import java.awt.*;
import java.awt.event.*;

public class Puzzle extends Frame
  implements WindowListener {

  private int size = 4;         // how many buttons wide and high
  private Button[][] buttons;
  private int blankRow, blankCol;  // position of the blank space

  public Puzzle(){
    setLayout(new GridLayout(size, size));
    buttons = new Button[size][size];
    int buttonCount = 0;
    for(int row = 0; row < size; row++){
      for(int col = 0; col < size; col++){
        Button b = new Button();
        buttons[row][col] = b;
        b.addActionListener(new TileActionListener
                            (this, row, col));
        buttonCount++;
        b.setLabel("" + buttonCount);
        add(b);
      }
    }
    blankRow = size - 1;
    blankCol = size - 1;
    buttons[blankRow][blankCol].setLabel("");
    setSize(250, 250);
    addWindowListener(this);
    setVisible(true);
  }

  public void pushTile(int row, int col){
    if(row == blankRow){
      for( ; blankCol < col; blankCol++){
        buttons[blankRow][blankCol].setLabel
          (buttons[blankRow][blankCol+1].getLabel());
      }
      for( ; blankCol > col; blankCol--){
        buttons[blankRow][blankCol].setLabel
          (buttons[blankRow][blankCol-1].getLabel());
      }
    } else if(col == blankCol){
      for( ; blankRow < row; blankRow++){
        buttons[blankRow][blankCol].setLabel
          (buttons[blankRow+1][blankCol].getLabel());
      }
      for( ; blankRow > row; blankRow--){
        buttons[blankRow][blankCol].setLabel
          (buttons[blankRow-1][blankCol].getLabel());
      }
    }
    buttons[blankRow][blankCol].setLabel("");
  }

  public void windowClosing(WindowEvent e){
    System.exit(0);
  }

  public void windowActivated(WindowEvent e){}
  public void windowClosed(WindowEvent e){}
  public void windowDeactivated(WindowEvent e){}
  public void windowDeiconified(WindowEvent e){}
  public void windowIconified(WindowEvent e){}
  public void windowOpened(WindowEvent e){}

  public static void main(String[] args){
    if(args.length > 0){
      System.err.println("Usage: java Puzzle");
      System.exit(1);
    }
    new Puzzle();
  }
}