Gives some insights into bitcoin markets from Bittrex stats

bittrex-watch.js

const fetch = require('node-fetch');
const chalk = require('chalk');
const term = require('terminal-kit').terminal;
const fs = require('fs'),
      path = require('path');


const timestamp = () => new Date().toLocaleTimeString();

const getMarketValue = market =>
  fetch(`https://bittrex.com/api/v1.1/public/getmarketsummary?market=${market}`).then(res => res.json());

const getLogColor = (currentValue, lastValue) => {
  if (currentValue === lastValue) return chalk.white;
  return currentValue > lastValue ? chalk.green : chalk.red;
};

const logValue = (marketResponse, watch, lastValue) => {
  const currentValue = marketResponse.result[0].Last;
  const color = getLogColor(currentValue, lastValue);
  if (currentValue === lastValue) {
    process.stdout.write('.');
    return;
  }

  const diff = (currentValue - lastValue).toFixed(8).replace(/^\d+/, m => `+${m}`);
  console.log(`\n${timestamp()} ${watch.market} = ${color(currentValue.toFixed(8))} (${diff} ${color(diffGraph(lastValue, currentValue))})`);
};

const nowSecond = () => Math.floor(Date.now() / 1000);

const diffGraph = (prev, curr) => {
  const diff = Math.abs(prev - curr);
  const dots = Math.round((diff / prev) * 3000);
  return '*'.repeat(dots === Infinity ? 0 : dots);
};

const appendStats = (stats, value) => {
  stats[nowSecond()] = value;
  delete stats[nowSecond() - (181 * 60)];
};

const statusBar = stats => [1, 5, 15, 30].map(m => `${m}m ${statusDiff(stats, m * 60)}`).join(' | ');

const closestStat = (stats, time) =>
  stats[time] || stats[time - 1] || stats[time - 2] || stats[time - 3];

const statusDiff = (stats, secondsAgo) => {
  const now = nowSecond();
  const earliest = closestStat(stats, now - secondsAgo);
  const current = stats[now] || Object.keys(stats).sort((a, b) => a < b ? 1 : -1)[0];

  const diff = current - earliest;
  const percentage = ((current / earliest) * 100) - 100;
  return `${diff.toFixed(8)} (${percentage.toFixed(3)})`;
};

const writeStats = (statsPath, stats) => {
  fs.writeFile(statsPath, JSON.stringify(stats, null, 2), () => {});
};

const startWatching = watch => {
  let lastValue = 0;
  const stats = fs.existsSync(statsPath) ?
    JSON.parse(fs.readFileSync(statsPath)) :
    {};

  function lookupMarket() {
    const mv = getMarketValue(watch.market);
    mv.then(marketResponse => logValue(marketResponse, watch, lastValue));
    mv.then(marketResponse => lastValue = marketResponse.result[0].Last)
      .then(val => appendStats(stats, val))
      .then(() => writeStats(statsPath, stats))
      .then(() => {
        term.saveCursor();
        term.moveTo(1, 1).eraseLine();
        term(statusBar(stats));
        term.restoreCursor();
      });
    setTimeout(lookupMarket, 1000);
  }

  lookupMarket();
};

const appWatch = {
  market: process.argv[2],
};

const statsPath = path.resolve(__dirname, '..', `${appWatch.market}.json`);

startWatching(appWatch, statsPath);