// This package implements a simple XMPP client according to RFCs 3920

// and 3921, plus the various XEPs at http://xmpp.org/protocols/. The

// implementation is structured as a stack of layers, with TCP at the

// bottom and the application at the top. The application receives and

// sends structures representing XMPP stanzas. Additional stanza

// parsers can be inserted into the stack of layers as extensions.

package xmpp

import (

	"crypto/tls"

	"encoding/xml"

	"fmt"

	"io"

	"net"

	"reflect"

	"sync"

)

const (

	// Version of RFC 3920 that we implement.

	XMPPVersion = "1.0"

	// Various XML namespaces.

	NsClient  = "jabber:client"

	NsStreams = "urn:ietf:params:xml:ns:xmpp-streams"

	NsStream  = "http://etherx.jabber.org/streams"

	NsTLS     = "urn:ietf:params:xml:ns:xmpp-tls"

	NsSASL    = "urn:ietf:params:xml:ns:xmpp-sasl"

	NsBind    = "urn:ietf:params:xml:ns:xmpp-bind"

	NsSession = "urn:ietf:params:xml:ns:xmpp-session"

	NsRoster  = "jabber:iq:roster"

	// DNS SRV names

	serverSrv = "xmpp-server"

	clientSrv = "xmpp-client"

)

// A filter can modify the XMPP traffic to or from the remote

// server. It's part of an Extension. The filter function will be

// called in a new goroutine, so it doesn't need to return. The filter

// should close its output when its input is closed.

type Filter func(in <-chan Stanza, out chan<- Stanza)

// Extensions can add stanza filters and/or new XML element types.

type Extension struct {

	// Maps from an XML name to a structure which holds stanza

	// contents with that name.

	StanzaTypes map[xml.Name]reflect.Type

	// If non-nil, will be called once to start the filter

	// running. RecvFilter intercepts incoming messages on their

	// way from the remote server to the application; SendFilter

	// intercepts messages going the other direction.

	RecvFilter Filter

	SendFilter Filter

}

// The client in a client-server XMPP connection.

type Client struct {

	// This client's full JID, including resource

	Jid          JID

	password     string

	saslExpected string

	authDone     bool

	handlers     chan *callback

	// Incoming XMPP stanzas from the remote will be published on

	// this channel. Information which is used by this library to

	// set up the XMPP stream will not appear here.

	Recv <-chan Stanza

	// Outgoing XMPP stanzas to the server should be sent to this

	// channel. The application should not close this channel;

	// rather, call Close().

	Send    chan<- Stanza

	sendRaw chan<- interface{}

	statmgr *statmgr

	// The client's roster is also known as the buddy list. It's

	// the set of contacts which are known to this JID, or which

	// this JID is known to.

	Roster Roster

	// Features advertised by the remote.

	Features                     *Features

	sendFilterAdd, recvFilterAdd chan Filter

	tlsConfig                    tls.Config

	layer1                       *layer1

	error                        chan error

	shutdownOnce                 sync.Once

}

// Creates an XMPP client identified by the given JID, authenticating

// with the provided password and TLS config. Zero or more extensions

// may be specified. The initial presence will be broadcast. If status

// is non-nil, connection progress information will be sent on it.

func NewClient(jid *JID, password string, tlsconf tls.Config, exts []Extension,

	pr Presence, status chan<- Status) (*Client, error) {

	// Resolve the domain in the JID.

	_, srvs, err := net.LookupSRV(clientSrv, "tcp", jid.Domain)

	if err != nil {

		return nil, fmt.Errorf("LookupSrv %s: %v", jid.Domain, err)

	}

	if len(srvs) == 0 {

		return nil, fmt.Errorf("LookupSrv %s: no results", jid.Domain)

	}

	var tcp *net.TCPConn

	for _, srv := range srvs {

		addrStr := fmt.Sprintf("%s:%d", srv.Target, srv.Port)

		var addr *net.TCPAddr

		addr, err = net.ResolveTCPAddr("tcp", addrStr)

		if err != nil {

			err = fmt.Errorf("ResolveTCPAddr(%s): %s",

				addrStr, err.Error())

			continue

		}

		tcp, err = net.DialTCP("tcp", nil, addr)

		if tcp != nil {

			break

		}

	}

	if tcp == nil {

		return nil, err

	}

	return newClient(tcp, jid, password, tlsconf, exts, pr, status)

}

// Connect to the specified host and port. This is otherwise identical

// to NewClient.

func NewClientFromHost(jid *JID, password string, tlsconf tls.Config,

	exts []Extension, pr Presence, status chan<- Status, host string,

	port int) (*Client, error) {

	addrStr := fmt.Sprintf("%s:%d", host, port)

	addr, err := net.ResolveTCPAddr("tcp", addrStr)

	if err != nil {

		return nil, err

	}

	tcp, err := net.DialTCP("tcp", nil, addr)

	if err != nil {

		return nil, err

	}

	return newClient(tcp, jid, password, tlsconf, exts, pr, status)

}

func newClient(tcp *net.TCPConn, jid *JID, password string, tlsconf tls.Config,

	exts []Extension, pr Presence, status chan<- Status) (*Client, error) {

	// Include the mandatory extensions.

	roster := newRosterExt()

	exts = append(exts, roster.Extension)

	exts = append(exts, bindExt)

	cl := new(Client)

	cl.Roster = *roster

	cl.password = password

	cl.Jid = *jid

	cl.handlers = make(chan *callback, 100)

	cl.tlsConfig = tlsconf

	cl.sendFilterAdd = make(chan Filter)

	cl.recvFilterAdd = make(chan Filter)

	cl.statmgr = newStatmgr(status)

	cl.error = make(chan error, 1)

	extStanza := make(map[xml.Name]reflect.Type)

	for _, ext := range exts {

		for k, v := range ext.StanzaTypes {

			if _, ok := extStanza[k]; ok {

				return nil, fmt.Errorf("duplicate handler %s",

					k)

			}

			extStanza[k] = v

		}

	}

	// The thing that called this made a TCP connection, so now we

	// can signal that it's connected.

	cl.setStatus(StatusConnected)

	// Start the transport handler, initially unencrypted.

	recvReader, recvWriter := io.Pipe()

	sendReader, sendWriter := io.Pipe()

	cl.layer1 = cl.startLayer1(tcp, recvWriter, sendReader,

		cl.statmgr.newListener())

	// Start the reader and writer that convert to and from XML.

	recvXmlCh := make(chan interface{})

	go cl.recvXml(recvReader, recvXmlCh, extStanza)

	sendXmlCh := make(chan interface{})

	cl.sendRaw = sendXmlCh

	go cl.sendXml(sendWriter, sendXmlCh)

	// Start the reader and writer that convert between XML and

	// XMPP stanzas.

	recvRawXmpp := make(chan Stanza)

	go cl.recvStream(recvXmlCh, recvRawXmpp, cl.statmgr.newListener())

	sendRawXmpp := make(chan Stanza)

	go sendStream(sendXmlCh, sendRawXmpp, cl.statmgr.newListener())

	// Start the managers for the filters that can modify what the

	// app sees or sends.

	recvFiltXmpp := make(chan Stanza)

	cl.Recv = recvFiltXmpp

	go filterMgr(cl.recvFilterAdd, recvRawXmpp, recvFiltXmpp)

	sendFiltXmpp := make(chan Stanza)

	cl.Send = sendFiltXmpp

	go filterMgr(cl.sendFilterAdd, sendFiltXmpp, sendRawXmpp)

	// Set up the initial filters.

	for _, ext := range exts {

		cl.AddRecvFilter(ext.RecvFilter)

		cl.AddSendFilter(ext.SendFilter)

	}

	// Initial handshake.

	hsOut := &stream{To: jid.Domain, Version: XMPPVersion}

	cl.sendRaw <- hsOut

	// Wait until resource binding is complete.

	if err := cl.statmgr.awaitStatus(StatusBound); err != nil {

		return nil, cl.getError(err)

	}

	// Forget about the password, for paranoia's sake.

	cl.password = ""

	// Initialize the session.

	id := NextId()

	iq := &Iq{Header: Header{To: cl.Jid.Domain, Id: id, Type: "set",

		Nested: []interface{}{Generic{XMLName: xml.Name{Space: NsSession, Local: "session"}}}}}

	ch := make(chan error)

	f := func(st Stanza) {

		iq, ok := st.(*Iq)

		if !ok {

			ch <- fmt.Errorf("bad session start reply: %#v", st)

		}

		if iq.Type == "error" {

			ch <- fmt.Errorf("Can't start session: %v", iq.Error)

		}

		ch <- nil

	}

	cl.SetCallback(id, f)

	cl.sendRaw <- iq

	// Now wait until the callback is called.

	if err := <-ch; err != nil {

		return nil, cl.getError(err)

	}

	// This allows the client to receive stanzas.

	cl.setStatus(StatusRunning)

	// Request the roster.

	cl.Roster.update()

	// Send the initial presence.

	cl.Send <- &pr

	return cl, cl.getError(nil)

}

func (cl *Client) Close() {

	// Shuts down the receivers:

	cl.setStatus(StatusShutdown)

	// Shuts down the senders:

	cl.shutdownOnce.Do(func() { close(cl.Send) })

}

// If there's a buffered error in the channel, return it. Otherwise,

// return what was passed to us. The idea is that the error in the

// channel probably preceded (and caused) the one that's passed as an

// argument here.

func (cl *Client) getError(err1 error) error {

	select {

	case err0 := <-cl.error:

		return err0

	default:

		return err1

	}

}

// Register an error that happened in the internals somewhere. If

// there's already an error in the channel, discard the newer one in

// favor of the older.

func (cl *Client) setError(err error) {

	defer cl.Close()

	defer cl.setStatus(StatusError)

	if len(cl.error) > 0 {

		return

	}

	// If we're in a race between two calls to this function,

	// trying to set the "first" error, just arbitrarily let one

	// of them win.

	select {

	case cl.error <- err:

	default:

	}

}