org.jline.reader.impl.UndoTree Maven / Gradle / Ivy
/*
* Copyright (c) 2002-2016, the original author or authors.
*
* This software is distributable under the BSD license. See the terms of the
* BSD license in the documentation provided with this software.
*
* http://www.opensource.org/licenses/bsd-license.php
*/
package org.jline.reader.impl;
import java.util.function.Consumer;
/**
* Simple undo tree.
* Note that the first added state can't be undone
*/
public class UndoTree {
private final Consumer state;
private final Node parent;
private Node current;
public UndoTree(Consumer s) {
state = s;
parent = new Node(null);
parent.left = parent;
clear();
}
public void clear() {
current = parent;
}
public void newState(T state) {
Node node = new Node(state);
current.right = node;
node.left = current;
current = node;
}
public boolean canUndo() {
return current.left != parent;
}
public boolean canRedo() {
return current.right != null;
}
public void undo() {
if (!canUndo()) {
throw new IllegalStateException("Cannot undo.");
}
current = current.left;
state.accept(current.state);
}
public void redo() {
if (!canRedo()) {
throw new IllegalStateException("Cannot redo.");
}
current = current.right;
state.accept(current.state);
}
private class Node {
private final T state;
private Node left = null;
private Node right = null;
public Node(T s) {
state = s;
}
}
}