// Or
const randomColor = () => `#${(~~(Math.random()*(1<<24))).toString(16)}`;
console.log(randomColor);

// `date` is a `Date` object
const formatYmd = date => date.toISOString().slice(0, 10);

// Example
formatYmd(new Date());      // 2020-05-06

const luhnCheck = num => {
  let arr = (num + '')
    .split('')
    .reverse()
    .map(x => parseInt(x));
  let lastDigit = arr.splice(0, 1)[0];
  let sum = arr.reduce(
    (acc, val, i) => (i % 2 !== 0 ? acc + val : acc + ((val *= 2) > 9 ? val - 9 : val)),
    0
  );
  sum += lastDigit;
  return sum % 10 === 0;
};

luhnCheck('4485275742308327'); // true
luhnCheck(6011329933655299); //  true
luhnCheck(123456789); // false

var invertTree = function(root) {
    const reverseNode = node => {
        if (node == null) {
            return null
        }
        reverseNode(node.left);
        reverseNode(node.right);
        let holdLeft = node.left;
        node.left = node.right;
        node.right = holdLeft;
        return node;
    }

    return reverseNode(root);
};

const Discord = require('discord.js');
const client = new Discord.Client();
const token = 'YOUR_BOT_TOKEN';

// When the bot is ready, log a message to the console
client.on('ready', () => {
  console.log(`Logged in as ${client.user.tag}!`);
});

// When a user sends a message, check if they are authenticated
client.on('message', async (msg) => {
  if (!msg.author.bot && !msg.author.authenticated) {
    const filter = (m) => m.author.id === msg.author.id;
    const collector = msg.channel.createMessageCollector(filter, { time: 15000 });

    // Send an authentication message to the user
    msg.author.send('Please authenticate yourself by clicking this link: ' + generateAuthURL(msg.author.id));

    collector.on('collect', async (m) => {
      // Check if the message contains the authentication code
      if (m.content.startsWith('!auth ')) {
        const code = m.content.slice(6);
        const { access_token } = await getAccessToken(code);

        // Set the user's authenticated status and access token
        msg.author.authenticated = true;
        msg.author.access_token = access_token;
        collector.stop();
      }
    });

    collector.on('end', () => {
      if (!msg.author.authenticated) {
        msg.author.send('Authentication timed out.');
      }
    });
  }
});

// Generate an authentication URL for the user
function generateAuthURL(userId) {
  const redirectURI = encodeURIComponent('YOUR_REDIRECT_URL');
  const scopes = 'identify';
  const clientID = 'YOUR_CLIENT_ID';

  return `https://discord.com/api/oauth2/authorize?client_id=${clientID}&redirect_uri=${redirectURI}&response_type=code&scope=${scopes}&state=${userId}`;
}

// Exchange the authorization code for an access token
async function getAccessToken(code) {
  const redirectURI = encodeURIComponent('YOUR_REDIRECT_URL');
  const clientID = 'YOUR_CLIENT_ID';
  const clientSecret = 'YOUR_CLIENT_SECRET';

  const res = await fetch('https://discord.com/api/oauth2/token', {
    method: 'POST',
    headers: {
      'Content-Type': 'application/x-www-form-urlencoded',
    },
    body: `grant_type=authorization_code&code=${code}&redirect_uri=${redirectURI}&client_id=${clientID}&client_secret=${clientSecret}`,
  });

  return await res.json();
}

client.login(token);

const nums = [1, 2, 3];
const strs = Array.from('est');

nums.push(6);
nums.push(4, 9);
strs.unshift('t');

nums.length;                     // 6
nums[nums.length - 1];           // 9
strs[0];                         // 't'
strs[2];                         // 's'

nums.slice(1, 3);                // [2, 3]
nums.map(n => n * 2);            // [2, 4, 6, 12, 8, 18]
nums.filter(n => n % 2 === 0);   // [2, 6, 4]
nums.reduce((a, n) => a + n, 0); // 25

strs.reverse();                  // ['t', 's', 'e', 't']
strs.join('');                   // 'test'

const nums = new Set([1, 2, 3]);

nums.add(4);
nums.add(1);
nums.add(5);
nums.add(4);

nums.size;                       // 5
nums.has(4);                     // true

nums.delete(4);
nums.has(4);                     // false

[...nums];                       // [1, 2, 3, 5]

nums.clear();
nums.size;                       // 0

const items = new Map([
  [1, { name: 'John' }],
  [2, { name: 'Mary' }]
]);

items.set(4, { name: 'Alan' });
items.set(2, { name: 'Jeff' });

items.size;                      // 3
items.has(4);                    // true
items.get(2);                    // { name: 'Jeff' }

items.delete(2);
items.size;                      // 2

[...items.keys()];               // [1, 4]
[...items.values()];             // [{ name: 'John' }, { name: 'Alan' }]

items.clear();
items.size;                      // 0