/* show a ball bouncing in a box using curses */

#include <stdio.h>
#include <curses.h>
#include <sys/time.h>
#include <signal.h>
#include <stdlib.h>

struct ball_s {
  int ballxold;
  int ballyold;
  int ballx;
  int bally;
  int ballx_vel;
  int bally_vel;
};

void drawStart(WINDOW *win);
void drawScreen(WINDOW *win, struct ball_s * one, struct ball_s * two);
void cleanUp(int sig);
void moveBall(struct ball_s * ball);
void moveCursor(WINDOW *win);

#define MIN_X		11
#define MAX_X		69
#define MIN_Y		5
#define MAX_Y 		19

int main(int argc, char *argv[]) {
   WINDOW *main_window;
   struct ball_s one;
   struct ball_s two;

   /* initialize curses stuff */  
   initscr();
   main_window = newwin(0,0,0,0);
   leaveok(main_window,TRUE);
   curs_set(0);			/* turn off cursor */

   /* initialize ball */
   one.ballx = (MAX_X - MIN_X) / 3 + MIN_X;
   one.bally = (MAX_Y - MIN_Y) / 3 + MIN_Y;
   one.ballxold = one.ballx;
   one.ballyold = one.bally;
   one.ballx_vel = -1;
   one.bally_vel = +1;
   
   two.ballx = (MAX_X - MIN_X) * 2 / 3 + MIN_X;
   two.bally = (MAX_Y - MIN_Y) * 2 / 3 + MIN_Y;
   two.ballxold = two.ballx;
   two.ballyold = two.bally;
   two.ballx_vel = -1;
   two.bally_vel = +1;
   
   /* draw starting box */
   drawStart(main_window);

   /* loop until exit on Ctrl-C */
   while (1) {
     // imagine this is a I/O call necessary to compute the next motion
     usleep(1000000);
     moveBall(&one);
     drawScreen(main_window, &one, &two);

     // same here
     usleep(300000);
     moveBall(&two);
     drawScreen(main_window, &one, &two);
   }
}

/* move the ball based on x,y velocity and walls */
void moveBall(struct ball_s * ball) {

  /* move the ball */
  ball->ballxold = ball->ballx;
  ball->ballyold = ball->bally;
  ball->ballx = ball->ballx + ball->ballx_vel;
  ball->bally = ball->bally + ball->bally_vel; 

  /* hit side wall? */
  if (ball->ballx == MIN_X || ball->ballx == MAX_X)
    ball->ballx_vel = ball->ballx_vel * -1; 
  
  /* hit top/bottom wall? */
  if (ball->bally == MAX_Y || ball->bally == MIN_Y)
    ball->bally_vel = ball->bally_vel * -1; 
}

/* draw the screen */
void drawScreen(WINDOW *win, struct ball_s * one, struct ball_s * two){
  mvwaddch(win, one->ballyold, one->ballxold,' ');
  mvwaddch(win, one->bally, one->ballx, '*');
  mvwaddch(win, two->ballyold, two->ballxold,' ');
  mvwaddch(win, two->bally, two->ballx, '*');
  wrefresh(win);
}

/* draw the starting box */
void drawStart(WINDOW *win) {
  int i;

  /* horizontal bars */
  for (i=MIN_X-1; i<=MAX_X+1; i++) {
    mvwaddch(win, MIN_Y-1, i, '-');
    mvwaddch(win, MAX_Y+1, i, '-');
  }

  /* vertical bars */
  for (i=MIN_Y-1; i<=MAX_Y+1; i++) {
    mvwaddch(win, i, MIN_X-1, '|');
    mvwaddch(win, i, MAX_X+1, '|');
  }    

  wrefresh(win);
}

/* close curses and exit */
void cleanUp(int sig) {
  endwin();
  exit(0);
}