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);
+  }
+}

package-lock.json

@@ -16191,6 +16191,63 @@
         "bser": "2.1.1"
       }
     },
+    "fetch-mock": {
+      "version": "9.10.7",
+      "resolved": "https://registry.npmjs.org/fetch-mock/-/fetch-mock-9.10.7.tgz",
+      "integrity": "sha512-YkiMHSL8CQ0vlWYpqGvlaZjViFk0Kar9jonPjSvaWoztkeHH6DENqUzBIsffzjVKhwchPI74SZRLRpIsEyNcZQ==",
+      "dev": true,
+      "requires": {
+        "babel-runtime": "^6.26.0",
+        "core-js": "^3.0.0",
+        "debug": "^4.1.1",
+        "glob-to-regexp": "^0.4.0",
+        "is-subset": "^0.1.1",
+        "lodash.isequal": "^4.5.0",
+        "path-to-regexp": "^2.2.1",
+        "querystring": "^0.2.0",
+        "whatwg-url": "^6.5.0"
+      },
+      "dependencies": {
+        "core-js": {
+          "version": "3.6.5",
+          "resolved": "https://registry.npmjs.org/core-js/-/core-js-3.6.5.tgz",
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+          "dev": true
+        },
+        "debug": {
+          "version": "4.2.0",
+          "resolved": "https://registry.npmjs.org/debug/-/debug-4.2.0.tgz",
+          "integrity": "sha512-IX2ncY78vDTjZMFUdmsvIRFY2Cf4FnD0wRs+nQwJU8Lu99/tPFdb0VybiiMTPe3I6rQmwsqQqRBvxU+bZ/I8sg==",
+          "dev": true,
+          "requires": {
+            "ms": "2.1.2"
+          }
+        },
+        "ms": {
+          "version": "2.1.2",
+          "resolved": "https://registry.npmjs.org/ms/-/ms-2.1.2.tgz",
+          "integrity": "sha512-sGkPx+VjMtmA6MX27oA4FBFELFCZZ4S4XqeGOXCv68tT+jb3vk/RyaKWP0PTKyWtmLSM0b+adUTEvbs1PEaH2w==",
+          "dev": true
+        },
+        "path-to-regexp": {
+          "version": "2.4.0",
+          "resolved": "https://registry.npmjs.org/path-to-regexp/-/path-to-regexp-2.4.0.tgz",
+          "integrity": "sha512-G6zHoVqC6GGTQkZwF4lkuEyMbVOjoBKAEybQUypI1WTkqinCOrq2x6U2+phkJ1XsEMTy4LjtwPI7HW+NVrRR2w==",
+          "dev": true
+        },
+        "whatwg-url": {
+          "version": "6.5.0",
+          "resolved": "https://registry.npmjs.org/whatwg-url/-/whatwg-url-6.5.0.tgz",
+          "integrity": "sha512-rhRZRqx/TLJQWUpQ6bmrt2UV4f0HCQ463yQuONJqC6fO2VoEb1pTYddbe59SkYq87aoM5A3bdhMZiUiVws+fzQ==",
+          "dev": true,
+          "requires": {
+            "lodash.sortby": "^4.7.0",
+            "tr46": "^1.0.1",
+            "webidl-conversions": "^4.0.2"
+          }
+        }
+      }
+    },
     "figgy-pudding": {
       "version": "3.5.2",
       "resolved": "https://registry.npmjs.org/figgy-pudding/-/figgy-pudding-3.5.2.tgz",
@@ -16930,6 +16987,12 @@
         }
       }
     },
+    "glob-to-regexp": {
+      "version": "0.4.1",
+      "resolved": "https://registry.npmjs.org/glob-to-regexp/-/glob-to-regexp-0.4.1.tgz",
+      "integrity": "sha512-lkX1HJXwyMcprw/5YUZc2s7DrpAiHB21/V+E1rHUrVNokkvB6bqMzT0VfV6/86ZNabt1k14YOIaT7nDvOX3Iiw==",
+      "dev": true
+    },
     "global": {
       "version": "4.3.2",
       "resolved": "https://registry.npmjs.org/global/-/global-4.3.2.tgz",
@@ -18352,6 +18415,12 @@
       "integrity": "sha1-EtSj3U5o4Lec6428hBc66A2RykQ=",
       "dev": true
     },
+    "is-subset": {
+      "version": "0.1.1",
+      "resolved": "https://registry.npmjs.org/is-subset/-/is-subset-0.1.1.tgz",
+      "integrity": "sha1-ilkRfZMt4d4A8kX83TnOQ/HpOaY=",
+      "dev": true
+    },
     "is-symbol": {
       "version": "1.0.2",
       "resolved": "https://registry.npmjs.org/is-symbol/-/is-symbol-1.0.2.tgz",
@@ -19495,6 +19564,12 @@
       "integrity": "sha1-eeTriMNqgSKvhvhEqpvNhRtfu1U=",
       "dev": true
     },
+    "lodash.isequal": {
+      "version": "4.5.0",
+      "resolved": "https://registry.npmjs.org/lodash.isequal/-/lodash.isequal-4.5.0.tgz",
+      "integrity": "sha1-QVxEePK8wwEgwizhDtMib30+GOA=",
+      "dev": true
+    },
     "lodash.isfunction": {
       "version": "2.3.0",
       "resolved": "https://registry.npmjs.org/lodash.isfunction/-/lodash.isfunction-2.3.0.tgz",

package.json

@@ -67,6 +67,7 @@
     "eslint-plugin-ember": "^8.5.2",
     "eslint-plugin-node": "^11.1.0",
     "ethers": "^4.0.47",
+    "fetch-mock": "^9.10.7",
     "kredits-contracts": "github:67P/kredits-contracts#feature/expenses",
     "loader.js": "^4.7.0",
     "localforage": "^1.7.3",

tests/unit/utils/fetch-exchange-rate-test.js

@@ -0,0 +1,31 @@
+import fetchExchangeRate from 'kredits-web/utils/fetch-exchange-rate';
+import { module, test } from 'qunit';
+import fetchMock from 'fetch-mock';
+
+fetchMock.get('https://www.bitstamp.net/api/v2/ticker/btceur/', {
+  "high": "9258.43", "last": "9165.14", "timestamp": "1601455909", "bid":
+  "9159.93", "vwap": "9167.57", "volume": "1542.54764854", "low": "9080.20",
+  "ask": "9165.14", "open": "9240.84"
+});
+
+fetchMock.get('https://www.bitstamp.net/api/v2/ticker/btcusd/', {
+  "high": "10865.00", "last": "10714.62", "timestamp": "1601455914", "bid":
+  "10711.31", "vwap": "10749.70", "volume": "4460.32091975", "low": "10636.66",
+  "ask": "10715.99", "open": "10840.00"
+});
+
+module('Unit | Utility | fetch-exchange-rate', function() {
+  test('it requires a currency pair', function(assert) {
+    assert.throws(fetchExchangeRate);
+  });
+
+  test('it fetches BTCEUR from Bitstamp', async function(assert) {
+    let result = await fetchExchangeRate('btceur');
+    assert.equal(result, 9167.57, 'returns 24-hour volume-weighted average price');
+  });
+
+  test('it fetches BTCUSD from Bitstamp', async function(assert) {
+    let result = await fetchExchangeRate('btcusd');
+    assert.equal(result, 10749.70, 'returns 24-hour volume-weighted average price');
+  });
+});