dolar-blue/lib/sources/Bluelytics.js

dolar-blue ==========

var http = require('http');

// Bluelytics displays values from a number of sources. This will
// determine the average blue dolar rate from among these (excluding la nación rate)
var avg_blue = function(data) {

  // Filtered list containing only blue dolar values
  var only_blue = data.filter(function(s) {
    return (s.source !== 'la_nacion' && !isNaN(s.value_sell) && !isNaN(s.value_buy) && s.value_sell > 0 && s.value_buy > 0);
  });

  // Helper function to calculate the sum of a specific variable common to all data sources
  var sumVar = function(varName) {
    var passVar = varName;

    return function(a, b) {
      return a + b[passVar];
    };
  };

  // Helper function to determine the most recent of two dates being compared
  var lastDate = function(a, b) {
    ndate = new Date(b.date);
    return new Date(Math.max(a, ndate));
  };

  // Reduced (averaged) data product
  return {
    sell: parseFloat((only_blue.reduce(sumVar('value_sell'), 0) / only_blue.length).toFixed(4)),
    buy: parseFloat((only_blue.reduce(sumVar('value_buy'), 0) / only_blue.length).toFixed(4)),
    date: only_blue.reduce(lastDate, 0)
  };

};

// Public API for this package
exports.getData = function(cb) {

  var options = {
    name: 'Bluelytics',
    host: 'api.bluelytics.com.ar',
    path: '/json/last_price'
  };

  var req = http.request(options, function(res) {
    var str = '';

    res.on('data', function(chunk) {
      str += chunk;
    });

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

      // Set up return object
      var ret = {};
      ret.date = new Date();
      ret.source = {
        name: options.name,
        uri: 'http://' + options.host + options.path
      };

      // Parse response from Bluelytics
      try {
        ret.data = JSON.parse(str);
      } catch (err) {
        return cb('Bad JSON from ' + options.host + options.path + ':' + err + '\n' + str);
      }

      // Compute the rates using the average of all Bluelytics sources
      ret.rates = avg_blue(ret.data);
      ret.rates.source = options.name;

      if (!isNaN(ret.rates.sell) && !isNaN(ret.rates.buy)) {
        cb(null, ret);
      } else {
        cb('Unexpected response from ' + options.host + options.path);
      }
    });
  });

  req.end();

  req.on('error', function(e) {
    cb(e);
  });

};