DefaultUndoManager.java

package org.springframework.roo.file.undo;

import java.util.HashSet;
import java.util.Set;
import java.util.Stack;

import org.apache.commons.lang3.Validate;
import org.apache.felix.scr.annotations.Component;
import org.apache.felix.scr.annotations.Service;
import org.osgi.service.component.ComponentContext;
import org.springframework.roo.file.undo.UndoEvent.UndoOperation;

/**
 * Default implementation of the {@link UndoManager} interface.
 * 
 * @author Ben Alex
 * @since 1.0
 */
@Component
@Service
public class DefaultUndoManager implements UndoManager {

  private final Set<UndoListener> listeners = new HashSet<UndoListener>();
  private final Stack<UndoableOperation> stack = new Stack<UndoableOperation>();
  private boolean undoEnabled = true;

  protected void activate(final ComponentContext context) {}

  public void add(final UndoableOperation undoableOperation) {
    Validate.notNull(undoableOperation, "Undoable operation required");
    stack.push(undoableOperation);
  }

  public void addUndoListener(final UndoListener undoListener) {
    listeners.add(undoListener);
  }

  public void flush() {
    notifyListeners(UndoOperation.FLUSH);
  }

  private void notifyListeners(final UndoOperation operation) {
    for (final UndoListener listener : listeners) {
      listener.onUndoEvent(new UndoEvent(operation));
    }
  }

  public void removeUndoListener(final UndoListener undoListener) {
    listeners.remove(undoListener);
  }

  public void reset() {
    while (!stack.empty()) {
      final UndoableOperation op = stack.pop();
      try {
        op.reset();
      } catch (final Throwable t) {
        throw new IllegalStateException("UndoableOperation '" + op
            + "' threw an exception, in violation of the interface contract");
      }
    }
    notifyListeners(UndoOperation.RESET);
  }

  public void setUndoEnabled(final boolean undoEnabled) {
    this.undoEnabled = undoEnabled;
  }

  public boolean undo() {
    boolean undoMode = true;
    if (!undoEnabled) {
      // Force the undo stack to simply reset (but not perform any undos)
      undoMode = false;
    }
    while (!stack.empty()) {
      final UndoableOperation op = stack.pop();
      try {
        if (undoMode) {
          if (!op.undo()) {
            // Undo failed, so switch to reset mode going forward
            undoMode = false;
          }
        } else {
          // In reset mode
          op.reset();
        }
      } catch (final Throwable t) {
        throw new IllegalStateException("UndoableOperation '" + op
            + "' threw an exception, in violation of the interface contract");
      }
    }
    notifyListeners(UndoOperation.UNDO);
    return undoMode;
  }
}