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

package device

import (
	"container/list"
	"errors"
	"sync"
	"sync/atomic"
	"time"

	"golang.zx2c4.com/wireguard/conn"
)

type Peer struct {
	isRunning    AtomicBool
	sync.RWMutex // Mostly protects endpoint, but is generally taken whenever we modify peer
	keypairs     Keypairs
	handshake    Handshake
	device       *Device
	endpoint     conn.Endpoint
	stopping     sync.WaitGroup // routines pending stop

	// These fields are accessed with atomic operations, which must be
	// 64-bit aligned even on 32-bit platforms. Go guarantees that an
	// allocated struct will be 64-bit aligned. So we place
	// atomically-accessed fields up front, so that they can share in
	// this alignment before smaller fields throw it off.
	stats struct {
		txBytes           uint64 // bytes send to peer (endpoint)
		rxBytes           uint64 // bytes received from peer
		lastHandshakeNano int64  // nano seconds since epoch
	}

	disableRoaming bool

	timers struct {
		retransmitHandshake     *Timer
		sendKeepalive           *Timer
		newHandshake            *Timer
		zeroKeyMaterial         *Timer
		persistentKeepalive     *Timer
		handshakeAttempts       uint32
		needAnotherKeepalive    AtomicBool
		sentLastMinuteHandshake AtomicBool
	}

	state struct {
		sync.Mutex // protects against concurrent Start/Stop
	}

	queue struct {
		staged   chan *QueueOutboundElement // staged packets before a handshake is available
		outbound *autodrainingOutboundQueue // sequential ordering of udp transmission
		inbound  *autodrainingInboundQueue  // sequential ordering of tun writing
	}

	cookieGenerator             CookieGenerator
	trieEntries                 list.List
	persistentKeepaliveInterval uint32 // accessed atomically
}

func (device *Device) NewPeer(pk NoisePublicKey) (*Peer, error) {
	if device.isClosed() {
		return nil, errors.New("device closed")
	}

	// lock resources
	device.staticIdentity.RLock()
	defer device.staticIdentity.RUnlock()

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

	// check if over limit
	if len(device.peers.keyMap) >= MaxPeers {
		return nil, errors.New("too many peers")
	}

	// create peer
	peer := new(Peer)
	peer.Lock()
	defer peer.Unlock()

	peer.cookieGenerator.Init(pk)
	peer.device = device
	peer.queue.outbound = newAutodrainingOutboundQueue(device)
	peer.queue.inbound = newAutodrainingInboundQueue(device)
	peer.queue.staged = make(chan *QueueOutboundElement, QueueStagedSize)

	// map public key
	_, ok := device.peers.keyMap[pk]
	if ok {
		return nil, errors.New("adding existing peer")
	}

	// pre-compute DH
	handshake := &peer.handshake
	handshake.mutex.Lock()
	handshake.precomputedStaticStatic = device.staticIdentity.privateKey.sharedSecret(pk)
	handshake.remoteStatic = pk
	handshake.mutex.Unlock()

	// reset endpoint
	peer.endpoint = nil

	// add
	device.peers.keyMap[pk] = peer

	// start peer
	peer.timersInit()
	if peer.device.isUp() {
		peer.Start()
	}

	return peer, nil
}

func (peer *Peer) SendBuffer(buffer []byte) error {
	peer.device.net.RLock()
	defer peer.device.net.RUnlock()

	if peer.device.isClosed() {
		return nil
	}

	peer.RLock()
	defer peer.RUnlock()

	if peer.endpoint == nil {
		return errors.New("no known endpoint for peer")
	}

	err := peer.device.net.bind.Send(buffer, peer.endpoint)
	if err == nil {
		atomic.AddUint64(&peer.stats.txBytes, uint64(len(buffer)))
	}
	return err
}

func (peer *Peer) String() string {
	// The awful goo that follows is identical to:
	//
	//   base64Key := base64.StdEncoding.EncodeToString(peer.handshake.remoteStatic[:])
	//   abbreviatedKey := base64Key[0:4] + "…" + base64Key[39:43]
	//   return fmt.Sprintf("peer(%s)", abbreviatedKey)
	//
	// except that it is considerably more efficient.
	src := peer.handshake.remoteStatic
	b64 := func(input byte) byte {
		return input + 'A' + byte(((25-int(input))>>8)&6) - byte(((51-int(input))>>8)&75) - byte(((61-int(input))>>8)&15) + byte(((62-int(input))>>8)&3)
	}
	b := []byte("peer(____…____)")
	const first = len("peer(")
	const second = len("peer(____…")
	b[first+0] = b64((src[0] >> 2) & 63)
	b[first+1] = b64(((src[0] << 4) | (src[1] >> 4)) & 63)
	b[first+2] = b64(((src[1] << 2) | (src[2] >> 6)) & 63)
	b[first+3] = b64(src[2] & 63)
	b[second+0] = b64(src[29] & 63)
	b[second+1] = b64((src[30] >> 2) & 63)
	b[second+2] = b64(((src[30] << 4) | (src[31] >> 4)) & 63)
	b[second+3] = b64((src[31] << 2) & 63)
	return string(b)
}

func (peer *Peer) Start() {
	// should never start a peer on a closed device
	if peer.device.isClosed() {
		return
	}

	// prevent simultaneous start/stop operations
	peer.state.Lock()
	defer peer.state.Unlock()

	if peer.isRunning.Get() {
		return
	}

	device := peer.device
	device.log.Verbosef("%v - Starting", peer)

	// reset routine state
	peer.stopping.Wait()
	peer.stopping.Add(2)

	peer.handshake.mutex.Lock()
	peer.handshake.lastSentHandshake = time.Now().Add(-(RekeyTimeout + time.Second))
	peer.handshake.mutex.Unlock()

	peer.device.queue.encryption.wg.Add(1) // keep encryption queue open for our writes

	peer.timersStart()

	device.flushInboundQueue(peer.queue.inbound)
	device.flushOutboundQueue(peer.queue.outbound)
	go peer.RoutineSequentialSender()
	go peer.RoutineSequentialReceiver()

	peer.isRunning.Set(true)
}

func (peer *Peer) ZeroAndFlushAll() {
	device := peer.device

	// clear key pairs

	keypairs := &peer.keypairs
	keypairs.Lock()
	device.DeleteKeypair(keypairs.previous)
	device.DeleteKeypair(keypairs.current)
	device.DeleteKeypair(keypairs.loadNext())
	keypairs.previous = nil
	keypairs.current = nil
	keypairs.storeNext(nil)
	keypairs.Unlock()

	// clear handshake state

	handshake := &peer.handshake
	handshake.mutex.Lock()
	device.indexTable.Delete(handshake.localIndex)
	handshake.Clear()
	handshake.mutex.Unlock()

	peer.FlushStagedPackets()
}

func (peer *Peer) ExpireCurrentKeypairs() {
	handshake := &peer.handshake
	handshake.mutex.Lock()
	peer.device.indexTable.Delete(handshake.localIndex)
	handshake.Clear()
	peer.handshake.lastSentHandshake = time.Now().Add(-(RekeyTimeout + time.Second))
	handshake.mutex.Unlock()

	keypairs := &peer.keypairs
	keypairs.Lock()
	if keypairs.current != nil {
		atomic.StoreUint64(&keypairs.current.sendNonce, RejectAfterMessages)
	}
	if keypairs.next != nil {
		next := keypairs.loadNext()
		atomic.StoreUint64(&next.sendNonce, RejectAfterMessages)
	}
	keypairs.Unlock()
}

func (peer *Peer) Stop() {
	peer.state.Lock()
	defer peer.state.Unlock()

	if !peer.isRunning.Swap(false) {
		return
	}

	peer.device.log.Verbosef("%v - Stopping", peer)

	peer.timersStop()
	// Signal that RoutineSequentialSender and RoutineSequentialReceiver should exit.
	peer.queue.inbound.c <- nil
	peer.queue.outbound.c <- nil
	peer.stopping.Wait()
	peer.device.queue.encryption.wg.Done() // no more writes to encryption queue from us

	peer.ZeroAndFlushAll()
}

func (peer *Peer) SetEndpointFromPacket(endpoint conn.Endpoint) {
	if peer.disableRoaming {
		return
	}
	peer.Lock()
	peer.endpoint = endpoint
	peer.Unlock()
}