import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.util.Set;
import java.util.TreeSet;

/** This class finds all permutations of a specific
 *  set of letters of a specific length.
 *  
 *  It also animates the process to more easily see
 *  what is happening.
 *
 *  @author Adam Blank
 *
 */
public class Permutations {
    public static final int HEIGHT = 700;
    public static final int WIDTH = 440;
    private static int outputX = 15;
    private static int outputY = 150;
    private static int numPrinted = 0;
    private static DrawingPanel panel;
    private static boolean paused = false;
    
    /** This string is global state that represents a
     *  partially constructed solution.
     *  
     *  DO NOT DO THIS ON YOUR HOMEWORK.  IT IS HORRIBLE
     *  STYLE.  We have only done it here, because it makes
     *  the backtracking part more clear.
     */
    private static String part;

    public static boolean hasUniqueCharacters(String str) {
        for (char c : str.toCharArray()) {
            if (str.indexOf(c) != str.lastIndexOf(c)) {
                return false;
            }
        }
        return true;
    }

    
    /** This method prints all the permutations of length n
     *  using only the symbols a, b, c, and d.
     */
    private static void permutations(int length) {
        String[] choices = { "a", "b", "c", "d" };
        placePartial(part);

        if (hasUniqueCharacters(part)) {
            if (length == 0) {
                add(part);
            }
            else {
                for (String choice : choices) {
                    part += choice;
                    permutations(length - 1);
                    part = part.substring(0, part.length() - 1);
                }
            }
        }

    }

    public static void main(String[] args) {
        panel = new DrawingPanel(WIDTH, HEIGHT);
        panel.addMouseListener((MouseListener) new MouseAdapter() {
            public void mouseClicked(MouseEvent e) {
                Permutations.paused = !Permutations.paused;
            }
        });

        part = "";
        drawUnderline();
        permutations(4);
    }

    /** This method draws an underline to the top of the
     *  DrawingPanel to help demonstrate recursive backtracking
     *  via animation.
     */
    public static void drawUnderline() {
        Graphics g = panel.getGraphics();
        g.setColor(Color.RED);
        Font font = new Font("Arial", Font.PLAIN, 100);
        g.setFont(font);
        g.drawString("____", 100, 80);

    }

    /** This method draws the current partial string to the top 
     *  of the DrawingPanel to help demonstrate recursive backtracking
     *  via animation.
     */
    public static void placePartial(String x) {
        if (x.length() == 0) {
            return;
        }
        Graphics g = panel.getGraphics();
        g.setColor(Color.BLACK);
        Font font = new Font("Arial", Font.PLAIN, 100);
        g.setFont(font);
        g.setColor(Color.WHITE);
        g.fillRect(10, 5, 100 + 55 * (4), 80);

        if (x.length() > 1) {
            g.setColor(Color.BLACK);
            g.drawString(x.substring(0, x.length() - 1), 100, 80);
        }
        g.setColor(Color.BLUE);
        g.drawString(x.substring(x.length() - 1), 100 + 57 * (x.length() - 1),
                80);
        g.setColor(Color.BLACK);
        pause();
    }

    /** This method draws the given string to the bottom of the
     *  DrawingPanel where it represents a "found" solution.
     */
    public static void add(String x) {
        Graphics g = panel.getGraphics();
        Font font = new Font("Arial", Font.PLAIN, 20);
        g.setFont(font);
        g.drawString(x + ", ", outputX, outputY);
        outputX += 60;
        numPrinted++;
        if (numPrinted % 7 == 0) {
            outputY += 30;
            outputX = 15;
        }
    }

    /** This method causes the animation to pause until the
     *  DrawingPanel is clicked.
     */
    public static void pause() {
        panel.sleep(800);
        while (paused) {
            panel.sleep(200);
        }
    }
}