Learning concurrency in go

time.go

package main

import (
	"fmt"
	"time"
)

func seconds(done <-chan int) <-chan time.Time {
	out := make(chan time.Time)

	go func(out chan time.Time, done <-chan int) {
		for {
			select {
			case <-done:
				close(out)
				return
			case currentTime := <-time.After(time.Second):
				out <- currentTime
			}
		}
	}(out, done)

	return out
}

func formatTime(in <-chan time.Time) <-chan string {
	stringCh := make(chan string)

	go func() {
		for {
			timeValue, ok := <-in

			if !ok {
				close(stringCh)
				return
			}

			stringCh <- timeValue.Format("15:04:05")
		}
	}()

	return stringCh
}

func printTime(timeCh <-chan string) {
	for {
		time, ok := <-timeCh
		if !ok {
			return
		}

		fmt.Println(time)
	}
}

func main() {
	end := make(chan int)
	timer := formatTime(seconds(end))

	go printTime(timer)

	time.Sleep(60 * time.Second)
	end <- 1
	fmt.Println("Time has gone.")
}