/**
 * File: Sky.java
 * Author: Brian Borowski
 * Date created: August 1, 2011
 * Date last modified: January 21, 2013
 */
import java.awt.Color;
import java.awt.GradientPaint;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.util.Random;

import javax.swing.JPanel;

public class Sky {
    private final static int DEFAULT_HEIGHT = 40, NUM_STARS = 120;

    private final JPanel parent;
    private final int landscapeHeight;
    private final Color purple = new Color(38, 47, 145);
    private GradientPaint gradientPaint = null;
    private Star[] stars;

    class Star {
        public int x, y;

        public Star(final int x, final int y) {
            this.x = x;
            this.y = y;
        }
    }

    public Sky(final JPanel parent, final int landscapeHeight) {
        this.parent = parent;
        this.landscapeHeight = landscapeHeight;
        this.stars = null;
    }

    public int getHeight() {
        return DEFAULT_HEIGHT;
    }

    public void paintComponent(final Graphics g) {
        final int height = parent.getHeight(), width = parent.getWidth();        
        if (stars == null) {
            stars = new Star[NUM_STARS];
            final Random randomGenerator = new Random();
            for (int i = NUM_STARS - 1; i >= 0; --i) {
                final int x = randomGenerator.nextInt(parent.getWidth() - 3) + 3,
                          y = randomGenerator.nextInt(5 * parent.getHeight() / 6) + 3;
                stars[i] = new Star(x, y);
            }
            gradientPaint = new GradientPaint(0, 0, Color.black,
                                              0, height - landscapeHeight, purple);
        }
        final Graphics2D g2d = (Graphics2D)g;
        g2d.setPaint(gradientPaint);
        g2d.fillRect(0, 0, width, height - landscapeHeight);
        g2d.setColor(Color.white);
        for (Star star: stars) {
            g2d.fillOval(star.x, star.y, 1, 2);
        }
    }
}