package main

import (
	"context"
	"fmt"
	"math/rand"
	"time"
)

func pollSource(ctx context.Context) error {
	errChan := make(chan error, 1)
	tick := time.Tick(500 * time.Millisecond)
	for {
		select {
		// Parent canceled this job
		case <-ctx.Done():
			return fmt.Errorf("canceled")
		// Got a tick, we should do something
		case <-tick:
			go func() {
				if err := fetch(ctx); err != nil {
					errChan <- err
				}
			}()
		// Last tick caused an error, log it
		case err := <-errChan:
			fmt.Println(err)
		}
	}
}

func fetch(ctx context.Context) error {
	done := make(chan bool)
	timeout, _ := context.WithTimeout(ctx, 1*time.Second)

	// Do something with latency
	go func() {
		time.Sleep(time.Duration(rand.Intn(2000)) * time.Millisecond)
		fmt.Println("did something")
		done <- true
	}()

	// Got a timeout! fail with a timeout error
	select {
	case <-timeout.Done():
		return fmt.Errorf("timed out")
	case <-done:
		return nil
	}
}

func main() {
	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()
	go func() { fmt.Println(pollSource(ctx)) }()
	time.Sleep(10 * time.Second)
}