package main

import (
	"bytes"
	"fmt"
	"log"
	"runtime"
	"strconv"
	"time"
)

func main() {
	runtime.GOMAXPROCS(runtime.NumCPU())

	beginTime := time.Now()

	origin := make(chan int)
	wait := make(chan struct{})

	process(origin, wait)

	for num := 2; num < 10000; num++ {
		origin <- num
	}

	close(origin)
	<-wait

	fmt.Println("All done. Time: " + time.Now().Sub(beginTime).String())
}

func process(seq chan int, wait chan struct{}) {
	go func() {
		prime, ok := <-seq
		if !ok {
			close(wait)
			return
		}

		notifyGotPrime(prime)

		out := make(chan int)
		process(out, wait)

		for num := range seq {
			if num%prime != 0 {
				out <- num
			}
		}

		close(out)
	}()
}

func notifyGotPrime(prime int) {
	fmt.Printf("[%d]: %d\n", getGoRoutineId(), prime)
}

func getGoRoutineId() uint64 {
	b := make([]byte, 32)
	b = b[:runtime.Stack(b, false)]
	b = bytes.TrimPrefix(b, []byte("goroutine "))
	b = b[:bytes.IndexByte(b, ' ')]
	id, err := strconv.ParseUint(string(b), 10, 64)
	if err != nil {
		log.Panicf("Cannot parse goroutine id from %v: %v", b, err)
	}

	return id
}