feat: circuits now have a name based on the action

The name of the circuit can be supplied as an option.

```js
const circuit = circuitBreaker(() => {}, { name: 'identity' });
```

If not option is provided, the name will be based on the action's name
if there is one.

```js
const square = (x) => x*x;
const circuit = circuitBreaker(square);
circuit.name // 'square'
```

If no option is provided, and the circuit's action is an anonymous
function, then a UUID is generated.

lib/circuit.js

@@ -11,6 +11,7 @@ const PENDING_CLOSE = Symbol('pending-close');
 const FALLBACK_FUNCTION = Symbol('fallback');
 const NUM_FAILURES = Symbol('num-failures');
 const STATUS = Symbol('status');
+const NAME = Symbol('name');
 
 /**
  * @class CircuitBreaker
@@ -38,6 +39,7 @@ class CircuitBreaker extends EventEmitter {
     this[FALLBACK_FUNCTION] = null;
     this[PENDING_CLOSE] = false;
     this[NUM_FAILURES] = 0;
+    this[NAME] = options.name || action.name || nextName();
 
     if (typeof action !== 'function') this.action = () => this.Promise.resolve(action);
     else this.action = action;
@@ -100,6 +102,10 @@ class CircuitBreaker extends EventEmitter {
     }
   }
 
+  get name () {
+    return this[NAME];
+  }
+
   /**
    * True if the circuit is currently closed. False otherwise.
    */
@@ -262,4 +268,12 @@ function fail (circuit, err, args) {
   return circuit.Promise.reject.apply(null, [err]);
 }
 
+// http://stackoverflow.com/a/2117523
+const nextName = () =>
+  'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, (c) => {
+    const r = Math.random() * 16 | 0;
+    const v = c === 'x' ? r : (r & 0x3 | 0x8);
+    return v.toString(16);
+  });
+
 module.exports = exports = CircuitBreaker;

test/test.js

@@ -29,6 +29,25 @@ test('api', (t) => {
   t.end();
 });
 
+test('has a name based on the function name', (t) => {
+  const breaker = cb(passFail);
+  t.equals(breaker.name, passFail.name);
+  t.end();
+});
+
+test('accepts a name as an option', (t) => {
+  const breaker = cb(passFail, {name: 'tacoMachine'});
+  t.equals(breaker.name, 'tacoMachine');
+  t.end();
+});
+
+test('uses UUID as a name when none is provided and the function is anonymoys',
+  (t) => {
+    const breaker = cb((_) => _);
+    t.ok(breaker.name);
+    t.end();
+  });
+
 test('Passes parameters to the circuit function', (t) => {
   t.plan(1);
   const expected = 34;