package main

import (
	"fmt"
	"log"
	"net"
	"regexp"
	"strings"

	"golang.org/x/crypto/bcrypt"
)

var (
	nickRegexp    = regexp.MustCompile(`^[a-zA-Z\[\]_^{|}][a-zA-Z0-9\[\]_^{|}]*$`)
	channelRegexp = regexp.MustCompile(`^#[a-zA-Z0-9_\-]+$`)
)

func NewServer() *Server {
	return &Server{eventChan: make(chan Event),
		name:        "",
		clientMap:   make(map[string]*Client),
		channelMap:  make(map[string]*Channel),
		operatorMap: make(map[string][]byte),
		motd:        "",
	}
}

func (s *Server) Run() {
	for event := range s.eventChan {
		s.handleEvent(event)
	}
}

func (s *Server) HandleConnection(conn net.Conn) {
	client := &Client{server: s,
		connection: conn,
		outputChan: make(chan string),
		signalChan: make(chan signalCode, 3),
		channelMap: make(map[string]*Channel),
		connected:  true,
	}

	go client.clientThread()
}

func (s *Server) handleEvent(e Event) {
	defer func(event Event) {
		err := recover()
		if err != nil {
			log.Printf("Recovered from error when handling event: %+v", event)
			log.Println(err)
		}
	}(e)

	switch e.event {
	case connected:
		//Client connected
		e.client.reply(rplMOTDStart)
		motd := s.motd
		for len(motd) > 80 {
			e.client.reply(rplMOTD, motd[:80])
			motd = motd[80:]
		}
		if len(motd) > 0 {
			e.client.reply(rplMOTD, motd)
		}
		e.client.reply(rplEndOfMOTD)
	case disconnected:
		//Client disconnected
	case command:
		//Client send a command
		fields := strings.Fields(e.input)
		if len(fields) < 1 {
			return
		}

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

		s.handleCommand(e.client, command, args)
	}
}

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

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

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

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

	case "NICK":
		client.reply(rplKill, "Can't change nicks on this server", "")
		client.disconnect()

	case "USER":
		if client.nick == "" {
			client.reply(rplKill, "Your nickname is already being used", "")
			client.disconnect()
		} else {
			client.reply(rplWelcome)
			client.registered = true
		}

	case "JOIN":
		if client.registered == false {
			client.reply(errNotReg)
			return
		}

		if len(args) < 1 {
			client.reply(errMoreArgs)
			return
		}

		if args[0] == "0" {
			// Intend to quit all channels
			// But we don't allow that
			return
		}

		channels := strings.Split(args[0], ",")
		for _, channel := range channels {
			//Join the channel if it's valid
			if channelRegexp.MatchString(channel) {
				client.joinChannel(channel)
			}
		}

	case "PART":
		if client.registered == false {
			client.reply(errNotReg)
			return
		}

		// you can check out any time you like, but you can never leave
		// we'll need to transmit client.reply(rplPart, c.nick, channel.name, reason) messages on behalf of other nmdc users, though

	case "PRIVMSG":
		if client.registered == false {
			client.reply(errNotReg)
			return
		}

		if len(args) < 2 {
			client.reply(errMoreArgs)
			return
		}

		message := strings.Join(args[1:], " ")

		channel, chanExists := s.channelMap[strings.ToLower(args[0])]
		client2, clientExists := s.clientMap[strings.ToLower(args[0])]

		if chanExists {
			if channel.mode.noExternal {
				if _, inChannel := channel.clientMap[client.key]; !inChannel {
					//Not in channel, not allowed to send
					client.reply(errCannotSend, args[0])
					return
				}
			}
			if channel.mode.moderated {
				clientMode := channel.modeMap[client.key]
				if !clientMode.operator && !clientMode.voice {
					//It's moderated and we're not +v or +o, do nothing
					client.reply(errCannotSend, args[0])
					return
				}
			}
			for _, c := range channel.clientMap {
				if c != client {
					c.reply(rplMsg, client.nick, args[0], message)
				}
			}
		} else if clientExists {
			client2.reply(rplMsg, client.nick, client2.nick, message)
		} else {
			client.reply(errNoSuchNick, args[0])
		}

	case "QUIT":
		if client.registered == false {
			client.reply(errNotReg)
			return
		}

		client.disconnect()

	case "TOPIC":
		if client.registered == false {
			client.reply(errNotReg)
			return
		}

		if len(args) < 1 {
			client.reply(errMoreArgs)
			return
		}

		channel, exists := s.channelMap[strings.ToLower(args[0])]
		if exists == false {
			client.reply(errNoSuchNick, args[0])
			return
		}

		// Valid topic get
		if len(args) == 1 {
			client.reply(rplTopic, channel.name, s.name)
			return
		}

		// Disallow topic set
		client.reply(errNoPriv)
		return

	case "LIST":
		if client.registered == false {
			client.reply(errNotReg)
			return
		}

		if len(args) == 0 {
			for channelName, channel := range s.channelMap {
				if channel.mode.secret {
					if _, inChannel := channel.clientMap[client.key]; !inChannel {
						//Not in the channel, skip
						continue
					}
				}
				listItem := fmt.Sprintf("%s %d :%s", channelName, len(channel.clientMap), channel.topic)
				client.reply(rplList, listItem)
			}

			client.reply(rplListEnd)
		} else {
			channels := strings.Split(args[0], ",")

			for _, channelName := range channels {
				if channel, exists := s.channelMap[strings.ToLower(channelName)]; exists {
					listItem := fmt.Sprintf("%s %d :%s", channelName, len(channel.clientMap), channel.topic)
					client.reply(rplList, listItem)
				}
			}

			client.reply(rplListEnd)
		}
	case "OPER":
		if client.registered == false {
			client.reply(errNotReg)
			return
		}

		if len(args) < 2 {
			client.reply(errMoreArgs)
			return
		}

		username := args[0]
		password := args[1]

		if hashedPassword, exists := s.operatorMap[username]; exists {
			//nil means the passwords matched
			if err := bcrypt.CompareHashAndPassword(hashedPassword, []byte(password)); err == nil {
				client.operator = true
				client.reply(rplOper)
				return
			}
		}
		client.reply(errPassword)

	case "KILL":
		if client.registered == false {
			client.reply(errNotReg)
			return
		}

		if client.operator == false {
			client.reply(errNoPriv)
			return
		}

		if len(args) < 1 {
			client.reply(errMoreArgs)
			return
		}

		nick := args[0]

		reason := strings.Join(args[1:], " ")

		client, exists := s.clientMap[strings.ToLower(nick)]
		if !exists {
			client.reply(errNoSuchNick, nick)
			return
		}

		client.reply(rplKill, client.nick, reason)
		client.disconnect()

	case "KICK":
		if client.registered == false {
			client.reply(errNotReg)
			return
		}

		client.reply(errNoPriv)
		return

	case "MODE":
		if client.registered == false {
			client.reply(errNotReg)
			return
		}

		if len(args) < 1 {
			client.reply(errMoreArgs)
			return
		}

		channelKey := strings.ToLower(args[0])

		channel, channelExists := s.channelMap[channelKey]
		if !channelExists {
			client.reply(errNoSuchNick, args[0])
			return
		}
		mode := channel.mode

		if len(args) == 1 {
			//No more args, they just want the mode
			client.reply(rplChannelModeIs, args[0], mode.String(), "")
			return
		}

		// Setting modes is disallowed
		client.reply(errNoPriv)
		return

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