//12.2 - Bouncing Ball Program -Mark Lee -Prima Publishing
#include <windows.h>

LRESULT CALLBACK WndProc(HWND hWnd, UINT nMsg, WPARAM wParam,
                                     LPARAM lParam);

int WINAPI WinMain(HINSTANCE hInst, HINSTANCE hPreInst,
                       LPSTR lpszCmdLine, int nCmdShow)
{
     HWND          hWnd;
     MSG               msg;
     WNDCLASSEX     wc;

     //fill the WNDCLASSEX structure with the appropriate values
     wc.cbSize = sizeof(WNDCLASSEX);
     wc.style = CS_HREDRAW | CS_VREDRAW;
     wc.lpfnWndProc = WndProc;
     wc.cbClsExtra = 0;
     wc.cbWndExtra = 0;
     wc.hInstance = hInst;
     wc.hIcon = LoadIcon(NULL, IDI_EXCLAMATION);
     wc.hCursor = LoadCursor(NULL, IDC_ARROW);
     wc.hbrBackground = (HBRUSH)GetStockObject(WHITE_BRUSH);
     wc.lpszMenuName = NULL;
     wc.lpszClassName = "BouncingBall";
     wc.hIconSm = LoadIcon(NULL, IDI_EXCLAMATION);

     //register the new class
     RegisterClassEx(&wc);

     //create a window
     hWnd = CreateWindowEx(
          NULL,
          "BouncingBall",
          "The Bouncing Ball Program",
          WS_OVERLAPPEDWINDOW | WS_VISIBLE,
          CW_USEDEFAULT,
          CW_USEDEFAULT,
          CW_USEDEFAULT,
          CW_USEDEFAULT,
          NULL,
          NULL,
          hInst,
          NULL
     );

     //event loop - handle all messages
     while(GetMessage(&msg, NULL, 0, 0))
     {
          TranslateMessage(&msg);
          DispatchMessage(&msg);
     }

     //standard return value
     return (msg.wParam);
}

LRESULT CALLBACK WndProc(HWND hWnd, UINT nMsg, WPARAM wParam,
                                     LPARAM lParam)
{
     //static variables used to keep track of the balls position
     static int dX = 5, dY = 5; //stores direction
     static int x = 0, y = 0, oldX = 0, oldY = 0;//stores position
     //device context and brush used for drawing
     HDC hDC;
     HBRUSH brush;
     
     //find out which message is being sent
     switch(nMsg)
     {
          case WM_CREATE:
               //create the timer (0.02 seconds)
               SetTimer(hWnd, 1, 20, NULL);
               break;
     
          case WM_TIMER: //when the timer goes off (only one)
               //get the dc for drawing
               hDC = GetDC(hWnd);
               //use pure white
               brush = (HBRUSH)SelectObject(hDC, GetStockObject(WHITE_BRUSH));
               
               //fill a RECT object with the appropriate values
               RECT temp;
               temp.left = oldX;
               temp.top = oldY;
               temp.right = oldX + 30;
               temp.bottom = oldY + 30;
               
               //cover the old ellipse
               FillRect(hDC, &temp, brush);
               //get ready to draw the new ellipse
               brush = (HBRUSH)SelectObject(hDC, GetStockObject(GRAY_BRUSH));
               //draw it
               Ellipse(hDC, x, y, 30 + x, 30 + y);
               //update the values
               oldX = x;
               oldY = y;
               //prep the new coordinates for next time
               x += dX;
               y += dY;
               //get the window size and store it in rect
               RECT rect;
               GetClientRect(hWnd, &rect);
               //if the circle is going off the edge then reverse its direction
               if(x + 30 > rect.right || x < 0)
               {
                    dX = -dX;
               }
               if(y + 30 > rect.bottom || y < 0)
               {
                    dY = -dY;
               }
               //put the old brush back
               SelectObject(hDC, brush);
               //release the dc
               ReleaseDC(hWnd, hDC);
               break;

          case WM_DESTROY:
               //destroy the timer
               KillTimer(hWnd, 1);
               //end the program
               PostQuitMessage(0);
               break;
     
          default:
               //let Windows handle every other message
               return(DefWindowProc(hWnd, nMsg, wParam, lParam));
     }

     return 0;
}