package system

import (
	"syscall"
	"unsafe"
)

var (
	ntuserApiset = syscall.NewLazyDLL("ext-ms-win-ntuser-window-l1-1-0")
)

// OSVersion is a wrapper for Windows version information
// https://msdn.microsoft.com/en-us/library/windows/desktop/ms724439(v=vs.85).aspx
type OSVersion struct {
	Version      uint32
	MajorVersion uint8
	MinorVersion uint8
	Build        uint16
}

// GetOSVersion gets the operating system version on Windows. Note that
// docker.exe must be manifested to get the correct version information.
func GetOSVersion() OSVersion {
	var err error
	osv := OSVersion{}
	osv.Version, err = syscall.GetVersion()
	if err != nil {
		// GetVersion never fails.
		panic(err)
	}
	osv.MajorVersion = uint8(osv.Version & 0xFF)
	osv.MinorVersion = uint8(osv.Version >> 8 & 0xFF)
	osv.Build = uint16(osv.Version >> 16)
	return osv
}

// Unmount is a platform-specific helper function to call
// the unmount syscall. Not supported on Windows
func Unmount(dest string) error {
	return nil
}

// CommandLineToArgv wraps the Windows syscall to turn a commandline into an argument array.
func CommandLineToArgv(commandLine string) ([]string, error) {
	var argc int32

	argsPtr, err := syscall.UTF16PtrFromString(commandLine)
	if err != nil {
		return nil, err
	}

	argv, err := syscall.CommandLineToArgv(argsPtr, &argc)
	if err != nil {
		return nil, err
	}
	defer syscall.LocalFree(syscall.Handle(uintptr(unsafe.Pointer(argv))))

	newArgs := make([]string, argc)
	for i, v := range (*argv)[:argc] {
		newArgs[i] = string(syscall.UTF16ToString((*v)[:]))
	}

	return newArgs, nil
}

// HasWin32KSupport determines whether containers that depend on win32k can
// run on this machine. Win32k is the driver used to implement windowing.
func HasWin32KSupport() bool {
	// For now, check for ntuser API support on the host. In the future, a host
	// may support win32k in containers even if the host does not support ntuser
	// APIs.
	return ntuserApiset.Load() == nil
}