package dht

import (
	"bytes"
	"encoding/json"
	"fmt"
	"net"
	"sort"
	"strconv"
	"strings"
	"sync"
	"time"

	"github.com/lbryio/errors.go"

	"github.com/lyoshenka/bencode"
)

// TODO: if routing table is ever empty (aka the node is isolated), it should re-bootstrap

// TODO: use a tree with bucket splitting instead of a fixed bucket list. include jack's optimization (see link in commit mesg)
// https://github.com/lbryio/lbry/pull/1211/commits/341b27b6d21ac027671d42458826d02735aaae41

type Contact struct {
	ID   Bitmap
	IP   net.IP
	Port int
}

func (c Contact) Equals(other Contact) bool {
	return c.ID == other.ID
}

func (c Contact) Addr() *net.UDPAddr {
	return &net.UDPAddr{IP: c.IP, Port: c.Port}
}

func (c Contact) String() string {
	return c.ID.HexShort() + "@" + c.Addr().String()
}

func (c Contact) MarshalCompact() ([]byte, error) {
	if c.IP.To4() == nil {
		return nil, errors.Err("ip not set")
	}
	if c.Port < 0 || c.Port > 65535 {
		return nil, errors.Err("invalid port")
	}

	var buf bytes.Buffer
	buf.Write(c.IP.To4())
	buf.WriteByte(byte(c.Port >> 8))
	buf.WriteByte(byte(c.Port))
	buf.Write(c.ID[:])

	if buf.Len() != compactNodeInfoLength {
		return nil, errors.Err("i dont know how this happened")
	}

	return buf.Bytes(), nil
}

func (c *Contact) UnmarshalCompact(b []byte) error {
	if len(b) != compactNodeInfoLength {
		return errors.Err("invalid compact length")
	}
	c.IP = net.IPv4(b[0], b[1], b[2], b[3]).To4()
	c.Port = int(uint16(b[5]) | uint16(b[4])<<8)
	c.ID = BitmapFromBytesP(b[6:])
	return nil
}

func (c Contact) MarshalBencode() ([]byte, error) {
	return bencode.EncodeBytes([]interface{}{c.ID, c.IP.String(), c.Port})
}

func (c *Contact) UnmarshalBencode(b []byte) error {
	var raw []bencode.RawMessage
	err := bencode.DecodeBytes(b, &raw)
	if err != nil {
		return err
	}

	if len(raw) != 3 {
		return errors.Err("contact must have 3 elements; got %d", len(raw))
	}

	err = bencode.DecodeBytes(raw[0], &c.ID)
	if err != nil {
		return err
	}

	var ipStr string
	err = bencode.DecodeBytes(raw[1], &ipStr)
	if err != nil {
		return err
	}
	c.IP = net.ParseIP(ipStr).To4()
	if c.IP == nil {
		return errors.Err("invalid IP")
	}

	err = bencode.DecodeBytes(raw[2], &c.Port)
	if err != nil {
		return err
	}

	return nil
}

type sortedContact struct {
	contact             Contact
	xorDistanceToTarget Bitmap
}

type byXorDistance []sortedContact

func (a byXorDistance) Len() int      { return len(a) }
func (a byXorDistance) Swap(i, j int) { a[i], a[j] = a[j], a[i] }
func (a byXorDistance) Less(i, j int) bool {
	return a[i].xorDistanceToTarget.Less(a[j].xorDistanceToTarget)
}

// peer is a contact with extra freshness information
type peer struct {
	Contact      Contact
	LastActivity time.Time
	NumFailures  int
	//<lastPublished>,
	//<originallyPublished>
	//	<originalPublisherID>
}

func (p *peer) Touch() {
	p.LastActivity = time.Now()
	p.NumFailures = 0
}

// ActiveSince returns whether a peer has responded in the last `d` duration
// this is used to check if the peer is "good", meaning that we believe the peer will respond to our requests
func (p *peer) ActiveInLast(d time.Duration) bool {
	return time.Now().Sub(p.LastActivity) > d
}

// IsBad returns whether a peer is "bad", meaning that it has failed to respond to multiple pings in a row
func (p *peer) IsBad(maxFalures int) bool {
	return p.NumFailures >= maxFalures
}

// Fail marks a peer as having failed to respond. It returns whether or not the peer should be removed from the routing table
func (p *peer) Fail() {
	p.NumFailures++
}

type bucket struct {
	lock       *sync.RWMutex
	peers      []peer
	lastUpdate time.Time
}

// Len returns the number of peers in the bucket
func (b bucket) Len() int {
	b.lock.RLock()
	defer b.lock.RUnlock()
	return len(b.peers)
}

// Contacts returns a slice of the bucket's contacts
func (b bucket) Contacts() []Contact {
	b.lock.RLock()
	defer b.lock.RUnlock()
	contacts := make([]Contact, len(b.peers))
	for i := range b.peers {
		contacts[i] = b.peers[i].Contact
	}
	return contacts
}

// UpdateContact marks a contact as having been successfully contacted. if insertIfNew and the contact is does not exist yet, it is inserted
func (b *bucket) UpdateContact(c Contact, insertIfNew bool) {
	b.lock.Lock()
	defer b.lock.Unlock()

	peerIndex := find(c.ID, b.peers)
	if peerIndex >= 0 {
		b.lastUpdate = time.Now()
		b.peers[peerIndex].Touch()
		moveToBack(b.peers, peerIndex)

	} else if insertIfNew {
		hasRoom := true

		if len(b.peers) >= bucketSize {
			hasRoom = false
			for i := range b.peers {
				if b.peers[i].IsBad(maxPeerFails) {
					// TODO: Ping contact first. Only remove if it does not respond
					b.peers = append(b.peers[:i], b.peers[i+1:]...)
					hasRoom = true
					break
				}
			}
		}

		if hasRoom {
			b.lastUpdate = time.Now()
			peer := peer{Contact: c}
			peer.Touch()
			b.peers = append(b.peers, peer)
		}
	}
}

// FailContact marks a contact as having failed, and removes it if it failed too many times
func (b *bucket) FailContact(id Bitmap) {
	b.lock.Lock()
	defer b.lock.Unlock()
	i := find(id, b.peers)
	if i >= 0 {
		// BEP5 says not to remove the contact until the bucket is full and you try to insert
		b.peers[i].Fail()
	}
}

// find returns the contact in the bucket, or nil if the bucket does not contain the contact
func find(id Bitmap, peers []peer) int {
	for i := range peers {
		if peers[i].Contact.ID.Equals(id) {
			return i
		}
	}
	return -1
}

// NeedsRefresh returns true if bucket has not been updated in the last `refreshInterval`, false otherwise
func (b *bucket) NeedsRefresh(refreshInterval time.Duration) bool {
	b.lock.RLock()
	defer b.lock.RUnlock()
	return time.Now().Sub(b.lastUpdate) > refreshInterval
}

type routingTable struct {
	id      Bitmap
	buckets [nodeIDBits]bucket
}

func newRoutingTable(id Bitmap) *routingTable {
	var rt routingTable
	rt.id = id
	for i := range rt.buckets {
		rt.buckets[i] = bucket{
			peers: make([]peer, 0, bucketSize),
			lock:  &sync.RWMutex{},
		}
	}
	return &rt
}

func (rt *routingTable) BucketInfo() string {
	var bucketInfo []string
	for i, b := range rt.buckets {
		if b.Len() > 0 {
			contacts := b.Contacts()
			s := make([]string, len(contacts))
			for j, c := range contacts {
				s[j] = c.ID.HexShort()
			}
			bucketInfo = append(bucketInfo, fmt.Sprintf("Bucket %d: (%d) %s", i, len(contacts), strings.Join(s, ", ")))
		}
	}
	if len(bucketInfo) == 0 {
		return "buckets are empty"
	}
	return strings.Join(bucketInfo, "\n")
}

// Update inserts or refreshes a contact
func (rt *routingTable) Update(c Contact) {
	rt.bucketFor(c.ID).UpdateContact(c, true)
}

// Fresh refreshes a contact if its already in the routing table
func (rt *routingTable) Fresh(c Contact) {
	rt.bucketFor(c.ID).UpdateContact(c, false)
}

// FailContact marks a contact as having failed, and removes it if it failed too many times
func (rt *routingTable) Fail(c Contact) {
	rt.bucketFor(c.ID).FailContact(c.ID)
}

// GetClosest returns the closest `limit` contacts from the routing table
// It marks each bucket it accesses as having been accessed
func (rt *routingTable) GetClosest(target Bitmap, limit int) []Contact {
	var toSort []sortedContact
	var bucketNum int

	if rt.id.Equals(target) {
		bucketNum = 0
	} else {
		bucketNum = rt.bucketNumFor(target)
	}

	toSort = appendContacts(toSort, rt.buckets[bucketNum], target)

	for i := 1; (bucketNum-i >= 0 || bucketNum+i < nodeIDBits) && len(toSort) < limit; i++ {
		if bucketNum-i >= 0 {
			toSort = appendContacts(toSort, rt.buckets[bucketNum-i], target)
		}
		if bucketNum+i < nodeIDBits {
			toSort = appendContacts(toSort, rt.buckets[bucketNum+i], target)
		}
	}

	sort.Sort(byXorDistance(toSort))

	var contacts []Contact
	for _, sorted := range toSort {
		contacts = append(contacts, sorted.contact)
		if len(contacts) >= limit {
			break
		}
	}

	return contacts
}

func appendContacts(contacts []sortedContact, b bucket, target Bitmap) []sortedContact {
	for _, contact := range b.Contacts() {
		contacts = append(contacts, sortedContact{contact, contact.ID.Xor(target)})
	}
	return contacts
}

// Count returns the number of contacts in the routing table
func (rt *routingTable) Count() int {
	count := 0
	for _, bucket := range rt.buckets {
		count = bucket.Len()
	}
	return count
}

type Range struct {
	start Bitmap
	end   Bitmap
}

// BucketRanges returns a slice of ranges, where the `start` of each range is the smallest id that can
// go in that bucket, and the `end` is the largest id
func (rt *routingTable) BucketRanges() []Range {
	ranges := make([]Range, len(rt.buckets))
	for i := range rt.buckets {
		ranges[i] = Range{
			rt.id.Suffix(i, false).Set(nodeIDBits-1-i, !rt.id.Get(nodeIDBits-1-i)),
			rt.id.Suffix(i, true).Set(nodeIDBits-1-i, !rt.id.Get(nodeIDBits-1-i)),
		}
	}
	return ranges
}

func (rt *routingTable) bucketNumFor(target Bitmap) int {
	if rt.id.Equals(target) {
		panic("routing table does not have a bucket for its own id")
	}
	return nodeIDBits - 1 - target.Xor(rt.id).PrefixLen()
}

func (rt *routingTable) bucketFor(target Bitmap) *bucket {
	return &rt.buckets[rt.bucketNumFor(target)]
}

func (rt *routingTable) GetIDsForRefresh(refreshInterval time.Duration) []Bitmap {
	var bitmaps []Bitmap
	for i, bucket := range rt.buckets {
		if bucket.NeedsRefresh(refreshInterval) {
			bitmaps = append(bitmaps, RandomBitmapP().Prefix(i, false))
		}
	}
	return bitmaps
}

const rtContactSep = "-"

type rtSave struct {
	ID       string   `json:"id"`
	Contacts []string `json:"contacts"`
}

func (rt *routingTable) MarshalJSON() ([]byte, error) {
	var data rtSave
	data.ID = rt.id.Hex()
	for _, b := range rt.buckets {
		for _, c := range b.Contacts() {
			data.Contacts = append(data.Contacts, strings.Join([]string{c.ID.Hex(), c.IP.String(), strconv.Itoa(c.Port)}, rtContactSep))
		}
	}
	return json.Marshal(data)
}

func (rt *routingTable) UnmarshalJSON(b []byte) error {
	var data rtSave
	err := json.Unmarshal(b, &data)
	if err != nil {
		return err
	}

	rt.id, err = BitmapFromHex(data.ID)
	if err != nil {
		return errors.Prefix("decoding ID", err)
	}

	for _, s := range data.Contacts {
		parts := strings.Split(s, rtContactSep)
		if len(parts) != 3 {
			return errors.Err("decoding contact %s: wrong number of parts", s)
		}
		var c Contact
		c.ID, err = BitmapFromHex(parts[0])
		if err != nil {
			return errors.Err("decoding contact %s: invalid ID: %s", s, err)
		}
		c.IP = net.ParseIP(parts[1])
		if c.IP == nil {
			return errors.Err("decoding contact %s: invalid IP", s)
		}
		c.Port, err = strconv.Atoi(parts[2])
		if err != nil {
			return errors.Err("decoding contact %s: invalid port: %s", s, err)
		}
		rt.Update(c)
	}

	return nil
}

// RoutingTableRefresh refreshes any buckets that need to be refreshed
// It returns a channel that will be closed when the refresh is done
func RoutingTableRefresh(n *Node, refreshInterval time.Duration, cancel <-chan struct{}) <-chan struct{} {
	done := make(chan struct{})

	var wg sync.WaitGroup

	for _, id := range n.rt.GetIDsForRefresh(refreshInterval) {
		wg.Add(1)
		go func(id Bitmap) {
			defer wg.Done()

			nf := newContactFinder(n, id, false)

			if cancel != nil {
				go func() {
					select {
					case <-cancel:
						nf.Cancel()
					case <-done:
					}
				}()
			}

			nf.Find()
		}(id)
	}

	go func() {
		wg.Wait()
		close(done)
	}()

	return done
}

func moveToBack(peers []peer, index int) {
	if index < 0 || len(peers) <= index+1 {
		return
	}
	p := peers[index]
	for i := index; i < len(peers)-1; i++ {
		peers[i] = peers[i+1]
	}
	peers[len(peers)-1] = p
}