//go:build windows

package windows

import (
	"errors"
	"path/filepath"

	"golang.org/x/sys/windows"
	"golang.org/x/sys/windows/registry"
)

const machineGUIDRegistryPath = `SOFTWARE\Microsoft\Cryptography`

// MachineHash reads the two required Windows identifiers only for the duration
// of this call and returns their derived licensing hash.
func MachineHash() (string, error) {
	return machineHashFrom(readMachineGUID, readSystemVolumeSerial)
}

func readMachineGUID() (string, error) {
	key, err := registry.OpenKey(registry.LOCAL_MACHINE, machineGUIDRegistryPath, registry.QUERY_VALUE)
	if err != nil {
		return "", err
	}
	defer key.Close()

	value, _, err := key.GetStringValue("MachineGuid")
	if err != nil {
		return "", err
	}
	return value, nil
}

func readSystemVolumeSerial() (uint32, error) {
	windowsDirectory, err := windows.GetWindowsDirectory()
	if err != nil {
		return 0, err
	}
	volumeName := filepath.VolumeName(windowsDirectory)
	if len(volumeName) != 2 || volumeName[1] != ':' || !isASCIIAlpha(volumeName[0]) {
		return 0, errors.New("windows directory is not on a drive volume")
	}

	root, err := windows.UTF16PtrFromString(volumeName + `\`)
	if err != nil {
		return 0, err
	}
	var serial uint32
	if err := windows.GetVolumeInformation(root, nil, 0, &serial, nil, nil, nil, 0); err != nil {
		return 0, err
	}
	return serial, nil
}

func isASCIIAlpha(character byte) bool {
	return character >= 'a' && character <= 'z' || character >= 'A' && character <= 'Z'
}