package main

/*
Copyright (C) 2016 The `nmdc-ircfrontend' author(s)
Copyright (C) 2013 Harry Jeffery

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU Affero General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU Affero General Public License for more details.

You should have received a copy of the GNU Affero General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

import (
	"bytes"
	"fmt"
	"io"
	"libnmdc"
	"log"
	"net"
	"strings"
	"time"
)

type ClientState int

const (
	CSUnregistered ClientState = iota
	CSRegistered
	CSJoined
)

type Server struct {
	name string
	motd string

	clientConn  net.Conn
	clientState ClientState

	upstreamLauncher libnmdc.HubConnectionOptions
	upstreamCloser   chan struct{}
	upstream         *libnmdc.HubConnection

	verbose  bool
	autojoin bool

	lastMessage string // FIXME racey
}

func NewServer(name string, upstream libnmdc.HubAddress, conn net.Conn) *Server {
	self := libnmdc.NewUserInfo("")
	self.ClientTag = APP_DESCRIPTION

	return &Server{
		name:        name,
		clientConn:  conn,
		clientState: CSUnregistered,
		motd:        "Connected to " + name + ". You /must/ join " + BLESSED_CHANNEL + " to continue.",
		upstreamLauncher: libnmdc.HubConnectionOptions{
			Address: upstream,
			Self:    *self,
		},
		upstreamCloser: make(chan struct{}, 1),
	}
}

func (s *Server) verboseln(line string) {
	if s.verbose {
		log.Println(line)
	}
}

func (s *Server) verbosef(fmt string, args ...interface{}) {
	if s.verbose {
		log.Printf(fmt, args...)
	}
}

func (s *Server) RunWorker() {

	// Send the connection handshake.
	// Can't connect to the upstream server yet, until we've recieved a nick.
	s.sendMOTD(s.motd)

	for {
		if s.clientConn == nil {
			break // abandon thread
		}

		buf := make([]byte, CLIENT_READ_BUFFSIZE)

		ln, err := s.clientConn.Read(buf)
		if err != nil {
			if err == io.EOF {
				break // abandon thread
			}

			// If this was a /timeout/, send a KA and continue.

			// But otherwise, it was a real error (e.g. unexpected disconnect)
			s.verboseln(err.Error())
			break // abandon
		}

		rawLines := buf[:ln]
		rawLines = bytes.Replace(rawLines, []byte("\r\n"), []byte("\n"), -1)
		rawLines = bytes.Replace(rawLines, []byte("\r"), []byte("\n"), -1)
		lines := bytes.Split(rawLines, []byte("\n"))
		for _, line := range lines {
			if len(line) > 0 {

				// Client sent a command
				fields := strings.Fields(string(line))
				if len(fields) < 1 {
					return
				}

				if strings.HasPrefix(fields[0], ":") {
					fields = fields[1:]
				}

				s.handleCommand(strings.ToUpper(fields[0]), fields[1:])
			}
		}
	}

	s.verboseln("Broken loop.")

	// Cleanup upstream
	if s.upstream != nil {
		s.upstreamCloser <- struct{}{} // always safe to do this /once/
	}

	// Clean up ourselves
	s.DisconnectClient() // if not already done
}

func (s *Server) upstreamWorker() {

	// Read loop
	for {
		select {
		case <-s.upstreamCloser:
			// Abandon the upstream connection
			s.verboseln("Abandoning upstream connection...")
			s.upstream.Disconnect()
			return

		case hubEvent := <-s.upstream.OnEvent:
			switch hubEvent.EventType {
			case libnmdc.EVENT_USER_JOINED:
				s.reply(rplJoin, hubEvent.Nick, BLESSED_CHANNEL)

			case libnmdc.EVENT_USER_PART:
				s.reply(rplPart, hubEvent.Nick, BLESSED_CHANNEL, "Disconnected")

			case libnmdc.EVENT_USER_UPDATED_INFO:
				// description change - no relevance for IRC users

			case libnmdc.EVENT_CONNECTION_STATE_CHANGED:
				s.reply(rplMsg, "", BLESSED_CHANNEL, "* Upstream: "+hubEvent.StateChange.Format())

			case libnmdc.EVENT_HUBNAME_CHANGED:
				s.sendChannelTopic(hubEvent.Nick)

			case libnmdc.EVENT_PRIVATE:
				s.reply(rplMsg, hubEvent.Nick, s.upstreamLauncher.Self.Nick, hubEvent.Message)

			case libnmdc.EVENT_PUBLIC:
				if hubEvent.Nick == s.upstreamLauncher.Self.Nick && hubEvent.Message == s.lastMessage {
					s.lastMessage = "" // irc doesn't echo our own pubchat
				} else {
					s.reply(rplMsg, hubEvent.Nick, BLESSED_CHANNEL, hubEvent.Message)
				}

			case libnmdc.EVENT_SYSTEM_MESSAGE_FROM_CONN, libnmdc.EVENT_SYSTEM_MESSAGE_FROM_HUB:
				// FIXME blank names work well in hexchat, but not in yaaic
				s.reply(rplMsg, "", BLESSED_CHANNEL, hubEvent.Message)

			}
		}
	}
}

func (s *Server) handleCommand(command string, args []string) {

	s.verbosef(" >>> '%s' %v", command, args)

	switch command {
	case "PING":
		s.reply(rplPong)

	case "PONG":
		// do nothing

	case "INFO":
		s.reply(rplInfo, APP_DESCRIPTION)

	case "VERSION":
		s.reply(rplVersion, VERSION)

	case "MOTD":
		s.sendMOTD(s.motd)

	case "CAP":
		return
		/*
			if len(args) < 1 {
				s.reply(errMoreArgs)
				return
			}

			if args[0] == "LS" {
				s.writeClient("CAP * LS :nmdc-ircfrontend") // no special IRCv3 capabilities available
			} else {
				s.writeClient(fmt.Sprintf(":%s 410 * %s :Invalid CAP command", s.name, args[0]))
			}
		*/

	case "PASS":
		// RFC2812 registration. Stash the password for later
		if len(args) < 1 {
			s.reply(errMoreArgs)
			return
		}
		s.upstreamLauncher.NickPassword = args[0]

	case "NICK":
		if len(args) < 1 {
			s.reply(errMoreArgs)
			return
		}

		if s.upstreamLauncher.Self.Nick == "" {
			// allow set, as part of the login phase
			s.upstreamLauncher.Self.Nick = args[0]
		} else {
			s.reply(rplKill, "Can't change nicks on this server", "")
			s.DisconnectClient()
		}

	case "USER":
		// This command sets altname, realname, ... none of which we use
		// It's the final step in a PASS/NICK/USER login handshake.

		if s.clientState != CSUnregistered {
			s.reply(rplKill, "You're already registered.", "")
			s.DisconnectClient()
			return
		}

		if s.upstreamLauncher.Self.Nick == "" {
			s.reply(rplKill, "Your nickname is already being used", "")
			s.DisconnectClient()
			return
		}

		s.reply(rplWelcome)
		s.clientState = CSRegistered

		// TODO tell the client that they /must/ join #chat
		if s.autojoin {
			s.handleCommand("JOIN", []string{BLESSED_CHANNEL})
		}

		// Send a CTCP VERSION request to the client. If the IRC client can
		//   supply a client version string, we can replace our tag with it,
		//   but that's optional

	default:
		s.handleRegisteredCommand(command, args)
	}
}

func (s *Server) handleRegisteredCommand(command string, args []string) {

	if s.clientState == CSUnregistered {
		s.reply(errNotReg)
		return
	}

	switch command {
	case "JOIN":
		if len(args) < 1 {
			s.reply(errMoreArgs)
			return
		}

		switch args[0] {
		case BLESSED_CHANNEL:
			if s.clientState != CSJoined {
				// Join for the first time
				s.clientState = CSJoined

				// Acknowledge
				s.reply(rplJoin, s.upstreamLauncher.Self.Nick, BLESSED_CHANNEL)

				// Send (initially just us) nicklist for the chat channel
				s.sendNames()

				// Spawn upstream connection
				s.upstream = s.upstreamLauncher.Connect()
				go s.upstreamWorker()

			} else {
				// They're already here, ignore
				// Can happen if autojoin is enabled but the client already requested a login
			}

		case "0":
			// Quitting all channels? Drop client
			s.reply(rplKill, "Bye.", "")
			s.DisconnectClient()

		default:
			s.reply(rplKill, "There is only '"+BLESSED_CHANNEL+"'.", "")
			s.DisconnectClient()
		}

	case "PART":
		if len(args) < 1 {
			s.reply(errMoreArgs)
			return
		}

		if args[0] == BLESSED_CHANNEL {
			// You can check out any time you like, but you can never leave
			s.reply(rplJoin, s.upstreamLauncher.Self.Nick, BLESSED_CHANNEL)
			s.sendNames()
		}

	case "PRIVMSG", "NOTICE":
		if len(args) < 2 {
			s.reply(errMoreArgs)
			return
		}

		if s.upstream.State != libnmdc.CONNECTIONSTATE_CONNECTED {
			s.reply(errCannotSend, args[0])
			return
		}

		message := strings.Join(args[1:], " ")[1:] // strip leading colon

		// IRC is case-insensitive case-preserving. We can respect that for the
		//  channel name, but not really for user nicks

		if strings.ToLower(args[0]) == BLESSED_CHANNEL {
			s.lastMessage = message
			s.upstream.SayPublic(s.lastMessage)

		} else if _, clientExists := s.upstream.Users[args[0]]; clientExists {
			s.upstream.SayPrivate(args[0], message)

		} else {
			s.reply(errNoSuchNick, args[0])

		}

	case "QUIT":
		s.DisconnectClient()

	case "TOPIC":
		if len(args) < 1 {
			s.reply(errMoreArgs)
			return
		}

		if strings.ToLower(args[0]) != BLESSED_CHANNEL {
			s.reply(errNoSuchNick, args[0])
			return
		}

		if len(args) == 1 {
			s.sendChannelTopic(s.upstream.HubName) // Valid topic get
		} else {
			s.reply(errNoPriv) // Disallow topic set
		}

	case "LIST":
		listItem := fmt.Sprintf("%s %d :%s", BLESSED_CHANNEL, len(s.upstream.Users), s.upstream.HubName)
		s.reply(rplList, listItem)
		s.reply(rplListEnd)

	case "OPER":
		if len(args) < 2 {
			s.reply(errMoreArgs)
			return
		}

		// Can't use this command.
		s.reply(errPassword)

	case "KILL", "KICK":
		s.reply(errNoPriv)
		return

	case "WHO":
		if len(args) < 1 {
			s.reply(errMoreArgs)
			return
		}

		// Ignore what we're "supposed" to do
		s.sendNames()

		/*
			if args[0] == BLESSED_CHANNEL {
				// always include ourselves
				s.reply(rplWho, s.upstreamLauncher.Self.Nick, args[0])

				for nick, _ := range s.upstream.Users {
					if nick != s.upstreamLauncher.Self.Nick { // but don't repeat ourselves
						s.reply(rplWho, nick, args[0])
					}
				}
			} else {
				// argument is a filter
				for nick, _ := range s.upstream.Users {
					if strings.Contains(nick, args[0]) {
						s.reply(rplWho, nick, args[0])
					}
				}
			}
			s.reply(rplEndOfWho, args[0])
		*/

	case "MODE":
		if len(args) < 1 {
			s.reply(errMoreArgs)
			return
		}

		if strings.ToLower(args[0]) != BLESSED_CHANNEL {
			s.reply(errNoSuchNick, args[0])
			return
		}

		if len(args) == 1 {
			// No more args, they just want the mode
			s.reply(rplChannelModeIs, args[0], BLESSED_CHANNEL_MODE, "")
		} else {
			// Setting modes is disallowed
			s.reply(errNoPriv)
		}

		return

	default:
		s.reply(errUnknownCommand, command)
	}
}

func (s *Server) DisconnectClient() {
	if s.clientConn != nil {
		s.clientConn.Close()
	}
	s.clientConn = nil
	s.clientState = CSUnregistered

	// Readloop will stop, which kills the upstream connection too
}

func (s *Server) sendNames() {
	names := s.upstreamLauncher.Self.Nick
	if s.upstream != nil {
		for nick, _ := range s.upstream.Users {
			names += " " + nick
		}
	}

	s.reply(rplNames, BLESSED_CHANNEL, names)
	s.reply(rplEndOfNames, BLESSED_CHANNEL)
}

func (s *Server) sendChannelTopic(topic string) {
	if len(topic) > 0 {
		s.reply(rplTopic, BLESSED_CHANNEL, s.upstream.HubName)
	} else {
		s.reply(rplNoTopic, BLESSED_CHANNEL)
	}
}

func (s *Server) sendMOTD(motd string) {
	s.reply(rplMOTDStart)

	for len(motd) > 80 {
		s.reply(rplMOTD, motd[:80])
		motd = motd[80:]
	}
	if len(motd) > 0 {
		s.reply(rplMOTD, motd)
	}

	s.reply(rplEndOfMOTD)
}

// Send a reply to a user with the code specified
func (s *Server) reply(code replyCode, args ...string) {

	switch code {
	case rplWelcome:
		s.writeClient(fmt.Sprintf(":%s 001 %s :Welcome to %s", s.name, s.upstreamLauncher.Self.Nick, s.name))
	case rplJoin:
		s.writeClient(fmt.Sprintf(":%s JOIN %s", args[0], args[1]))
	case rplPart:
		s.writeClient(fmt.Sprintf(":%s PART %s %s", args[0], args[1], args[2]))
	case rplTopic:
		s.writeClient(fmt.Sprintf(":%s 332 %s %s :%s", s.name, s.upstreamLauncher.Self.Nick, args[0], args[1]))
	case rplNoTopic:
		s.writeClient(fmt.Sprintf(":%s 331 %s %s :No topic is set", s.name, s.upstreamLauncher.Self.Nick, args[0]))

	case rplNames:
		s.writeClient(fmt.Sprintf(":%s 353 %s = %s :%s", s.name, s.upstreamLauncher.Self.Nick, args[0], args[1]))
	case rplEndOfNames:
		s.writeClient(fmt.Sprintf(":%s 366 %s %s :End of NAMES list", s.name, s.upstreamLauncher.Self.Nick, args[0]))

	case rplWho:
		s.writeClient(fmt.Sprintf(":%s 352 %s %s %s %s %s %s H :0 %s", s.name, s.upstreamLauncher.Self.Nick, args[1], args[0], args[0], s.name, args[0], args[0]))
	case rplEndOfWho:
		s.writeClient(fmt.Sprintf(":%s 315 %s %s :End of WHO list", s.name, s.upstreamLauncher.Self.Nick, args[0]))

	case rplNickChange:
		s.writeClient(fmt.Sprintf(":%s NICK %s", args[0], args[1]))
	case rplKill:
		s.writeClient(fmt.Sprintf(":%s KILL %s A %s", args[0], s.upstreamLauncher.Self.Nick, args[1]))
	case rplMsg:
		for _, itm := range strings.Split(args[2], "\n") {
			s.writeClient(fmt.Sprintf(":%s PRIVMSG %s %s", args[0], args[1], itm))
		}
	case rplList:
		s.writeClient(fmt.Sprintf(":%s 322 %s %s", s.name, s.upstreamLauncher.Self.Nick, args[0]))
	case rplListEnd:
		s.writeClient(fmt.Sprintf(":%s 323 %s", s.name, s.upstreamLauncher.Self.Nick))
	case rplOper:
		s.writeClient(fmt.Sprintf(":%s 381 %s :You are now an operator", s.name, s.upstreamLauncher.Self.Nick))
	case rplChannelModeIs:
		s.writeClient(fmt.Sprintf(":%s 324 %s %s %s %s", s.name, s.upstreamLauncher.Self.Nick, args[0], args[1], args[2]))
	case rplKick:
		s.writeClient(fmt.Sprintf(":%s KICK %s %s %s", args[0], args[1], args[2], args[3]))
	case rplInfo:
		s.writeClient(fmt.Sprintf(":%s 371 %s :%s", s.name, s.upstreamLauncher.Self.Nick, args[0]))
	case rplVersion:
		s.writeClient(fmt.Sprintf(":%s 351 %s %s", s.name, s.upstreamLauncher.Self.Nick, args[0]))
	case rplMOTDStart:
		s.writeClient(fmt.Sprintf(":%s 375 %s :- Message of the day - ", s.name, s.upstreamLauncher.Self.Nick))
	case rplMOTD:
		s.writeClient(fmt.Sprintf(":%s 372 %s :- %s", s.name, s.upstreamLauncher.Self.Nick, args[0]))
	case rplEndOfMOTD:
		s.writeClient(fmt.Sprintf(":%s 376 %s :- End of MOTD", s.name, s.upstreamLauncher.Self.Nick))
	case rplPong:
		s.writeClient(fmt.Sprintf(":%s PONG %s %s", s.name, s.upstreamLauncher.Self.Nick, s.name))
	case errMoreArgs:
		s.writeClient(fmt.Sprintf(":%s 461 %s :Not enough params", s.name, s.upstreamLauncher.Self.Nick))
	case errNoNick:
		s.writeClient(fmt.Sprintf(":%s 431 %s :No nickname given", s.name, s.upstreamLauncher.Self.Nick))
	case errInvalidNick:
		s.writeClient(fmt.Sprintf(":%s 432 %s %s :Erronenous nickname", s.name, s.upstreamLauncher.Self.Nick, args[0]))
	case errNickInUse:
		s.writeClient(fmt.Sprintf(":%s 433 %s %s :Nick already in use", s.name, s.upstreamLauncher.Self.Nick, args[0]))
	case errAlreadyReg:
		s.writeClient(fmt.Sprintf(":%s 462 :You need a valid nick first", s.name))
	case errNoSuchNick:
		s.writeClient(fmt.Sprintf(":%s 401 %s %s :No such nick/channel", s.name, s.upstreamLauncher.Self.Nick, args[0]))
	case errUnknownCommand:
		s.writeClient(fmt.Sprintf(":%s 421 %s %s :Unknown command", s.name, s.upstreamLauncher.Self.Nick, args[0]))
	case errNotReg:
		s.writeClient(fmt.Sprintf(":%s 451 :- You have not registered", s.name))
	case errPassword:
		s.writeClient(fmt.Sprintf(":%s 464 %s :Error, password incorrect", s.name, s.upstreamLauncher.Self.Nick))
	case errNoPriv:
		s.writeClient(fmt.Sprintf(":%s 481 %s :Permission denied", s.name, s.upstreamLauncher.Self.Nick))
	case errCannotSend:
		s.writeClient(fmt.Sprintf(":%s 404 %s %s :Cannot send to channel", s.name, s.upstreamLauncher.Self.Nick, args[0]))
	}
}

func (s *Server) writeClient(output string) {
	if s.clientConn == nil {
		return
	}

	s.verbosef(" <<< %s", output)

	s.clientConn.SetWriteDeadline(time.Now().Add(time.Second * 30))
	if _, err := fmt.Fprintf(s.clientConn, "%s\r\n", output); err != nil {
		s.DisconnectClient()
		return
	}
}