// Parse a header string, producing one or more SipHeader objects.
// (SIP messages containing multiple headers of the same type can express them as a
// single header containing a comma-separated argument list).
func (p *parser) parseHeader(headerText string) (headers []base.SipHeader, err error) {
	log.Debug("Parser %p parsing header \"%s\"", p, headerText)
	headers = make([]base.SipHeader, 0)

	colonIdx := strings.Index(headerText, ":")
	if colonIdx == -1 {
		err = fmt.Errorf("Field name with no value in header: %s", headerText)
		return
	}

	fieldName := strings.ToLower(strings.TrimSpace(headerText[:colonIdx]))
	fieldText := strings.TrimSpace(headerText[colonIdx+1:])
	if headerParser, ok := p.headerParsers[fieldName]; ok {
		// We have a registered parser for this header type - use it.
		headers, err = headerParser(fieldName, fieldText)
	} else {
		// We have no registered parser for this header type,
		// so we encapsulate the header data in a GenericHeader struct.
		log.Debug("Parser %p has no parser for header type %s", p, fieldName)
		header := base.GenericHeader{fieldName, fieldText}
		headers = []base.SipHeader{&header}
	}

	return
}

// Poll for input from one end of the channel and add it to the buffer.
// Also poll sending buffered signals out over the output chan.
func (c *ElasticChan) manage() {
	for {
		if len(c.buffer) > 0 {
			// The buffer has something in it, so try to send as well as
			// receive.
			// (Receive first in order to minimize blocked Send() calls).
			select {
			case in, ok := <-c.In:
				if !ok {
					log.Debug("Chan %p will dispose", c)
					break
				}
				log.Debug("Chan %p gets '%v'", c, in)
				c.buffer = append(c.buffer, in)
			case c.Out <- c.buffer[0]:
				log.Debug("Chan %p sends '%v'", c, c.buffer[0])
				c.buffer = c.buffer[1:]
			}
		} else {
			// The buffer is empty, so there's nothing to send.
			// Just wait to receive.
			in, ok := <-c.In
			if !ok {
				log.Debug("Chan %p will dispose", c)
				break
			}
			log.Debug("Chan %p gets '%v'", c, in)
			c.buffer = append(c.buffer, in)
		}
	}

	c.dispose()
}

func (c *ElasticChan) dispose() {
	log.Debug("Chan %p disposing...", c)
	for len(c.buffer) > 0 {
		c.Out <- c.buffer[0]
		c.buffer = c.buffer[1:]
	}
	log.Debug("Chan %p disposed", c)
}

func (t *connTable) handleUpdate(update *connUpdate) {
	log.Debug("Update received in connTable %p for address %s", t, update.addr)
	watcher, entry_exists := t.conns[update.addr]
	if !entry_exists {
		log.Debug("No connection watcher registered for %s; spawn one", update.addr)
		watcher = &connWatcher{update.addr, update.conn, timing.NewTimer(c_SOCKET_EXPIRY), timing.Now().Add(c_SOCKET_EXPIRY), t.expiries, make(chan bool)}
		t.conns[update.addr] = watcher
		go watcher.loop()
	}

	watcher.Update(update.conn)
}

// Block until the buffer contains at least one CRLF-terminated line.
// Return the line, excluding the terminal CRLF, and delete it from the buffer.
// Returns an error if the parserbuffer has been stopped.
func (pb *parserBuffer) NextLine() (response string, err error) {
	var buffer bytes.Buffer
	var data string
	var b byte

	// There has to be a better way!
	for {
		data, err = pb.reader.ReadString('\r')
		if err != nil {
			return
		}

		buffer.WriteString(data)

		b, err = pb.reader.ReadByte()
		if err != nil {
			return
		}

		buffer.WriteByte(b)
		if b == '\n' {
			response = buffer.String()
			response = response[:len(response)-2]
			log.Debug("Parser buffer returns line '%s'", response)
			return
		}
	}
}

// Create Client transaction.
func (mng *Manager) Send(r *base.Request, dest string) *ClientTransaction {
	log.Debug("Sending to %v: %v", dest, r.String())

	tx := &ClientTransaction{}
	tx.origin = r
	tx.dest = dest
	tx.transport = mng.transport
	tx.tm = mng

	tx.initFSM()

	tx.tu = make(chan *base.Response, 3)
	tx.tu_err = make(chan error, 1)

	tx.timer_a_time = T1
	tx.timer_a = time.AfterFunc(tx.timer_a_time, func() {
		tx.fsm.Spin(client_input_timer_a)
	})
	tx.timer_b = time.AfterFunc(64*T1, func() {
		tx.fsm.Spin(client_input_timer_b)
	})

	// Timer D is set to 32 seconds for unreliable transports, and 0 seconds otherwise.
	tx.timer_d_time = 32 * time.Second

	err := mng.transport.Send(dest, r)
	if err != nil {
		log.Warn("Failed to send message: %s", err.Error())
		tx.fsm.Spin(client_input_transport_err)
	}

	mng.putTx(tx)

	return tx
}

// Management loop for the connTable.
// Handles notifications of connection updates, expiries of connections, and
// the termination of the routine.
func (t *connTable) manage() {
	for {
		select {
		case request := <-t.connRequests:
			watcher := t.conns[request.addr]
			if watcher != nil {
				request.responseChan <- watcher.conn
			} else {
				request.responseChan <- nil
			}
		case update := <-t.updates:
			t.handleUpdate(update)
		case addr := <-t.expiries:
			if t.conns[addr].expiryTime.Before(time.Now()) {
				log.Debug("Conntable %p notified that the watcher for address %s has expired. Remove it.", t, addr)
				t.conns[addr].stop <- true
				t.conns[addr].conn.Close()
				delete(t.conns, addr)
			} else {
				// Due to a race condition, the socket has been updated since this expiry happened.
				// Ignore the expiry since we already have a new socket for this address.
				log.Warn("Ignored spurious expiry for address %s in conntable %p", t, addr)
			}
		case <-t.stop:
			log.Info("Conntable %p stopped")
			t.stopped = true
			for _, watcher := range t.conns {
				watcher.stop <- true
				watcher.conn.Close()
			}
			break
		}
	}
}

// connWatcher main loop. Waits for the connection to expire, and notifies the connTable
// when it does.
func (watcher *connWatcher) loop() {
	// We expect to close off connections explicitly, but let's be safe and clean up
	// if we close unexpectedly.
	defer func(c *connection) {
		if c != nil {
			c.Close()
		}
	}(watcher.conn)

	for {
		select {
		case <-watcher.timer.C():
			// Socket expiry timer has run out. Close the connection.
			log.Debug("Socket %p (%s) inactive for too long; close it", watcher.conn, watcher.addr)
			watcher.expiry <- watcher.addr

		case stop := <-watcher.stop:
			// We've received a termination signal; stop managing this connection.
			if stop {
				log.Info("Connection watcher for address %s got the kill signal. Stopping.", watcher.addr)
				watcher.timer.Stop()
				break
			}
		}
	}
}

func (caller *endpoint) Invite(callee *endpoint) error {
	// Starting a dialog.
	callid := "thisisacall" + string(caller.dialogIx)
	tagString := fmt.Sprintf("tag.%s.%s", caller.username, caller.host)
	branch := "z9hG4bK.callbranch.INVITE"
	caller.dialog.callId = callid
	caller.dialog.from_tag = base.String{tagString}
	caller.dialog.currentTx = txInfo{}
	caller.dialog.currentTx.branch = branch

	invite := base.NewRequest(
		base.INVITE,
		&base.SipUri{
			User: &callee.username,
			Host: callee.host,
		},
		"SIP/2.0",
		[]base.SipHeader{
			Via(caller, branch),
			To(callee, caller.dialog.to_tag),
			From(caller, caller.dialog.from_tag),
			Contact(caller),
			CSeq(caller.dialog.cseq, base.INVITE),
			CallId(callid),
			ContentLength(0),
		},
		"",
	)
	caller.dialog.cseq += 1

	log.Info("Sending: %v", invite.Short())
	tx := caller.tm.Send(invite, fmt.Sprintf("%v:%v", callee.host, callee.port))
	caller.dialog.currentTx.tx = transaction.Transaction(tx)
	for {
		select {
		case r := <-tx.Responses():
			log.Info("Received response: %v", r.Short())
			log.Debug("Full form:\n%v\n", r.String())
			// Get To tag if present.
			tag, ok := r.Headers("To")[0].(*base.ToHeader).Params.Get("tag")
			if ok {
				caller.dialog.to_tag = tag.(base.String)
			}

			switch {
			case r.StatusCode >= 300:
				// Call setup failed.
				return fmt.Errorf("callee sent negative response code %v.", r.StatusCode)
			case r.StatusCode >= 200:
				// Ack 200s manually.
				log.Info("Sending Ack")
				tx.Ack()
				return nil
			}
		case e := <-tx.Errors():
			log.Warn(e.Error())
			return e
		}
	}
}

func (e *endpoint) ServeNonInvite() {
	log.Info("Listening for incoming requests...")
	tx := <-e.tm.Requests()
	r := tx.Origin()
	log.Info("Received request: %v", r.Short())
	log.Debug("Full form:\n%v\n", r.String())

	// Send a 200 OK
	resp := base.NewResponse(
		"SIP/2.0",
		200,
		"OK",
		[]base.SipHeader{},
		"",
	)

	base.CopyHeaders("Via", tx.Origin(), resp)
	base.CopyHeaders("From", tx.Origin(), resp)
	base.CopyHeaders("To", tx.Origin(), resp)
	base.CopyHeaders("Call-Id", tx.Origin(), resp)
	base.CopyHeaders("CSeq", tx.Origin(), resp)
	resp.AddHeader(
		&base.ContactHeader{
			DisplayName: &e.displayName,
			Address: &base.SipUri{
				User: &e.username,
				Host: e.host,
			},
		},
	)

	log.Info("Sending 200 OK")
	<-time.After(1 * time.Second)
	tx.Respond(resp)
}

func (connection *connection) pipeOutput() {
	for {
		select {
		case message, ok := <-connection.parsedMessages:
			if ok {
				log.Debug("Connection %p from %s to %s received message over the wire: %s",
					connection,
					connection.baseConn.RemoteAddr(),
					connection.baseConn.LocalAddr(),
					message.Short())
				connection.output <- message
			} else {
				break
			}
		case err, ok := <-connection.parserErrors:
			if ok {
				// The parser has hit a terminal error. We need to restart it.
				log.Warn("Failed to parse SIP message: %s", err.Error())
				connection.parser = parser.NewParser(connection.parsedMessages,
					connection.parserErrors, connection.isStreamed)
			} else {
				break
			}
		}
	}

	log.Info("Parser stopped in ConnWrapper %v (local addr %s; remote addr %s); stopping listening",
		connection, connection.baseConn.LocalAddr(), connection.baseConn.RemoteAddr())
}

// Push a connection to the connection table, registered under a specific address.
// If it is a new connection, start the socket expiry timer.
// If it is a known connection, restart the timer.
func (t *connTable) Notify(addr string, conn *connection) {
	if t.stopped {
		log.Debug("Ignoring conn notification for address %s after table stop.", addr)
		return
	}

	t.updates <- &connUpdate{addr, conn}
}

// Return an existing open socket for the given address, or nil if no such socket
// exists.
func (t *connTable) GetConn(addr string) *connection {
	responseChan := make(chan *connection)
	t.connRequests <- &connRequest{addr, responseChan}
	conn := <-responseChan

	log.Debug("Query connection for address %s returns %p", conn)
	return conn
}

func (n *notifier) register(l listener) {
	log.Debug("Notifier %p has new listener %p", n, l)
	if n.listeners == nil {
		n.listeners = make(map[listener]bool)
	}
	n.listenerLock.Lock()
	n.listeners[l] = true
	n.listenerLock.Unlock()
}

func (connection *connection) read() {
	buffer := make([]byte, c_BUFSIZE)
	for {
		log.Debug("Connection %p waiting for new data on sock", connection)
		num, err := connection.baseConn.Read(buffer)
		if err != nil {
			// If connections are broken, just let them drop.
			log.Debug("Lost connection to %s on %s",
				connection.baseConn.RemoteAddr().String(),
				connection.baseConn.LocalAddr().String())
			return
		}

		log.Debug("Connection %p received %d bytes", connection, num)
		pkt := append([]byte(nil), buffer[:num]...)
		connection.parser.Write(pkt)
	}
}

func (n *notifier) forward() {
	for msg := range n.inputs {
		deadListeners := make([]chan base.SipMessage, 0)
		n.listenerLock.Lock()
		log.Debug(fmt.Sprintf("Notify %d listeners of message", len(n.listeners)))
		for listener := range n.listeners {
			sent := listener.notify(msg)
			if !sent {
				deadListeners = append(deadListeners, listener)
			}
		}
		for _, deadListener := range deadListeners {
			log.Debug(fmt.Sprintf("Expiring listener %#v", deadListener))
			delete(n.listeners, deadListener)
		}
		n.listenerLock.Unlock()
	}
}

// Deletes a transaction from the transaction store.
// Should only be called inside the storage handling goroutine to ensure concurrency safety.
func (mng *Manager) delTx(t Transaction) {
	key, ok := mng.makeKey(t.Origin())
	if !ok {
		log.Debug("Could not build lookup key for transaction. Is it missing a branch parameter?")
	}

	mng.txLock.Lock()
	delete(mng.txs, key)
	mng.txLock.Unlock()
}

func (tcp *Tcp) serve(listeningPoint *net.TCPListener) {
	log.Info("Begin serving TCP on address " + listeningPoint.Addr().String())

	for {
		baseConn, err := listeningPoint.Accept()
		if err != nil {
			log.Severe("Failed to accept TCP conn on address " + listeningPoint.Addr().String() + "; " + err.Error())
			continue
		}

		conn := NewConn(baseConn, tcp.output)
		log.Debug("Accepted new TCP conn %p from %s on address %s", &conn, conn.baseConn.RemoteAddr(), conn.baseConn.LocalAddr())
		tcp.connTable.Notify(baseConn.RemoteAddr().String(), conn)
	}
}

// Block until the buffer contains at least n characters.
// Return precisely those n characters, then delete them from the buffer.
func (pb *parserBuffer) NextChunk(n int) (response string, err error) {
	var data []byte = make([]byte, n)

	var read int
	for total := 0; total < n; {
		read, err = pb.reader.Read(data[total:])
		total += read
		if err != nil {
			return
		}
	}

	response = string(data)
	log.Debug("Parser buffer returns chunk '%s'", response)
	return
}

func (connection *connection) Send(msg base.SipMessage) (err error) {
	log.Debug("Sending message over connection %p: %s", connection, msg.Short())
	msgData := msg.String()
	n, err := connection.baseConn.Write([]byte(msgData))

	if err != nil {
		return
	}

	if n != len(msgData) {
		return fmt.Errorf("not all data was sent when dispatching '%s' to %s",
			msg.Short(), connection.baseConn.RemoteAddr())
	}

	return
}