/**
 * Ball -- represents one ball in the Ball World application
 * @author Rhys Price Jones
 * @version 14xi08, revisited 23ii11
*/

import java.awt.*;

public class Ball implements CanBeTold
{
    protected Canvas canvas;
    protected int xpos, ypos;
    protected int xvelocity,yvelocity;
    protected int diameter;
    protected Color color;
    
    // Construct a ball of diameter d at (x, y) moving at (xv, yv) on Canvas c
        public Ball(Canvas canvas, int x, int y, 
                    int xv, int yv, int d, Color c) {
            xpos = x;
            ypos = y;
            xvelocity = xv;
            yvelocity = yv;
            diameter = d;
            color = c;
            this.canvas = canvas;
        }
    
    // Two getters and two setters
    // in case we want to reuse this code (currently not used)
    public int getXVelocity(){
        return xvelocity;
    }
    
    public int getYVelocity(){
        return yvelocity;
    }
    
    public void setXVelocity(int xv){
        xvelocity = xv;
    }
    
    public void setYVelocity(int yv){
        yvelocity = yv;
    }
    
    // How the ball moves around the campus
    public void move(){
        // by making width and height be recomputed at each
        // call to move() the application will immediately
        // respond to resizing by the user.  
        int width = canvas.getWidth();
        int height = canvas.getHeight();
        
        xpos+=xvelocity;  // advance in the horizontal direction, but...
        if(xpos+diameter > width){   // if you've gone over the right
            xpos = xpos - 2*(xpos+diameter-width);  // bounce back
            xvelocity = -xvelocity;
        }
        if(xpos < 0){    // if you've gone over the left edge
            xpos = -xpos;    // bounce back
            xvelocity = -xvelocity;
        }
        
        ypos+=yvelocity;
        if(ypos+diameter > height){  // if you've gone over the bottom
            ypos = ypos - 2*(ypos+diameter-height);  // bounce
            yvelocity = -yvelocity;
        }
        if(ypos < 0){  // if you've gone over the top
            ypos = -ypos;   // bounce
            yvelocity = -yvelocity;
        }
    }
    
    public void draw(){
        // Would it be more efficient to set myGraphics as an instance
        // variable, just once in the constructor?
        // Or is it better to recompute it every time we draw the ball?
        // See comments in method move() above.
        // Is that point applicable here too?
        Graphics myGraphics = canvas.getGraphics();
        myGraphics.setColor(color);
        myGraphics.fillOval(xpos,ypos,diameter,diameter);
    }
    
    public void respond(){
        move();
        draw();
    }
}