//go:build linux || darwin

package retention

import (
	"errors"
	"os"
	"syscall"
)

// lockJob 的非阻塞文件锁随进程退出自动释放，不使用永不过期的“锁目录”。
func lockJob(root *os.Root) (*os.File, error) {
	f, err := root.OpenFile(".lock", os.O_CREATE|os.O_RDWR|syscall.O_NOFOLLOW, 0600)
	if err != nil {
		return nil, err
	}
	info, err := f.Stat()
	if err != nil || !info.Mode().IsRegular() || info.Mode().Perm()&0077 != 0 {
		f.Close()
		return nil, errors.New("invalid archive lock file")
	}
	if err := syscall.Flock(int(f.Fd()), syscall.LOCK_EX|syscall.LOCK_NB); err != nil {
		f.Close()
		if errors.Is(err, syscall.EWOULDBLOCK) || errors.Is(err, syscall.EAGAIN) {
			return nil, ErrArchiveBusy
		}
		return nil, errors.New("archive filesystem does not support locking")
	}
	return f, nil
}