package main

import (
	"fmt"
	"log"
	"math/rand"
	"sync"

	"github.com/hashicorp/go-multierror"
)

func main() {
	if err := runConcurrently(); err != nil {
		log.Fatalf("errors occured: %v", err)
	}
	log.Printf("all done, no errors")
}

func runConcurrently() error {
	intChan := make(chan int)
	wg := sync.WaitGroup{}
	workers := 5
	errC := make(chan error)

	// producer
	wg.Add(1)
	go func() {
		defer wg.Done()
		defer close(intChan)
		// insert random numbers into the channel
		for i := 0; i < 30; i++ {
			intChan <- rand.Intn(100)
		}
	}()

	// consumer
	for i := 0; i < workers; i++ {
		wg.Add(1)
		go func() {
			defer wg.Done()
			for {
				select {
				case number, ok := <-intChan:
					if !ok {
						return
					}
					if err := doSomething(number); err != nil {
						errC <- err
					}
				}
			}
		}()
	}

	go func() {
		wg.Wait()
		close(errC)
	}()

	var errs *multierror.Error

	for {
		select {
		case err, ok := <-errC:
			if !ok {
				return errs.ErrorOrNil()
			}
			if err != nil {
				errs = multierror.Append(errs, err)
			}
		}
	}
}

func doSomething(i int) error {
	if i%15 == 0 {
		return fmt.Errorf("random error: %v", i)
	}
	log.Printf("doing something with %d", i)
	return nil
}