lazy.go

// Copyright 2024 Oliver Eikemeier. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// SPDX-License-Identifier: Apache-2.0

package lazydone

import "fillmore-labs.com/lazydone/atomic"

// Lazy is a lazily initialized done channel.
// The zero value for a Lazy is valid and can be closed.
// A Lazy must not be copied after first use.
type Lazy struct {
	done atomic.Chan[struct{}]
}

// Close closes the done channel. You shouldn't close the channel twice.
func (l *Lazy) Close() {
	if done := l.done.Swap(closedChan); done != nil && done != closedChan {
		close(done)
	}
}

// Done returns the done channel.
func (l *Lazy) Done() <-chan struct{} {
	if done := l.done.Load(); done != nil {
		return done
	}

	if done := make(chan struct{}); l.done.CompareAndSwap(nil, done) {
		return done
	}

	return l.done.Load()
}

// Closed returns true if the done channel is closed.
func (l *Lazy) Closed() bool {
	switch done := l.done.Load(); done {
	case nil:
		return false

	case closedChan:
		return true

	default:
		select {
		case <-done:
			return true
		default:
			return false
		}
	}
}

func (l *Lazy) String() string {
	if l.Closed() {
		return "done"
	}

	return "pending"
}