//go:build darwin || dragonfly || freebsd || linux || netbsd || openbsd

package btree

import (
	"os"
	"syscall"
)

type unixFileLock struct {
	f *os.File
}

func (fl *unixFileLock) release() error {
	if err := setFileLock(fl.f, false); err != nil {
		return err
	}
	return fl.f.Close()
}

func newFileLock(path string) (fl fileLock, err error) {
	flag := os.O_RDWR
	f, err := os.OpenFile(path, flag, 0)
	if os.IsNotExist(err) {
		f, err = os.OpenFile(path, flag|os.O_CREATE, 0644)
	}
	if err != nil {
		return
	}
	err = setFileLock(f, true)
	if err != nil {
		f.Close()
		return
	}
	fl = &unixFileLock{f: f}
	return
}

func setFileLock(f *os.File, lock bool) error {
	how := syscall.LOCK_UN
	if lock {
		how = syscall.LOCK_EX
	}
	return syscall.Flock(int(f.Fd()), how|syscall.LOCK_NB)
}