// StatSource creates metrics with the given name. The returned metrics should be
// concurrency-safe.
type StatSource interface {
	Timer(name string) Timer
	Counter(name string) Counter
}

// Timer emits the duration of a particular event. The duration value is
// typically used to measure latencies and create histograms thereof.
type Timer func(duration time.Duration)

// Counter emits any number of events happening at a given time. For example,
// Counters are often used to measure RPS.
type Counter func(delta int)

// A StatSet is the cached value.
type statSet struct {
	// Latency measures how long an Action takes
	Latency Timer
	// Success is incremented when an Action does not return an error
	Success Counter
	// Error is incremented when an Action results in an error
	Error Counter
}

// Cache describes a read-through cache to obtain
type statCache interface {
	// get returns a shared statSet for the given name, either from the cache or
	// a provided StatSource.
	get(name string) *statSet
}