package p2p

import (
	"bytes"
	"crypto/ecdsa"
	"errors"
	"fmt"
	"io"
	"net"
	"runtime"
	"sync"
	"time"

	"github.com/ethereum/go-ethereum/logger"
	"github.com/ethereum/go-ethereum/p2p/discover"
)

const (
	defaultDialTimeout        = 10 * time.Second
	refreshPeersInterval      = 30 * time.Second
	portMappingUpdateInterval = 15 * time.Minute
	portMappingTimeout        = 20 * time.Minute
)

var srvlog = logger.NewLogger("P2P Server")

// MakeName creates a node name that follows the ethereum convention
// for such names. It adds the operation system name and Go runtime version
// the name.
func MakeName(name, version string) string {
	return fmt.Sprintf("%s/v%s/%s/%s", name, version, runtime.GOOS, runtime.Version())
}

// Server manages all peer connections.
//
// The fields of Server are used as configuration parameters.
// You should set them before starting the Server. Fields may not be
// modified while the server is running.
type Server struct {
	// This field must be set to a valid secp256k1 private key.
	PrivateKey *ecdsa.PrivateKey

	// MaxPeers is the maximum number of peers that can be
	// connected. It must be greater than zero.
	MaxPeers int

	// Name sets the node name of this server.
	// Use MakeName to create a name that follows existing conventions.
	Name string

	// Bootstrap nodes are used to establish connectivity
	// with the rest of the network.
	BootstrapNodes []discover.Node

	// Protocols should contain the protocols supported
	// by the server. Matching protocols are launched for
	// each peer.
	Protocols []Protocol

	// If Blacklist is set to a non-nil value, the given Blacklist
	// is used to verify peer connections.
	Blacklist Blacklist

	// If ListenAddr is set to a non-nil address, the server
	// will listen for incoming connections.
	//
	// If the port is zero, the operating system will pick a port. The
	// ListenAddr field will be updated with the actual address when
	// the server is started.
	ListenAddr string

	// If set to a non-nil value, the given NAT port mapper
	// is used to make the listening port available to the
	// Internet.
	NAT NAT

	// If Dialer is set to a non-nil value, the given Dialer
	// is used to dial outbound peer connections.
	Dialer *net.Dialer

	// If NoDial is true, the server will not dial any peers.
	NoDial bool

	// Hooks for testing. These are useful because we can inhibit
	// the whole protocol stack.
	handshakeFunc
	newPeerHook

	lock     sync.RWMutex
	running  bool
	listener net.Listener
	laddr    *net.TCPAddr // real listen addr
	peers    map[discover.NodeID]*Peer

	ntab *discover.Table

	quit        chan struct{}
	loopWG      sync.WaitGroup // {dial,listen,nat}Loop
	peerWG      sync.WaitGroup // active peer goroutines
	peerConnect chan *discover.Node
}

// NAT is implemented by NAT traversal methods.
type NAT interface {
	GetExternalAddress() (net.IP, error)
	AddPortMapping(protocol string, extport, intport int, name string, lifetime time.Duration) error
	DeletePortMapping(protocol string, extport, intport int) error

	// Should return name of the method.
	String() string
}

type handshakeFunc func(io.ReadWriter, *ecdsa.PrivateKey, *discover.Node) (discover.NodeID, []byte, error)
type newPeerHook func(*Peer)

// Peers returns all connected peers.
func (srv *Server) Peers() (peers []*Peer) {
	srv.lock.RLock()
	defer srv.lock.RUnlock()
	for _, peer := range srv.peers {
		if peer != nil {
			peers = append(peers, peer)
		}
	}
	return
}

// PeerCount returns the number of connected peers.
func (srv *Server) PeerCount() int {
	srv.lock.RLock()
	n := len(srv.peers)
	srv.lock.RUnlock()
	return n
}

// SuggestPeer creates a connection to the given Node if it
// is not already connected.
func (srv *Server) SuggestPeer(ip net.IP, port int, id discover.NodeID) {
	srv.peerConnect <- &discover.Node{ID: id, IP: ip, TCPPort: port}
}

// Broadcast sends an RLP-encoded message to all connected peers.
// This method is deprecated and will be removed later.
func (srv *Server) Broadcast(protocol string, code uint64, data ...interface{}) {
	var payload []byte
	if data != nil {
		payload = encodePayload(data...)
	}
	srv.lock.RLock()
	defer srv.lock.RUnlock()
	for _, peer := range srv.peers {
		if peer != nil {
			var msg = Msg{Code: code}
			if data != nil {
				msg.Payload = bytes.NewReader(payload)
				msg.Size = uint32(len(payload))
			}
			peer.writeProtoMsg(protocol, msg)
		}
	}
}

// Start starts running the server.
// Servers can be re-used and started again after stopping.
func (srv *Server) Start() (err error) {
	srv.lock.Lock()
	defer srv.lock.Unlock()
	if srv.running {
		return errors.New("server already running")
	}
	srvlog.Infoln("Starting Server")

	// initialize all the fields
	if srv.PrivateKey == nil {
		return fmt.Errorf("Server.PrivateKey must be set to a non-nil key")
	}
	if srv.MaxPeers <= 0 {
		return fmt.Errorf("Server.MaxPeers must be > 0")
	}
	srv.quit = make(chan struct{})
	srv.peers = make(map[discover.NodeID]*Peer)
	srv.peerConnect = make(chan *discover.Node)

	if srv.handshakeFunc == nil {
		srv.handshakeFunc = encHandshake
	}
	if srv.Blacklist == nil {
		srv.Blacklist = NewBlacklist()
	}
	if srv.ListenAddr != "" {
		if err := srv.startListening(); err != nil {
			return err
		}
	}

	// dial stuff
	dt, err := discover.ListenUDP(srv.PrivateKey, srv.ListenAddr)
	if err != nil {
		return err
	}
	srv.ntab = dt
	if srv.Dialer == nil {
		srv.Dialer = &net.Dialer{Timeout: defaultDialTimeout}
	}
	if !srv.NoDial {
		srv.loopWG.Add(1)
		go srv.dialLoop()
	}

	if srv.NoDial && srv.ListenAddr == "" {
		srvlog.Warnln("I will be kind-of useless, neither dialing nor listening.")
	}

	srv.running = true
	return nil
}

func (srv *Server) startListening() error {
	listener, err := net.Listen("tcp", srv.ListenAddr)
	if err != nil {
		return err
	}
	srv.ListenAddr = listener.Addr().String()
	srv.laddr = listener.Addr().(*net.TCPAddr)
	srv.listener = listener
	srv.loopWG.Add(1)
	go srv.listenLoop()
	if !srv.laddr.IP.IsLoopback() && srv.NAT != nil {
		srv.loopWG.Add(1)
		go srv.natLoop(srv.laddr.Port)
	}
	return nil
}

// Stop terminates the server and all active peer connections.
// It blocks until all active connections have been closed.
func (srv *Server) Stop() {
	srv.lock.Lock()
	if !srv.running {
		srv.lock.Unlock()
		return
	}
	srv.running = false
	srv.lock.Unlock()

	srvlog.Infoln("Stopping Server")
	srv.ntab.Close()
	if srv.listener != nil {
		// this unblocks listener Accept
		srv.listener.Close()
	}
	close(srv.quit)
	srv.loopWG.Wait()

	// No new peers can be added at this point because dialLoop and
	// listenLoop are down. It is safe to call peerWG.Wait because
	// peerWG.Add is not called outside of those loops.
	for _, peer := range srv.peers {
		peer.Disconnect(DiscQuitting)
	}
	srv.peerWG.Wait()
}

// main loop for adding connections via listening
func (srv *Server) listenLoop() {
	defer srv.loopWG.Done()
	srvlog.Infoln("Listening on", srv.listener.Addr())
	for {
		conn, err := srv.listener.Accept()
		if err != nil {
			return
		}
		srvlog.Debugf("Accepted conn %v\n", conn.RemoteAddr())
		srv.peerWG.Add(1)
		go srv.startPeer(conn, nil)
	}
}

func (srv *Server) natLoop(port int) {
	defer srv.loopWG.Done()
	for {
		srv.updatePortMapping(port)
		select {
		case <-time.After(portMappingUpdateInterval):
			// one more round
		case <-srv.quit:
			srv.removePortMapping(port)
			return
		}
	}
}

func (srv *Server) updatePortMapping(port int) {
	srvlog.Infoln("Attempting to map port", port, "with", srv.NAT)
	err := srv.NAT.AddPortMapping("tcp", port, port, "ethereum p2p", portMappingTimeout)
	if err != nil {
		srvlog.Errorln("Port mapping error:", err)
		return
	}
	extip, err := srv.NAT.GetExternalAddress()
	if err != nil {
		srvlog.Errorln("Error getting external IP:", err)
		return
	}
	srv.lock.Lock()
	extaddr := *(srv.listener.Addr().(*net.TCPAddr))
	extaddr.IP = extip
	srvlog.Infoln("Mapped port, external addr is", &extaddr)
	srv.laddr = &extaddr
	srv.lock.Unlock()
}

func (srv *Server) removePortMapping(port int) {
	srvlog.Infoln("Removing port mapping for", port, "with", srv.NAT)
	srv.NAT.DeletePortMapping("tcp", port, port)
}

func (srv *Server) dialLoop() {
	defer srv.loopWG.Done()
	refresh := time.NewTicker(refreshPeersInterval)
	defer refresh.Stop()

	srv.ntab.Bootstrap(srv.BootstrapNodes)
	go srv.findPeers()

	dialed := make(chan *discover.Node)
	dialing := make(map[discover.NodeID]bool)

	// TODO: limit number of active dials
	// TODO: ensure only one findPeers goroutine is running
	// TODO: pause findPeers when we're at capacity

	for {
		select {
		case <-refresh.C:

			go srv.findPeers()

		case dest := <-srv.peerConnect:
			srv.lock.Lock()
			_, isconnected := srv.peers[dest.ID]
			srv.lock.Unlock()
			if isconnected || dialing[dest.ID] {
				continue
			}

			dialing[dest.ID] = true
			srv.peerWG.Add(1)
			go func() {
				srv.dialNode(dest)
				// at this point, the peer has been added
				// or discarded. either way, we're not dialing it anymore.
				dialed <- dest
			}()

		case dest := <-dialed:
			delete(dialing, dest.ID)

		case <-srv.quit:
			// TODO: maybe wait for active dials
			return
		}
	}
}

func (srv *Server) dialNode(dest *discover.Node) {
	addr := &net.TCPAddr{IP: dest.IP, Port: dest.TCPPort}
	srvlog.Debugf("Dialing %v\n", dest)
	conn, err := srv.Dialer.Dial("tcp", addr.String())
	if err != nil {
		srvlog.DebugDetailf("dial error: %v", err)
		return
	}
	srv.startPeer(conn, dest)
}

func (srv *Server) findPeers() {
	far := srv.ntab.Self()
	for i := range far {
		far[i] = ^far[i]
	}
	closeToSelf := srv.ntab.Lookup(srv.ntab.Self())
	farFromSelf := srv.ntab.Lookup(far)

	for i := 0; i < len(closeToSelf) || i < len(farFromSelf); i++ {
		if i < len(closeToSelf) {
			srv.peerConnect <- closeToSelf[i]
		}
		if i < len(farFromSelf) {
			srv.peerConnect <- farFromSelf[i]
		}
	}
}

func (srv *Server) startPeer(conn net.Conn, dest *discover.Node) {
	// TODO: I/O timeout, handle/store session token
	remoteID, _, err := srv.handshakeFunc(conn, srv.PrivateKey, dest)
	if err != nil {
		conn.Close()
		srvlog.Debugf("Encryption Handshake with %v failed: %v", conn.RemoteAddr(), err)
		return
	}

	ourID := srv.ntab.Self()
	p := newPeer(conn, srv.Protocols, srv.Name, &ourID, &remoteID)
	if ok, reason := srv.addPeer(remoteID, p); !ok {
		p.Disconnect(reason)
		return
	}

	srv.newPeerHook(p)
	p.run()
	srv.removePeer(p)
}

func (srv *Server) addPeer(id discover.NodeID, p *Peer) (bool, DiscReason) {
	srv.lock.Lock()
	defer srv.lock.Unlock()
	switch {
	case !srv.running:
		return false, DiscQuitting
	case len(srv.peers) >= srv.MaxPeers:
		return false, DiscTooManyPeers
	case srv.peers[id] != nil:
		return false, DiscAlreadyConnected
	case srv.Blacklist.Exists(id[:]):
		return false, DiscUselessPeer
	case id == srv.ntab.Self():
		return false, DiscSelf
	}
	srvlog.Debugf("Adding %v\n", p)
	srv.peers[id] = p
	return true, 0
}

// removes peer: sending disconnect msg, stop peer, remove rom list/table, release slot
func (srv *Server) removePeer(p *Peer) {
	srvlog.Debugf("Removing %v\n", p)
	srv.lock.Lock()
	delete(srv.peers, *p.remoteID)
	srv.lock.Unlock()
	srv.peerWG.Done()
}

type Blacklist interface {
	Get([]byte) (bool, error)
	Put([]byte) error
	Delete([]byte) error
	Exists(pubkey []byte) (ok bool)
}

type BlacklistMap struct {
	blacklist map[string]bool
	lock      sync.RWMutex
}

func NewBlacklist() *BlacklistMap {
	return &BlacklistMap{
		blacklist: make(map[string]bool),
	}
}

func (self *BlacklistMap) Get(pubkey []byte) (bool, error) {
	self.lock.RLock()
	defer self.lock.RUnlock()
	v, ok := self.blacklist[string(pubkey)]
	var err error
	if !ok {
		err = fmt.Errorf("not found")
	}
	return v, err
}

func (self *BlacklistMap) Exists(pubkey []byte) (ok bool) {
	self.lock.RLock()
	defer self.lock.RUnlock()
	_, ok = self.blacklist[string(pubkey)]
	return
}

func (self *BlacklistMap) Put(pubkey []byte) error {
	self.lock.RLock()
	defer self.lock.RUnlock()
	self.blacklist[string(pubkey)] = true
	return nil
}

func (self *BlacklistMap) Delete(pubkey []byte) error {
	self.lock.RLock()
	defer self.lock.RUnlock()
	delete(self.blacklist, string(pubkey))
	return nil
}