ADD: prepare for currency conversion

App.test.js

@@ -250,3 +250,16 @@ it('Wallet can fetch balance', async () => {
   assert.ok(w.getUnconfirmedBalance() === 0);
   assert.ok(w._lastBalanceFetch > 0);
 });
+
+describe('currency', () => {
+  it.only('fetches exchange rate and saves to AsyncStorage', async () => {
+    AsyncStorage.storageCache = {}; // cleanup from other tests
+    let currency = require('./currency');
+    await currency.startUpdater(true);
+    let cur = AsyncStorage.storageCache[AppStorage.CURRENCY];
+    cur = JSON.parse(cur);
+    assert.ok(Number.isInteger(cur[currency.STRUCT.LAST_UPDATED]));
+    assert.ok(cur[currency.STRUCT.LAST_UPDATED] > 0);
+    assert.ok(cur[currency.STRUCT.BTC_USD] > 0);
+  });
+});

currency.js

@@ -0,0 +1,63 @@
+import Frisbee from 'frisbee';
+import { AsyncStorage } from 'react-native';
+import { AppStorage } from './class';
+
+let lang = {};
+// let btcusd = 6500; // default
+
+const STRUCT = {
+  LAST_UPDATED: 'LAST_UPDATED',
+  BTC_USD: 'BTC_USD',
+};
+
+async function updateExchangeRate() {
+  if (+new Date() - lang[STRUCT.LAST_UPDATED] <= 30 * 60 * 1000) {
+    // not updating too often
+    return;
+  }
+
+  let json;
+  try {
+    const api = new Frisbee({
+      baseURI: 'https://www.bitstamp.net',
+    });
+
+    let response = await api.get('/api/v2/ticker/btcusd');
+    json = response.body;
+    if (typeof json === 'undefined' || typeof json.last === 'undefined') {
+      throw new Error('Could not update currency rate: ' + response.err);
+    }
+  } catch (Err) {
+    console.warn(Err);
+  }
+
+  lang[STRUCT.LAST_UPDATED] = +new Date();
+  lang[STRUCT.BTC_USD] = json.last * 1;
+  await AsyncStorage.setItem(AppStorage.CURRENCY, JSON.stringify(lang));
+  console.log('updated currency exchange:', lang);
+}
+
+async function startUpdater(doNotSetInterval) {
+  lang = await AsyncStorage.getItem(AppStorage.CURRENCY);
+  try {
+    lang = JSON.parse(lang);
+  } catch (Err) {
+    lang = {};
+  }
+  if (lang) {
+    console.log('lang is true');
+  }
+  lang = lang || {};
+
+  lang[STRUCT.LAST_UPDATED] = lang[STRUCT.LAST_UPDATED] || 0;
+  lang[STRUCT.BTC_USD] = lang[STRUCT.BTC_USD] || 6500;
+
+  if (!doNotSetInterval) {
+    setInterval(() => updateExchangeRate(), 2 * 60 * 100);
+  }
+  return updateExchangeRate();
+}
+
+module.exports.updateExchangeRate = updateExchangeRate;
+module.exports.startUpdater = startUpdater;
+module.exports.STRUCT = STRUCT;