feat: add function to get metrics for all circuits (#328)

feat: add function to get metrics for all circuits

Prior to this, it was only possible to get metrics from the circuit itself. And if multiple circuits were created, the last one would have all metrics available, which isn't very intuitive. It makes more sense to obtain metrics for all circuits from the factory.

Fixes: #327

index.js

@@ -1,6 +1,7 @@
 'use strict';
 
 const CircuitBreaker = require('./lib/circuit');
+const circuits = [];
 
 const defaults = {
   timeout: 10000, // 10 seconds
@@ -63,7 +64,10 @@ const defaults = {
  * @return {CircuitBreaker} a newly created {@link CircuitBreaker} instance
  */
 function factory (action, options) {
-  return new CircuitBreaker(action, Object.assign({}, defaults, options));
+  const circuit = new CircuitBreaker(action,
+    Object.assign({}, defaults, options));
+  circuits.push(circuit);
+  return circuit;
 }
 
 /**
@@ -80,6 +84,17 @@ function factory (action, options) {
  *     const breaker = circuitBreaker(readFilePromised);
  */
 factory.promisify = require('./lib/promisify');
+
+/**
+ * Get the Prometheus metrics for all circuits.
+ * @function factory.metrics
+ * @return {String} the metrics for all circuits
+ */
+factory.metrics = function metrics() {
+  const lastCircuit = circuits[circuits.length - 1];
+  if (lastCircuit.metrics) return lastCircuit.metrics.metrics;
+}
+
 let warningIssued = false;
 Object.defineProperty(factory, 'stats', {
   get: _ => {

test/prometheus-test.js

@@ -20,6 +20,17 @@ test('Does not load Prometheus when the option is not provided', t => {
   t.end();
 });
 
+test('The factory function provides access to metrics for all circuits', t => {
+  t.plan(4);
+  const c1 = cb(passFail, { usePrometheus: true, name: 'fred' });
+  const c2 = cb(passFail, { usePrometheus: true, name: 'bob' });
+  t.equal(c1.name, 'fred');
+  t.equal(c2.name, 'bob');
+  t.ok(/circuit_fred_/.test(cb.metrics()));
+  t.ok(/circuit_bob_/.test(cb.metrics()));
+  t.end();
+});
+
 
 // All of the additional tests only make sense when running in a Node.js context
 if (!process.env.WEB) {