index.js

const fs = require('mz/fs');
const http = require('http');
const url = require('url');
const { Readable } = require('stream');
const colors = require('colors/safe');

const frames = [];
const flipped = [];

// Setup frames in memory
fs.readdir('./frames').then(data => {
  data.forEach(async frame => {
    const f = await fs.readFile(`./frames/${frame}`);
    frames.push(f.toString());
    flipped.push(
      f
        .toString()
        .split('')
        .reverse()
        .join('')
    );
  });
});

const colorsOptions = [
  'red',
  'yellow',
  'green',
  'blue',
  'magenta',
  'cyan',
  'white'
];
const numColors = colorsOptions.length;

const streamer = (stream, opts) => {
  const { flip } = opts;

  let index = 0;
  let lastColor = -1;
  let newColor = 0;
  let frame = null;

  return setInterval(() => {
    if (index >= frames.length) index = 0;
    if (index < 0) index = frames.length - 1;

    stream.push('\033[2J\033[H');
    newColor = Math.floor(Math.random() * numColors);

    // Reroll for a new color if it was the same as last frame
    if (newColor == lastColor) {
      newColor += 1 + Math.floor(Math.random() * (numColors - 1));
      newColor %= numColors;
    }

    lastColor = newColor;
    frame = flip ? flipped[index] : frames[index];
    stream.push(colors[colorsOptions[newColor]](frame));
    index++;
  }, 100);
};

const validateQuery = query => {
  const { flip } = query;
  return {
    flip: typeof flip === 'string' && flip.toLowerCase() == 'true'
  };
};

const server = http.createServer((req, res) => {
  if (
    req.headers &&
    req.headers['user-agent'] &&
    !req.headers['user-agent'].includes('curl')
  ) {
    res.writeHead(302, { Location: 'https://github.com/joeheyming/ascii_nyan' });
    return res.end();
  }
  const { query } = url.parse(req.url, true);
  const stream = new Readable();
  stream._read = function noop() {};
  stream.pipe(res);
  const interval = streamer(stream, validateQuery(query));

  req.on('close', () => {
    stream.destroy();
    clearInterval(interval);
  });
});

const port = process.env.NYAN_PORT || 3000;
server.listen(port, err => {
  if (err) throw err;
  console.log(`Listening on localhost:${port}`);
});