rate service + tests

js/models/RateService.js

@@ -0,0 +1,125 @@
+'use strict';
+
+var util = require('util');
+var _ = require('lodash');
+var log = require('../log');
+var preconditions = require('preconditions').singleton();
+var request = require('request');
+
+/*
+  This class lets interfaces with BitPay's exchange rate API.
+*/
+
+var RateService = function(opts) {
+  var self = this;
+
+  self.SAT_TO_BTC = 1 / 1e8;
+  self.BTC_TO_SAT = 1e8;
+  self.UNAVAILABLE_ERROR = 'Service is not available - check for service.isAvailable() or use service.whenAvailable()';
+  self.UNSUPPORTED_CURRENCY_ERROR = 'Currency not supported';
+
+  self._isAvailable = false;
+  self._rates = {};
+  self._alternatives = {};
+  self.queued = [];
+
+  self._fetchCurrencies();
+}
+
+RateService.prototype._fetchCurrencies = function() {
+  var self = this;
+
+  var backoffSeconds = 5;
+  var updateFrequencySeconds = 3600;
+  var rateServiceUrl = 'https://bitpay.com/api/rates';
+
+  request.get({
+    url: rateServiceUrl,
+    json: true
+  }, function(err, res, body) {
+    if (err || !body) {
+      backoffSeconds *= 1.5;
+      setTimeout(retrieve, backoffSeconds * 1000);
+      return;
+    }
+    _.each(body, function(currency) {
+      self.rates[currency.code] = currency.rate;
+      self.alternatives.push({
+        name: currency.name,
+        isoCode: currency.code,
+        rate: currency.rate
+      });
+    });
+    self._isAvailable = true;
+    _.each(self.queued, function(callback) {
+      setTimeout(callback, 1);
+    });
+    setTimeout(function() {
+      self._fetchCurrencies()
+    }, updateFrequencySeconds * 1000);
+  });
+};
+
+RateService.prototype._getRate = function(code) {
+  return this._rates[code];
+};
+
+RateService.prototype._getHistoricRate = function(code, date, cb) {
+  // TODO (isocolsky): implement with a remote call
+  return cb(new Error('Not implemented'));
+};
+
+RateService.prototype._getAlternatives = function() {
+  return this._alternatives;
+};
+
+RateService.prototype.isAvailable = function() {
+  return this._isAvailable;
+};
+
+RateService.prototype.whenAvailable = function(callback) {
+  if (!this.isAvailable()) {
+    setTimeout(callback, 1);
+  } else {
+    this.queued.push(callback);
+  }
+};
+
+RateService.prototype.toFiat = function(satoshis, code) {
+  if (!this.isAvailable()) {
+    throw new Error(this.UNAVAILABLE_ERROR);
+  }
+  return satoshis * this.SAT_TO_BTC * this._getRate(code);
+};
+
+RateService.prototype.toFiatHistoric = function(satoshis, code, date, cb) {
+  var self = this;
+
+  self._getHistoricRate(code, date, function(err, rate) {
+    if (err) return cb(err);
+    return cb(null, satoshis * self.SAT_TO_BTC * rate);
+  });
+};
+
+RateService.prototype.fromFiat = function(amount, code) {
+  if (!this.isAvailable()) {
+    throw new Error(this.UNAVAILABLE_ERROR);
+  }
+  return amount / this._getRate(code) * this.BTC_TO_SAT;
+};
+
+RateService.prototype.listAlternatives = function() {
+  if (!this.isAvailable()) {
+    throw new Error(this.UNAVAILABLE_ERROR);
+  }
+
+  return _.map(this._getAlternatives(), function(item) {
+    return {
+      name: item.name,
+      isoCode: item.isoCode
+    }
+  });
+};
+
+
+module.exports = RateService;