// Copyright (c) 2012-2014 Jeremy Latt
// Copyright (c) 2014-2015 Edmund Huber
// Copyright (c) 2016-2017 Daniel Oaks <daniel@danieloaks.net>
// released under the MIT license

package irc

import (
	"fmt"
	"net"
	"runtime/debug"
	"strconv"
	"strings"
	"sync"
	"sync/atomic"
	"time"

	"github.com/goshuirc/irc-go/ircfmt"
	"github.com/goshuirc/irc-go/ircmsg"
	ident "github.com/oragono/go-ident"
	"github.com/oragono/oragono/irc/caps"
	"github.com/oragono/oragono/irc/connection_limits"
	"github.com/oragono/oragono/irc/history"
	"github.com/oragono/oragono/irc/modes"
	"github.com/oragono/oragono/irc/sno"
	"github.com/oragono/oragono/irc/utils"
)

const (
	// IdentTimeoutSeconds is how many seconds before our ident (username) check times out.
	IdentTimeoutSeconds  = 1.5
	IRCv3TimestampFormat = "2006-01-02T15:04:05.000Z"
)

// ResumeDetails is a place to stash data at various stages of
// the resume process: when handling the RESUME command itself,
// when completing the registration, and when rejoining channels.
type ResumeDetails struct {
	OldClient         *Client
	PresentedToken    string
	Timestamp         time.Time
	ResumedAt         time.Time
	Channels          []string
	HistoryIncomplete bool
}

// Client is an IRC client.
type Client struct {
	account            string
	accountName        string // display name of the account: uncasefolded, '*' if not logged in
	atime              time.Time
	awayMessage        string
	capabilities       caps.Set
	capState           caps.State
	capVersion         caps.Version
	certfp             string
	channels           ChannelSet
	ctime              time.Time
	exitedSnomaskSent  bool
	fakelag            Fakelag
	flags              modes.ModeSet
	hasQuit            bool
	hops               int
	hostname           string
	idletimer          IdleTimer
	invitedTo          map[string]bool
	isDestroyed        bool
	isTor              bool
	isQuitting         bool
	languages          []string
	loginThrottle      connection_limits.GenericThrottle
	maxlenRest         uint32
	nick               string
	nickCasefolded     string
	nickMaskCasefolded string
	nickMaskString     string // cache for nickmask string since it's used with lots of replies
	nickTimer          NickTimer
	oper               *Oper
	preregNick         string
	proxiedIP          net.IP // actual remote IP if using the PROXY protocol
	quitMessage        string
	rawHostname        string
	realname           string
	realIP             net.IP
	registered         bool
	resumeDetails      *ResumeDetails
	resumeID           string
	saslInProgress     bool
	saslMechanism      string
	saslValue          string
	sentPassCommand    bool
	server             *Server
	skeleton           string
	socket             *Socket
	stateMutex         sync.RWMutex // tier 1
	username           string
	vhost              string
	history            *history.Buffer
}

// WhoWas is the subset of client details needed to answer a WHOWAS query
type WhoWas struct {
	nick           string
	nickCasefolded string
	username       string
	hostname       string
	realname       string
}

// ClientDetails is a standard set of details about a client
type ClientDetails struct {
	WhoWas

	nickMask           string
	nickMaskCasefolded string
	account            string
	accountName        string
}

// NewClient sets up a new client and runs its goroutine.
func RunNewClient(server *Server, conn clientConn) {
	now := time.Now()
	config := server.Config()
	fullLineLenLimit := ircmsg.MaxlenTagsFromClient + config.Limits.LineLen.Rest
	// give them 1k of grace over the limit:
	socket := NewSocket(conn.Conn, fullLineLenLimit+1024, config.Server.MaxSendQBytes)
	client := &Client{
		atime:      now,
		capState:   caps.NoneState,
		capVersion: caps.Cap301,
		channels:   make(ChannelSet),
		ctime:      now,
		isTor:      conn.IsTor,
		languages:  server.Languages().Default(),
		loginThrottle: connection_limits.GenericThrottle{
			Duration: config.Accounts.LoginThrottling.Duration,
			Limit:    config.Accounts.LoginThrottling.MaxAttempts,
		},
		server:         server,
		socket:         socket,
		accountName:    "*",
		nick:           "*", // * is used until actual nick is given
		nickCasefolded: "*",
		nickMaskString: "*", // * is used until actual nick is given
		history:        history.NewHistoryBuffer(config.History.ClientLength),
	}

	client.recomputeMaxlens()

	if conn.IsTLS {
		client.SetMode(modes.TLS, true)
		// error is not useful to us here anyways so we can ignore it
		client.certfp, _ = client.socket.CertFP()
	}

	if conn.IsTor {
		client.SetMode(modes.TLS, true)
		client.realIP = utils.IPv4LoopbackAddress
		client.rawHostname = config.Server.TorListeners.Vhost
	} else {
		remoteAddr := conn.Conn.RemoteAddr()
		client.realIP = utils.AddrToIP(remoteAddr)
		// Set the hostname for this client
		// (may be overridden by a later PROXY command from stunnel)
		client.rawHostname = utils.LookupHostname(client.realIP.String())
		if config.Server.CheckIdent && !utils.AddrIsUnix(remoteAddr) {
			client.doIdentLookup(conn.Conn)
		}
	}

	client.run()
}

func (client *Client) doIdentLookup(conn net.Conn) {
	_, serverPortString, err := net.SplitHostPort(conn.LocalAddr().String())
	if err != nil {
		client.server.logger.Error("internal", "bad server address", err.Error())
		return
	}
	serverPort, _ := strconv.Atoi(serverPortString)
	clientHost, clientPortString, err := net.SplitHostPort(conn.RemoteAddr().String())
	if err != nil {
		client.server.logger.Error("internal", "bad client address", err.Error())
		return
	}
	clientPort, _ := strconv.Atoi(clientPortString)

	client.Notice(client.t("*** Looking up your username"))
	resp, err := ident.Query(clientHost, serverPort, clientPort, IdentTimeoutSeconds)
	if err == nil {
		err := client.SetNames(resp.Identifier, "", true)
		if err == nil {
			client.Notice(client.t("*** Found your username"))
			// we don't need to updateNickMask here since nickMask is not used for anything yet
		} else {
			client.Notice(client.t("*** Got a malformed username, ignoring"))
		}
	} else {
		client.Notice(client.t("*** Could not find your username"))
	}
}

func (client *Client) isAuthorized(config *Config) bool {
	saslSent := client.account != ""
	// PASS requirement
	if (config.Server.passwordBytes != nil) && !client.sentPassCommand && !(config.Accounts.SkipServerPassword && saslSent) {
		return false
	}
	// Tor connections may be required to authenticate with SASL
	if client.isTor && config.Server.TorListeners.RequireSasl && !saslSent {
		return false
	}
	// finally, enforce require-sasl
	return !config.Accounts.RequireSasl.Enabled || saslSent || utils.IPInNets(client.IP(), config.Accounts.RequireSasl.exemptedNets)
}

func (client *Client) resetFakelag() {
	var flc FakelagConfig = client.server.Config().Fakelag
	flc.Enabled = flc.Enabled && !client.HasRoleCapabs("nofakelag")
	client.fakelag.Initialize(flc)
}

// IP returns the IP address of this client.
func (client *Client) IP() net.IP {
	client.stateMutex.RLock()
	defer client.stateMutex.RUnlock()

	if client.proxiedIP != nil {
		return client.proxiedIP
	}
	return client.realIP
}

// IPString returns the IP address of this client as a string.
func (client *Client) IPString() string {
	ip := client.IP().String()
	if 0 < len(ip) && ip[0] == ':' {
		ip = "0" + ip
	}
	return ip
}

//
// command goroutine
//

func (client *Client) recomputeMaxlens() int {
	maxlenRest := 512
	if client.capabilities.Has(caps.MaxLine) {
		maxlenRest = client.server.Limits().LineLen.Rest
	}

	atomic.StoreUint32(&client.maxlenRest, uint32(maxlenRest))

	return maxlenRest
}

// allow these negotiated length limits to be read without locks; this is a convenience
// so that Client.Send doesn't have to acquire any Client locks
func (client *Client) MaxlenRest() int {
	return int(atomic.LoadUint32(&client.maxlenRest))
}

func (client *Client) run() {
	var err error
	var isExiting bool
	var line string
	var msg ircmsg.IrcMessage

	defer func() {
		if r := recover(); r != nil {
			client.server.logger.Error("internal",
				fmt.Sprintf("Client caused panic: %v\n%s", r, debug.Stack()))
			if client.server.RecoverFromErrors() {
				client.server.logger.Error("internal", "Disconnecting client and attempting to recover")
			} else {
				panic(r)
			}
		}
		// ensure client connection gets closed
		client.destroy(false)
	}()

	client.idletimer.Initialize(client)

	client.nickTimer.Initialize(client)

	client.resetFakelag()

	firstLine := true

	for {
		maxlenRest := client.recomputeMaxlens()

		line, err = client.socket.Read()
		if err != nil {
			quitMessage := "connection closed"
			if err == errReadQ {
				quitMessage = "readQ exceeded"
			}
			client.Quit(quitMessage)
			break
		}

		if client.server.logger.IsLoggingRawIO() {
			client.server.logger.Debug("userinput", client.nick, "<- ", line)
		}

		// special-cased handling of PROXY protocol, see `handleProxyCommand` for details:
		if firstLine {
			firstLine = false
			if strings.HasPrefix(line, "PROXY") {
				err = handleProxyCommand(client.server, client, line)
				if err != nil {
					break
				} else {
					continue
				}
			}
		}

		msg, err = ircmsg.ParseLineStrict(line, true, maxlenRest)
		if err == ircmsg.ErrorLineIsEmpty {
			continue
		} else if err == ircmsg.ErrorLineTooLong {
			client.Send(nil, client.server.name, ERR_INPUTTOOLONG, client.nick, client.t("Input line too long"))
			continue
		} else if err != nil {
			client.Quit(client.t("Received malformed line"))
			break
		}

		cmd, exists := Commands[msg.Command]
		if !exists {
			if len(msg.Command) > 0 {
				client.Send(nil, client.server.name, ERR_UNKNOWNCOMMAND, client.nick, msg.Command, client.t("Unknown command"))
			} else {
				client.Send(nil, client.server.name, ERR_UNKNOWNCOMMAND, client.nick, "lastcmd", client.t("No command given"))
			}
			continue
		}

		isExiting = cmd.Run(client.server, client, msg)
		if isExiting || client.isQuitting {
			break
		}
	}
}

//
// idle, quit, timers and timeouts
//

// Active updates when the client was last 'active' (i.e. the user should be sitting in front of their client).
func (client *Client) Active() {
	client.stateMutex.Lock()
	defer client.stateMutex.Unlock()
	client.atime = time.Now()
}

// Ping sends the client a PING message.
func (client *Client) Ping() {
	client.Send(nil, "", "PING", client.nick)

}

// tryResume tries to resume if the client asked us to.
func (client *Client) tryResume() (success bool) {
	server := client.server
	config := server.Config()

	defer func() {
		if !success {
			client.resumeDetails = nil
		}
	}()

	timestamp := client.resumeDetails.Timestamp
	var timestampString string
	if !timestamp.IsZero() {
		timestampString = timestamp.UTC().Format(IRCv3TimestampFormat)
	}

	oldClient := server.resumeManager.VerifyToken(client.resumeDetails.PresentedToken)
	if oldClient == nil {
		client.Send(nil, server.name, "RESUME", "ERR", client.t("Cannot resume connection, token is not valid"))
		return
	}
	oldNick := oldClient.Nick()
	oldNickmask := oldClient.NickMaskString()

	resumeAllowed := config.Server.AllowPlaintextResume || (oldClient.HasMode(modes.TLS) && client.HasMode(modes.TLS))
	if !resumeAllowed {
		client.Send(nil, server.name, "RESUME", "ERR", client.t("Cannot resume connection, old and new clients must have TLS"))
		return
	}

	if oldClient.isTor != client.isTor {
		client.Send(nil, server.name, "RESUME", "ERR", client.t("Cannot resume connection from Tor to non-Tor or vice versa"))
		return
	}

	err := server.clients.Resume(client, oldClient)
	if err != nil {
		client.Send(nil, server.name, "RESUME", "ERR", client.t("Cannot resume connection"))
		return
	}

	success = true

	// this is a bit racey
	client.resumeDetails.ResumedAt = time.Now()

	client.nickTimer.Touch()

	// resume successful, proceed to copy client state (nickname, flags, etc.)
	// after this, the server thinks that `newClient` owns the nickname

	client.resumeDetails.OldClient = oldClient

	// transfer monitor stuff
	server.monitorManager.Resume(client, oldClient)

	// record the names, not the pointers, of the channels,
	// to avoid dumb annoying race conditions
	channels := oldClient.Channels()
	client.resumeDetails.Channels = make([]string, len(channels))
	for i, channel := range channels {
		client.resumeDetails.Channels[i] = channel.Name()
	}

	username := client.Username()
	hostname := client.Hostname()

	friends := make(ClientSet)
	oldestLostMessage := time.Now()

	// work out how much time, if any, is not covered by history buffers
	for _, channel := range channels {
		for _, member := range channel.Members() {
			friends.Add(member)
			lastDiscarded := channel.history.LastDiscarded()
			if lastDiscarded.Before(oldestLostMessage) {
				oldestLostMessage = lastDiscarded
			}
		}
	}
	privmsgMatcher := func(item history.Item) bool {
		return item.Type == history.Privmsg || item.Type == history.Notice
	}
	privmsgHistory := oldClient.history.Match(privmsgMatcher, false, 0)
	lastDiscarded := oldClient.history.LastDiscarded()
	if lastDiscarded.Before(oldestLostMessage) {
		oldestLostMessage = lastDiscarded
	}
	for _, item := range privmsgHistory {
		// TODO this is the nickmask, fix that
		sender := server.clients.Get(item.Nick)
		if sender != nil {
			friends.Add(sender)
		}
	}

	gap := lastDiscarded.Sub(timestamp)
	client.resumeDetails.HistoryIncomplete = gap > 0
	gapSeconds := int(gap.Seconds()) + 1 // round up to avoid confusion

	// send quit/resume messages to friends
	for friend := range friends {
		if friend.capabilities.Has(caps.Resume) {
			if timestamp.IsZero() {
				friend.Send(nil, oldNickmask, "RESUMED", username, hostname)
			} else {
				friend.Send(nil, oldNickmask, "RESUMED", username, hostname, timestampString)
			}
		} else {
			if client.resumeDetails.HistoryIncomplete {
				friend.Send(nil, oldNickmask, "QUIT", fmt.Sprintf(friend.t("Client reconnected (up to %d seconds of history lost)"), gapSeconds))
			} else {
				friend.Send(nil, oldNickmask, "QUIT", fmt.Sprintf(friend.t("Client reconnected")))
			}
		}
	}

	if client.resumeDetails.HistoryIncomplete {
		client.Send(nil, client.server.name, "RESUME", "WARN", fmt.Sprintf(client.t("Resume may have lost up to %d seconds of history"), gapSeconds))
	}

	client.Send(nil, client.server.name, "RESUME", "SUCCESS", oldNick)

	// after we send the rest of the registration burst, we'll try rejoining channels
	return
}

func (client *Client) tryResumeChannels() {
	details := client.resumeDetails

	channels := make([]*Channel, len(details.Channels))
	for _, name := range details.Channels {
		channel := client.server.channels.Get(name)
		if channel == nil {
			continue
		}
		channel.Resume(client, details.OldClient, details.Timestamp)
		channels = append(channels, channel)
	}

	// replay direct PRIVSMG history
	if !details.Timestamp.IsZero() {
		now := time.Now()
		items, complete := client.history.Between(details.Timestamp, now, false, 0)
		rb := NewResponseBuffer(client)
		client.replayPrivmsgHistory(rb, items, complete)
		rb.Send(true)
	}

	details.OldClient.destroy(true)
}

func (client *Client) replayPrivmsgHistory(rb *ResponseBuffer, items []history.Item, complete bool) {
	nick := client.Nick()
	serverTime := client.capabilities.Has(caps.ServerTime)
	for _, item := range items {
		var command string
		switch item.Type {
		case history.Privmsg:
			command = "PRIVMSG"
		case history.Notice:
			command = "NOTICE"
		default:
			continue
		}
		var tags map[string]string
		if serverTime {
			tags = map[string]string{"time": item.Time.Format(IRCv3TimestampFormat)}
		}
		rb.AddSplitMessageFromClient(item.Nick, item.AccountName, tags, command, nick, item.Message)
	}
	if !complete {
		rb.Add(nil, "HistServ", "NOTICE", nick, client.t("Some additional message history may have been lost"))
	}
}

// copy applicable state from oldClient to client as part of a resume
func (client *Client) copyResumeData(oldClient *Client) {
	oldClient.stateMutex.RLock()
	history := oldClient.history
	nick := oldClient.nick
	nickCasefolded := oldClient.nickCasefolded
	vhost := oldClient.vhost
	account := oldClient.account
	accountName := oldClient.accountName
	skeleton := oldClient.skeleton
	oldClient.stateMutex.RUnlock()

	// copy all flags, *except* TLS (in the case that the admins enabled
	// resume over plaintext)
	hasTLS := client.flags.HasMode(modes.TLS)
	temp := modes.NewModeSet()
	temp.Copy(&oldClient.flags)
	temp.SetMode(modes.TLS, hasTLS)
	client.flags.Copy(temp)

	client.stateMutex.Lock()
	defer client.stateMutex.Unlock()

	// reuse the old client's history buffer
	client.history = history
	// copy other data
	client.nick = nick
	client.nickCasefolded = nickCasefolded
	client.vhost = vhost
	client.account = account
	client.accountName = accountName
	client.skeleton = skeleton
	client.updateNickMaskNoMutex()
}

// IdleTime returns how long this client's been idle.
func (client *Client) IdleTime() time.Duration {
	client.stateMutex.RLock()
	defer client.stateMutex.RUnlock()
	return time.Since(client.atime)
}

// SignonTime returns this client's signon time as a unix timestamp.
func (client *Client) SignonTime() int64 {
	return client.ctime.Unix()
}

// IdleSeconds returns the number of seconds this client's been idle.
func (client *Client) IdleSeconds() uint64 {
	return uint64(client.IdleTime().Seconds())
}

// HasNick returns true if the client's nickname is set (used in registration).
func (client *Client) HasNick() bool {
	client.stateMutex.RLock()
	defer client.stateMutex.RUnlock()
	return client.nick != "" && client.nick != "*"
}

// HasUsername returns true if the client's username is set (used in registration).
func (client *Client) HasUsername() bool {
	client.stateMutex.RLock()
	defer client.stateMutex.RUnlock()
	return client.username != "" && client.username != "*"
}

// SetNames sets the client's ident and realname.
func (client *Client) SetNames(username, realname string, fromIdent bool) error {
	limit := client.server.Config().Limits.IdentLen
	if !fromIdent {
		limit -= 1 // leave room for the prepended ~
	}
	if limit < len(username) {
		username = username[:limit]
	}

	if !isIdent(username) {
		return errInvalidUsername
	}

	if !fromIdent {
		username = "~" + username
	}

	client.stateMutex.Lock()
	defer client.stateMutex.Unlock()

	if client.username == "" {
		client.username = username
	}

	if client.realname == "" {
		client.realname = realname
	}

	return nil
}

// HasRoleCapabs returns true if client has the given (role) capabilities.
func (client *Client) HasRoleCapabs(capabs ...string) bool {
	oper := client.Oper()
	if oper == nil {
		return false
	}

	for _, capab := range capabs {
		if !oper.Class.Capabilities[capab] {
			return false
		}
	}

	return true
}

// ModeString returns the mode string for this client.
func (client *Client) ModeString() (str string) {
	return "+" + client.flags.String()
}

// Friends refers to clients that share a channel with this client.
func (client *Client) Friends(capabs ...caps.Capability) ClientSet {
	friends := make(ClientSet)

	// make sure that I have the right caps
	hasCaps := true
	for _, capab := range capabs {
		if !client.capabilities.Has(capab) {
			hasCaps = false
			break
		}
	}
	if hasCaps {
		friends.Add(client)
	}

	for _, channel := range client.Channels() {
		for _, member := range channel.Members() {
			// make sure they have all the required caps
			hasCaps = true
			for _, capab := range capabs {
				if !member.capabilities.Has(capab) {
					hasCaps = false
					break
				}
			}
			if hasCaps {
				friends.Add(member)
			}
		}
	}
	return friends
}

func (client *Client) SetOper(oper *Oper) {
	client.stateMutex.Lock()
	defer client.stateMutex.Unlock()
	client.oper = oper
	// operators typically get a vhost, update the nickmask
	client.updateNickMaskNoMutex()
}

// XXX: CHGHOST requires prefix nickmask to have original hostname,
// this is annoying to do correctly
func (client *Client) sendChghost(oldNickMask string, vhost string) {
	username := client.Username()
	for fClient := range client.Friends(caps.ChgHost) {
		fClient.sendFromClientInternal(false, time.Time{}, "", oldNickMask, client.AccountName(), nil, "CHGHOST", username, vhost)
	}
}

// choose the correct vhost to display
func (client *Client) getVHostNoMutex() string {
	// hostserv vhost OR operclass vhost OR nothing (i.e., normal rdns hostmask)
	if client.vhost != "" {
		return client.vhost
	} else if client.oper != nil {
		return client.oper.Vhost
	} else {
		return ""
	}
}

// SetVHost updates the client's hostserv-based vhost
func (client *Client) SetVHost(vhost string) (updated bool) {
	client.stateMutex.Lock()
	defer client.stateMutex.Unlock()
	updated = (client.vhost != vhost)
	client.vhost = vhost
	if updated {
		client.updateNickMaskNoMutex()
	}
	return
}

// updateNick updates `nick` and `nickCasefolded`.
func (client *Client) updateNick(nick, nickCasefolded, skeleton string) {
	client.stateMutex.Lock()
	defer client.stateMutex.Unlock()
	client.nick = nick
	client.nickCasefolded = nickCasefolded
	client.skeleton = skeleton
	client.updateNickMaskNoMutex()
}

// updateNickMaskNoMutex updates the casefolded nickname and nickmask, not acquiring any mutexes.
func (client *Client) updateNickMaskNoMutex() {
	client.hostname = client.getVHostNoMutex()
	if client.hostname == "" {
		client.hostname = client.rawHostname
	}

	cfhostname, err := Casefold(client.hostname)
	if err != nil {
		client.server.logger.Error("internal", "hostname couldn't be casefolded", client.hostname, err.Error())
		cfhostname = client.hostname // YOLO
	}

	client.nickMaskString = fmt.Sprintf("%s!%s@%s", client.nick, client.username, client.hostname)
	client.nickMaskCasefolded = fmt.Sprintf("%s!%s@%s", client.nickCasefolded, strings.ToLower(client.username), cfhostname)
}

// AllNickmasks returns all the possible nickmasks for the client.
func (client *Client) AllNickmasks() (masks []string) {
	client.stateMutex.RLock()
	nick := client.nickCasefolded
	username := client.username
	rawHostname := client.rawHostname
	vhost := client.getVHostNoMutex()
	client.stateMutex.RUnlock()
	username = strings.ToLower(username)

	if len(vhost) > 0 {
		cfvhost, err := Casefold(vhost)
		if err == nil {
			masks = append(masks, fmt.Sprintf("%s!%s@%s", nick, username, cfvhost))
		}
	}

	var rawhostmask string
	cfrawhost, err := Casefold(rawHostname)
	if err == nil {
		rawhostmask = fmt.Sprintf("%s!%s@%s", nick, username, cfrawhost)
		masks = append(masks, rawhostmask)
	}

	ipmask := fmt.Sprintf("%s!%s@%s", nick, username, client.IPString())
	if ipmask != rawhostmask {
		masks = append(masks, ipmask)
	}

	return
}

// LoggedIntoAccount returns true if this client is logged into an account.
func (client *Client) LoggedIntoAccount() bool {
	return client.Account() != ""
}

// RplISupport outputs our ISUPPORT lines to the client. This is used on connection and in VERSION responses.
func (client *Client) RplISupport(rb *ResponseBuffer) {
	translatedISupport := client.t("are supported by this server")
	nick := client.Nick()
	for _, cachedTokenLine := range client.server.ISupport().CachedReply {
		length := len(cachedTokenLine) + 2
		tokenline := make([]string, length)
		tokenline[0] = nick
		copy(tokenline[1:], cachedTokenLine)
		tokenline[length-1] = translatedISupport
		rb.Add(nil, client.server.name, RPL_ISUPPORT, tokenline...)
	}
}

// Quit sets the given quit message for the client.
// (You must ensure separately that destroy() is called, e.g., by returning `true` from
// the command handler or calling it yourself.)
func (client *Client) Quit(message string) {
	client.stateMutex.Lock()
	alreadyQuit := client.isQuitting
	if !alreadyQuit {
		client.isQuitting = true
		client.quitMessage = message
	}
	registered := client.registered
	prefix := client.nickMaskString
	client.stateMutex.Unlock()

	if alreadyQuit {
		return
	}

	var finalData []byte
	// #364: don't send QUIT lines to unregistered clients
	if registered {
		quitMsg := ircmsg.MakeMessage(nil, prefix, "QUIT", message)
		finalData, _ = quitMsg.LineBytesStrict(false, 512)
	}

	errorMsg := ircmsg.MakeMessage(nil, "", "ERROR", message)
	errorMsgBytes, _ := errorMsg.LineBytesStrict(false, 512)
	finalData = append(finalData, errorMsgBytes...)

	client.socket.SetFinalData(finalData)
}

// destroy gets rid of a client, removes them from server lists etc.
func (client *Client) destroy(beingResumed bool) {
	// allow destroy() to execute at most once
	client.stateMutex.Lock()
	isDestroyed := client.isDestroyed
	client.isDestroyed = true
	quitMessage := client.quitMessage
	nickMaskString := client.nickMaskString
	accountName := client.accountName
	client.stateMutex.Unlock()

	if isDestroyed {
		return
	}

	// see #235: deduplicating the list of PART recipients uses (comparatively speaking)
	// a lot of RAM, so limit concurrency to avoid thrashing
	client.server.semaphores.ClientDestroy.Acquire()
	defer client.server.semaphores.ClientDestroy.Release()

	if beingResumed {
		client.server.logger.Debug("quit", fmt.Sprintf("%s is being resumed", client.nick))
	} else {
		client.server.logger.Debug("quit", fmt.Sprintf("%s is no longer on the server", client.nick))
	}

	// send quit/error message to client if they haven't been sent already
	client.Quit("Connection closed")

	if !beingResumed {
		client.server.whoWas.Append(client.WhoWas())
	}

	// remove from connection limits
	if client.isTor {
		client.server.torLimiter.RemoveClient()
	} else {
		client.server.connectionLimiter.RemoveClient(client.IP())
	}

	client.server.resumeManager.Delete(client)

	// alert monitors
	client.server.monitorManager.AlertAbout(client, false)
	// clean up monitor state
	client.server.monitorManager.RemoveAll(client)

	// clean up channels
	friends := make(ClientSet)
	for _, channel := range client.Channels() {
		if !beingResumed {
			channel.Quit(client)
			channel.history.Add(history.Item{
				Type:        history.Quit,
				Nick:        nickMaskString,
				AccountName: accountName,
				Message:     utils.MakeSplitMessage(quitMessage, true),
			})
		}
		for _, member := range channel.Members() {
			friends.Add(member)
		}
	}
	friends.Remove(client)

	// clean up server
	if !beingResumed {
		client.server.clients.Remove(client)
	}

	// clean up self
	client.idletimer.Stop()
	client.nickTimer.Stop()

	client.server.accounts.Logout(client)

	client.socket.Close()

	// send quit messages to friends
	if !beingResumed {
		if client.Registered() {
			client.server.stats.ChangeTotal(-1)
		}
		if client.HasMode(modes.Invisible) {
			client.server.stats.ChangeInvisible(-1)
		}
		if client.HasMode(modes.Operator) || client.HasMode(modes.LocalOperator) {
			client.server.stats.ChangeOperators(-1)
		}

		for friend := range friends {
			if quitMessage == "" {
				quitMessage = "Exited"
			}
			friend.Send(nil, client.nickMaskString, "QUIT", quitMessage)
		}
	}
	if !client.exitedSnomaskSent {
		if beingResumed {
			client.server.snomasks.Send(sno.LocalQuits, fmt.Sprintf(ircfmt.Unescape("%s$r is resuming their connection, old client has been destroyed"), client.nick))
		} else {
			client.server.snomasks.Send(sno.LocalQuits, fmt.Sprintf(ircfmt.Unescape("%s$r exited the network"), client.nick))
		}
	}
}

// SendSplitMsgFromClient sends an IRC PRIVMSG/NOTICE coming from a specific client.
// Adds account-tag to the line as well.
func (client *Client) SendSplitMsgFromClient(from *Client, tags map[string]string, command, target string, message utils.SplitMessage) {
	client.sendSplitMsgFromClientInternal(false, time.Time{}, from.NickMaskString(), from.AccountName(), tags, command, target, message)
}

func (client *Client) sendSplitMsgFromClientInternal(blocking bool, serverTime time.Time, nickmask, accountName string, tags map[string]string, command, target string, message utils.SplitMessage) {
	if client.capabilities.Has(caps.MaxLine) || message.Wrapped == nil {
		client.sendFromClientInternal(blocking, serverTime, message.Msgid, nickmask, accountName, tags, command, target, message.Message)
	} else {
		for _, messagePair := range message.Wrapped {
			client.sendFromClientInternal(blocking, serverTime, messagePair.Msgid, nickmask, accountName, tags, command, target, messagePair.Message)
		}
	}
}

// SendFromClient sends an IRC line coming from a specific client.
// Adds account-tag to the line as well.
func (client *Client) SendFromClient(msgid string, from *Client, tags map[string]string, command string, params ...string) error {
	return client.sendFromClientInternal(false, time.Time{}, msgid, from.NickMaskString(), from.AccountName(), tags, command, params...)
}

// this is SendFromClient, but directly exposing nickmask and accountName,
// for things like history replay and CHGHOST where they no longer (necessarily)
// correspond to the current state of a client
func (client *Client) sendFromClientInternal(blocking bool, serverTime time.Time, msgid string, nickmask, accountName string, tags map[string]string, command string, params ...string) error {
	msg := ircmsg.MakeMessage(tags, nickmask, command, params...)
	// attach account-tag
	if client.capabilities.Has(caps.AccountTag) && accountName != "*" {
		msg.SetTag("account", accountName)
	}
	// attach message-id
	if msgid != "" && client.capabilities.Has(caps.MessageTags) {
		msg.SetTag("draft/msgid", msgid)
	}
	// attach server-time
	if client.capabilities.Has(caps.ServerTime) {
		msg.SetTag("time", time.Now().UTC().Format(IRCv3TimestampFormat))
	}

	return client.SendRawMessage(msg, blocking)
}

var (
	// these are all the output commands that MUST have their last param be a trailing.
	// this is needed because dumb clients like to treat trailing params separately from the
	// other params in messages.
	commandsThatMustUseTrailing = map[string]bool{
		"PRIVMSG": true,
		"NOTICE":  true,

		RPL_WHOISCHANNELS: true,
		RPL_USERHOST:      true,
	}
)

// SendRawMessage sends a raw message to the client.
func (client *Client) SendRawMessage(message ircmsg.IrcMessage, blocking bool) error {
	// use dumb hack to force the last param to be a trailing param if required
	var usedTrailingHack bool
	if commandsThatMustUseTrailing[message.Command] && len(message.Params) > 0 {
		lastParam := message.Params[len(message.Params)-1]
		// to force trailing, we ensure the final param contains a space
		if strings.IndexByte(lastParam, ' ') == -1 {
			message.Params[len(message.Params)-1] = lastParam + " "
			usedTrailingHack = true
		}
	}

	// assemble message
	maxlenRest := client.MaxlenRest()
	line, err := message.LineBytesStrict(false, maxlenRest)
	if err != nil {
		logline := fmt.Sprintf("Error assembling message for sending: %v\n%s", err, debug.Stack())
		client.server.logger.Error("internal", logline)

		message = ircmsg.MakeMessage(nil, client.server.name, ERR_UNKNOWNERROR, "*", "Error assembling message for sending")
		line, _ := message.LineBytesStrict(false, 0)

		if blocking {
			client.socket.BlockingWrite(line)
		} else {
			client.socket.Write(line)
		}
		return err
	}

	// if we used the trailing hack, we need to strip the final space we appended earlier on
	if usedTrailingHack {
		copy(line[len(line)-3:], "\r\n")
		line = line[:len(line)-1]
	}

	if client.server.logger.IsLoggingRawIO() {
		logline := string(line[:len(line)-2]) // strip "\r\n"
		client.server.logger.Debug("useroutput", client.nick, " ->", logline)
	}

	if blocking {
		return client.socket.BlockingWrite(line)
	} else {
		return client.socket.Write(line)
	}
}

// Send sends an IRC line to the client.
func (client *Client) Send(tags map[string]string, prefix string, command string, params ...string) error {
	msg := ircmsg.MakeMessage(tags, prefix, command, params...)
	if client.capabilities.Has(caps.ServerTime) && !msg.HasTag("time") {
		msg.SetTag("time", time.Now().UTC().Format(IRCv3TimestampFormat))
	}
	return client.SendRawMessage(msg, false)
}

// Notice sends the client a notice from the server.
func (client *Client) Notice(text string) {
	limit := 400
	if client.capabilities.Has(caps.MaxLine) {
		limit = client.server.Limits().LineLen.Rest - 110
	}
	lines := utils.WordWrap(text, limit)

	// force blank lines to be sent if we receive them
	if len(lines) == 0 {
		lines = []string{""}
	}

	for _, line := range lines {
		client.Send(nil, client.server.name, "NOTICE", client.nick, line)
	}
}

func (client *Client) addChannel(channel *Channel) {
	client.stateMutex.Lock()
	client.channels[channel] = true
	client.stateMutex.Unlock()
}

func (client *Client) removeChannel(channel *Channel) {
	client.stateMutex.Lock()
	delete(client.channels, channel)
	client.stateMutex.Unlock()
}

// Records that the client has been invited to join an invite-only channel
func (client *Client) Invite(casefoldedChannel string) {
	client.stateMutex.Lock()
	defer client.stateMutex.Unlock()

	if client.invitedTo == nil {
		client.invitedTo = make(map[string]bool)
	}

	client.invitedTo[casefoldedChannel] = true
}

// Checks that the client was invited to join a given channel
func (client *Client) CheckInvited(casefoldedChannel string) (invited bool) {
	client.stateMutex.Lock()
	defer client.stateMutex.Unlock()

	invited = client.invitedTo[casefoldedChannel]
	// joining an invited channel "uses up" your invite, so you can't rejoin on kick
	delete(client.invitedTo, casefoldedChannel)
	return
}