// operation is a cleanup function on shutting down
type operation func(ctx context.Context) error

// gracefulShutdown waits for termination syscalls and doing clean up operations after received it
func gracefulShutdown(ctx context.Context, timeout time.Duration, ops map[string]operation) <-chan struct{} {
	wait := make(chan struct{})
	go func() {
		s := make(chan os.Signal, 1)

		// add any other syscalls that you want to be notified with
		signal.Notify(s, syscall.SIGINT, syscall.SIGTERM, syscall.SIGHUP)
		<-s

		log.Println("shutting down")

		// set timeout for the ops to be done to prevent system hang
		timeoutFunc := time.AfterFunc(timeout, func() {
			log.Printf("timeout %d ms has been elapsed, force exit", timeout.Milliseconds())
			os.Exit(0)
		})

		defer timeoutFunc.Stop()

		var wg sync.WaitGroup

		// Do the operations asynchronously to save time
		for key, op := range ops {
			wg.Add(1)
			innerOp := op
			innerKey := key
			go func() {
				defer wg.Done()

				log.Printf("cleaning up: %s", innerKey)
				if err := innerOp(ctx); err != nil {
					log.Printf("%s: clean up failed: %s", innerKey, err.Error())
					return
				}

				log.Printf("%s was shutdown gracefully", innerKey)
			}()
		}

		wg.Wait()

		close(wait)
	}()

	return wait
}

func main() {
	// initialize some resources
	// e.g:
	// db, err := database.Initialize()
	// server, err := http.Initialize()

	db, err := sdb.Open("db", &opt.Options{
		Filter: filter.NewBloomFilter(10), // 一般取10
	})
	if err != nil {
		log.Fatalf("Connect Error: %v", err)
	}

	// wait for termination signal and register database & http server clean-up operations
	wait := gracefulShutdown(context.Background(), 8*time.Second, map[string]operation{
		"database": func(ctx context.Context) error {
			log.Println("db close()")
			return db.Close()
		},
		//"http-server": func(ctx context.Context) error {
		//	return server.Shutdown()
		//},
		// Add other cleanup operations here
	})

	go func() {
		for {
			fmt.Println("go -bg")
			time.Sleep(5 * time.Second)
			fmt.Println("go -ed")
		}
	}()

	log.Println("wait...")
	<-wait

	log.Println("main done")
}