package copyfile

import (
	"fmt"
	"syscall"
	"unsafe"
)

var (
	modkernel32   = syscall.NewLazyDLL("kernel32.dll")
	procCopyFileW = modkernel32.NewProc("CopyFileW")
)

// CopyFile is a utility for copying a file - used for the LCOW scratch cache.
// Uses CopyFileW win32 API for performance.
func CopyFile(srcFile, destFile string, overwrite bool) error {
	var bFailIfExists uint32 = 1
	if overwrite {
		bFailIfExists = 0
	}

	lpExistingFileName, err := syscall.UTF16PtrFromString(srcFile)
	if err != nil {
		return err
	}
	lpNewFileName, err := syscall.UTF16PtrFromString(destFile)
	if err != nil {
		return err
	}
	r1, _, err := syscall.Syscall(
		procCopyFileW.Addr(),
		3,
		uintptr(unsafe.Pointer(lpExistingFileName)),
		uintptr(unsafe.Pointer(lpNewFileName)),
		uintptr(bFailIfExists))
	if r1 == 0 {
		return fmt.Errorf("failed CopyFileW Win32 call from '%s' to '%s': %s", srcFile, destFile, err)
	}
	return nil
}