/*
 * File: BouncingBall.java
 * -----------------------
 * This program graphically simulates a bouncing ball.
 */
import acm.program.*;
import acm.graphics.*;

public class BouncingBall extends GraphicsProgram {

	/** Size (diameter) of the ball */
	private static final int DIAM_BALL = 80;
	
	/**
	 * Amount Y velocity is increased each cycle as a result of gravity
	 */
	private static final double GRAVITY = 3;

	/** Animation delay or pause time between ball moves */
	private static final int DELAY = 20;

	/** Initial X and Y location of ball */
	private static final double X_START = DIAM_BALL / 2;
	private static final double Y_START = 100;

	/** X Velocity */
	private static final double X_VEL = 2;

	/** Amount Y Velocity is reduced when it bounces */
	private static final double BOUNCE_REDUCE = 0.85;

	/** Starting X and Y Velocties */
	private double xVel = X_VEL;
	private double yVel = 0.0;

	/* private instance variable */
	private GOval ball;

	
	public void run() {
		setup();
		// Simulation ends when ball goes off right hand
		// end of screen
		while (ball.getX() < getWidth()) {
			moveBall();
			checkForCollision();
			pause(DELAY);
		}
		System.exit(0);
	}

	/** Create and place ball. */
	private void setup() {
		ball = new GOval(X_START, Y_START, DIAM_BALL, DIAM_BALL);
		ball.setFilled(true);
		add(ball);
	}

	/** Update and move ball */
	private void moveBall() {
		// increase yVelocity due to gravity on each cycle
		yVel += GRAVITY;
		ball.move(xVel, yVel);
	}

	/**
	 * Determine if collision with floor, update velocities and location as
	 * appropriate.
	 */
	private void checkForCollision() {
		// determine if ball has dropped below the floor
		if (ball.getY() > getHeight() - DIAM_BALL) {
			// change ball's Y velocity to now bounce upwards
			yVel = -yVel * BOUNCE_REDUCE;
			// assume bounce will move ball an amount above the
			// floor equal to the amount it would have dropped
			// below the floor.
			double diff = ball.getY() - (getHeight() - DIAM_BALL);
			ball.move(0, -2 * diff);
		}
	}
}