format PE GUI 4.0
entry start

include 'win32w.inc'

; Data
section '.data' data readable writeable

   _name TCHAR 'HelloWnd', 0
   _hwnd dd ?

   WinMain dd _WinMain

; Code
section '.code' code readable executable
start:
   invoke GetModuleHandle, 0
   mov ebx, eax
   invoke GetCommandLine
   invoke WinMain, ebx, NULL, eax, SW_SHOWDEFAULT
   invoke ExitProcess, eax

proc WndProc uses ebx, hwnd, msg, wParam, lParam
   mov ebx, [msg]
   cmp ebx, WM_CLOSE
   je .close
   cmp ebx, WM_DESTROY
   je .destroy
   jmp .default

 .close:
   invoke DestroyWindow, [hwnd]
   mov eax, 0
   jmp .quit

 .destroy:
   invoke PostQuitMessage, 0
   mov eax, 0
   jmp .quit

 .default:
   invoke DefWindowProc, [hwnd], [msg], [wParam], [lParam]
   ; WINAPI return values are already stored in eax

 .quit:
   ret
endp

proc _WinMain uses ebx, hInstance, hPrevInstance, lpCmdLine, nCmdShow
   local msg:MSG
   local wc:WNDCLASSEX
   locals
      szError:TCHAR rb 512
   endl

   mov eax, 0

   mov ebx, [hInstance]
   mov [wc.cbSize], sizeof.WNDCLASSEX
   mov [wc.style], 0
   mov [wc.lpfnWndProc], WndProc
   mov [wc.cbClsExtra], 0
   mov [wc.cbWndExtra], 0
   mov [wc.hInstance], ebx
   mov [wc.hIcon], NULL
   mov [wc.hCursor], NULL
   mov [wc.hbrBackground], COLOR_WINDOW+1
   mov [wc.lpszMenuName], NULL
   mov [wc.lpszClassName], _name
   mov [wc.hIconSm], NULL

   invoke RegisterClassEx, addr wc
   test eax, eax ; if true zero flag will be 0
   jnz .registered

   locals
      szRegFail TCHAR 'Window registration failed! GLE=0x%.8x', 0
   endl
   invoke GetLastError
   ccall [swprintf_s], addr szError, 512, addr szRegFail, eax
   invoke MessageBox, HWND_DESKTOP, addr szError, _name, MB_OK
   jmp .quit

 .registered:
   invoke CreateWindowEx,\
      WS_EX_CLIENTEDGE,\
      _name,\
      _name,\
      WS_OVERLAPPEDWINDOW,\
      CW_USEDEFAULT, CW_USEDEFAULT, 640, 360,\
      HWND_DESKTOP, NULL, [hInstance], NULL

   mov [_hwnd], eax
   test eax, eax
   jz .created
   locals
      szCreationFail TCHAR 'Window creation failed! GLE=0x%.8x', 0
   endl
   invoke GetLastError
   ccall [swprintf_s], addr szError, 512, addr szCreationFail, eax
   invoke MessageBox, HWND_DESKTOP, addr szError, _name, MB_OK
   jmp .quit

 .created:
   invoke ShowWindow, [_hwnd], [nCmdShow]
   invoke UpdateWindow, [_hwnd]

 .message_loop:
   invoke GetMessage, addr msg, NULL, 0, 0
   test eax, eax
   jz .message_loop_end
   invoke TranslateMessage, addr msg
   invoke DispatchMessage, addr msg
   jmp .message_loop

 .message_loop_end:
   mov eax, [msg.wParam]

 .quit:
  ret
endp

; Imports
section '.idata' import data readable writeable

   library kernel32, 'KERNEL32.DLL',\
           user32, 'USER32.DLL',\
           msvcrt, 'MSVCRT.DLL'

   include 'api\kernel32.inc'
   include 'api\user32.inc'

   import msvcrt,\
      swprintf_s, 'swprintf_s'