go-by-test/countdown/countdown.go

package countdown

import (
	"fmt"
	"io"
	"time"
)

const (
	finalWord      = "Go!"
	countdownStart = 3
)

type Sleeper interface {
	Sleep()
}

type ConfigurableSleeper struct {
	duration time.Duration
	sleep    func(time.Duration)
}

func NewConfigurableSleeper(
	duration time.Duration,
	sleep func(time.Duration),
) *ConfigurableSleeper {
	return &ConfigurableSleeper{
		duration: duration,
		sleep:    sleep,
	}
}

func (s *ConfigurableSleeper) Sleep() {
	s.sleep(s.duration)
}

func Countdown(out io.Writer, sleeper Sleeper) {
	// XXX: The sequence is not tested
	for i := countdownStart; i > 0; i-- {
		fmt.Fprintf(out, "%d\n", i)
		// This is difficult to test!
		sleeper.Sleep()
	}
	fmt.Fprint(out, finalWord)
}