linjam/JuceLibraryCode/modules/juce_data_structures/undomanager/juce_UndoManager.h

/*
  ==============================================================================

   This file is part of the JUCE library.
   Copyright (c) 2017 - ROLI Ltd.

   JUCE is an open source library subject to commercial or open-source
   licensing.

   By using JUCE, you agree to the terms of both the JUCE 5 End-User License
   Agreement and JUCE 5 Privacy Policy (both updated and effective as of the
   27th April 2017).

   End User License Agreement: www.juce.com/juce-5-licence
   Privacy Policy: www.juce.com/juce-5-privacy-policy

   Or: You may also use this code under the terms of the GPL v3 (see
   www.gnu.org/licenses).

   JUCE IS PROVIDED "AS IS" WITHOUT ANY WARRANTY, AND ALL WARRANTIES, WHETHER
   EXPRESSED OR IMPLIED, INCLUDING MERCHANTABILITY AND FITNESS FOR PURPOSE, ARE
   DISCLAIMED.

  ==============================================================================
*/

namespace juce
{

//==============================================================================
/**
    Manages a list of undo/redo commands.

    An UndoManager object keeps a list of past actions and can use these actions
    to move backwards and forwards through an undo history.

    To use it, create subclasses of UndoableAction which perform all the
    actions you need, then when you need to actually perform an action, create one
    and pass it to the UndoManager's perform() method.

    The manager also uses the concept of 'transactions' to group the actions
    together - all actions performed between calls to beginNewTransaction() are
    grouped together and are all undone/redone as a group.

    The UndoManager is a ChangeBroadcaster, so listeners can register to be told
    when actions are performed or undone.

    @see UndoableAction

    @tags{DataStructures}
*/
class JUCE_API  UndoManager  : public ChangeBroadcaster
{
public:
    //==============================================================================
    /** Creates an UndoManager.

        @param maxNumberOfUnitsToKeep       each UndoableAction object returns a value
                                            to indicate how much storage it takes up
                                            (UndoableAction::getSizeInUnits()), so this
                                            lets you specify the maximum total number of
                                            units that the undomanager is allowed to
                                            keep in memory before letting the older actions
                                            drop off the end of the list.
        @param minimumTransactionsToKeep    this specifies the minimum number of transactions
                                            that will be kept, even if this involves exceeding
                                            the amount of space specified in maxNumberOfUnitsToKeep
    */
    UndoManager (int maxNumberOfUnitsToKeep = 30000,
                 int minimumTransactionsToKeep = 30);

    /** Destructor. */
    ~UndoManager() override;

    //==============================================================================
    /** Deletes all stored actions in the list. */
    void clearUndoHistory();

    /** Returns the current amount of space to use for storing UndoableAction objects.
        @see setMaxNumberOfStoredUnits
    */
    int getNumberOfUnitsTakenUpByStoredCommands() const;

    /** Sets the amount of space that can be used for storing UndoableAction objects.

        @param maxNumberOfUnitsToKeep       each UndoableAction object returns a value
                                            to indicate how much storage it takes up
                                            (UndoableAction::getSizeInUnits()), so this
                                            lets you specify the maximum total number of
                                            units that the undomanager is allowed to
                                            keep in memory before letting the older actions
                                            drop off the end of the list.
        @param minimumTransactionsToKeep    this specifies the minimum number of transactions
                                            that will be kept, even if this involves exceeding
                                            the amount of space specified in maxNumberOfUnitsToKeep
        @see getNumberOfUnitsTakenUpByStoredCommands
    */
    void setMaxNumberOfStoredUnits (int maxNumberOfUnitsToKeep,
                                    int minimumTransactionsToKeep);

    //==============================================================================
    /** Performs an action and adds it to the undo history list.

        @param action   the action to perform - this object will be deleted by
                        the UndoManager when no longer needed
        @returns true if the command succeeds - see UndoableAction::perform
        @see beginNewTransaction
    */
    bool perform (UndoableAction* action);

    /** Performs an action and also gives it a name.

        @param action       the action to perform - this object will be deleted by
                            the UndoManager when no longer needed
        @param actionName   if this string is non-empty, the current transaction will be
                            given this name; if it's empty, the current transaction name will
                            be left unchanged. See setCurrentTransactionName()
        @returns true if the command succeeds - see UndoableAction::perform
        @see beginNewTransaction
    */
    bool perform (UndoableAction* action, const String& actionName);

    /** Starts a new group of actions that together will be treated as a single transaction.

        All actions that are passed to the perform() method between calls to this
        method are grouped together and undone/redone together by a single call to
        undo() or redo().
    */
    void beginNewTransaction();

    /** Starts a new group of actions that together will be treated as a single transaction.

        All actions that are passed to the perform() method between calls to this
        method are grouped together and undone/redone together by a single call to
        undo() or redo().

        @param actionName   a description of the transaction that is about to be
                            performed
    */
    void beginNewTransaction (const String& actionName);

    /** Changes the name stored for the current transaction.

        Each transaction is given a name when the beginNewTransaction() method is
        called, but this can be used to change that name without starting a new
        transaction.
    */
    void setCurrentTransactionName (const String& newName);

    /** Returns the name of the current transaction.
        @see setCurrentTransactionName
    */
    String getCurrentTransactionName() const;

    //==============================================================================
    /** Returns true if there's at least one action in the list to undo.
        @see getUndoDescription, undo, canRedo
    */
    bool canUndo() const;

    /** Tries to roll-back the last transaction.
        @returns    true if the transaction can be undone, and false if it fails, or
                    if there aren't any transactions to undo
        @see undoCurrentTransactionOnly
    */
    bool undo();

    /** Tries to roll-back any actions that were added to the current transaction.

        This will perform an undo() only if there are some actions in the undo list
        that were added after the last call to beginNewTransaction().

        This is useful because it lets you call beginNewTransaction(), then
        perform an operation which may or may not actually perform some actions, and
        then call this method to get rid of any actions that might have been done
        without it rolling back the previous transaction if nothing was actually
        done.

        @returns true if any actions were undone.
    */
    bool undoCurrentTransactionOnly();

    /** Returns the name of the transaction that will be rolled-back when undo() is called.
        @see undo, canUndo, getUndoDescriptions
    */
    String getUndoDescription() const;

    /** Returns the names of the sequence of transactions that will be performed if undo()
        is repeatedly called. Note that for transactions where no name was provided, the
        corresponding string will be empty.
        @see undo, canUndo, getUndoDescription
    */
    StringArray getUndoDescriptions() const;

    /** Returns the time to which the state would be restored if undo() was to be called.
        If an undo isn't currently possible, it'll return Time().
    */
    Time getTimeOfUndoTransaction() const;

    /** Returns a list of the UndoableAction objects that have been performed during the
        transaction that is currently open.

        Effectively, this is the list of actions that would be undone if undoCurrentTransactionOnly()
        were to be called now.

        The first item in the list is the earliest action performed.
    */
    void getActionsInCurrentTransaction (Array<const UndoableAction*>& actionsFound) const;

    /** Returns the number of UndoableAction objects that have been performed during the
        transaction that is currently open.
        @see getActionsInCurrentTransaction
    */
    int getNumActionsInCurrentTransaction() const;

    //==============================================================================
    /** Returns true if there's at least one action in the list to redo.
        @see getRedoDescription, redo, canUndo
    */
    bool canRedo() const;

    /** Tries to redo the last transaction that was undone.
        @returns   true if the transaction can be redone, and false if it fails, or
                   if there aren't any transactions to redo
    */
    bool redo();

    /** Returns the name of the transaction that will be redone when redo() is called.
        @see redo, canRedo, getRedoDescriptions
    */
    String getRedoDescription() const;

    /** Returns the names of the sequence of transactions that will be performed if redo()
        is repeatedly called. Note that for transactions where no name was provided, the
        corresponding string will be empty.
        @see redo, canRedo, getRedoDescription
    */
    StringArray getRedoDescriptions() const;

    /** Returns the time to which the state would be restored if redo() was to be called.
        If a redo isn't currently possible, it'll return Time::getCurrentTime().
        @see redo, canRedo
    */
    Time getTimeOfRedoTransaction() const;

    /** Returns true if the caller code is in the middle of an undo or redo action. */
    bool isPerformingUndoRedo() const;

private:
    //==============================================================================
    struct ActionSet;
    OwnedArray<ActionSet> transactions, stashedFutureTransactions;
    String newTransactionName;
    int totalUnitsStored = 0, maxNumUnitsToKeep = 0, minimumTransactionsToKeep = 0, nextIndex = 0;
    bool newTransaction = true, isInsideUndoRedoCall = false;
    ActionSet* getCurrentSet() const;
    ActionSet* getNextSet() const;
    void moveFutureTransactionsToStash();
    void restoreStashedFutureTransactions();
    void dropOldTransactionsIfTooLarge();

    JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (UndoManager)
};

} // namespace juce