Watches an item in the Steam market place and highlights it if price drops below desired value

steamMarketWatch.js

'use strict';

// npm install colors moment optimist

// builtins
var http   = require('http'),
// 3rd party
    colors = require('colors/safe'),
    moment = require('moment');

var currency = 'USD'; // can be USD, GBP or EUR

var argv = require('optimist')
             .usage('\nWatch steam market items.\n\nUsage: $0')
             .demand(['a', 'c', 'i', 'n', 'p', 'w'])
             .default({a: 730, i: 60, n: 'Fire Serpent', 'c': 'BS', w: 'AK-47'})
             .describe({'a':'a steam application id',
                        'c':'a weapon condition (e.g. MW)',
                        'i':'an interval in seconds',
                        'n':'a skin name',
                        'p':'a price in ' + currency,
                        'q':'quiet - only alert when price drops below target',
                        's':'StatTrak\u2122',
                        't':'Souvenir ("tournament" quality)',
                        'u':'\u2605 ("unusual" quality - e.g. knives)',
                        'w':'a weapon name'})
             .argv;

// globals
var checkInterval = (parseInt(argv.i) * 1000),
    condition = '',
    currencyValue = '';

//
// main
//
switch (currency) {
  case 'USD':
    currencyValue = '1';
    break;

  case 'GBP':
    currencyValue = '2';
    break;

  case 'EUR':
    currencyValue = '3';
    break;

  default:
    currencyValue = '1';
}

switch (argv.c) {
  case 'BS':
    condition = '(Battle-Scarred)';
    break;

  case 'FN':
    condition = '(Factory New)';
    break;

  case 'FT':
    condition = '(Field-Tested)';
    break;

  case 'MW':
    condition = '(Minimal Wear)';
    break;

  case 'WW':
    condition = '(Well-Worn)';
    break;

  default:
    condition = '(Factory New)';
    break;
}

var s = argv.s ? 'StatTrak\u2122 ' : '';

var t = argv.t ? 'Souvenir ' : '';

var u = argv.u ? '\u2605 ' : '';

var market_hash_name = t + u + s + argv.w + ' | ' + argv.n + ' ' + condition;

console.log('\nchecking item ' + colors.green(market_hash_name) + ' every ' + argv.i + ' seconds.\n');

checkItem(market_hash_name);

setInterval(function() { checkItem(market_hash_name); }, checkInterval);

//
// functions
//
function checkItem(item) {

  var qs = '?currency=' + currencyValue + '&appid=' + argv.a + '&market_hash_name=' + encodeURI(item);

  var marketData = '',
      options = {
        headers: {
          'user-agent':'Mozilla/5.0 (Windows NT 6.3; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/37.0.2049.0 Safari/537.36'
        },
        host: 'steamcommunity.com',
        path: '/market/priceoverview/' + qs
      };

  var req = http.request(options, function (res) {
    if (res.statusCode === 500 ) {
      console.log('item does not exist');
      return;
    }

    if (res.statusCode !== 200) {
      console.log('bad http response, is steam market down?');
      return;
    }

    res.on('data', function (chunk) {

      marketData += chunk;

    }).on('end', function () {

      var d = JSON.parse(marketData);

      if (!d.lowest_price) {
        console.log('no listing');
      } else {
        var price  = getPrice(d.lowest_price),
            median = getPrice(d.median_price),
            max    = parseFloat(argv.p);
        if ( price < max ) {
          console.log(colors.green('\u2192 ' + price.toFixed(2)) + ' ' + moment().format('HH:mm:ss'));
        } else {
          if (!argv.q) {
            console.log(price.toFixed(2) + ' (' + median.toFixed(2) + ')');
          }
        }
      }
    });
  });

  req.on('error', function (err) {
    console.log('error: ' + err.message);
  });

  req.write('\n');

  req.end();
}

function getPrice(s) {
  if (currency === 'USD') {
    // s is something like "$314.60"
    return parseFloat(s.slice(1));
  } else {
    // s is something like "&#36;314.60"
    return parseFloat(s.split(';')[1]);
  }
}

Added Souvenir and 'unusual quality' (anything with a ★) options, refactored currency stuff and default is now USD.

fixed getPrice()... different format for USD!