import org.eclipse.swt.internal.Callback;
import org.eclipse.swt.internal.win32.MSG;
import org.eclipse.swt.internal.win32.OS;
import org.eclipse.swt.internal.win32.PAINTSTRUCT;
import org.eclipse.swt.internal.win32.RECT;
import org.eclipse.swt.internal.win32.TCHAR;
import org.eclipse.swt.internal.win32.WNDCLASS;

public class Hello {
    public static int WndProc(int hWnd, int uMsg, int wParam, int lParam) {
        int hdc;
        PAINTSTRUCT lpPaint = new PAINTSTRUCT();
        String strMessage = "Hello, Win32 GUI(SWT) World!";
        
        switch (uMsg) {
        case OS.WM_PAINT:
            RECT rect = new RECT();
            hdc = OS.BeginPaint(hWnd, lpPaint);
            OS.GetClientRect(hWnd, rect);
            OS.DrawTextW(hdc, strMessage.toCharArray(), strMessage.length(), rect, OS.DT_SINGLELINE);
            OS.EndPaint(hWnd, lpPaint);
            return 0;
        case OS.WM_DESTROY:
            System.exit(wParam);
        default:
            return OS.DefWindowProc(hWnd, uMsg, wParam, lParam);
        }
    }

    public static void WinMain(String[] args) {
        int hInstance = OS.GetModuleHandle(null);
        TCHAR className  = new TCHAR(0, "helloWindow", true);
        TCHAR windowName = new TCHAR(0, "Hello, World", true);

        WNDCLASS wc      = new WNDCLASS();
        wc.style         = OS.CS_HREDRAW | OS.CS_VREDRAW;
        wc.lpfnWndProc   = new Callback(Hello.class, "WndProc", 4).getAddress();
        wc.hInstance     = hInstance;
        wc.hCursor       = OS.LoadCursor(0, OS.IDC_ARROW);
        wc.hbrBackground = OS.GetStockObject(OS.COLOR_WINDOW + 1 );
        wc.lpszClassName = OS.HeapAlloc(OS.GetProcessHeap(), OS.HEAP_ZERO_MEMORY, className.length() * 2);
        OS.MoveMemory(wc.lpszClassName, className, className.length() * 2);
        
        OS.RegisterClass(wc);

        int hWnd = OS.CreateWindowEx(
            0,
            className,
            windowName,
            OS.WS_OVERLAPPEDWINDOW,
            OS.CW_USEDEFAULT, 
            OS.CW_USEDEFAULT,
            640,
            480,
            0,
            0,
            hInstance,
            null);
        
        OS.ShowWindow(hWnd, OS.SW_SHOW);
        OS.UpdateWindow(hWnd);

        MSG lpMsg = new MSG();
        while (OS.GetMessage(lpMsg, 0, 0, 0)) {
            OS.TranslateMessage(lpMsg);
            OS.DispatchMessage(lpMsg);
        }
    }

    public static void main(String[] args) {
        WinMain( args );
    }

}