package ircserver

import (
	"bufio"
	"context"
	"fmt"
	"log/slog"
	"net"
	"strconv"
	"strings"
	"sync"
	"time"

	"git.eeqj.de/sneak/neoirc/internal/broker"
	"git.eeqj.de/sneak/neoirc/internal/config"
	"git.eeqj.de/sneak/neoirc/internal/db"
	"git.eeqj.de/sneak/neoirc/internal/service"
	"git.eeqj.de/sneak/neoirc/pkg/irc"
)

const (
	maxLineLen     = 512
	readTimeout    = 5 * time.Minute
	writeTimeout   = 30 * time.Second
	dnsTimeout     = 3 * time.Second
	pollInterval   = 100 * time.Millisecond
	pingInterval   = 90 * time.Second
	pongDeadline   = 30 * time.Second
	maxNickLen     = 32
	minPasswordLen = 8
)

// cmdHandler is the signature for registered IRC command
// handlers.
type cmdHandler func(ctx context.Context, msg *Message)

// Conn represents a single IRC client TCP connection.
type Conn struct {
	conn      net.Conn
	log       *slog.Logger
	database  *db.Database
	brk       *broker.Broker
	cfg       *config.Config
	svc       *service.Service
	serverSfx string
	commands  map[string]cmdHandler

	mu        sync.Mutex
	nick      string
	username  string
	realname  string
	hostname  string
	remoteIP  string
	sessionID int64
	clientID  int64

	registered bool
	gotNick    bool
	gotUser    bool
	passWord   string

	lastQueueID int64
	closed      bool
	cancel      context.CancelFunc
}

func newConn(
	ctx context.Context,
	tcpConn net.Conn,
	log *slog.Logger,
	database *db.Database,
	brk *broker.Broker,
	cfg *config.Config,
	svc *service.Service,
) *Conn {
	host, _, _ := net.SplitHostPort(tcpConn.RemoteAddr().String())

	srvName := cfg.ServerName
	if srvName == "" {
		srvName = "neoirc"
	}

	conn := &Conn{ //nolint:exhaustruct // zero-value defaults
		conn:      tcpConn,
		log:       log,
		database:  database,
		brk:       brk,
		cfg:       cfg,
		svc:       svc,
		serverSfx: srvName,
		remoteIP:  host,
		hostname:  resolveHost(ctx, host),
	}

	conn.commands = conn.buildCommandMap()

	return conn
}

// buildCommandMap returns a map from IRC command strings
// to handler functions.
func (c *Conn) buildCommandMap() map[string]cmdHandler {
	return map[string]cmdHandler{
		irc.CmdPing: func(_ context.Context, msg *Message) {
			c.handlePing(msg)
		},
		"PONG":         func(context.Context, *Message) {},
		irc.CmdNick:    c.handleNick,
		irc.CmdPrivmsg: c.handlePrivmsg,
		irc.CmdNotice:  c.handlePrivmsg,
		irc.CmdJoin:    c.handleJoin,
		irc.CmdPart:    c.handlePart,
		irc.CmdQuit: func(_ context.Context, msg *Message) {
			c.handleQuit(msg)
		},
		irc.CmdTopic:  c.handleTopic,
		irc.CmdMode:   c.handleMode,
		irc.CmdNames:  c.handleNames,
		irc.CmdList:   func(ctx context.Context, _ *Message) { c.handleList(ctx) },
		irc.CmdWhois:  c.handleWhois,
		irc.CmdWho:    c.handleWho,
		irc.CmdLusers: func(ctx context.Context, _ *Message) { c.handleLusers(ctx) },
		irc.CmdMotd:   func(context.Context, *Message) { c.deliverMOTD() },
		irc.CmdOper:   c.handleOper,
		irc.CmdAway:   c.handleAway,
		irc.CmdKick:   c.handleKick,
		irc.CmdPass:   c.handlePassPostReg,
		"INVITE":      c.handleInvite,
		"CAP": func(_ context.Context, msg *Message) {
			c.handleCAP(msg)
		},
		"USERHOST": c.handleUserhost,
	}
}

// resolveHost does a reverse DNS lookup, returning the IP
// on failure.
func resolveHost(ctx context.Context, addr string) string {
	ctx, cancel := context.WithTimeout(ctx, dnsTimeout)
	defer cancel()

	resolver := &net.Resolver{} //nolint:exhaustruct

	names, err := resolver.LookupAddr(ctx, addr)
	if err != nil || len(names) == 0 {
		return addr
	}

	return strings.TrimSuffix(names[0], ".")
}

// serve is the main loop for a single IRC client connection.
func (c *Conn) serve(ctx context.Context) {
	ctx, c.cancel = context.WithCancel(ctx)
	defer c.cleanup(ctx)

	scanner := bufio.NewScanner(c.conn)
	scanner.Buffer(make([]byte, maxLineLen), maxLineLen)

	for {
		_ = c.conn.SetReadDeadline(
			time.Now().Add(readTimeout),
		)

		if !scanner.Scan() {
			return
		}

		line := scanner.Text()
		if line == "" {
			continue
		}

		msg := ParseMessage(line)
		if msg == nil {
			continue
		}

		c.handleMessage(ctx, msg)

		if c.closed {
			return
		}
	}
}

func (c *Conn) cleanup(ctx context.Context) {
	c.mu.Lock()
	wasRegistered := c.registered
	sessID := c.sessionID
	nick := c.nick
	c.closed = true
	c.mu.Unlock()

	if wasRegistered && sessID > 0 {
		c.svc.BroadcastQuit(
			ctx, sessID, nick, "Connection closed",
		)
	}

	c.conn.Close() //nolint:errcheck,gosec
}

// send writes a formatted IRC line to the connection.
func (c *Conn) send(line string) {
	_ = c.conn.SetWriteDeadline(
		time.Now().Add(writeTimeout),
	)

	_, _ = fmt.Fprintf(c.conn, "%s\r\n", line)
}

// sendNumeric sends a numeric reply from the server.
func (c *Conn) sendNumeric(
	code irc.IRCMessageType,
	params ...string,
) {
	nick := c.nick
	if nick == "" {
		nick = "*"
	}

	allParams := make([]string, 0, 1+len(params))
	allParams = append(allParams, nick)
	allParams = append(allParams, params...)

	c.send(FormatMessage(
		c.serverSfx, code.Code(), allParams...,
	))
}

// sendFromServer sends a message from the server.
func (c *Conn) sendFromServer(
	command string, params ...string,
) {
	c.send(FormatMessage(c.serverSfx, command, params...))
}

// hostmask returns the client's full hostmask
// (nick!user@host).
func (c *Conn) hostmask() string {
	user := c.username
	if user == "" {
		user = c.nick
	}

	host := c.hostname
	if host == "" {
		host = c.remoteIP
	}

	return c.nick + "!" + user + "@" + host
}

// handleMessage dispatches a parsed IRC message using
// the command handler map.
func (c *Conn) handleMessage(
	ctx context.Context,
	msg *Message,
) {
	// Before registration, only NICK, USER, PASS, PING,
	// QUIT, and CAP are accepted.
	if !c.registered {
		c.handlePreRegistration(ctx, msg)

		return
	}

	handler, ok := c.commands[msg.Command]
	if !ok {
		c.sendNumeric(
			irc.ErrUnknownCommand,
			msg.Command, "Unknown command",
		)

		return
	}

	handler(ctx, msg)
}

// handlePreRegistration handles messages before the
// connection is registered (NICK+USER received).
func (c *Conn) handlePreRegistration(
	ctx context.Context,
	msg *Message,
) {
	switch msg.Command {
	case irc.CmdPass:
		if len(msg.Params) < 1 {
			c.sendNumeric(
				irc.ErrNeedMoreParams,
				"PASS", "Not enough parameters",
			)

			return
		}

		c.passWord = msg.Params[0]
	case irc.CmdNick:
		if len(msg.Params) < 1 {
			c.sendNumeric(
				irc.ErrNoNicknameGiven,
				"No nickname given",
			)

			return
		}

		c.nick = msg.Params[0]
		if len(c.nick) > maxNickLen {
			c.nick = c.nick[:maxNickLen]
		}

		c.gotNick = true
	case irc.CmdUser:
		if len(msg.Params) < 4 { //nolint:mnd
			c.sendNumeric(
				irc.ErrNeedMoreParams,
				"USER", "Not enough parameters",
			)

			return
		}

		c.username = msg.Params[0]
		c.realname = msg.Params[3]
		c.gotUser = true
	case irc.CmdPing:
		c.handlePing(msg)

		return
	case irc.CmdQuit:
		c.handleQuit(msg)

		return
	case "CAP":
		c.handleCAP(msg)

		return
	default:
		c.sendNumeric(
			irc.ErrNotRegistered,
			"You have not registered",
		)

		return
	}

	// Try to complete registration once we have both
	// NICK and USER.
	if c.gotNick && c.gotUser {
		c.completeRegistration(ctx)
	}
}

// completeRegistration creates a session and sends the
// welcome burst.
func (c *Conn) completeRegistration(ctx context.Context) {
	// Check if nick is valid.
	if c.nick == "" {
		c.sendNumeric(
			irc.ErrNoNicknameGiven, "No nickname given",
		)

		return
	}

	// Create session in DB.
	sessionID, clientID, _, err := c.database.CreateSession(
		ctx, c.nick, c.username, c.hostname, c.remoteIP,
	)
	if err != nil {
		if strings.Contains(err.Error(), "UNIQUE constraint") ||
			strings.Contains(err.Error(), "nick") {
			c.sendNumeric(
				irc.ErrNicknameInUse,
				c.nick, "Nickname is already in use",
			)

			return
		}

		c.log.Error(
			"failed to create session", "error", err,
		)
		c.send("ERROR :Internal server error")
		c.closed = true

		return
	}

	c.mu.Lock()
	c.sessionID = sessionID
	c.clientID = clientID
	c.registered = true
	c.mu.Unlock()

	// If PASS was provided before registration, set the
	// session password.
	if c.passWord != "" && len(c.passWord) >= minPasswordLen {
		c.setPassword(ctx, c.passWord)
	}

	// Send welcome burst.
	c.deliverWelcome()
	c.deliverLusers(ctx)
	c.deliverMOTD()

	// Start the message relay goroutine.
	go c.relayMessages(ctx)
}

// deliverWelcome sends 001-005 welcome numerics.
func (c *Conn) deliverWelcome() {
	c.sendNumeric(irc.RplWelcome, fmt.Sprintf(
		"Welcome to the %s Network, %s",
		c.serverSfx, c.hostmask(),
	))
	c.sendNumeric(irc.RplYourHost, fmt.Sprintf(
		"Your host is %s, running version neoirc",
		c.serverSfx,
	))
	c.sendNumeric(
		irc.RplCreated,
		"This server was created recently",
	)
	c.sendNumeric(
		irc.RplMyInfo,
		c.serverSfx, "neoirc", "", "mnst",
	)
	c.sendNumeric(
		irc.RplIsupport,
		"CHANTYPES=#",
		"NICKLEN=32",
		"PREFIX=(ov)@+",
		"CHANMODES=,,H,mnst",
		"NETWORK="+c.serverSfx,
		"are supported by this server",
	)
}

// deliverLusers sends 251/252/254/255 server statistics.
func (c *Conn) deliverLusers(ctx context.Context) {
	users, _ := c.database.GetUserCount(ctx)
	opers, _ := c.database.GetOperCount(ctx)
	channels, _ := c.database.GetChannelCount(ctx)

	c.sendNumeric(irc.RplLuserClient, fmt.Sprintf(
		"There are %d users and 0 invisible on 1 servers",
		users,
	))
	c.sendNumeric(
		irc.RplLuserOp,
		strconv.FormatInt(opers, 10),
		"operator(s) online",
	)
	c.sendNumeric(
		irc.RplLuserChannels,
		strconv.FormatInt(channels, 10),
		"channels formed",
	)
	c.sendNumeric(irc.RplLuserMe, fmt.Sprintf(
		"I have %d clients and 1 servers", users,
	))
}

// deliverMOTD sends 375/372/376 MOTD lines.
func (c *Conn) deliverMOTD() {
	motd := c.cfg.MOTD
	if motd == "" {
		c.sendNumeric(
			irc.ErrNoMotd, "MOTD File is missing",
		)

		return
	}

	c.sendNumeric(irc.RplMotdStart, fmt.Sprintf(
		"- %s Message of the Day -", c.serverSfx,
	))

	for _, line := range strings.Split(motd, "\n") {
		c.sendNumeric(irc.RplMotd, "- "+line)
	}

	c.sendNumeric(
		irc.RplEndOfMotd, "End of /MOTD command",
	)
}

// setPassword sets a bcrypt password on the session.
func (c *Conn) setPassword(ctx context.Context, pw string) {
	// Use the database's auth module to hash and store.
	err := c.database.SetPassword(ctx, c.sessionID, pw)
	if err != nil {
		c.log.Error(
			"failed to set password", "error", err,
		)
	}
}