/*
goircd -- minimalistic simple Internet Relay Chat (IRC) server
Copyright (C) 2014-2020 Sergey Matveev <stargrave@stargrave.org>

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, version 3 of the License.

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 General Public License for more details.

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

package main

import (
	"bytes"
	"crypto/sha256"
	"crypto/subtle"
	"encoding/hex"
	"fmt"
	"io/ioutil"
	"log"
	"net"
	"regexp"
	"sort"
	"strings"
	"sync"
	"time"
)

const (
	BufSize   = 1500
	MaxOutBuf = 128
)

var (
	CRLF       []byte = []byte{'\x0d', '\x0a'}
	RENickname        = regexp.MustCompile("^[a-zA-Z0-9-]{1,24}$")

	clients     map[*Client]struct{} = make(map[*Client]struct{})
	clientsLock sync.RWMutex
	clientsWG   sync.WaitGroup
)

type Client struct {
	conn          net.Conn
	registered    bool
	nickname      string
	username      string
	realname      string
	password      string
	away          string
	recvTimestamp time.Time
	sendTimestamp time.Time
	outBuf        chan string
	alive         bool
	sync.Mutex
}

func (c *Client) Host() string {
	if *cloak != "" {
		return *cloak
	}
	addr := c.conn.RemoteAddr().String()
	if host, _, err := net.SplitHostPort(addr); err == nil {
		addr = host
	}
	if domains, err := net.LookupAddr(addr); err == nil {
		addr = strings.TrimSuffix(domains[0], ".")
	}
	return addr
}

func (c *Client) String() string {
	return strings.Join([]string{c.nickname, "!", c.username, "@", c.Host()}, "")
}

func NewClient(conn net.Conn, events chan ClientEvent) *Client {
	c := Client{
		conn:          conn,
		nickname:      "*",
		username:      "",
		recvTimestamp: time.Now(),
		sendTimestamp: time.Now(),
		alive:         true,
		outBuf:        make(chan string, MaxOutBuf),
	}
	clientsWG.Add(2)
	go c.MsgSender()
	go c.Processor(events)
	return &c
}

func (c *Client) Close() {
	c.Lock()
	if c.alive {
		close(c.outBuf)
		c.alive = false
	}
	c.Unlock()
}

func (c *Client) Processor(events chan ClientEvent) {
	events <- ClientEvent{c, EventNew, ""}
	if *verbose {
		log.Println(c, "connected")
	}
	buf := make([]byte, BufSize*2)
	var n, prev, i int
	var msg string
	var err error
	for {
		if prev == BufSize {
			log.Println(c, "input buffer size exceeded, kicking him")
			break
		}
		n, err = c.conn.Read(buf[prev:])
		if err != nil {
			break
		}
		prev += n
	CheckMore:
		i = bytes.Index(buf[:prev], CRLF)
		if i == -1 {
			continue
		}
		if *debug {
			log.Println(c, "<-", msg)
		}
		msg = string(buf[:i])
		if *debug {
			log.Println(c, "->", msg)
		}
		events <- ClientEvent{c, EventMsg, msg}
		copy(buf, buf[i+2:prev])
		prev -= (i + 2)
		goto CheckMore
	}
	c.Close()
	if *verbose {
		log.Println(c, "disconnected")
	}
	events <- ClientEvent{c, EventDel, ""}
	clientsWG.Done()
}

func (c *Client) MsgSender() {
	var err error
	for msg := range c.outBuf {
		if *debug {
			log.Println(c, "<-", msg)
		}
		if _, err = c.conn.Write(append([]byte(msg), CRLF...)); err != nil {
			if *verbose {
				log.Println(c, "error writing", err)
			}
			break
		}
	}
	c.conn.Close()
	clientsWG.Done()
}

func (c *Client) Msg(text string) {
	c.Lock()
	defer c.Unlock()
	if !c.alive {
		return
	}
	if len(c.outBuf) == MaxOutBuf {
		log.Println(c, "output buffer size exceeded, kicking him")
		if c.alive {
			close(c.outBuf)
			c.alive = false
		}
		return
	}
	c.outBuf <- text
}

func (c *Client) Reply(text string) {
	c.Msg(":" + *hostname + " " + text)
}

func (c *Client) ReplyParts(code string, text ...string) {
	parts := []string{code}
	for _, t := range text {
		parts = append(parts, t)
	}
	parts[len(parts)-1] = ":" + parts[len(parts)-1]
	c.Reply(strings.Join(parts, " "))
}

func (c *Client) ReplyNicknamed(code string, text ...string) {
	c.ReplyParts(code, append([]string{c.nickname}, text...)...)
}

func (c *Client) ReplyNotEnoughParameters(command string) {
	c.ReplyNicknamed("461", command, "Not enough parameters")
}

func (c *Client) ReplyNoChannel(channel string) {
	c.ReplyNicknamed("403", channel, "No such channel")
}

func (c *Client) ReplyNoNickChan(channel string) {
	c.ReplyNicknamed("401", channel, "No such nick/channel")
}

func (c *Client) SendLusers() {
	lusers := 0
	clientsLock.RLock()
	for client := range clients {
		if client.registered {
			lusers++
		}
	}
	clientsLock.RUnlock()
	c.ReplyNicknamed(
		"251",
		fmt.Sprintf("There are %d users and 0 invisible on 1 servers",
			lusers,
		))
}

func (c *Client) SendMotd() {
	if motd == nil {
		c.ReplyNicknamed("422", "MOTD File is missing")
		return
	}
	motdText, err := ioutil.ReadFile(*motd)
	if err != nil {
		log.Printf("can not read motd file %s: %v", *motd, err)
		c.ReplyNicknamed("422", "Error reading MOTD File")
		return
	}
	c.ReplyNicknamed("375", "- "+*hostname+" Message of the day -")
	for _, s := range strings.Split(strings.TrimSuffix(string(motdText), "\n"), "\n") {
		c.ReplyNicknamed("372", "- "+s)
	}
	c.ReplyNicknamed("376", "End of /MOTD command")
}

func (c *Client) Join(cmd string) {
	args := strings.Split(cmd, " ")
	rs := strings.Split(args[0], ",")
	keys := []string{}
	if len(args) > 1 {
		keys = strings.Split(args[1], ",")
	}
RoomCycle:
	for n, roomName := range rs {
		if !RERoom.MatchString(roomName) {
			c.ReplyNoChannel(roomName)
			continue
		}
		var key string
		if (n < len(keys)) && (keys[n] != "") {
			key = keys[n]
		}
		roomsLock.RLock()
		for roomNameExisting, room := range rooms {
			if roomName != roomNameExisting {
				continue
			}
			if (room.key != "") && (room.key != key) {
				c.ReplyNicknamed("475", roomName, "Cannot join channel (+k)")
				roomsLock.RUnlock()
				return
			}
			room.events <- ClientEvent{c, EventNew, ""}
			roomsLock.RUnlock()
			continue RoomCycle
		}
		roomsLock.RUnlock()
		roomNew := RoomRegister(roomName)
		if *verbose {
			log.Println("room", roomName, "created")
		}
		if key != "" {
			roomNew.key = key
			roomNew.StateSave()
		}
		roomNew.events <- ClientEvent{c, EventNew, ""}
	}
}

func (client *Client) SendWhois(nicknames []string) {
	var c *Client
	for _, nickname := range nicknames {
		nickname = strings.ToLower(nickname)
		clientsLock.RLock()
		for c = range clients {
			if strings.ToLower(c.nickname) == nickname {
				clientsLock.RUnlock()
				goto Found
			}
		}
		clientsLock.RUnlock()
		client.ReplyNoNickChan(nickname)
		continue
	Found:
		var host string
		if *cloak != "" {
			host = *cloak
		} else {
			host, _, err := net.SplitHostPort(c.conn.RemoteAddr().String())
			if err != nil {
				log.Printf("can't parse RemoteAddr %q: %v", host, err)
				host = "Unknown"
			}
		}
		client.ReplyNicknamed("311", c.nickname, c.username, host, "*", c.realname)
		client.ReplyNicknamed("312", c.nickname, *hostname, *hostname)
		if c.away != "" {
			client.ReplyNicknamed("301", c.nickname, c.away)
		}
		subscriptions := make([]string, 0)
		roomsLock.RLock()
		for _, room := range rooms {
			for subscriber := range room.members {
				if subscriber.nickname == nickname {
					subscriptions = append(subscriptions, room.name)
				}
			}
		}
		roomsLock.RUnlock()
		sort.Strings(subscriptions)
		client.ReplyNicknamed("319", c.nickname, strings.Join(subscriptions, " "))
		client.ReplyNicknamed("318", c.nickname, "End of /WHOIS list")
	}
}

func (c *Client) SendList(cols []string) {
	var rs []string
	if (len(cols) > 1) && (cols[1] != "") {
		rs = strings.Split(strings.Split(cols[1], " ")[0], ",")
	} else {
		rs = make([]string, 0)
		roomsLock.RLock()
		for r := range rooms {
			rs = append(rs, r)
		}
		roomsLock.RUnlock()
	}
	sort.Strings(rs)
	roomsLock.RLock()
	for _, r := range rs {
		if room, found := rooms[r]; found {
			c.ReplyNicknamed(
				"322",
				r,
				fmt.Sprintf("%d", len(room.members)),
				room.topic,
			)
		}
	}
	roomsLock.RUnlock()
	c.ReplyNicknamed("323", "End of /LIST")
}

func (c *Client) Register(cmd string, cols []string) {
	switch cmd {
	case "PASS":
		if len(cols) == 1 || len(cols[1]) < 1 {
			c.ReplyNotEnoughParameters("PASS")
			return
		}
		password := strings.TrimPrefix(cols[1], ":")
		c.password = password
	case "NICK":
		if len(cols) == 1 || len(cols[1]) < 1 {
			c.ReplyParts("431", "No nickname given")
			return
		}
		nickname := cols[1]
		// Compatibility with some clients prepending colons to nickname
		nickname = strings.TrimPrefix(nickname, ":")
		nickname = strings.ToLower(nickname)
		if !RENickname.MatchString(nickname) {
			c.ReplyParts("432", "*", cols[1], "Erroneous nickname")
			return
		}
		clientsLock.RLock()
		for existingClient := range clients {
			if existingClient.nickname == nickname {
				clientsLock.RUnlock()
				c.ReplyParts("433", "*", nickname, "Nickname is already in use")
				return
			}
		}
		clientsLock.RUnlock()
		c.nickname = nickname
	case "USER":
		if len(cols) == 1 {
			c.ReplyNotEnoughParameters("USER")
			return
		}
		args := strings.SplitN(cols[1], " ", 4)
		if len(args) < 4 {
			c.ReplyNotEnoughParameters("USER")
			return
		}
		c.username = args[0]
		realname := strings.TrimLeft(args[3], ":")
		c.realname = realname
	}
	if c.nickname != "*" && c.username != "" {
		if *passwords != "" {
			authenticated := false
			if c.password == "" {
				c.ReplyParts("462", "You may not register")
				c.Close()
				return
			}
			contents, err := ioutil.ReadFile(*passwords)
			if err != nil {
				log.Fatalf("can not read passwords file %s: %s", *passwords, err)
				return
			}
			for n, entry := range strings.Split(string(contents), "\n") {
				if entry == "" || strings.HasPrefix(entry, "#") {
					continue
				}
				cols := strings.Split(entry, ":")
				if len(cols) != 2 {
					log.Fatalf("bad passwords format: %s:%d", *passwords, n)
					continue
				}
				if cols[0] != c.nickname {
					continue
				}
				h := sha256.Sum256([]byte(c.password))
				authenticated = subtle.ConstantTimeCompare(
					[]byte(hex.EncodeToString(h[:])),
					[]byte(cols[1]),
				) == 1
				break
			}
			if !authenticated {
				c.ReplyParts("462", "You may not register")
				c.Close()
				return
			}
		}
		c.registered = true
		c.ReplyNicknamed("001", "Hi, welcome to IRC")
		c.ReplyNicknamed("002", "Your host is "+*hostname+", running goircd "+Version)
		c.ReplyNicknamed("003", "This server was created sometime")
		c.ReplyNicknamed("004", *hostname+" goircd o o")
		c.SendLusers()
		c.SendMotd()
		if *verbose {
			log.Println(c, "logged in")
		}
	}
}