/*
 * A simple Java program that demonstrates how undo works with Command objects
 *
 * Ben Bederson, May 8, 2002
 */

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.text.*;
import java.util.*;

public class UndoExample extends JFrame {
    JMenuBar menuBar;
    JTextArea textArea;
    JMenu fileMenu;
    JMenu editMenu;
    Stack undoStack;
    Stack redoStack;

    JMenuItem undoMenu;
    JMenuItem redoMenu;

    public UndoExample() {
	setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
	undoStack = new Stack();
	redoStack = new Stack();

				// Create a menu
	menuBar = new JMenuBar();
	fileMenu = new JMenu("File");
	fileMenu.add(new AbstractAction("Exit") {
		public void actionPerformed(ActionEvent e) {
		    System.exit(0);
		}
	    });
	editMenu = new JMenu("Edit");
	undoMenu = new JMenuItem(new AbstractAction("undo") {
		public void actionPerformed(ActionEvent e) {
		    undo();
		}
	    });
	undoMenu.setEnabled(false);
	editMenu.add(undoMenu);
	redoMenu = new JMenuItem(new AbstractAction("redo") {
		public void actionPerformed(ActionEvent e) {
		    redo();
		}
	    });
	redoMenu.setEnabled(false);
	editMenu.add(redoMenu);
	editMenu.add(new JSeparator());
	editMenu.add(new AbstractAction("insert some text") {
		public void actionPerformed(ActionEvent e) {
		    insertSomeText();
		}
	    });
	menuBar.add(fileMenu);
	menuBar.add(editMenu);

	                        // Create a text box 
	textArea = new JTextArea();
	textArea.setRows(20);
	textArea.setColumns(50);
	JScrollPane scrollPane = new JScrollPane(textArea);
		
				// Set up the GUI
	setJMenuBar(menuBar);
	getContentPane().add(scrollPane);
	pack();           // Calculate the size of the window
	setVisible(true); // Make the window visible
    }

    void insertSomeText() {
	String[] randomText = {"Hello world\n", "What's up\n", "FooBar\n", "Question Technology\n"};
	int index = (int)(Math.random() * randomText.length);
	String text = randomText[index];
	InsertCommand insertCommand = new InsertCommand(textArea, text);
	insertCommand.execute();
	undoStack.push(insertCommand);
	redoStack.clear();

	undoMenu.setEnabled(true);
    }

    void undo() {
	if (!undoStack.isEmpty()) {
	    Command command = (Command)undoStack.pop();
	    command.undo();
	    redoStack.push(command);
	    redoMenu.setEnabled(true);
	}
	if (undoStack.isEmpty()) {
	    undoMenu.setEnabled(false);
	}
    }

    void redo() {
	if (!redoStack.isEmpty()) {
	    Command command = (Command)redoStack.pop();
	    command.redo();
	    undoStack.push(command);
	    undoMenu.setEnabled(true);
	}
	if (redoStack.isEmpty()) {
	    redoMenu.setEnabled(false);
	}
    }

    public static void main(String[] args) {
	new UndoExample();
    }
}

interface Command {
    public void execute();
    public void undo();
    public void redo();
}

class InsertCommand implements Command {
    JTextArea textArea;
    String textToInsert;
    String origText;
    String newText;

    public InsertCommand(JTextArea textArea, String textToInsert) {
	this.textArea = textArea;
	this.textToInsert = textToInsert;
    }

    public void execute() {
	origText = textArea.getText();
	textArea.insert(textToInsert, textArea.getCaretPosition());
	newText = textArea.getText();
    }

    public void undo() {
	textArea.setText(origText);
    }

    public void redo() {
	textArea.setText(newText);
    }
}