package main

import (
	"bufio"
	"fmt"
	"os"
	"sync"
	"time"
)

func expensive(worker int, task string) error {
	time.Sleep(250 * time.Millisecond)
	return fmt.Errorf("worker %d is done with %q", worker, task)
}

func worker(id int, work chan string, results chan error, wg *sync.WaitGroup) {
	defer wg.Done()
	for {
		i, ok := <-work
		if !ok {
			return
		}
		results <- expensive(id, i)
	}
}

func main() {
	work := make(chan string)
	results := make(chan error)

	numWorkers := 4
	wwg := &sync.WaitGroup{}
	wg := &sync.WaitGroup{}
	for w := 0; w < numWorkers; w++ {
		wwg.Add(1)
		go worker(w, work, results, wwg)
	}

	s := bufio.NewScanner(os.Stdin)
	go func(wg *sync.WaitGroup) {
		for s.Scan() {
			wg.Add(1)
			work <- s.Text()
		}
		if err := s.Err(); err != nil {
			panic(err)
		}
		close(work)
	}(wg)

	go func() {
		wwg.Wait()
		wg.Wait()
		close(results)
	}()

	for e := range results {
		fmt.Printf("received: %+v\n", e)
		wg.Done()
	}
}