UT/UT_DelegatedUndo.h

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/*
 * PROPRIETARY INFORMATION.  This software is proprietary to
 * Side Effects Software Inc., and is not to be reproduced,
 * transmitted, or disclosed in any way without written permission.
 * 
 * Produced by:
 *      Luke Moore
 *      Side Effects Software Inc
 *      477 Richmond Street West
 *      Toronto, Ontario
 *      Canada   M5V 3E7
 *      416-504-9876
 *
 * NAME:        UT_DelegatedUndo.h
 *
 * COMMENTS:
 *      This class is the base class for undo objects that delegate their
 *      work to someone else (the undo worker).  It uses UT_UndoWorkerFinder's
 *      to see if the undo worker has been deleted.
 *
 *      See the comments in UT_UndoWorkerFinder.h for instructions on how
 *      to use this class.
 */

#ifndef __UT_DelegatedUndo_h__
#define __UT_DelegatedUndo_h__

#include "UT_API.h"
#include "UT_Undo.h"
#include "UT_UndoWorkerFinder.h"

// Undo classes do not need to work with UT_DelegatedUndoBase directly.
class UT_API UT_DelegatedUndoBase : public UT_Undo
{
public:
    UT_DelegatedUndoBase(int undo_worker_id);

    // We can't undo or redo anything if our undo worker has been deleted.
    virtual bool isValid()      { return opaqueUndoWorker() != 0; }

protected:
    void        *opaqueUndoWorker();

private:
    int          myUndoWorkerId;
};


// This templated class is a convenience class to avoid casting.
template <class UndoWorker>
class UT_DelegatedUndo : public UT_DelegatedUndoBase
{
public:
    UT_DelegatedUndo(const UT_UndoWorkerFinder<UndoWorker> &undo_worker_finder)
        : UT_DelegatedUndoBase(undo_worker_finder.undoWorkerId()) {}

protected:
    // A null pointer is returned if the undo work has been deleted.
    // The undo() and redo() methods will not be called when undoWorker()
    // returns null.
    UndoWorker  *undoWorker() { return (UndoWorker *)opaqueUndoWorker(); }
};


#endif

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