win32 text prompt box, like MessageBox but for text

prompt.cpp

INT_PTR PromptText(const wchar_t* title, wchar_t* text, size_t len)
{
  __pragma(pack(push, 1)) struct alignas(DWORD)
  {
    DLGTEMPLATE hdr{
      WS_POPUP | WS_CAPTION | WS_SYSMENU | DS_CENTER,
      0,
      1,
      100,
      100,
      200,
      10
    };
    WORD menu = 0x0000;
    WORD clazz = 0x0000;
    WORD title = 0x0000;
    alignas(DWORD) DLGITEMTEMPLATE edit {
      WS_VISIBLE | ES_AUTOHSCROLL,
      0,
      0,
      0,
      200,
      10,
      101
    };
    WORD edit_class_marker = 0xFFFF;
    WORD edit_class_selector = 0x0081;
    WORD edit_title = 0x0000;
    WORD edit_extra = 0x0000;
  } __pragma(pack(pop)) dlg;

  const auto old_awareness = SetThreadDpiAwarenessContext(DPI_AWARENESS_CONTEXT_SYSTEM_AWARE);
  const auto dpi = GetDpiForSystem();
  
  NONCLIENTMETRICS ncm;
  ncm.cbSize = sizeof(ncm);
  SystemParametersInfoW(
    SPI_GETNONCLIENTMETRICS,
    0,
    &ncm,
    0
  );
  const auto fontheight = abs(ncm.lfMessageFont.lfHeight);

  dlg.hdr.x = dlg.hdr.x * dpi / 96;
  dlg.hdr.y = dlg.hdr.y * dpi / 96;
  dlg.hdr.cx = dlg.hdr.cx * dpi / 96;
  dlg.hdr.cy = fontheight * 72 / 96;
  dlg.edit.x = dlg.edit.x * dpi / 96;
  dlg.edit.y = dlg.edit.y * dpi / 96;
  dlg.edit.cx = dlg.edit.cx * dpi / 96;
  dlg.edit.cy = fontheight * 72 / 96;

  struct Params
  {
    HFONT font;
    const wchar_t* title;
    wchar_t* text;
    size_t len;
  } p{ CreateFontIndirectW(&ncm.lfMessageFont), title, text, len };
  
  const static auto dlg_proc = (DLGPROC)[](HWND hDlg, UINT uMsg, WPARAM wParam, LPARAM lParam) -> INT_PTR
  {
    Params* p;
    if (uMsg == WM_INITDIALOG)
    {
      p = (Params*)lParam;
      SetWindowLongPtrW(hDlg, GWLP_USERDATA, lParam);

      const auto edit = GetDlgItem(hDlg, 101);
      SetWindowFont(edit, p->font, TRUE);
      SetWindowTextW(edit, p->text);
      SetWindowTextW(hDlg, p->title);
    }
    else
    {
      p = (Params*)GetWindowLongPtrW(hDlg, GWLP_USERDATA);

      if(uMsg == WM_COMMAND && HIWORD(wParam) == BN_CLICKED)
      {
        const auto btn = LOWORD(wParam);
        if (btn == IDCANCEL)
        {
          EndDialog(hDlg, IDCANCEL);
        }
        else if (btn == IDOK)
        {
          GetWindowTextW(GetDlgItem(hDlg, 101), p->text, p->len);
          p->text[p->len - 1] = 0;
          EndDialog(hDlg, IDOK);
        }
      }
    }
    
    return FALSE;
  };
  const auto ret = DialogBoxIndirectParamW(
    GetModuleHandleA(nullptr),
    (LPCDLGTEMPLATE)&dlg,
    nullptr,
    dlg_proc,
    (LPARAM)&p
  );

  SetThreadDpiAwarenessContext(old_awareness);

  DeleteObject(p.font);

  return ret;
}