/* SPDX-License-Identifier: MIT
 *
 * Copyright (C) 2017-2021 WireGuard LLC. All Rights Reserved.
 */

package device

import (
	"runtime"
	"sync"
	"sync/atomic"
	"time"

	"golang.org/x/net/ipv4"
	"golang.org/x/net/ipv6"

	"golang.zx2c4.com/wireguard/conn"
	"golang.zx2c4.com/wireguard/ratelimiter"
	"golang.zx2c4.com/wireguard/rwcancel"
	"golang.zx2c4.com/wireguard/tun"
)

type Device struct {
	log *Logger

	// synchronized resources (locks acquired in order)

	state struct {
		// state holds the device's state. It is accessed atomically.
		// Use the device.deviceState method to read it.
		// If state.mu is (r)locked, state is the current state of the device.
		// Without state.mu (r)locked, state is either the current state
		// of the device or the intended future state of the device.
		// For example, while executing a call to Up, state will be deviceStateUp.
		// There is no guarantee that that intended future state of the device
		// will become the actual state; Up can fail.
		// The device can also change state multiple times between time of check and time of use.
		// Unsynchronized uses of state must therefore be advisory/best-effort only.
		state uint32 // actually a deviceState, but typed uint32 for conveniene
		// stopping blocks until all inputs to Device have been closed.
		stopping sync.WaitGroup
		// mu protects state changes.
		mu sync.Mutex
	}

	net struct {
		stopping sync.WaitGroup
		sync.RWMutex
		bind          conn.Bind // bind interface
		netlinkCancel *rwcancel.RWCancel
		port          uint16 // listening port
		fwmark        uint32 // mark value (0 = disabled)
	}

	staticIdentity struct {
		sync.RWMutex
		privateKey NoisePrivateKey
		publicKey  NoisePublicKey
	}

	peers struct {
		empty        AtomicBool // empty reports whether len(keyMap) == 0
		sync.RWMutex            // protects keyMap
		keyMap       map[NoisePublicKey]*Peer
	}

	// unprotected / "self-synchronising resources"

	allowedips    AllowedIPs
	indexTable    IndexTable
	cookieChecker CookieChecker

	rate struct {
		underLoadUntil int64
		limiter        ratelimiter.Ratelimiter
	}

	pool struct {
		messageBuffers   *WaitPool
		inboundElements  *WaitPool
		outboundElements *WaitPool
	}

	queue struct {
		encryption *outboundQueue
		decryption *inboundQueue
		handshake  *handshakeQueue
	}

	tun struct {
		device tun.Device
		mtu    int32
	}

	ipcMutex sync.RWMutex
	closed   chan struct{}
}

// deviceState represents the state of a Device.
// There are four states: new, down, up, closed.
// However, state new should never be observable.
// Transitions:
//
//   new -> down -----+
//            ↑↓      ↓
//            up -> closed
//
type deviceState uint32

//go:generate stringer -type deviceState -trimprefix=deviceState
const (
	deviceStateNew deviceState = iota
	deviceStateDown
	deviceStateUp
	deviceStateClosed
)

// deviceState returns device.state.state as a deviceState
// See those docs for how to interpret this value.
func (device *Device) deviceState() deviceState {
	return deviceState(atomic.LoadUint32(&device.state.state))
}

// isClosed reports whether the device is closed (or is closing).
// See device.state.state comments for how to interpret this value.
func (device *Device) isClosed() bool {
	return device.deviceState() == deviceStateClosed
}

// isUp reports whether the device is up (or is attempting to come up).
// See device.state.state comments for how to interpret this value.
func (device *Device) isUp() bool {
	return device.deviceState() == deviceStateUp
}

// An outboundQueue is a channel of QueueOutboundElements awaiting encryption.
// An outboundQueue is ref-counted using its wg field.
// An outboundQueue created with newOutboundQueue has one reference.
// Every additional writer must call wg.Add(1).
// Every completed writer must call wg.Done().
// When no further writers will be added,
// call wg.Done to remove the initial reference.
// When the refcount hits 0, the queue's channel is closed.
type outboundQueue struct {
	c  chan *QueueOutboundElement
	wg sync.WaitGroup
}

func newOutboundQueue() *outboundQueue {
	q := &outboundQueue{
		c: make(chan *QueueOutboundElement, QueueOutboundSize),
	}
	q.wg.Add(1)
	go func() {
		q.wg.Wait()
		close(q.c)
	}()
	return q
}

// A inboundQueue is similar to an outboundQueue; see those docs.
type inboundQueue struct {
	c  chan *QueueInboundElement
	wg sync.WaitGroup
}

func newInboundQueue() *inboundQueue {
	q := &inboundQueue{
		c: make(chan *QueueInboundElement, QueueInboundSize),
	}
	q.wg.Add(1)
	go func() {
		q.wg.Wait()
		close(q.c)
	}()
	return q
}

// A handshakeQueue is similar to an outboundQueue; see those docs.
type handshakeQueue struct {
	c  chan QueueHandshakeElement
	wg sync.WaitGroup
}

func newHandshakeQueue() *handshakeQueue {
	q := &handshakeQueue{
		c: make(chan QueueHandshakeElement, QueueHandshakeSize),
	}
	q.wg.Add(1)
	go func() {
		q.wg.Wait()
		close(q.c)
	}()
	return q
}

/* Converts the peer into a "zombie", which remains in the peer map,
 * but processes no packets and does not exists in the routing table.
 *
 * Must hold device.peers.Mutex
 */
func unsafeRemovePeer(device *Device, peer *Peer, key NoisePublicKey) {
	// stop routing and processing of packets
	device.allowedips.RemoveByPeer(peer)
	peer.Stop()

	// remove from peer map
	delete(device.peers.keyMap, key)
	device.peers.empty.Set(len(device.peers.keyMap) == 0)
}

// changeState attempts to change the device state to match want.
func (device *Device) changeState(want deviceState) {
	device.state.mu.Lock()
	defer device.state.mu.Unlock()
	old := device.deviceState()
	if old == deviceStateClosed {
		// once closed, always closed
		device.log.Verbosef("Interface closed, ignored requested state %s", want)
		return
	}
	switch want {
	case old:
		device.log.Verbosef("Interface already in state %s", want)
		return
	case deviceStateUp:
		atomic.StoreUint32(&device.state.state, uint32(deviceStateUp))
		if ok := device.upLocked(); ok {
			break
		}
		fallthrough // up failed; bring the device all the way back down
	case deviceStateDown:
		atomic.StoreUint32(&device.state.state, uint32(deviceStateDown))
		device.downLocked()
	}
	device.log.Verbosef("Interface state was %s, requested %s, now %s", old, want, device.deviceState())
}

// upLocked attempts to bring the device up and reports whether it succeeded.
// The caller must hold device.state.mu and is responsible for updating device.state.state.
func (device *Device) upLocked() bool {
	if err := device.BindUpdate(); err != nil {
		device.log.Errorf("Unable to update bind: %v", err)
		return false
	}

	device.peers.RLock()
	for _, peer := range device.peers.keyMap {
		peer.Start()
		if atomic.LoadUint32(&peer.persistentKeepaliveInterval) > 0 {
			peer.SendKeepalive()
		}
	}
	device.peers.RUnlock()
	return true
}

// downLocked attempts to bring the device down.
// The caller must hold device.state.mu and is responsible for updating device.state.state.
func (device *Device) downLocked() {
	err := device.BindClose()
	if err != nil {
		device.log.Errorf("Bind close failed: %v", err)
	}

	device.peers.RLock()
	for _, peer := range device.peers.keyMap {
		peer.Stop()
	}
	device.peers.RUnlock()
}

func (device *Device) Up() {
	device.changeState(deviceStateUp)
}

func (device *Device) Down() {
	device.changeState(deviceStateDown)
}

func (device *Device) IsUnderLoad() bool {
	// check if currently under load
	now := time.Now()
	underLoad := len(device.queue.handshake.c) >= UnderLoadQueueSize
	if underLoad {
		atomic.StoreInt64(&device.rate.underLoadUntil, now.Add(UnderLoadAfterTime).UnixNano())
		return true
	}
	// check if recently under load
	return atomic.LoadInt64(&device.rate.underLoadUntil) > now.UnixNano()
}

func (device *Device) SetPrivateKey(sk NoisePrivateKey) error {
	// lock required resources

	device.staticIdentity.Lock()
	defer device.staticIdentity.Unlock()

	if sk.Equals(device.staticIdentity.privateKey) {
		return nil
	}

	device.peers.Lock()
	defer device.peers.Unlock()

	lockedPeers := make([]*Peer, 0, len(device.peers.keyMap))
	for _, peer := range device.peers.keyMap {
		peer.handshake.mutex.RLock()
		lockedPeers = append(lockedPeers, peer)
	}

	// remove peers with matching public keys

	publicKey := sk.publicKey()
	for key, peer := range device.peers.keyMap {
		if peer.handshake.remoteStatic.Equals(publicKey) {
			peer.handshake.mutex.RUnlock()
			unsafeRemovePeer(device, peer, key)
			peer.handshake.mutex.RLock()
		}
	}

	// update key material

	device.staticIdentity.privateKey = sk
	device.staticIdentity.publicKey = publicKey
	device.cookieChecker.Init(publicKey)

	// do static-static DH pre-computations

	expiredPeers := make([]*Peer, 0, len(device.peers.keyMap))
	for _, peer := range device.peers.keyMap {
		handshake := &peer.handshake
		handshake.precomputedStaticStatic = device.staticIdentity.privateKey.sharedSecret(handshake.remoteStatic)
		expiredPeers = append(expiredPeers, peer)
	}

	for _, peer := range lockedPeers {
		peer.handshake.mutex.RUnlock()
	}
	for _, peer := range expiredPeers {
		peer.ExpireCurrentKeypairs()
	}

	return nil
}

func NewDevice(tunDevice tun.Device, logger *Logger) *Device {
	device := new(Device)
	device.state.state = uint32(deviceStateDown)
	device.closed = make(chan struct{})
	device.log = logger
	device.tun.device = tunDevice
	mtu, err := device.tun.device.MTU()
	if err != nil {
		device.log.Errorf("Trouble determining MTU, assuming default: %v", err)
		mtu = DefaultMTU
	}
	device.tun.mtu = int32(mtu)
	device.peers.keyMap = make(map[NoisePublicKey]*Peer)
	device.rate.limiter.Init()
	device.indexTable.Init()
	device.PopulatePools()

	// create queues

	device.queue.handshake = newHandshakeQueue()
	device.queue.encryption = newOutboundQueue()
	device.queue.decryption = newInboundQueue()

	// prepare net

	device.net.port = 0
	device.net.bind = nil

	// start workers

	cpus := runtime.NumCPU()
	device.state.stopping.Wait()
	for i := 0; i < cpus; i++ {
		go device.RoutineEncryption()
		go device.RoutineDecryption()
		go device.RoutineHandshake()
	}

	device.state.stopping.Add(2)
	go device.RoutineReadFromTUN()
	go device.RoutineTUNEventReader()

	return device
}

func (device *Device) LookupPeer(pk NoisePublicKey) *Peer {
	device.peers.RLock()
	defer device.peers.RUnlock()

	return device.peers.keyMap[pk]
}

func (device *Device) RemovePeer(key NoisePublicKey) {
	device.peers.Lock()
	defer device.peers.Unlock()
	// stop peer and remove from routing

	peer, ok := device.peers.keyMap[key]
	if ok {
		unsafeRemovePeer(device, peer, key)
	}
}

func (device *Device) RemoveAllPeers() {
	device.peers.Lock()
	defer device.peers.Unlock()

	for key, peer := range device.peers.keyMap {
		unsafeRemovePeer(device, peer, key)
	}

	device.peers.keyMap = make(map[NoisePublicKey]*Peer)
}

func (device *Device) Close() {
	device.state.mu.Lock()
	defer device.state.mu.Unlock()
	if device.isClosed() {
		return
	}
	atomic.StoreUint32(&device.state.state, uint32(deviceStateClosed))
	device.log.Verbosef("Device closing")

	device.tun.device.Close()
	device.downLocked()

	// Remove peers before closing queues,
	// because peers assume that queues are active.
	device.RemoveAllPeers()

	// We kept a reference to the encryption and decryption queues,
	// in case we started any new peers that might write to them.
	// No new peers are coming; we are done with these queues.
	device.queue.encryption.wg.Done()
	device.queue.decryption.wg.Done()
	device.queue.handshake.wg.Done()
	device.state.stopping.Wait()

	device.rate.limiter.Close()

	device.log.Verbosef("Device closed")
	close(device.closed)
}

func (device *Device) Wait() chan struct{} {
	return device.closed
}

func (device *Device) SendKeepalivesToPeersWithCurrentKeypair() {
	if !device.isUp() {
		return
	}

	device.peers.RLock()
	for _, peer := range device.peers.keyMap {
		peer.keypairs.RLock()
		sendKeepalive := peer.keypairs.current != nil && !peer.keypairs.current.created.Add(RejectAfterTime).Before(time.Now())
		peer.keypairs.RUnlock()
		if sendKeepalive {
			peer.SendKeepalive()
		}
	}
	device.peers.RUnlock()
}

func unsafeCloseBind(device *Device) error {
	var err error
	netc := &device.net
	if netc.netlinkCancel != nil {
		netc.netlinkCancel.Cancel()
	}
	if netc.bind != nil {
		err = netc.bind.Close()
		netc.bind = nil
	}
	netc.stopping.Wait()
	return err
}

func (device *Device) Bind() conn.Bind {
	device.net.Lock()
	defer device.net.Unlock()
	return device.net.bind
}

func (device *Device) BindSetMark(mark uint32) error {
	device.net.Lock()
	defer device.net.Unlock()

	// check if modified
	if device.net.fwmark == mark {
		return nil
	}

	// update fwmark on existing bind
	device.net.fwmark = mark
	if device.isUp() && device.net.bind != nil {
		if err := device.net.bind.SetMark(mark); err != nil {
			return err
		}
	}

	// clear cached source addresses
	device.peers.RLock()
	for _, peer := range device.peers.keyMap {
		peer.Lock()
		defer peer.Unlock()
		if peer.endpoint != nil {
			peer.endpoint.ClearSrc()
		}
	}
	device.peers.RUnlock()

	return nil
}

func (device *Device) BindUpdate() error {
	device.net.Lock()
	defer device.net.Unlock()

	// close existing sockets
	if err := unsafeCloseBind(device); err != nil {
		return err
	}

	// open new sockets
	if !device.isUp() {
		return nil
	}

	// bind to new port
	var err error
	netc := &device.net
	netc.bind, netc.port, err = conn.CreateBind(netc.port)
	if err != nil {
		netc.bind = nil
		netc.port = 0
		return err
	}
	netc.netlinkCancel, err = device.startRouteListener(netc.bind)
	if err != nil {
		netc.bind.Close()
		netc.bind = nil
		netc.port = 0
		return err
	}

	// set fwmark
	if netc.fwmark != 0 {
		err = netc.bind.SetMark(netc.fwmark)
		if err != nil {
			return err
		}
	}

	// clear cached source addresses
	device.peers.RLock()
	for _, peer := range device.peers.keyMap {
		peer.Lock()
		defer peer.Unlock()
		if peer.endpoint != nil {
			peer.endpoint.ClearSrc()
		}
	}
	device.peers.RUnlock()

	// start receiving routines
	device.net.stopping.Add(2)
	device.queue.decryption.wg.Add(2) // each RoutineReceiveIncoming goroutine writes to device.queue.decryption
	device.queue.handshake.wg.Add(2)  // each RoutineReceiveIncoming goroutine writes to device.queue.handshake
	go device.RoutineReceiveIncoming(ipv4.Version, netc.bind)
	go device.RoutineReceiveIncoming(ipv6.Version, netc.bind)

	device.log.Verbosef("UDP bind has been updated")
	return nil
}

func (device *Device) BindClose() error {
	device.net.Lock()
	err := unsafeCloseBind(device)
	device.net.Unlock()
	return err
}