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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

 * “redo” menu commands, the application invokes the

 * UndoManager’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

 * “undo” and “redo.” 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());

  }

}