package discv5

import (
	"context"
	"crypto/ecdsa"
	"fmt"
	"math"
	"math/rand"
	"net"
	"sync"
	"time"

	"github.com/ethereum/go-ethereum/p2p/discover"
	"github.com/ethereum/go-ethereum/p2p/enode"
	"github.com/ethereum/go-ethereum/p2p/enr"
	"github.com/ethereum/go-ethereum/p2p/nat"
	logging "github.com/ipfs/go-log"
	"github.com/libp2p/go-libp2p-core/discovery"
	"github.com/libp2p/go-libp2p-core/host"
	"github.com/libp2p/go-libp2p-core/peer"
	"github.com/status-im/go-waku/waku/v2/utils"
)

var log = logging.Logger("waku_discv5")

type DiscoveryV5 struct {
	sync.Mutex

	discovery.Discovery

	params    *discV5Parameters
	host      host.Host
	config    discover.Config
	udpAddr   *net.UDPAddr
	listener  *discover.UDPv5
	localnode *enode.LocalNode
	NAT       nat.Interface
	quit      chan struct{}

	wg *sync.WaitGroup

	peerCache peerCache
}

type peerCache struct {
	sync.RWMutex
	recs map[peer.ID]peerRecord
	rng  *rand.Rand
}

type peerRecord struct {
	expire int64
	peer   peer.AddrInfo
}

type discV5Parameters struct {
	autoUpdate    bool
	bootnodes     []*enode.Node
	udpPort       int
	tcpPort       int
	advertiseAddr *net.IP
}

type DiscoveryV5Option func(*discV5Parameters)

func WithAutoUpdate(autoUpdate bool) DiscoveryV5Option {
	return func(params *discV5Parameters) {
		params.autoUpdate = autoUpdate
	}
}

func WithBootnodes(bootnodes []*enode.Node) DiscoveryV5Option {
	return func(params *discV5Parameters) {
		params.bootnodes = bootnodes
	}
}

func WithAdvertiseAddr(addr net.IP) DiscoveryV5Option {
	return func(params *discV5Parameters) {
		params.advertiseAddr = &addr
	}
}

func WithUDPPort(port int) DiscoveryV5Option {
	return func(params *discV5Parameters) {
		params.udpPort = port
	}
}

func DefaultOptions() []DiscoveryV5Option {
	return []DiscoveryV5Option{
		WithUDPPort(9000),
	}
}

func NewDiscoveryV5(host host.Host, ipAddr net.IP, tcpPort int, priv *ecdsa.PrivateKey, wakuFlags utils.WakuEnrBitfield, opts ...DiscoveryV5Option) (*DiscoveryV5, error) {
	params := new(discV5Parameters)
	optList := DefaultOptions()
	optList = append(optList, opts...)
	for _, opt := range optList {
		opt(params)
	}

	params.tcpPort = tcpPort

	localnode, err := newLocalnode(priv, ipAddr, params.udpPort, tcpPort, wakuFlags, params.advertiseAddr)
	if err != nil {
		return nil, err
	}

	var NAT nat.Interface = nil
	if params.advertiseAddr == nil {
		NAT = nat.Any()
	}

	return &DiscoveryV5{
		host:   host,
		params: params,
		NAT:    NAT,
		wg:     &sync.WaitGroup{},
		peerCache: peerCache{
			rng:  rand.New(rand.NewSource(rand.Int63())),
			recs: make(map[peer.ID]peerRecord),
		},
		localnode: localnode,
		config: discover.Config{
			PrivateKey: priv,
			Bootnodes:  params.bootnodes,
		},
		udpAddr: &net.UDPAddr{
			IP:   net.IPv4zero,
			Port: params.udpPort,
		},
	}, nil
}

func newLocalnode(priv *ecdsa.PrivateKey, ipAddr net.IP, udpPort int, tcpPort int, wakuFlags utils.WakuEnrBitfield, advertiseAddr *net.IP) (*enode.LocalNode, error) {
	db, err := enode.OpenDB("")
	if err != nil {
		return nil, err
	}
	localnode := enode.NewLocalNode(db, priv)
	localnode.SetFallbackIP(net.IP{127, 0, 0, 1})
	localnode.SetFallbackUDP(udpPort)
	localnode.Set(enr.WithEntry(utils.WakuENRField, wakuFlags))
	localnode.Set(enr.IP(ipAddr))

	if udpPort > 0 && udpPort <= math.MaxUint16 {
		localnode.Set(enr.UDP(uint16(udpPort))) // lgtm [go/incorrect-integer-conversion]
	} else {
		log.Error("could not set udpPort ", udpPort)
	}

	if tcpPort > 0 && tcpPort <= math.MaxUint16 {
		localnode.Set(enr.TCP(uint16(tcpPort))) // lgtm [go/incorrect-integer-conversion]
	} else {
		log.Error("could not set tcpPort ", tcpPort)
	}

	if advertiseAddr != nil {
		localnode.SetStaticIP(*advertiseAddr)
	}

	return localnode, nil
}

func (d *DiscoveryV5) listen() error {
	conn, err := net.ListenUDP("udp", d.udpAddr)
	if err != nil {
		return err
	}

	d.udpAddr = conn.LocalAddr().(*net.UDPAddr)

	if d.NAT != nil && !d.udpAddr.IP.IsLoopback() {
		d.wg.Add(1)
		go func() {
			defer d.wg.Done()
			nat.Map(d.NAT, d.quit, "udp", d.udpAddr.Port, d.udpAddr.Port, "go-waku discv5 discovery")
		}()

	}

	d.localnode.SetFallbackUDP(d.udpAddr.Port)

	listener, err := discover.ListenV5(conn, d.localnode, d.config)
	if err != nil {
		return err
	}

	d.listener = listener

	log.Info(fmt.Sprintf("Started Discovery V5 at %s:%d, advertising IP: %s:%d", d.udpAddr.IP, d.udpAddr.Port, d.localnode.Node().IP(), d.params.tcpPort))
	log.Info("Discovery V5 ", d.localnode.Node())

	return nil
}

func (d *DiscoveryV5) Start() error {
	d.Lock()
	defer d.Unlock()

	d.wg.Wait() // Waiting for other go routines to stop

	d.quit = make(chan struct{}, 1)

	err := d.listen()
	if err != nil {
		return err
	}

	return nil
}

func (d *DiscoveryV5) Stop() {
	d.Lock()
	defer d.Unlock()

	close(d.quit)

	d.listener.Close()
	d.listener = nil

	log.Info("Stopped Discovery V5")

	d.wg.Wait()
}

// IsPrivate reports whether ip is a private address, according to
// RFC 1918 (IPv4 addresses) and RFC 4193 (IPv6 addresses).
// Copied/Adapted from https://go-review.googlesource.com/c/go/+/272668/11/src/net/ip.go
// Copyright (c) The Go Authors. All rights reserved.
// @TODO: once Go 1.17 is released in Q42021, remove this function as it will become part of the language
func IsPrivate(ip net.IP) bool {
	if ip4 := ip.To4(); ip4 != nil {
		// Following RFC 4193, Section 3. Local IPv6 Unicast Addresses which says:
		//   The Internet Assigned Numbers Authority (IANA) has reserved the
		//   following three blocks of the IPv4 address space for private internets:
		//     10.0.0.0        -   10.255.255.255  (10/8 prefix)
		//     172.16.0.0      -   172.31.255.255  (172.16/12 prefix)
		//     192.168.0.0     -   192.168.255.255 (192.168/16 prefix)
		return ip4[0] == 10 ||
			(ip4[0] == 172 && ip4[1]&0xf0 == 16) ||
			(ip4[0] == 192 && ip4[1] == 168)
	}
	// Following RFC 4193, Section 3. Private Address Space which says:
	//   The Internet Assigned Numbers Authority (IANA) has reserved the
	//   following block of the IPv6 address space for local internets:
	//     FC00::  -  FDFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF (FC00::/7 prefix)
	return len(ip) == net.IPv6len && ip[0]&0xfe == 0xfc
}

func (d *DiscoveryV5) UpdateAddr(addr net.IP) error {
	if !d.params.autoUpdate {
		return nil
	}

	d.Lock()
	defer d.Unlock()

	if addr.IsUnspecified() || d.localnode.Node().IP().Equal(addr) {
		return nil
	}

	// TODO: improve this logic to determine if an address should be replaced or not
	if !(d.localnode.Node().IP().IsLoopback() && IsPrivate(addr)) && !(IsPrivate(d.localnode.Node().IP()) && !addr.IsLoopback() && !IsPrivate(addr)) {
		return nil
	}

	d.localnode.Set(enr.IP(addr))

	log.Info(fmt.Sprintf("Updated Discovery V5 node IP: %s", d.localnode.Node().IP()))
	log.Info("Discovery V5 ", d.localnode.Node())

	return nil
}

func isWakuNode(node *enode.Node) bool {
	enrField := new(utils.WakuEnrBitfield)
	if err := node.Record().Load(enr.WithEntry(utils.WakuENRField, &enrField)); err != nil {
		if !enr.IsNotFound(err) {
			log.Error("could not retrieve port for enr ", node)
		}
		return false
	}

	if enrField != nil {
		return *enrField != uint8(0)
	}

	return false
}

func hasTCPPort(node *enode.Node) bool {
	enrTCP := new(enr.TCP)
	if err := node.Record().Load(enr.WithEntry(enrTCP.ENRKey(), enrTCP)); err != nil {
		if !enr.IsNotFound(err) {
			log.Error("could not retrieve port for enr ", node)
		}
		return false
	}

	return true
}

func (d *DiscoveryV5) evaluateNode(node *enode.Node) bool {
	if node == nil || node.IP() == nil {
		return false
	}

	if !isWakuNode(node) || !hasTCPPort(node) {
		return false
	}

	_, err := utils.EnodeToPeerInfo(node)

	if err != nil {
		log.Error("could not obtain peer info from enode:", err)
		return false
	}

	return true
}

func (c *DiscoveryV5) Advertise(ctx context.Context, ns string, opts ...discovery.Option) (time.Duration, error) {
	// Get options
	var options discovery.Options
	err := options.Apply(opts...)
	if err != nil {
		return 0, err
	}

	// TODO: once discv5 spec introduces capability and topic discovery, implement this function

	return 20 * time.Minute, nil
}

func (d *DiscoveryV5) iterate(ctx context.Context, iterator enode.Iterator, limit int, doneCh chan struct{}) {
	defer d.wg.Done()

	for {
		if len(d.peerCache.recs) >= limit {
			break
		}

		if ctx.Err() != nil {
			break
		}

		exists := iterator.Next()
		if !exists {
			break
		}

		address, err := utils.EnodeToMultiAddr(iterator.Node())
		if err != nil {
			log.Error(err)
			continue
		}

		peerInfo, err := peer.AddrInfoFromP2pAddr(address)
		if err != nil {
			log.Error(err)
			continue
		}

		d.peerCache.recs[peerInfo.ID] = peerRecord{
			expire: time.Now().Unix() + 3600, // Expires in 1hr
			peer:   *peerInfo,
		}
	}

	close(doneCh)
}

func (d *DiscoveryV5) removeExpiredPeers() int {
	// Remove all expired entries from cache
	currentTime := time.Now().Unix()
	newCacheSize := len(d.peerCache.recs)

	for p := range d.peerCache.recs {
		rec := d.peerCache.recs[p]
		if rec.expire < currentTime {
			newCacheSize--
			delete(d.peerCache.recs, p)
		}
	}

	return newCacheSize
}

func (d *DiscoveryV5) FindPeers(ctx context.Context, topic string, opts ...discovery.Option) (<-chan peer.AddrInfo, error) {
	// Get options
	var options discovery.Options
	err := options.Apply(opts...)
	if err != nil {
		return nil, err
	}

	const maxLimit = 100
	limit := options.Limit
	if limit == 0 || limit > maxLimit {
		limit = maxLimit
	}

	// We are ignoring the topic. Future versions might use a map[string]*peerCache instead where the string represents the pubsub topic

	d.peerCache.Lock()
	defer d.peerCache.Unlock()

	cacheSize := d.removeExpiredPeers()

	// Discover new records if we don't have enough
	if cacheSize < limit && d.listener != nil {
		d.Lock()

		iterator := d.listener.RandomNodes()
		iterator = enode.Filter(iterator, d.evaluateNode)
		defer iterator.Close()

		doneCh := make(chan struct{})

		d.wg.Add(1)
		go d.iterate(ctx, iterator, limit, doneCh)

		select {
		case <-ctx.Done():
		case <-doneCh:
		}

		d.Unlock()
	}

	// Randomize and fill channel with available records
	count := len(d.peerCache.recs)
	if limit < count {
		count = limit
	}

	chPeer := make(chan peer.AddrInfo, count)

	perm := d.peerCache.rng.Perm(len(d.peerCache.recs))[0:count]
	permSet := make(map[int]int)
	for i, v := range perm {
		permSet[v] = i
	}

	sendLst := make([]*peer.AddrInfo, count)
	iter := 0
	for k := range d.peerCache.recs {
		if sendIndex, ok := permSet[iter]; ok {
			peerInfo := d.peerCache.recs[k].peer
			sendLst[sendIndex] = &peerInfo
		}
		iter++
	}

	for _, send := range sendLst {
		chPeer <- *send
	}

	close(chPeer)

	return chPeer, err
}