// Copyright 2015 The Vanadium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Utilities for running tasks asynchronously.
package util

import (
	"v.io/v23/verror"
)

type Task func() error
type ErrorCb func(err error)

// AsyncRun asynchronously starts task and returns a function that can be used
// to wait for task completion, returning the error if any. In addition, if the
// task returns a non-nil error, onError is called with the error. onError can
// be nil. ErrCanceled is ignored (treated as a nil error).
func AsyncRun(task Task, onError ErrorCb) (wait func() error) {
	var err error
	done := make(chan error, 1)
	go func() {
		defer close(done)
		err = task()
		// Ignore ErrCanceled.
		if verror.ErrorID(err) == verror.ErrCanceled.ID {
			err = nil
		}
		// Call onError if provided and err is not nil.
		if err != nil && onError != nil {
			onError(err)
		}
	}()
	return func() error {
		<-done
		return err
	}
}