package main

import (
	"fmt"
	"time"
)

// PubSub setup
type SimpleSignalChannel chan int

type SimpleSignal struct {
	sig SimpleSignalChannel
}

func NewSimpleSignal() *SimpleSignal {
	s := new(SimpleSignal)
	s.sig = make(SimpleSignalChannel)
	return s
}

func (s *SimpleSignal) WaitForSignal() {
	// block until channel closed
	for range s.sig {
	}
}

func (s *SimpleSignal) SignalAll() {
	// signal all sleeping subscribers by closing the old channel
	defer close(s.sig)
	// BUT FIRST make a new channel for any new subscribers
	s.sig = make(SimpleSignalChannel)
}

// example usage
func subscriber(x int, ps *SimpleSignal) {
	for {
		ps.WaitForSignal()
		fmt.Println("subscriber", x, "got signal")
	}
}

func publisher(ps *SimpleSignal) {
	for {
		time.Sleep(time.Second * 3)
		fmt.Println("publishing")
		ps.SignalAll()
		fmt.Println("published signal")
	}
}

func main() {
	fmt.Println("starting subscribers")
	ps := NewSimpleSignal()
	for i := range 10 {
		go subscriber(i, ps)
	}
	fmt.Println("starting publisher")
	go publisher(ps)
	select {}
}