when a new authenticated message has been received
 *
 * NOTE: Not thread safe, but called by sequential receiver!
 */
func (peer *Peer) keepKeyFreshReceiving() {
	if peer.timers.sentLastMinuteHandshake.Load() {
		return
	}
	keypair := peer.keypairs.Current()
	if keypair != nil && keypair.isInitiator && time.Since(keypair.created) > (RejectAfterTime-KeepaliveTimeout-RekeyTimeout) {
		peer.timers.sentLastMinuteHandshake.Store(true)
		peer.SendHandshakeInitiation(false)
	}
}

/* Receives incoming datagrams for the device
 *
 * Every time the bind is updated a new routine is started for
 * IPv4 and IPv6 (separately)
 */
func (device *Device) RoutineReceiveIncoming(maxBatchSize int, recv conn.ReceiveFunc) {
	recvName := recv.PrettyName()
	defer func() {
		device.log.Verbosef("Routine: receive incoming %s - stopped", recvName)
		device.queue.decryption.wg.Done()
		device.queue.handshake.wg.Done()
		device.net.stopping.Done()
	}()

	device.log.Verbosef("Routine: receive incoming %s - started", recvName)

	// receive datagrams until conn is closed

	var (
		packets = make([]conn.ReceivedPacket, maxBatchSize)
		buf     = device.getPacketBuf()
		// bufDirty tracks whether the current buf has been pushed downstream to
		// crypto and per-peer/handshake functions, or can be re-used across the
		// next read cycle
		bufDirty    bool
		err         error
		count       int
		deathSpiral int
		elemsByPeer = make(map[*Peer]*QueueInboundElementsContainer, maxBatchSize)
	)

	defer func() {
		buf.decRef()
	}()

	for {
		if bufDirty {
			buf.decRef()
			buf = device.getPacketBuf()
			bufDirty = false
		}
		count, err = recv(buf.slab, packets)
		if err != nil {
			if errors.Is(err, net.ErrClosed) {
				return
			}
			device.log.Verbosef("Failed to receive %s packet: %v", recvName, err)
			if neterr, ok := err.(net.Error); ok && !neterr.Temporary() {
				return
			}
			if deathSpiral < 10 {
				deathSpiral++
				time.Sleep(time.Second / 3)
				continue
			}
			return
		}
		deathSpiral = 0

		// handle each packet in the batch
		for _, meta := range packets[:count] {
			if meta.Size < MinMessageSize {
				continue
			}

			// check size of packet

			packet := meta.Bytes(buf.slab)
			msgType := binary.LittleEndian.Uint32(packet[:4])

			switch msgType {

			// check if transport

			case MessageTransportType:

				// check size

				if len(packet) < MessageTransportSize {
					continue
				}

				// lookup key pair

				receiver := binary.LittleEndian.Uint32(
					packet[MessageTransportOffsetReceiver:MessageTransportOffsetCounter],
				)
				value := device.indexTable.Lookup(receiver)
				keypair := value.keypair
				if keypair == nil {
					continue
				}

				// check keypair expiry

				if keypair.created.Add(RejectAfterTime).Before(time.Now()) {
					continue
				}

				// create work element
				peer := value.peer
				elem := device.GetInboundElement()
				bufDirty = true
				buf.incRef()
				elem.buffer = buf
				elem.packet = packet
				elem.packetMeta = meta
				elem.keypair = keypair
				elem.counter = 0

				elemsForPeer, ok := elemsByPeer[peer]
				if !ok {
					elemsForPeer = device.GetInboundElementsContainer()
					elemsByPeer[peer] = elemsForPeer
				}
				elemsForPeer.elems = append(elemsForPeer.elems, elem)
				continue

			// otherwise it is a fixed size & handshake related packet

			case MessageInitiationType:
				if len(packet) != MessageInitiationSize {
					continue
				}

			case MessageResponseType:
				if len(packet) != MessageResponseSize {
					continue
				}

			case MessageCookieReplyType:
				if len(packet) != MessageCookieReplySize {
					continue
				}

			default:
				device.log.Verbosef("Received message with unknown type")
				continue
			}

			buf.incRef()
			select {
			case device.queue.handshake.c <- QueueHandshakeElement{
				msgType:    msgType,
				buffer:     buf,
				packet:     packet,
				packetMeta: meta,
			}:
				bufDirty = true
			default:
				buf.decRef()
			}
		}
		for peer, elemsContainer := range elemsByPeer {
			peer.queueInboundIfRunning(elemsContainer)
			delete(elemsByPeer, peer)
		}
	}
}

func (device *Device) RoutineDecryption(id int) {
	var nonce [chacha20poly1305.NonceSize]byte

	defer device.log.Verbosef("Routine: decryption worker %d - stopped", id)
	device.log.Verbosef("Routine: decryption worker %d - started", id)

	for elemsContainer := range device.queue.decryption.c {
		for _, elem := range elemsContainer.elems {
			// split message into fields
			counter := elem.packet[MessageTransportOffsetCounter:MessageTransportOffsetContent]
			content := elem.packet[MessageTransportOffsetContent:]

			// decrypt and release to consumer
			var err error
			elem.counter = binary.LittleEndian.Uint64(counter)
			// copy counter to nonce
			binary.LittleEndian.PutUint64(nonce[0x4:0xc], elem.counter)
			elem.packet, err = elem.keypair.receive.Open(
				content[:0],
				nonce[:],
				content,
				nil,
			)
			if err != nil {
				elem.packet = nil
			}
		}
		elemsContainer.filling.Done()
	}
}

/* Handles incoming packets related to handshake
 */
func (device *Device) RoutineHandshake(id int) {
	defer func() {
		device.log.Verbosef("Routine: handshake worker %d - stopped", id)
		device.queue.encryption.wg.Done()
	}()
	device.log.Verbosef("Routine: handshake worker %d - started", id)

	for elem := range device.queue.handshake.c {

		// handle cookie fields and ratelimiting

		switch elem.msgType {

		case MessageCookieReplyType:

			// unmarshal packet

			var reply MessageCookieReply
			err := reply.unmarshal(elem.packet)
			if err != nil {
				device.log.Verbosef("Failed to decode cookie reply")
				goto skip
			}

			// lookup peer from index

			entry := device.indexTable.Lookup(reply.Receiver)

			if entry.peer == nil {
				goto skip
			}

			// consume reply

			if peer := entry.peer; peer.runningState.isRunning.Load() {
				device.log.Verbosef("Receiving cookie response from %s", elem.packetMeta.Endpoint.DstToString())
				if !peer.cookieGenerator.ConsumeReply(&reply) {
					device.log.Verbosef("Could not decrypt invalid cookie response")
				}
			}

			goto skip

		case MessageInitiationType, MessageResponseType:

			// check mac fields and maybe ratelimit

			if !device.cookieChecker.CheckMAC1(elem.packet) {
				device.log.Verbosef("Received packet with invalid mac1")
				goto skip
			}

			// endpoints destination address is the source of the datagram

			if device.IsUnderLoad() {

				// verify MAC2 field

				if !device.cookieChecker.CheckMAC2(elem.packet, elem.packetMeta.Endpoint.DstToBytes()) {
					device.SendHandshakeCookie(&elem)
					goto skip
				}

				// check ratelimiter

				if !device.rate.limiter.Allow(elem.packetMeta.Endpoint.DstIP()) {
					goto skip
				}
			}

		default:
			device.log.Errorf("Invalid packet ended up in the handshake queue")
			goto skip
		}

		// handle handshake initiation/response content

		switch elem.msgType {
		case MessageInitiationType:

			// unmarshal

			var msg MessageInitiation
			err := msg.unmarshal(elem.packet)
			if err != nil {
				device.log.Errorf("Failed to decode initiation message")
				goto skip
			}

			// consume initiation

			peer := device.ConsumeMessageInitiation(&msg, elem.packetMeta.Endpoint)
			if peer == nil {
				device.log.Verbosef("Received invalid initiation message from %s", elem.packetMeta.Endpoint.DstToString())
				goto skip
			}

			// update timers

			peer.timersAnyAuthenticatedPacketTraversal()
			peer.timersAnyAuthenticatedPacketReceived()

			device.log.Verbosef("%v - Received handshake initiation", peer)
			peer.rxBytes.Add(uint64(len(elem.packet)))

			peer.SendHandshakeResponse()

		case MessageResponseType:

			// unmarshal

			var msg MessageResponse
			err := msg.unmarshal(elem.packet)
			if err != nil {
				device.log.Errorf("Failed to decode response message")
				goto skip
			}

			// consume response

			peer := device.ConsumeMessageResponse(&msg)
			if peer == nil {
				device.log.Verbosef("Received invalid response message from %s", elem.packetMeta.Endpoint.DstToString())
				goto skip
			}

			device.log.Verbosef("%v - Received handshake response", peer)
			peer.rxBytes.Add(uint64(len(elem.packet)))

			// update timers

			peer.timersAnyAuthenticatedPacketTraversal()
			peer.timersAnyAuthenticatedPacketReceived()

			// derive keypair

			err = peer.BeginSymmetricSession()

			if err != nil {
				device.log.Errorf("%v - Failed to derive keypair: %v", peer, err)
				goto skip
			}

			device.config.metrics.HandshakeInitiatorCompleted.Add(1)
			peer.timersSessionDerived()
			peer.timersHandshakeComplete()
			peer.SendPriorityMessage()
			peer.SendKeepalive()
		}
	skip:
		elem.buffer.decRef()
	}
}

func (peer *Peer) RoutineSequentialReceiver(maxBatchSize int) {
	device := peer.device
	defer func() {
		device.log.Verbosef("%v - Routine: sequential receiver - stopped", peer)
		peer.runningState.queueReaders.Done()
	}()
	device.log.Verbosef("%v - Routine: sequential receiver - started", peer)

	bufs := make([][]byte, 0, maxBatchSize)

	for elemsContainer := range peer.queue.inbound {
		peer.processInboundContainer(elemsContainer, bufs[:0])
	}
}

// processInboundContainer waits for the decryption routine to finish
// filling elemsContainer, then writes the valid packets to the TUN
// device and returns the container to the pool.
//
// scratch is a length-0 slice used to assemble the per-packet buffers
// passed to tun.device.Write; its backing array is reused across calls.
func (peer *Peer) processInboundContainer(elemsContainer *QueueInboundElementsContainer, scratch [][]byte) {
	// Invariants from RoutineSequentialReceiver; all should be unreachable.
	if len(scratch) != 0 || cap(scratch) == 0 {
		panic(fmt.Sprintf("processInboundContainer: scratch must be empty with non-zero cap; got len=%d cap=%d",
			len(scratch), cap(scratch)))
	}
	if cap(scratch) < len(elemsContainer.elems) {
		panic(fmt.Sprintf("processInboundContainer: scratch cap %d < elems %d",
			cap(scratch), len(elemsContainer.elems)))
	}

	device := peer.device
	defer device.PutInboundElementsContainer(elemsContainer)

	// Wait for RoutineDecryption to finish filling the container. After
	// Wait returns we have happens-before with that goroutine and are the
	// sole owner of the container until Put hands it back to the pool.
	elemsContainer.filling.Wait()
	elems := elemsContainer.elems

	validTailPacket := -1
	dataPacketReceived := false
	rxBytesLen := uint64(0)
	for i, elem := range elems {
		if elem.packet == nil {
			// decryption failed
			continue
		}

		if !elem.keypair.replayFilter.ValidateCounter(elem.counter, RejectAfterMessages) {
			device.config.metrics.MessageTransportRXDroppedReplay.Add(1)
			continue
		}

		validTailPacket = i
		if peer.ReceivedWithKeypair(elem.keypair) {
			peer.device.config.metrics.HandshakeResponderCompleted.Add(1)
			peer.timersHandshakeComplete()
			peer.SendPriorityMessage()
			peer.SendStagedPackets()
		}
		if ep, ok := elem.packetMeta.Endpoint.(conn.PeerAwareEndpoint); ok {
			ep.FromPeer(peer.handshake.remoteStatic)
		}
		rxBytesLen += uint64(len(elem.packet) + MinMessageSize)

		if len(elem.packet) == 0 {
			device.log.Verbosef("%v - Receiving keepalive packet", peer)
			continue
		}
		dataPacketReceived = true

		switch elem.packet[0] >> 4 {
		case 4:
			if len(elem.packet) < ipv4.HeaderLen {
				continue
			}
			field := elem.packet[IPv4offsetTotalLength : IPv4offsetTotalLength+2]
			length := binary.BigEndian.Uint16(field)
			if int(length) > len(elem.packet) || int(length) < ipv4.HeaderLen {
				continue
			}
			elem.packet = elem.packet[:length]
			src := elem.packet[IPv4offsetSrc : IPv4offsetSrc+net.IPv4len]
			srcAddr, _ := netip.AddrFromSlice(src)
			if !peer.AllowedPeerSourceIP(srcAddr) {
				device.log.Verbosef("IPv4 packet with disallowed source address from %v", peer)
				continue
			}

		case 6:
			if len(elem.packet) < ipv6.HeaderLen {
				continue
			}
			field := elem.packet[IPv6offsetPayloadLength : IPv6offsetPayloadLength+2]
			length := binary.BigEndian.Uint16(field)
			length += ipv6.HeaderLen
			if int(length) > len(elem.packet) {
				continue
			}
			elem.packet = elem.packet[:length]
			src := elem.packet[IPv6offsetSrc : IPv6offsetSrc+net.IPv6len]
			srcAddr, _ := netip.AddrFromSlice(src)
			if !peer.AllowedPeerSourceIP(srcAddr) {
				device.log.Verbosef("IPv6 packet with disallowed source address from %v", peer)
				continue
			}

		default:
			device.log.Verbosef("Packet with invalid IP version from %v", peer)
			continue
		}

		elem.packetMeta.Size = MessageTransportOffsetContent + len(elem.packet)
		scratch = append(scratch, elem.packetMeta.Bytes(elem.buffer.slab))
	}

	peer.rxBytes.Add(rxBytesLen)
	if validTailPacket >= 0 {
		peer.keepKeyFreshReceiving()
		peer.timersAnyAuthenticatedPacketTraversal()
		peer.timersAnyAuthenticatedPacketReceived()
	}
	if dataPacketReceived {
		peer.timersDataReceived()
	}
	if len(scratch) > 0 {
		_, err := peer.writeTUN(scratch, MessageTransportOffsetContent)
		if err != nil && !device.isClosed() {
			device.log.Errorf("Failed to write packets to TUN device: %v", err)
		}
	}
	for _, elem := range elems {
		device.PutInboundElement(elem)
	}
}