package p2p

import (
	"bytes"
	"errors"
	"fmt"
	"io"
	"sync/atomic"
	"time"

	. "github.com/tendermint/tendermint/binary"
	. "github.com/tendermint/tendermint/common"
)

var pexErrInvalidMessage = errors.New("Invalid PEX message")

const (
	PexCh                    = byte(0x00)
	ensurePeersPeriodSeconds = 30
	minNumOutboundPeers      = 10
	maxNumPeers              = 50
)

/*
PEXReactor handles PEX (peer exchange) and ensures that an
adequate number of peers are connected to the switch.
*/
type PEXReactor struct {
	sw      *Switch
	quit    chan struct{}
	started uint32
	stopped uint32

	book *AddrBook
}

func NewPEXReactor(sw *Switch, book *AddrBook) *PEXReactor {
	pexR := &PEXReactor{
		sw:   sw,
		quit: make(chan struct{}),
		book: book,
	}
	return pexR
}

func (pexR *PEXReactor) Start() {
	if atomic.CompareAndSwapUint32(&pexR.started, 0, 1) {
		log.Info("Starting PEXReactor")
		go pexR.ensurePeersRoutine()
	}
}

func (pexR *PEXReactor) Stop() {
	if atomic.CompareAndSwapUint32(&pexR.stopped, 0, 1) {
		log.Info("Stopping PEXReactor")
		close(pexR.quit)
	}
}

// Asks peer for more addresses.
func (pexR *PEXReactor) RequestPEX(peer *Peer) {
	peer.TrySend(PexCh, &pexRequestMessage{})
}

func (pexR *PEXReactor) SendAddrs(peer *Peer, addrs []*NetAddress) {
	peer.Send(PexCh, &pexRddrsMessage{Addrs: addrs})
}

// Implements Reactor
func (pexR *PEXReactor) GetChannels() []*ChannelDescriptor {
	return []*ChannelDescriptor{
		&ChannelDescriptor{
			Id:       PexCh,
			Priority: 1,
		},
	}
}

// Implements Reactor
func (pexR *PEXReactor) AddPeer(peer *Peer) {
	if peer.IsOutbound() {
		pexR.SendAddrs(peer, pexR.book.OurAddresses())
		if pexR.book.NeedMoreAddrs() {
			pexR.RequestPEX(peer)
		}
	}
}

// Implements Reactor
func (pexR *PEXReactor) RemovePeer(peer *Peer, err error) {
	// TODO
}

// Implements Reactor
// Handles incoming PEX messages.
func (pexR *PEXReactor) Receive(chId byte, src *Peer, msgBytes []byte) {

	// decode message
	msg := decodeMessage(msgBytes)
	log.Info("requestRoutine received %v", msg)

	switch msg.(type) {
	case *pexRequestMessage:
		// src requested some peers.
		// TODO: prevent abuse.
		addrs := pexR.book.GetSelection()
		msg := &pexRddrsMessage{Addrs: addrs}
		queued := src.TrySend(PexCh, msg)
		if !queued {
			// ignore
		}
	case *pexRddrsMessage:
		// We received some peer addresses from src.
		// TODO: prevent abuse.
		// (We don't want to get spammed with bad peers)
		srcAddr := src.RemoteAddress()
		for _, addr := range msg.(*pexRddrsMessage).Addrs {
			pexR.book.AddAddress(addr, srcAddr)
		}
	default:
		// Ignore unknown message.
	}

}

// Ensures that sufficient peers are connected. (continuous)
func (pexR *PEXReactor) ensurePeersRoutine() {
	// fire once immediately.
	pexR.ensurePeers()
	// fire periodically
	timer := NewRepeatTimer(ensurePeersPeriodSeconds * time.Second)
FOR_LOOP:
	for {
		select {
		case <-timer.Ch:
			pexR.ensurePeers()
		case <-pexR.quit:
			break FOR_LOOP
		}
	}

	// Cleanup
	timer.Stop()
}

// Ensures that sufficient peers are connected. (once)
func (pexR *PEXReactor) ensurePeers() {
	numOutPeers, _, numDialing := pexR.sw.NumPeers()
	numToDial := minNumOutboundPeers - (numOutPeers + numDialing)
	if numToDial <= 0 {
		return
	}
	toDial := NewCMap()

	// Try to pick numToDial addresses to dial.
	// TODO: improve logic.
	for i := 0; i < numToDial; i++ {
		newBias := MinInt(numOutPeers, 8)*10 + 10
		var picked *NetAddress
		// Try to fetch a new peer 3 times.
		// This caps the maximum number of tries to 3 * numToDial.
		for j := 0; i < 3; j++ {
			picked = pexR.book.PickAddress(newBias)
			if picked == nil {
				return
			}
			if toDial.Has(picked.String()) ||
				pexR.sw.IsDialing(picked) ||
				pexR.sw.Peers().Has(picked.String()) {
				continue
			} else {
				break
			}
		}
		if picked == nil {
			continue
		}
		toDial.Set(picked.String(), picked)
	}

	// Dial picked addresses
	for _, item := range toDial.Values() {
		picked := item.(*NetAddress)
		go func() {
			_, err := pexR.sw.DialPeerWithAddress(picked)
			if err != nil {
				pexR.book.MarkAttempt(picked)
			}
		}()
	}
}

//-----------------------------------------------------------------------------

/* Messages */

const (
	msgTypeUnknown = byte(0x00)
	msgTypeRequest = byte(0x01)
	msgTypeAddrs   = byte(0x02)
)

// TODO: check for unnecessary extra bytes at the end.
func decodeMessage(bz []byte) (msg interface{}) {
	var n int64
	var err error
	// log.Debug("decoding msg bytes: %X", bz)
	switch bz[0] {
	case msgTypeRequest:
		return &pexRequestMessage{}
	case msgTypeAddrs:
		return readPexAddrsMessage(bytes.NewReader(bz[1:]), &n, &err)
	default:
		return nil
	}
}

/*
A pexRequestMessage requests additional peer addresses.
*/
type pexRequestMessage struct {
}

func (m *pexRequestMessage) WriteTo(w io.Writer) (n int64, err error) {
	WriteByte(w, msgTypeRequest, &n, &err)
	return
}

func (m *pexRequestMessage) String() string {
	return "[pexRequest]"
}

/*
A message with announced peer addresses.
*/
type pexRddrsMessage struct {
	Addrs []*NetAddress
}

func readPexAddrsMessage(r io.Reader, n *int64, err *error) *pexRddrsMessage {
	numAddrs := int(ReadUInt32(r, n, err))
	addrs := []*NetAddress{}
	for i := 0; i < numAddrs; i++ {
		addr := ReadNetAddress(r, n, err)
		addrs = append(addrs, addr)
	}
	return &pexRddrsMessage{
		Addrs: addrs,
	}
}

func (m *pexRddrsMessage) WriteTo(w io.Writer) (n int64, err error) {
	WriteByte(w, msgTypeAddrs, &n, &err)
	WriteUInt32(w, uint32(len(m.Addrs)), &n, &err)
	for _, addr := range m.Addrs {
		WriteBinary(w, addr, &n, &err)
	}
	return
}

func (m *pexRddrsMessage) String() string {
	return fmt.Sprintf("[pexRddrs %v]", m.Addrs)
}