package westworldwithmessaging

import (
	"sync"
	"time"
)

// clockSingleton is our own stand-in for whatever timer/clock utility
// class the book uses elsewhere (it only shows up here as
// "Clock->GetCurrentTime()" - the book hasn't shown us that class's
// actual source, likely a separate timer file). All DispatchMessage
// and DispatchDelayedMessages actually need is a steadily increasing
// number of seconds, so this just measures time elapsed since the
// clock was first used.
type clockSingleton struct {
	start time.Time
}

var (
	clockInstance *clockSingleton
	clockOnce     sync.Once
)

func newClock() *clockSingleton {
	clockOnce.Do(func() {
		clockInstance = &clockSingleton{start: time.Now()}
	})
	return clockInstance
}

// Clock is a shorthand for the clock singleton, same "#define"-style
// convenience pattern as EntityMgr and Dispatch.
var Clock = newClock()

// GetCurrentTime returns the number of seconds elapsed since the
// clock started, matching the book's
// "double CurrentTime = Clock->GetCurrentTime();".
func (c *clockSingleton) GetCurrentTime() float64 {
	return time.Since(c.start).Seconds()
}