#include <windows.h>
#include <sstream>

enum WindowsId
{
   FirstEditId = 256,
   SecondEditId,
   ResultEditId,
   ButtonId
};

HINSTANCE InstanceHandle;
int NumPush = 0;

template <typename T>
bool GetDlgItemNumber(HWND aHwndDlg, int aDlgItemId, T &aVal)
{
   char Buffer[256];
   if(!GetDlgItemText(aHwndDlg, aDlgItemId, Buffer, sizeof(Buffer)))
      return false;
   std::stringstream ss(Buffer);
   return ss >> aVal;
}

template <typename T>
bool SetDlgItemNumber(HWND aHwndDlg, int aDlgItemId, const T &aValue)
{
   std::stringstream ss;
   ss << aValue;
   return SetDlgItemText(aHwndDlg, aDlgItemId, ss.str().c_str());
}

LRESULT CALLBACK DialogProc(HWND hwndDlg, UINT msg, WPARAM wParam, LPARAM lParam)
{
   switch(msg)
   {
   case WM_CREATE:
      CreateWindowEx(WS_EX_CLIENTEDGE,
                     "EDIT",
                     "", // Initial Text
                     WS_CHILD | WS_VISIBLE | WS_TABSTOP | WS_GROUP,  // Style
                     5, 5, 120, 20, // position
                     hwndDlg, // Owner
                     (HMENU)(FirstEditId), // ID
                     InstanceHandle,  // The application
                     0);
      CreateWindowEx(WS_EX_CLIENTEDGE,
                     "EDIT",
                     "", // Initial Text
                     WS_CHILD | WS_VISIBLE | WS_TABSTOP,  // Style
                     5, 35, 120, 20, // position
                     hwndDlg, // Owner
                     (HMENU)(SecondEditId), // ID
                     InstanceHandle,  // The application
                     0);

      CreateWindowEx(WS_EX_CLIENTEDGE,
                     "EDIT",
                     "0", // Initial Text
                     WS_CHILD | WS_VISIBLE | ES_NUMBER | ES_READONLY,  // Style
                     5, 65, 120, 20, // position
                     hwndDlg, // Owner
                     (HMENU)(ResultEditId), // ID
                     InstanceHandle,  // The application
                     0);

      CreateWindow("BUTTON",
                   "Add",                        // Button Text
                   WS_CHILD | WS_VISIBLE | WS_TABSTOP,  // Style
                   5, 90, 120, 30, // position
                   hwndDlg, // Owner
                   (HMENU)(ButtonId), // ID
                   InstanceHandle,  // The application
                   0);

      break;
   case WM_COMMAND:
      if(HIWORD(wParam) == BN_CLICKED && LOWORD(wParam) == ButtonId)
      {
         double First;
         double Second;
         if(!GetDlgItemNumber(hwndDlg, FirstEditId, First))
         {
            MessageBox(hwndDlg, "Failed to convert first string", "Calculator", MB_OK);
         }
         else
         {
            if(!GetDlgItemNumber(hwndDlg, SecondEditId, Second))
            {
                MessageBox(hwndDlg, "Failed to convert second string", "Calculator", MB_OK);
            }
            else
            {
               double Result = First + Second;
               if(!SetDlgItemNumber(hwndDlg, ResultEditId, Result))
               {
                  MessageBox(hwndDlg, "Failed to set result", "Calculator", MB_OK);
               }
            }
         }
      }
      break;
   }
   return DefWindowProc(hwndDlg, msg, wParam, lParam);
}

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE, LPSTR, INT)
{
   InstanceHandle = hInstance;

   WNDCLASS wc;
   memset(&wc, 0, sizeof(WNDCLASS));
   wc.style = CS_HREDRAW | CS_VREDRAW | CS_DBLCLKS;
   wc.lpfnWndProc = DialogProc;
   wc.hInstance = InstanceHandle;
   wc.hbrBackground = (HBRUSH )(COLOR_BTNFACE + 1);
   wc.lpszClassName = "WhateverClass";
   wc.hCursor = LoadCursor(NULL, IDC_ARROW);
   if(!RegisterClass(&wc))
      return FALSE;

   HWND WindowHandle = CreateWindow("WhateverClass",
                                    "Calc", // Caption text
                                    WS_MINIMIZEBOX | WS_VISIBLE | WS_CLIPSIBLINGS |
                                    WS_CLIPCHILDREN | WS_MAXIMIZEBOX | WS_CAPTION | WS_BORDER | WS_SYSMENU,
                                    100, 100, 140, 160,  // Position
                                    NULL,
                                    NULL,
                                    InstanceHandle,
                                    0);
   MSG Msg;
   while(GetMessage(&Msg, WindowHandle, 0, 0xFFFF) > 0)
   {
      if(!IsDialogMessage(WindowHandle, &Msg))
      {
         TranslateMessage(&Msg);
         DispatchMessage(&Msg);
      }
   }
   return 0;
}