fix: Add status for fallback calls.

Fixes: nodeshift#2
`CircuitBreaker` status include the number of times the circuit
was fired (regardless of success or failure), the number of failures,
and the number of fallback executions. Failures reset to 0 every
time there is a successful execution.

README.md

@@ -73,7 +73,7 @@ const readFile = circuitBreaker.promisify(fs.readFile);
 const breaker = circuitBreaker(readFile, options);
 
 breaker.fire('./package.json', 'utf-8')
-  .then((result) => console.log(result.toString()))
+  .then(console.log)
   .catch(console.error);
 ```
 

lib/circuit.js

@@ -36,6 +36,7 @@ class CircuitBreaker {
   }
 
   fire () {
+    this.status.fires++;
     const args = Array.prototype.slice.call(arguments);
 
     if (this.open || (this.halfOpen && this[halfOpenAttempted])) {
@@ -68,6 +69,7 @@ class CircuitBreaker {
 function failFast (circuit, args) {
   if (circuit[fallbackFunction]) {
     return new circuit.Promise((resolve, reject) => {
+      circuit.status.fallbacks++;
       resolve(circuit[fallbackFunction].apply(circuit[fallbackFunction], args));
     });
   }
@@ -76,7 +78,7 @@ function failFast (circuit, args) {
 
 function succeed (circuit) {
   circuit.status.failures = 0;
-  circuit.status.fires++;
+  circuit.status.successes++;
   circuit[state] = closed;
 }
 
@@ -91,8 +93,10 @@ function fail (circuit) {
 }
 
 class Status {
-  constructor (failures, fires) {
-    this.failures = failures || 0;
+  constructor () {
+    this.failures = 0;
+    this.fallbacks = 0;
+    this.successes = 0;
     this.fires = 0;
   }
 }

test/test.js

@@ -151,6 +151,40 @@ test('Passes arguments to the fallback function', (t) => {
     });
 });
 
+test('CircuitBreaker status', (t) => {
+  const breaker = circuitBreaker(passFail, { maxFailures: 1 });
+  const deepEqual = (t, expected) => (actual) => t.deepEqual(actual, expected);
+
+  Fidelity.all([
+    breaker.fire(10).then(deepEqual(t, 10)),
+    breaker.fire(20).then(deepEqual(t, 20)),
+    breaker.fire(30).then(deepEqual(t, 30))
+  ])
+    .then(() => t.deepEqual(breaker.status.fires, 3))
+    .catch(t.fail)
+    .then(() => {
+      breaker.fire(-10)
+        .then(t.fail)
+        .catch((value) => {
+          t.deepEqual(value, -10);
+          t.deepEqual(breaker.status.failures, 1);
+          t.deepEqual(breaker.status.fires, 4);
+        })
+        .then(() => {
+          breaker.fallback(() => 'Fallback called');
+          breaker.fire(-20)
+            .then((result) => {
+              // t.deepEqual(result, 'Fallback called');
+              t.deepEqual(breaker.status.failures, 1);
+              t.deepEqual(breaker.status.fires, 5);
+              t.deepEqual(breaker.status.fallbacks, 1);
+            })
+            .catch(t.fail);
+        })
+        .then(t.end);
+    });
+});
+
 /**
  * Returns a promise that resolves if the parameter
  * 'x' evaluates to >= 0. Otherwise the returned promise fails.