Add util for fetching bitcoin exchange rate

app/utils/fetch-exchange-rate.js

@@ -0,0 +1,20 @@
+const bitstampBaseUrl = 'https://www.bitstamp.net/api/v2';
+
+async function fetchFromBitstamp(currencyPair) {
+  try {
+    const res = await fetch(`${bitstampBaseUrl}/ticker/${currencyPair}/`).then(r => r.json());
+    return res.vwap; // Last 24 hours volume weighted average price
+  } catch(e) {
+    console.error('Could not fetch exchange rate from Bitstamp:', e);
+    return 0;
+  }
+}
+
+export default function fetchExchangeRate(currencyPair, source='bitstamp') {
+  if (!currencyPair) throw 'Currency pair required';
+
+  switch(source) {
+    case 'bitstamp':
+      return fetchFromBitstamp(currencyPair);
+  }
+}