import java.awt.*;
import java.awt.geom.*;

/**
 * A circle that can be manipulated and that draws itself on a canvas.
 * 
 * @author  Michael Kölling and David J. Barnes (modified vy Dave Reed)
 * @version 2011.07.31
 */
public class Circle {
    private int diameter;
    private int xPosition;
    private int yPosition;
    private String color;
    private boolean isVisible;
    
    /**
     * Create a new circle at default position with default color.
     */
    public Circle() {
        this.diameter = 68;
        this.xPosition = 230;
        this.yPosition = 90;
        this.color = "blue";
    }

    /**
     * Make this circle visible. If it was already visible, do nothing.
     */
    public void makeVisible() {
        this.isVisible = true;
        this.draw();
    }
    
    /**
     * Make this circle invisible. If it was already invisible, do nothing.
     */
    public void makeInvisible() {
        this.erase();
        this.isVisible = false;
    }
    
    /**
     * Move the circle a few pixels to the right.
     */
    public void moveRight() {
        this.moveHorizontal(20);
    }

    /**
     * Move the circle a few pixels to the left.
     */
    public void moveLeft() {
        this.moveHorizontal(-20);
    }

    /**
     * Move the circle a few pixels up.
     */
    public void moveUp() {
        this.moveVertical(-20);
    }

    /**
     * Move the circle a few pixels down.
     */
    public void moveDown() {
        this.moveVertical(20);
    }

    /**
     * Move the circle horizontally by 'distance' pixels.
     */
    public void moveHorizontal(int distance) {
        this.erase();
        this.xPosition += distance;
        this.draw();
    }

    /**
     * Move the circle vertically by 'distance' pixels.
     */
    public void moveVertical(int distance) {
        this.erase();
        this.yPosition += distance;
        this.draw();
    }

    /**
     * Slowly move the circle horizontally by 'distance' pixels.
     */
    public void slowMoveHorizontal(int distance) {
        int delta;

        if(distance < 0) {
            delta = -1;
            distance = -distance;
        }
        else {
            delta = 1;
        }

        for(int i = 0; i < distance; i++) {
            this.xPosition += delta;
            this.draw();
        }
    }

    /**
     * Slowly move the circle vertically by 'distance' pixels.
     */
    public void slowMoveVertical(int distance) {
        int delta;

        if(distance < 0) {
            delta = -1;
            distance = -distance;
        }
        else {
            delta = 1;
        }

        for(int i = 0; i < distance; i++) {
            this.yPosition += delta;
            this.draw();
        }
    }

    public void moveTo(int xpos, int ypos) {
        this.erase();
        this.xPosition = xpos;
        this.yPosition = ypos;
        this.draw();
    }
    
    /**
     * Change the size to the new size (in pixels). Size must be >= 0.
     */
    public void changeSize(int newDiameter) {
        this.erase();
        this.diameter = newDiameter;
        this.draw();
    }

    /**
     * Change the color. Valid colors are "red", "yellow", "blue", "green",
     * "magenta" and "black".
     */
    public void changeColor(String newColor) {
        this.color = newColor;
        this.draw();
    }

    /**
     * Draw the circle with current specifications on screen.
     */
    private void draw() {
        if(this.isVisible) {
            Canvas canvas = Canvas.getCanvas();
            canvas.draw(this, this.color, new Ellipse2D.Double(this.xPosition, this.yPosition, 
                                                          this.diameter, this.diameter));
            canvas.wait(10);
        }
    }

    /**
     * Erase the circle on screen.
     */
    private void erase() {
        if(this.isVisible) {
            Canvas canvas = Canvas.getCanvas();
            canvas.erase(this);
        }
    }
}