index.js

const IRC = require('irc-framework');
const { Client, GatewayIntentBits } = require('discord.js');
const fs = require('fs');

let bots = {};
let channels = {};

const config = JSON.parse(fs.readFileSync('config.json'));

const client = new Client({
    intents: [
        GatewayIntentBits.Guilds,
        GatewayIntentBits.GuildMessages,
        GatewayIntentBits.MessageContent,
        GatewayIntentBits.GuildMembers
    ],
});

client.login(config.discordToken);

client.on('ready', () => {
    console.log(`Bot is ready!`);

    Object.values(config.channels).forEach(channelId => {
        channels[channelId] = client.channels.cache.get(channelId);
    });

    bots[client.user.id] = createBot(config.nick, 'relay', () => {
        bots[client.user.id].on('message', function (event) {
            if(config.excludeNicks.includes(event.nick))
                return;
    
            let channel = channels[config.channels[event.target]];
            
            if (!messageIsFromRelay(event.nick)) {
                event.nick = stripColours(event.nick);
                event.message = stripColours(event.message);
                channel
                    .send(`<${event.nick}> ${event.message}`)
                    .catch(console.error);
            }
        });
    
        bots[client.user.id].on('nick', function (event) {
            event.nick = stripColours(event.nick);
            event.new_nick = stripColours(event.new_nick);
            Object.values(channels).forEach(channel => {
                channel
                    .send(`**${event.nick}** is now known as **${event.new_nick}**`)
                    .catch(console.error);
            });
        });
    });
});

client.on('messageCreate', message => {
    const ircChannel = getIrcChannelFromDiscordChannel(message.channel.id);

    if (!ircChannel || message.author.id == client.user.id)
        return;

    if (bots[message.author.id] == null) {
        client.guilds.fetch(message.guildId).then(guild => {
            guild.members.fetch(message.author.id).then(member => {
                bots[message.author.id] = createBot(member.nickname, message.author.username, () => {
                    relayMessage(ircChannel, message);
                });
            });
        });
    } else {
        relayMessage(ircChannel, message);
    }
});

client.on('guildMemberUpdate', (oldMember, newMember) => {
    if (bots[newMember.user.id]) {
        changeNick(bots[newMember.user.id], newMember.nickname||newMember.user.username)
    }
});

function createBot(nick, username, registerCallback) {
    console.log(`Creating bot for ${nick||username}`);

    var bot = new IRC.Client();

    bot.connect({
        host: config.host,
        port: config.port,
        nick: sanitizeDiscordUsername(nick||username),
        username: sanitizeDiscordUsername(username).substring(0, 8),
        tls: config.port == 6697 ? true : false,
        rejectUnauthorized: false,
    });

    bot.on('registered', () => {
        Object.keys(config.channels).forEach(channel => {
            bot.join(channel);
        });
        if (registerCallback != null)
            registerCallback();
    });

    return bot;
}

function relayMessage(ircChannel, message) {
    let msg = '';

    if(message.mentions && message.mentions.repliedUser)
        msg += `${message.mentions.repliedUser.username}: `;
    msg += message.content;

    bots[message.author.id].say(ircChannel, msg);

    if (message.attachments.size > 0) {
        message.attachments.forEach(attachment => {
            bots[message.author.id].say(ircChannel, attachment.url);
        });
    }
}

function changeNick(bot, nick){
    let newNick = sanitizeDiscordUsername(nick);
    bot.changeNick(newNick);
    bot.options.nick = newNick;
}

function getIrcChannelFromDiscordChannel(discordChannelId) {
    let ircChannel = false;
    Object.keys(config.channels).forEach(ircChannelId => {
        if (config.channels[ircChannelId] == discordChannelId)
            ircChannel = ircChannelId;
    });
    return ircChannel;
};

function messageIsFromRelay(nick) {
    let isFromRelay = false;
    Object.values(bots).forEach(bot => {
        if (bot.options.nick == nick)
            isFromRelay = true;
    });

    return isFromRelay;
}

function sanitizeDiscordUsername(username) {
    return username.replace(/[^a-zA-Z0-9]/g, '').substring(0, config.maxNickLength);
}

function stripColours(str) {
    str = str.replace(/\x03[0-9]{1,2}(,[0-9]{1,2})?/g, '');
    str = str.replace(/[\x00-\x1F\x7F-\x9F]/g, '');
    return str;
}