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/* UndoManager.java --
   Copyright (C) 2002, 2004, 2005, 2006,  Free Software Foundation, Inc.
 
This file is part of GNU Classpath.
 
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package javax.swing.undo;
 
import javax.swing.UIManager;
import javax.swing.event.UndoableEditEvent;
import javax.swing.event.UndoableEditListener;
 
 
/**
 * A manager for providing an application’s undo/redo
 * functionality.
 *
 * <p>Tyipcally, an application will create only one single instance
 * of UndoManager. When the user performs an undoable action, for
 * instance changing the color of an object from green to blue, the
 * application registers an {@link UndoableEdit} object with the
 * <code>UndoManager</code>. To implement the &#x201c;undo&#x201d; and
 * &#x201c;redo&#x201d; menu commands, the application invokes the
 * UndoManager&#x2019;s {@link #undo} and {@link #redo} methods.  The
 * human-readable text of these menu commands is provided by {@link
 * #getUndoPresentationName} and {@link #getRedoPresentationName},
 * respectively. To determine whether the menu item should be
 * selectable or greyed out, use {@link #canUndo} and {@link
 * #canRedo}.
 *
 * <p>The UndoManager will only keep a specified number of editing
 * actions, the <em>limit</em>. The value of this parameter can be
 * retrieved by calling {@link #getLimit} and set with {@link
 * #setLimit}.  If more UndoableEdits are added to the UndoManager,
 * the oldest actions will be discarded.
 *
 * <p>Some applications do not provide separate menu commands for
 * &#x201c;undo&#x201d; and &#x201c;redo.&#x201d; Instead, they
 * have just a single command whose text switches between the two.
 * Such applications would use an UndoManager with a <code>limit</code>
 * of 1. The text of this combined menu item is available via
 * {@link #getUndoOrRedoPresentationName}, and it is implemented
 * by calling {@link #undoOrRedo}.
 *
 * <p><b>Thread Safety:</b> In constrast to the other classes of the
 * <code>javax.swing.undo</code> package, the public methods of an
 * <code>UndoManager</code> are safe to call from concurrent threads.
 * The caller does not need to perform external synchronization, and
 * {@link javax.swing.event.UndoableEditEvent} sources do not need to
 * broadcast their events from inside the Swing worker thread.
 *
 * @author Sascha Brawer (brawer@dandelis.ch)
 */
public class UndoManager
  extends CompoundEdit
  implements UndoableEditListener
{
  /**
   * The unique ID for serializing instances of this class. Determined
   * using the <code>serialver</code> tool of Sun JDK 1.4.1_01 on
   * GNU/Linux.
   */
  static final long serialVersionUID = -2077529998244066750L;
 
 
  /**
   * An index into the inherited {@link #edits} Vector that indicates
   * at which position newly added editing actions would get inserted.
   *
   * <p>Normally, the value of <code>indexOfNextAdd</code> equals
   * the number of UndoableEdits stored by this UndoManager, i.e.
   * <code>edits.size()</code>. For each call to {@link #undo},
   * <code>indexOfNextAdd</code> is decremented by one. For each
   * call to {@link #redo}, it is incremented again.
   */
  int indexOfNextAdd;
 
 
  /**
   * The maximum number of UndoableEdits stored by this UndoManager.
   */
  int limit;
 
 
  /**
   * Constructs an UndoManager.
   *
   * <p>The <code>limit</code> of the freshly constructed UndoManager
   * is 100.
   */
  public UndoManager()
  {
    limit = 100;
  }
 
 
  /**
   * Returns a string representation for this UndoManager. This may be
   * useful for debugging purposes. For the text of menu items, please
   * refer to {@link #getUndoPresentationName}, {@link
   * #getRedoPresentationName}, and {@link
   * #getUndoOrRedoPresentationName}.
   */
  public String toString()
  {
    return super.toString()
      + " limit: " + limit
      + " indexOfNextAdd: " + indexOfNextAdd;
  }
 
 
  /**
   * Puts this UndoManager into a state where it acts as a normal
   * {@link CompoundEdit}. It is unlikely that an application would
   * want to do this.
   */
  public synchronized void end()
  {
    super.end();
    trimEdits(indexOfNextAdd, edits.size() - 1);
  }
 
 
  /**
   * Returns how many edits this UndoManager can maximally hold.
   *
   * @see #setLimit
   */
  public synchronized int getLimit()
  {
    return limit;
  }
 
 
  /**
   * Changes the maximal number of edits that this UndoManager can
   * process. If there are currently more edits than the new limit
   * allows, they will receive a {@link UndoableEdit#die() die}
   * message in reverse order of addition.
   *
   * @param limit the new limit.
   *
   * @throws IllegalStateException if {@link #end()} has already been
   * called on this UndoManager.
   */
  public synchronized void setLimit(int limit)
  {
    if (!isInProgress())
      throw new IllegalStateException();
 
    this.limit = limit;
    trimForLimit();
  }
 
 
  /**
   * Discards all editing actions that are currently registered with
   * this UndoManager. Each {@link UndoableEdit} will receive a {@link
   * UndoableEdit#die() die message}.
   */
  public synchronized void discardAllEdits()
  {
    int size;
 
    size = edits.size();
    for (int i = size - 1; i >= 0; i--)
      edits.get(i).die();
    indexOfNextAdd = 0;
    edits.clear();
  }
 
 
  /**
   * Called by various internal methods in order to enforce
   * the <code>limit</code> value.
   */
  protected void trimForLimit()
  {
    int high, s;
 
    s = edits.size();
 
    /* The Sun J2SE1.4.1_01 implementation can be observed to do
     * nothing (instead of throwing an exception) with a negative or
     * zero limit. It may be debatable whether this is the best
     * behavior, but we replicate it for sake of compatibility.
     */
    if (limit <= 0 || s <= limit)
      return;
 
    high = Math.min(indexOfNextAdd + limit/2 - 1, s - 1);
    trimEdits(high + 1, s - 1);
    trimEdits(0, high - limit);
  }
 
 
  /**
   * Discards a range of edits. All edits in the range <code>[from
   * .. to]</code> will receive a {@linkplain UndoableEdit#die() die
   * message} before being removed from the edits array.  If
   * <code>from</code> is greater than <code>to</code>, nothing
   * happens.
   *
   * @param from the lower bound of the range of edits to be
   * discarded.
   *
   * @param to the upper bound of the range of edits to be discarded.
   */
  protected void trimEdits(int from, int to)
  {
    if (from > to)
      return;
 
    for (int i = to; i >= from; i--)
        edits.get(i).die();
 
    // Remove the range [from .. to] from edits. If from == to, which
    // is likely to be a very common case, we can do better than
    // creating a sub-list and clearing it.
    if (to == from)
      edits.remove(from);
    else
      edits.subList(from, to + 1).clear();
 
    if (indexOfNextAdd > to)
      indexOfNextAdd = indexOfNextAdd - to + from - 1;
    else if (indexOfNextAdd >= from)
      indexOfNextAdd = from;
  }
 
 
  /**
   * Determines which significant edit would be undone if {@link
   * #undo()} was called.
   *
   * @return the significant edit that would be undone, or
   * <code>null</code> if no significant edit would be affected by
   * calling {@link #undo()}.
   */
  protected UndoableEdit editToBeUndone()
  {
    UndoableEdit result;
 
    for (int i = indexOfNextAdd - 1; i >= 0; i--)
      {
        result = edits.get(i);
        if (result.isSignificant())
          return result;
      }
 
    return null;
  }
 
 
  /**
   * Determines which significant edit would be redone if {@link
   * #redo()} was called.
   *
   * @return the significant edit that would be redone, or
   * <code>null</code> if no significant edit would be affected by
   * calling {@link #redo()}.
   */
  protected UndoableEdit editToBeRedone()
  {
    UndoableEdit result;
 
    for (int i = indexOfNextAdd; i < edits.size(); i++)
      {
        result = edits.get(i);
        if (result.isSignificant())
          return result;
      }
 
    return null;
  }
 
 
  /**
   * Undoes all editing actions in reverse order of addition,
   * up to the specified action,
   *
   * @param edit the last editing action to be undone.
   */
  protected void undoTo(UndoableEdit edit)
    throws CannotUndoException
  {
    UndoableEdit cur;
 
    if (!edits.contains(edit))
      throw new CannotUndoException();
 
    while (true)
      {
        indexOfNextAdd -= 1;
        cur = edits.get(indexOfNextAdd);
        cur.undo();
        if (cur == edit)
          return;
      }
  }
 
 
  /**
   * Redoes all editing actions in the same order as they were
   * added to this UndoManager, up to the specified action.
   *
   * @param edit the last editing action to be redone.
   */
  protected void redoTo(UndoableEdit edit)
    throws CannotRedoException
  {
    UndoableEdit cur;
 
    if (!edits.contains(edit))
      throw new CannotRedoException();
 
    while (true)
      {
        cur = edits.get(indexOfNextAdd);
        indexOfNextAdd += 1;
        cur.redo();
        if (cur == edit)
          return;
      }
  }
 
 
  /**
   * Undoes or redoes the last action. If the last action has already
   * been undone, it will be re-done, and vice versa.
   *
   * <p>This is useful for applications that do not present a separate
   * undo and redo facility, but just have a single menu item for
   * undoing and redoing the very last action. Such applications will
   * use an <code>UndoManager</code> whose <code>limit</code> is 1.
   */
  public synchronized void undoOrRedo()
    throws CannotRedoException, CannotUndoException
  {
    if (indexOfNextAdd == edits.size())
      undo();
    else
      redo();
  }
 
 
  /**
   * Determines whether it would be possible to either undo or redo
   * this editing action.
   *
   * <p>This is useful for applications that do not present a separate
   * undo and redo facility, but just have a single menu item for
   * undoing and redoing the very last action. Such applications will
   * use an <code>UndoManager</code> whose <code>limit</code> is 1.
   *
   * @return <code>true</code> to indicate that this action can be
   * undone or redone; <code>false</code> if neither is possible at
   * the current time.
   */
  public synchronized boolean canUndoOrRedo()
  {
    return indexOfNextAdd == edits.size() ? canUndo() : canRedo();
  }
 
 
  /**
   * Undoes one significant edit action. If insignificant actions have
   * been posted after the last signficant action, the insignificant
   * ones will be undone first.
   *
   * <p>However, if {@link #end()} has been called on this
   * UndoManager, it will behave like a normal {@link
   * CompoundEdit}. In this case, all actions will be undone in
   * reverse order of addition. Typical applications will never call
   * {@link #end()} on their <code>UndoManager</code>.
   *
   * @throws CannotUndoException if no action can be undone.
   *
   * @see #canUndo()
   * @see #redo()
   * @see #undoOrRedo()
   */
  public synchronized void undo()
    throws CannotUndoException
  {
    if (!isInProgress())
      {
        super.undo();
        return;
      }
 
    UndoableEdit edit = editToBeUndone();
    if (edit == null)
      throw new CannotUndoException();
 
    undoTo(edit);
  }
 
 
  /**
   * Determines whether it would be possible to undo this editing
   * action.
   *
   * @return <code>true</code> to indicate that this action can be
   * undone; <code>false</code> otherwise.
   *
   * @see #undo()
   * @see #canRedo()
   * @see #canUndoOrRedo()
   */
  public synchronized boolean canUndo()
  {
    UndoableEdit edit;
 
    if (!isInProgress())
      return super.canUndo();
 
    edit = editToBeUndone();
    return edit != null && edit.canUndo();
  }
 
 
 
  /**
   * Redoes one significant edit action. If insignificant actions have
   * been posted in between, the insignificant ones will be redone
   * first.
   *
   * <p>However, if {@link #end()} has been called on this
   * UndoManager, it will behave like a normal {@link
   * CompoundEdit}. In this case, <em>all</em> actions will be redone
   * in order of addition. Typical applications will never call {@link
   * #end()} on their <code>UndoManager</code>.
   *
   * @throws CannotRedoException if no action can be redone.
   *
   * @see #canRedo()
   * @see #redo()
   * @see #undoOrRedo()
   */
  public synchronized void redo()
    throws CannotRedoException
  {
    if (!isInProgress())
      {
        super.redo();
        return;
      }
 
    UndoableEdit edit = editToBeRedone();
    if (edit == null)
      throw new CannotRedoException();
 
    redoTo(edit);
  }
 
 
  /**
   * Determines whether it would be possible to redo this editing
   * action.
   *
   * @return <code>true</code> to indicate that this action can be
   * redone; <code>false</code> otherwise.
   *
   * @see #redo()
   * @see #canUndo()
   * @see #canUndoOrRedo()
   */
  public synchronized boolean canRedo()
  {
    UndoableEdit edit;
 
    if (!isInProgress())
      return super.canRedo();
 
    edit = editToBeRedone();
    return edit != null && edit.canRedo();
  }
 
 
  /**
   * Registers an undoable editing action with this UndoManager.  If
   * the capacity <code>limit</code> is reached, the oldest action
   * will be discarded (and receives a {@linkplain UndoableEdit#die()
   * die message}. Equally, any actions that were undone (but not re-done)
   * will be discarded, too.
   *
   * @param edit the editing action that is added to this UndoManager.
   *
   * @return <code>true</code> if <code>edit</code> could be
   * incorporated; <code>false</code> if <code>edit</code> has not
   * been incorporated because {@link #end()} has already been called
   * on this <code>UndoManager</code>.
   */
  public synchronized boolean addEdit(UndoableEdit edit)
  {
    boolean result;
 
    // Discard any edits starting at indexOfNextAdd.
    trimEdits(indexOfNextAdd, edits.size() - 1);
 
    result = super.addEdit(edit);
    indexOfNextAdd = edits.size();
    trimForLimit();
    return result;
  }
 
 
  /**
   * Calculates a localized text for presenting the undo or redo
   * action to the user, for example in the form of a menu command.
   *
   * <p>This is useful for applications that do not present a separate
   * undo and redo facility, but just have a single menu item for
   * undoing and redoing the very last action. Such applications will
   * use an <code>UndoManager</code> whose <code>limit</code> is 1.
   *
   * @return the redo presentation name if the last action has already
   * been undone, or the undo presentation name otherwise.
   *
   * @see #getUndoPresentationName()
   * @see #getRedoPresentationName()
   */
  public synchronized String getUndoOrRedoPresentationName()
  {
    if (indexOfNextAdd == edits.size())
      return getUndoPresentationName();
    else
      return getRedoPresentationName();
  }
 
 
  /**
   * Calculates a localized text for presenting the undo action
   * to the user, for example in the form of a menu command.
   */
  public synchronized String getUndoPresentationName()
  {
    UndoableEdit edit;
 
    if (!isInProgress())
      return super.getUndoPresentationName();
 
    edit = editToBeUndone();
    if (edit == null)
      return UIManager.getString("AbstractUndoableEdit.undoText");
    else
      return edit.getUndoPresentationName();
  }
 
 
  /**
   * Calculates a localized text for presenting the redo action
   * to the user, for example in the form of a menu command.
   */
  public synchronized String getRedoPresentationName()
  {
    UndoableEdit edit;
 
    if (!isInProgress())
      return super.getRedoPresentationName();
 
    edit = editToBeRedone();
    if (edit == null)
      return UIManager.getString("AbstractUndoableEdit.redoText");
    else
      return edit.getRedoPresentationName();
  }
 
 
  /**
   * Registers the edit action of an {@link UndoableEditEvent}
   * with this UndoManager.
   *
   * <p><b>Thread Safety:</b> This method may safely be invoked from
   * concurrent threads.  The caller does not need to perform external
   * synchronization. This means that {@link
   * javax.swing.event.UndoableEditEvent} sources do not need to broadcast
   * their events from inside the Swing worker thread.
   *
   * @param event the event whose <code>edit</code> will be
   * passed to {@link #addEdit}.
   *
   * @see UndoableEditEvent#getEdit()
   * @see #addEdit
   */
  public void undoableEditHappened(UndoableEditEvent event)
  {
    // Note that this method does not need to be synchronized,
    // because addEdit will obtain and release the mutex.
    addEdit(event.getEdit());
  }
}