package lockfile

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


type Lockfile struct {
	path string
	fd int
}

func New(path string) *Lockfile {
	return &Lockfile{path: path}
}

func (lf *Lockfile) Lock() error {
	fd, err := syscall.Open(lf.path, syscall.O_CREAT | syscall.O_RDWR, 0600)
	if err != nil {
		return err
	}
	lf.fd = fd
	err = syscall.Flock(lf.fd, syscall.LOCK_EX | syscall.LOCK_NB)
	if err != nil {
		return err
	}
	return nil
}

func (lf *Lockfile) Unlock() error {
	if lf.fd == 0 {
		panic(errors.New("Lockfile was not locked"))
	}
	err := syscall.Flock(lf.fd, syscall.LOCK_UN)
	if err != nil {
		return err
	}
	err = syscall.Close(lf.fd)
	if err != nil {
		return err
	}
	os.Remove(lf.path)
	if err != nil {
		return err
	}
	return nil
}