package p2p

import (
	"bytes"
	"encoding/hex"
	"fmt"
	"io"
	"net"
	"runtime/debug"
	"strings"
	"sync"
	"time"

	"github.com/tendermint/tendermint/libs/cmap"
	"github.com/tendermint/tendermint/libs/log"
	"github.com/tendermint/tendermint/libs/service"

	tmconn "github.com/tendermint/tendermint/p2p/conn"
)

// PeerID is a unique peer ID, generally expressed in hex form.
type PeerID []byte

// String implements the fmt.Stringer interface for the PeerID type.
func (pid PeerID) String() string {
	return strings.ToLower(hex.EncodeToString(pid))
}

// Empty returns true if the PeerID is considered empty.
func (pid PeerID) Empty() bool {
	return len(pid) == 0
}

// PeerIDFromString returns a PeerID from an encoded string or an error upon
// decode failure.
func PeerIDFromString(s string) (PeerID, error) {
	bz, err := hex.DecodeString(s)
	if err != nil {
		return nil, fmt.Errorf("failed to decode PeerID (%s): %w", s, err)
	}

	return PeerID(bz), nil
}

// Equal reports whether two PeerID are equal.
func (pid PeerID) Equal(other PeerID) bool {
	return bytes.Equal(pid, other)
}

// PeerStatus specifies peer statuses.
type PeerStatus string

const (
	PeerStatusNew     = PeerStatus("new")     // New peer which we haven't tried to contact yet.
	PeerStatusUp      = PeerStatus("up")      // Peer which we have an active connection to.
	PeerStatusDown    = PeerStatus("down")    // Peer which we're temporarily disconnected from.
	PeerStatusRemoved = PeerStatus("removed") // Peer which has been removed.
	PeerStatusBanned  = PeerStatus("banned")  // Peer which is banned for misbehavior.
)

// PeerPriority specifies peer priorities.
type PeerPriority int

const (
	PeerPriorityNormal PeerPriority = iota + 1
	PeerPriorityValidator
	PeerPriorityPersistent
)

// PeerError is a peer error reported by a reactor via the Error channel. The
// severity may cause the peer to be disconnected or banned depending on policy.
type PeerError struct {
	PeerID   PeerID
	Err      error
	Severity PeerErrorSeverity
}

// PeerErrorSeverity determines the severity of a peer error.
type PeerErrorSeverity string

const (
	PeerErrorSeverityLow      PeerErrorSeverity = "low"      // Mostly ignored.
	PeerErrorSeverityHigh     PeerErrorSeverity = "high"     // May disconnect.
	PeerErrorSeverityCritical PeerErrorSeverity = "critical" // Ban.
)

// PeerUpdatesCh defines a wrapper around a PeerUpdate go channel that allows
// a reactor to listen for peer updates and safely close it when stopping.
type PeerUpdatesCh struct {
	closeOnce sync.Once

	// updatesCh defines the go channel in which the router sends peer updates to
	// reactors. Each reactor will have its own PeerUpdatesCh to listen for updates
	// from.
	updatesCh chan PeerUpdate

	// doneCh is used to signal that a PeerUpdatesCh is closed. It is the
	// reactor's responsibility to invoke Close.
	doneCh chan struct{}
}

// NewPeerUpdates returns a reference to a new PeerUpdatesCh.
func NewPeerUpdates() *PeerUpdatesCh {
	return &PeerUpdatesCh{
		updatesCh: make(chan PeerUpdate),
		doneCh:    make(chan struct{}),
	}
}

// Updates returns a read-only go channel where a consuming reactor can listen
// for peer updates sent from the router.
func (puc *PeerUpdatesCh) Updates() <-chan PeerUpdate {
	return puc.updatesCh
}

// Close closes the PeerUpdatesCh channel. It should only be closed by the respective
// reactor when stopping and ensure nothing is listening for updates.
//
// NOTE: After a PeerUpdatesCh is closed, the router may safely assume it can no
// longer send on the internal updatesCh, however it should NEVER explicitly close
// it as that could result in panics by sending on a closed channel.
func (puc *PeerUpdatesCh) Close() {
	puc.closeOnce.Do(func() {
		close(puc.doneCh)
	})
}

// Done returns a read-only version of the PeerUpdatesCh's internal doneCh go
// channel that should be used by a router to signal when it is safe to explicitly
// not send any peer updates.
func (puc *PeerUpdatesCh) Done() <-chan struct{} {
	return puc.doneCh
}

// PeerUpdate is a peer status update for reactors.
type PeerUpdate struct {
	PeerID PeerID
	Status PeerStatus
}

// ============================================================================
// Types and business logic below may be deprecated.
//
// TODO: Rename once legacy p2p types are removed.
// ref: https://github.com/tendermint/tendermint/issues/5670
// ============================================================================

//go:generate mockery --case underscore --name Peer

const metricsTickerDuration = 10 * time.Second

// Peer is an interface representing a peer connected on a reactor.
type Peer interface {
	service.Service
	FlushStop()

	ID() ID               // peer's cryptographic ID
	RemoteIP() net.IP     // remote IP of the connection
	RemoteAddr() net.Addr // remote address of the connection

	IsOutbound() bool   // did we dial the peer
	IsPersistent() bool // do we redial this peer when we disconnect

	CloseConn() error // close original connection

	NodeInfo() NodeInfo // peer's info
	Status() tmconn.ConnectionStatus
	SocketAddr() *NetAddress // actual address of the socket

	Send(byte, []byte) bool
	TrySend(byte, []byte) bool

	Set(string, interface{})
	Get(string) interface{}
}

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

// peerConn contains the raw connection and its config.
type peerConn struct {
	outbound   bool
	persistent bool
	conn       Connection
	ip         net.IP // cached RemoteIP()
}

func newPeerConn(outbound, persistent bool, conn Connection) peerConn {
	return peerConn{
		outbound:   outbound,
		persistent: persistent,
		conn:       conn,
	}
}

// ID only exists for SecretConnection.
func (pc peerConn) ID() ID {
	return PubKeyToID(pc.conn.PubKey())
}

// Return the IP from the connection RemoteAddr
func (pc peerConn) RemoteIP() net.IP {
	if pc.ip == nil {
		pc.ip = pc.conn.RemoteEndpoint().IP
	}
	return pc.ip
}

// peer implements Peer.
//
// Before using a peer, you will need to perform a handshake on connection.
type peer struct {
	service.BaseService

	// raw peerConn and the multiplex connection
	peerConn

	// peer's node info and the channel it knows about
	// channels = nodeInfo.Channels
	// cached to avoid copying nodeInfo in hasChannel
	nodeInfo    NodeInfo
	channels    []byte
	reactors    map[byte]Reactor
	onPeerError func(Peer, interface{})

	// User data
	Data *cmap.CMap

	metrics       *Metrics
	metricsTicker *time.Ticker
}

type PeerOption func(*peer)

func newPeer(
	pc peerConn,
	reactorsByCh map[byte]Reactor,
	onPeerError func(Peer, interface{}),
	options ...PeerOption,
) *peer {
	nodeInfo := pc.conn.NodeInfo()
	p := &peer{
		peerConn:      pc,
		nodeInfo:      nodeInfo,
		channels:      nodeInfo.Channels, // TODO
		reactors:      reactorsByCh,
		onPeerError:   onPeerError,
		Data:          cmap.NewCMap(),
		metricsTicker: time.NewTicker(metricsTickerDuration),
		metrics:       NopMetrics(),
	}

	p.BaseService = *service.NewBaseService(nil, "Peer", p)
	for _, option := range options {
		option(p)
	}

	return p
}

// onError calls the peer error callback.
func (p *peer) onError(err interface{}) {
	p.onPeerError(p, err)
}

// String representation.
func (p *peer) String() string {
	if p.outbound {
		return fmt.Sprintf("Peer{%v %v out}", p.conn, p.ID())
	}

	return fmt.Sprintf("Peer{%v %v in}", p.conn, p.ID())
}

//---------------------------------------------------
// Implements service.Service

// SetLogger implements BaseService.
func (p *peer) SetLogger(l log.Logger) {
	p.Logger = l
}

// OnStart implements BaseService.
func (p *peer) OnStart() error {
	if err := p.BaseService.OnStart(); err != nil {
		return err
	}

	go p.processMessages()
	go p.metricsReporter()

	return nil
}

// processMessages processes messages received from the connection.
func (p *peer) processMessages() {
	defer func() {
		if r := recover(); r != nil {
			p.Logger.Error("peer message processing panic", "err", r, "stack", string(debug.Stack()))
			p.onError(fmt.Errorf("panic during peer message processing: %v", r))
		}
	}()

	for {
		chID, msg, err := p.conn.ReceiveMessage()
		if err != nil {
			p.onError(err)
			return
		}
		reactor, ok := p.reactors[chID]
		if !ok {
			p.onError(fmt.Errorf("unknown channel %v", chID))
			return
		}
		reactor.Receive(chID, p, msg)
	}
}

// FlushStop mimics OnStop but additionally ensures that all successful
// .Send() calls will get flushed before closing the connection.
// NOTE: it is not safe to call this method more than once.
func (p *peer) FlushStop() {
	p.metricsTicker.Stop()
	p.BaseService.OnStop()
	if err := p.conn.FlushClose(); err != nil {
		p.Logger.Debug("error while stopping peer", "err", err)
	}
}

// OnStop implements BaseService.
func (p *peer) OnStop() {
	p.metricsTicker.Stop()
	p.BaseService.OnStop()
	if err := p.conn.Close(); err != nil {
		p.Logger.Debug("error while stopping peer", "err", err)
	}
}

//---------------------------------------------------
// Implements Peer

// ID returns the peer's ID - the hex encoded hash of its pubkey.
func (p *peer) ID() ID {
	return p.nodeInfo.ID()
}

// IsOutbound returns true if the connection is outbound, false otherwise.
func (p *peer) IsOutbound() bool {
	return p.peerConn.outbound
}

// IsPersistent returns true if the peer is persitent, false otherwise.
func (p *peer) IsPersistent() bool {
	return p.peerConn.persistent
}

// NodeInfo returns a copy of the peer's NodeInfo.
func (p *peer) NodeInfo() NodeInfo {
	return p.nodeInfo
}

// SocketAddr returns the address of the socket.
// For outbound peers, it's the address dialed (after DNS resolution).
// For inbound peers, it's the address returned by the underlying connection
// (not what's reported in the peer's NodeInfo).
func (p *peer) SocketAddr() *NetAddress {
	return p.peerConn.conn.RemoteEndpoint().NetAddress()
}

// Status returns the peer's ConnectionStatus.
func (p *peer) Status() tmconn.ConnectionStatus {
	return p.conn.Status()
}

// Send msg bytes to the channel identified by chID byte. Returns false if the
// send queue is full after timeout, specified by MConnection.
func (p *peer) Send(chID byte, msgBytes []byte) bool {
	if !p.IsRunning() {
		// see Switch#Broadcast, where we fetch the list of peers and loop over
		// them - while we're looping, one peer may be removed and stopped.
		return false
	} else if !p.hasChannel(chID) {
		return false
	}
	res, err := p.conn.SendMessage(chID, msgBytes)
	if err == io.EOF {
		return false
	} else if err != nil {
		p.onError(err)
		return false
	}
	if res {
		labels := []string{
			"peer_id", string(p.ID()),
			"chID", fmt.Sprintf("%#x", chID),
		}
		p.metrics.PeerSendBytesTotal.With(labels...).Add(float64(len(msgBytes)))
	}
	return res
}

// TrySend msg bytes to the channel identified by chID byte. Immediately returns
// false if the send queue is full.
func (p *peer) TrySend(chID byte, msgBytes []byte) bool {
	if !p.IsRunning() {
		return false
	} else if !p.hasChannel(chID) {
		return false
	}
	res, err := p.conn.TrySendMessage(chID, msgBytes)
	if err == io.EOF {
		return false
	} else if err != nil {
		p.onError(err)
		return false
	}
	if res {
		labels := []string{
			"peer_id", string(p.ID()),
			"chID", fmt.Sprintf("%#x", chID),
		}
		p.metrics.PeerSendBytesTotal.With(labels...).Add(float64(len(msgBytes)))
	}
	return res
}

// Get the data for a given key.
func (p *peer) Get(key string) interface{} {
	return p.Data.Get(key)
}

// Set sets the data for the given key.
func (p *peer) Set(key string, data interface{}) {
	p.Data.Set(key, data)
}

// hasChannel returns true if the peer reported
// knowing about the given chID.
func (p *peer) hasChannel(chID byte) bool {
	for _, ch := range p.channels {
		if ch == chID {
			return true
		}
	}
	// NOTE: probably will want to remove this
	// but could be helpful while the feature is new
	p.Logger.Debug(
		"Unknown channel for peer",
		"channel",
		chID,
		"channels",
		p.channels,
	)
	return false
}

// CloseConn closes original connection. Used for cleaning up in cases where the peer had not been started at all.
func (p *peer) CloseConn() error {
	return p.peerConn.conn.Close()
}

//---------------------------------------------------
// methods only used for testing
// TODO: can we remove these?

// CloseConn closes the underlying connection
func (pc *peerConn) CloseConn() {
	pc.conn.Close()
}

// RemoteAddr returns peer's remote network address.
func (p *peer) RemoteAddr() net.Addr {
	endpoint := p.conn.RemoteEndpoint()
	return &net.TCPAddr{
		IP:   endpoint.IP,
		Port: int(endpoint.Port),
	}
}

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

func PeerMetrics(metrics *Metrics) PeerOption {
	return func(p *peer) {
		p.metrics = metrics
	}
}

func (p *peer) metricsReporter() {
	for {
		select {
		case <-p.metricsTicker.C:
			status := p.conn.Status()
			var sendQueueSize float64
			for _, chStatus := range status.Channels {
				sendQueueSize += float64(chStatus.SendQueueSize)
			}

			p.metrics.PeerPendingSendBytes.With("peer_id", string(p.ID())).Set(sendQueueSize)
		case <-p.Quit():
			return
		}
	}
}