GUndo.h

#ifndef __GUNDO_H__
#define __GUNDO_H__

class GUndoEvent
{
public:
    virtual ~GUndoEvent() {}
    virtual void ApplyChange() {}
    virtual void RemoveChange() {}
};

class GUndo
{
    int Pos;
    List<GUndoEvent> Events;

public:
    GUndo() { Pos = 0; }
    ~GUndo() { Empty(); }

    bool CanUndo() { return (Pos > 0) AND (Events.Length() > 0); }
    bool CanRedo() { return (Pos < Events.Length()) AND (Events.Length() > 0); }
    void Empty() { Events.DeleteObjects(); Pos = 0; }

    GUndo &operator +=(GUndoEvent *e)
    {
        while (Events.Length() > Pos)
        {
            GUndoEvent *u = Events.Last();
            Events.Delete(u);
            DeleteObj(u);
        }

        Events.Insert(e);
        Pos++;
        return *this;
    }

    void Undo()
    {
        if (CanUndo())
        {
            GUndoEvent *e = Events.ItemAt(Pos-1);
            if (e)
            {
                e->RemoveChange();
                Pos--;
            }
        }
    }

    void Redo()
    {
        if (CanRedo())
        {
            GUndoEvent *e = Events.ItemAt(Pos);
            if (e)
            {
                e->ApplyChange();
                Pos++;
            }
        }
    }
};

#endif

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