// Manages all our circuits
h := circuit.Manager{}
// Create a circuit with a unique name
c := h.MustCreateCircuit("hello-world")
// Call the circuit
errResult := c.Execute(context.Background(), func(ctx context.Context) error {
  return nil
}, nil)
fmt.Println("Result of execution:", errResult)
// Output: Result of execution: <nil>

// You can create circuits without using the manager
c := circuit.NewCircuitFromConfig("hello-world-fallback", circuit.Config{})
errResult := c.Execute(context.Background(), func(ctx context.Context) error {
	return errors.New("this will fail")
}, func(ctx context.Context, err error) error {
	fmt.Println("Circuit failed with error, but fallback returns nil")
	return nil
})
fmt.Println("Execution result:", errResult)
// Output: Circuit failed with error, but fallback returns nil
// Execution result: <nil>

h := circuit.Manager{}
c := h.MustCreateCircuit("untrusting-circuit", circuit.Config{
  Execution: circuit.ExecutionConfig{
    // Time out the context after a few ms
    Timeout: time.Millisecond * 30,
  },
})

errResult := c.Go(context.Background(), func(ctx context.Context) error {
  // Sleep 30 seconds, way longer than our timeout
  time.Sleep(time.Second * 30)
  return nil
}, nil)
fmt.Printf("err=%v", errResult)
// Output: err=context deadline exceeded

configuration := hystrix.Factory{
  // Hystrix open logic is to open the circuit after an % of errors
  ConfigureOpener: hystrix.ConfigureOpener{
    // We change the default to wait for 10 requests, not 20, before checking to close
    RequestVolumeThreshold: 10,
    // The default values match what hystrix does by default
  },
  // Hystrix close logic is to sleep then check
  ConfigureCloser: hystrix.ConfigureCloser{
    // The default values match what hystrix does by default
  },
}
h := circuit.Manager{
  // Tell the manager to use this configuration factory whenever it makes a new circuit
  DefaultCircuitProperties: []circuit.CommandPropertiesConstructor{configuration.Configure},
}
// This circuit will inherit the configuration from the example
c := h.MustCreateCircuit("hystrix-circuit")
fmt.Println("This is a hystrix configured circuit", c.Name())
// Output: This is a hystrix configured circuit hystrix-circuit

// metriceventstream uses rolling stats to report circuit information
sf := rolling.StatFactory{}
h := circuit.Manager{
  DefaultCircuitProperties: []circuit.CommandPropertiesConstructor{sf.CreateConfig},
}
es := metriceventstream.MetricEventStream{
  Manager: &h,
}
go func() {
  if err := es.Start(); err != nil {
    log.Fatal(err)
  }
}()
// ES is a http.Handler, so you can pass it directly to your mux
http.Handle("/hystrix.stream", &es)
// ...
if err := es.Close(); err != nil {
  log.Fatal(err)
}
// Output:

h := circuit.Manager{}
expvar.Publish("hystrix", h.Var())

config := circuit.Config{
  Metrics: circuit.MetricsCollectors{
    Run: []circuit.RunMetrics{
      // Here is where I would insert my custom metric collector
    },
  },
}
circuit.NewCircuitFromConfig("custom-metrics", config)

h := circuit.Manager{}
c := h.MustCreateCircuit("panic_up")

defer func() {
 r := recover()
 if r != nil {
   fmt.Println("I recovered from a panic", r)
 }
}()
c.Execute(context.Background(), func(ctx context.Context) error {
 panic("oh no")
}, nil)
// Output: I recovered from a panic oh no

// Start off using the defaults
configuration := hystrix.ConfigFactory{}
h := circuit.Manager{
  // Tell the manager to use this configuration factory whenever it makes a new circuit
  DefaultCircuitProperties: []circuit.CommandPropertiesConstructor{configuration.Configure},
}
c := h.MustCreateCircuit("hystrix-circuit")
fmt.Println("The default sleep window", c.OpenToClose.(*hystrix.Closer).Config().SleepWindow)
// This configuration update function is thread safe.  We can modify this at runtime while the circuit is active
c.OpenToClose.(*hystrix.Closer).SetConfigThreadSafe(hystrix.ConfigureCloser{
  SleepWindow: time.Second * 3,
})
fmt.Println("The new sleep window", c.OpenToClose.(*hystrix.Closer).Config().SleepWindow)
// Output:
// The default sleep window 5s
// The new sleep window 3s

// Inject stat collection to prove these failures don't count
f := rolling.StatFactory{}
manager := circuit.Manager{
  DefaultCircuitProperties: []circuit.CommandPropertiesConstructor{
    f.CreateConfig,
  },
}
c := manager.MustCreateCircuit("don't fail me bro")
// The passed in context times out in one millisecond
ctx, cancel := context.WithTimeout(context.Background(), time.Millisecond)
defer cancel()
errResult := c.Execute(ctx, func(ctx context.Context) error {
  select {
  case <- ctx.Done():
    // This will return early, with an error, since the parent context was canceled after 1 ms
    return ctx.Err()
  case <- time.After(time.Hour):
    panic("We never actually get this far")
  }
}, nil)
rs := f.RunStats("don't fail me bro")
fmt.Println("errResult is", errResult)
fmt.Println("The error and timeout count is", rs.ErrTimeouts.TotalSum() + rs.ErrFailures.TotalSum())
// Output: errResult is context deadline exceeded
// The error and timeout count is 0

myFactory := func(circuitName string) circuit.Config {
  timeoutsByName := map[string]time.Duration{
    "v1": time.Second,
    "v2": time.Second * 2,
  }
  customTimeout := timeoutsByName[circuitName]
  if customTimeout == 0 {
    // Just return empty if you don't want to set any config
    return circuit.Config{}
  }
  return circuit.Config{
    Execution: circuit.ExecutionConfig{
      Timeout: customTimeout,
    },
  }
}

// Hystrix manages circuits with unique names
h := circuit.Manager{
  DefaultCircuitProperties: []circuit.CommandPropertiesConstructor{myFactory},
}
h.MustCreateCircuit("v1")
fmt.Println("The timeout of v1 is", h.GetCircuit("v1").Config().Execution.Timeout)
// Output: The timeout of v1 is 1s

// This factory allows us to report statsd metrics from the circuit
f := statsdmetrics.CommandFactory{
  SubStatter: &statsd.NoopClient{},
}

// Wire the statsd factory into the circuit manager
h := circuit.Manager{
  DefaultCircuitProperties: []circuit.CommandPropertiesConstructor{f.CommandProperties},
}
// This created circuit will now use statsd
h.MustCreateCircuit("using-statsd")
// Output:

sloTrackerFactory := responsetimeslo.Factory{
  Config: responsetimeslo.Config{
    // Consider requests faster than 20 ms as passing
    MaximumHealthyTime: time.Millisecond * 20,
  },
  // Pass in your collector here: for example, statsd
  CollectorConstructors: nil,
}
h := circuit.Manager{
  DefaultCircuitProperties: []circuit.CommandPropertiesConstructor{sloTrackerFactory.CommandProperties},
}
h.CreateCircuit("circuit-with-slo")

c := circuit.NewCircuitFromConfig("divider", circuit.Config{})
divideInCircuit := func(numerator, denominator int) (int, error) {
  var result int
  err := c.Run(context.Background(), func(ctx context.Context) error {
    if denominator == 0 {
      // This error type is not counted as a failure of the circuit
      return &circuit.SimpleBadRequest{
        Err: errors.New("someone tried to divide by zero"),
      }
    }
    result = numerator / denominator
    return nil
  })
  return result, err
}
_, err := divideInCircuit(10, 0)
fmt.Println("Result of 10/0 is", err)
// Output: Result of 10/0 is someone tried to divide by zero