package gitcache

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

const errorSharingViolation syscall.Errno = 32

// lockFile opens path with no sharing, so no other handle can open it while
// this one is open.
func lockFile(path string) (*os.File, error) {
	name, err := syscall.UTF16PtrFromString(path)
	if err != nil {
		return nil, err
	}
	h, err := syscall.CreateFile(name, syscall.GENERIC_READ|syscall.GENERIC_WRITE, 0, nil,
		syscall.OPEN_ALWAYS, syscall.FILE_ATTRIBUTE_NORMAL, 0)
	if errors.Is(err, errorSharingViolation) {
		return nil, errLocked
	}
	if err != nil {
		return nil, err
	}
	return os.NewFile(uintptr(h), path), nil
}