index.js

const fs = require('fs');
const Discord = require('discord.js');
const DISCORD_BOT_TOKEN = process.env.DISCORD_BOT_TOKEN;
const BOT_NICKNAME = process.env.BOT_NICKNAME || 'GM Emulator';
const prefix = process.env.BOT_COMMAND_PREFIX;

const client = new Discord.Client();
client.commands = new Discord.Collection();

const commandFiles = fs.readdirSync('./commands').filter(file => file.endsWith('.js'));

for (const file of commandFiles) {
	const command = require(`./commands/${file}`);
	client.commands.set(command.name, command);
}

const cooldowns = new Discord.Collection();

client.on('ready', () => {
	console.log(`Ready! Listening for commands with ${prefix}`);
	client.user.setUsername('Game Master Emulator');
	client.guilds.cache.every((guild) => guild.me.setNickname(BOT_NICKNAME));
	client.user.setPresence({
		activity: {
			name: `*${prefix}* commands`,
			type: 'LISTENING',
		},
		status: 'online',
	});
});

client.on('message', message => {
	if (!message.content.startsWith(prefix) || message.author.bot) return;
	// && message.channel.type !== 'dm'

	const args = message.content.slice(prefix.length).trim().split(/ +/);
	const commandName = args.shift().toLowerCase() || 'ask';

	let command = client.commands.get(commandName)
	|| client.commands.find(cmd => cmd.aliases && cmd.aliases.includes(commandName));

	if (!command) {
		args.unshift(commandName);
		command = client.commands.get('ask');
	}

	console.log('got command', command.name, args);

	if (command.guildOnly && message.channel.type !== 'text') {
		return message.reply('I can\'t execute that command inside DMs!');
	}

	if (command.args && !args.length) {
		let reply = `You didn't provide any arguments, ${message.author}! Try ${prefix} help ${commandName}`;

		if (command.usage) {
			reply += `\nThe proper usage would be: \`${prefix} ${command.name} ${command.usage}\``;
		}

		return message.channel.send(reply);
	}

	if (!cooldowns.has(command.name)) {
		cooldowns.set(command.name, new Discord.Collection());
	}

	const now = Date.now();
	const timestamps = cooldowns.get(command.name);
	const cooldownAmount = (command.cooldown || 3) * 1000;

	if (!timestamps.has(message.author.id)) {
		timestamps.set(message.author.id, now);
		setTimeout(() => timestamps.delete(message.author.id), cooldownAmount);
	}
	else {
		const expirationTime = timestamps.get(message.author.id) + cooldownAmount;

		if (now < expirationTime) {
			const timeLeft = (expirationTime - now) / 1000;
			return message.reply(`please wait ${timeLeft.toFixed(1)} more second(s) before reusing the \`${command.name}\` command.`);
		}

		timestamps.set(message.author.id, now);
		setTimeout(() => timestamps.delete(message.author.id), cooldownAmount);
	}

	try {
		command.execute(message, args);
	}
	catch (error) {
		console.error(error);
		message.reply('there was an error trying to execute that command!');
	}
});

client.login(DISCORD_BOT_TOKEN);

// so the program will not close instantly
process.stdin.resume();

function exitHandler(options, err) {
	if (options.cleanup) cleanup();
	if (err && err.stack) {
		console.log('error stack:', err.stack);
	}
	if (options.exit) process.exit();
}

function cleanup() {
	if (client) {
		console.log('going offline.');
		client.user.setStatus('invisible');
	}
}

// do something when app is closing
process.on('exit', exitHandler.bind(null, { cleanup: true }));

// catches ctrl+c event
process.on('SIGINT', exitHandler.bind(null, { exit: true }));
process.on('SIGTERM', exitHandler.bind(null, { exit: true }));

// catches "kill pid" (for example: nodemon restart)
process.on('SIGUSR1', exitHandler.bind(null, { exit: true }));
process.on('SIGUSR2', exitHandler.bind(null, { exit: true }));

// catches uncaught exceptions
process.on('uncaughtException', exitHandler.bind(null, { exit: true }));