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diff --git a/src/composite-undo-stack-observer.h b/src/composite-undo-stack-observer.h
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+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Authors:
+ * David Yip <yipdw@rose-hulman.edu>
+ *
+ * Copyright (c) 2005 Authors
+ *
+ * Released under GNU GPL v2+, read the file 'COPYING' for more information.
+ */
+
+#ifndef SEEN_COMPOSITE_UNDO_COMMIT_OBSERVER_H
+#define SEEN_COMPOSITE_UNDO_COMMIT_OBSERVER_H
+
+#include "inkgc/gc-alloc.h"
+#include "undo-stack-observer.h"
+
+#include <list>
+
+namespace Inkscape {
+
+struct Event;
+
+/**
+ * Aggregates UndoStackObservers for management and triggering in an SPDocument's undo/redo
+ * system.
+ *
+ * Heavily inspired by Inkscape::XML::CompositeNodeObserver.
+ */
+class CompositeUndoStackObserver : public UndoStackObserver {
+public:
+
+	/**
+	 * Structure for tracking UndoStackObservers.
+	 */
+	struct UndoStackObserverRecord {
+	public:
+		/**
+		 * Constructor.
+		 *
+		 * \param o Reference to the UndoStackObserver that this UndoStackObserverRecord
+		 * will track.
+		 */
+		UndoStackObserverRecord(UndoStackObserver& o) : to_remove(false), _observer(o) { }
+		bool to_remove;
+
+		/**
+		 * Overloaded equality test operator to facilitate usage of STL find algorithms.
+		 */
+		bool operator==(UndoStackObserverRecord const& _x) const
+		{
+			return &(this->_observer) == &(_x._observer);
+		}
+
+		/**
+		 * Issue a redo event to the UndoStackObserver that is associated with this UndoStackObserverRecord.
+		 *
+		 * \param log The event log generated by the redo event.
+		 */
+		void issueRedo(Event* log)
+		{
+			this->_observer.notifyRedoEvent(log);
+		}
+
+		/**
+		 * Issue an undo event to the UndoStackObserver that is associated with this
+		 * UndoStackObserverRecord.
+		 *
+		 * \param log The event log generated by the undo event.
+		 */
+		void issueUndo(Event* log)
+		{
+			this->_observer.notifyUndoEvent(log);
+		}
+
+		/**
+		 * Issues a committed event to the UndoStackObserver that is associated with this
+		 * UndoStackObserverRecord.
+		 *
+		 * \param log The event log being committed to the undo stack.
+		 */
+		void issueUndoCommit(Event* log)
+		{
+			this->_observer.notifyUndoCommitEvent(log);
+		}
+
+		/**
+		 * Issue a clear undo event to the UndoStackObserver
+		 * that is associated with this
+		 * UndoStackObserverRecord.
+		 */
+		void issueClearUndo()
+		{
+			this->_observer.notifyClearUndoEvent();
+		}
+	     
+		/**
+		 * Issue a clear redo event to the UndoStackObserver
+		 * that is associated with this
+		 * UndoStackObserverRecord.
+		 */
+		void issueClearRedo()
+		{
+			this->_observer.notifyClearRedoEvent();
+		}
+
+	private:
+		UndoStackObserver& _observer;
+	};
+
+	/// A list of UndoStackObserverRecords, used to aggregate multiple UndoStackObservers.
+	typedef std::list< UndoStackObserverRecord, GC::Alloc< UndoStackObserverRecord, GC::MANUAL > > UndoObserverRecordList;
+
+	/**
+	 * Constructor.
+	 */
+	CompositeUndoStackObserver();
+
+    ~CompositeUndoStackObserver() override;
+
+	/**
+	 * Add an UndoStackObserver.
+	 *
+	 * \param observer Reference to an UndoStackObserver to add.
+	 */
+	void add(UndoStackObserver& observer);
+
+	/**
+	 * Remove an UndoStackObserver.
+	 *
+	 * \param observer Reference to an UndoStackObserver to remove.
+	 */
+	void remove(UndoStackObserver& observer);
+
+	/**
+	 * Notify all registered UndoStackObservers of an undo event.
+	 *
+	 * \param log The event log generated by the undo event.
+	 */
+	void notifyUndoEvent(Event* log) override;
+
+	/**
+	 * Notify all registered UndoStackObservers of a redo event.
+	 *
+	 * \param log The event log generated by the redo event.
+	 */
+	void notifyRedoEvent(Event* log) override;
+
+	/**
+	 * Notify all registered UndoStackObservers of an event log being committed to the undo stack.
+	 *
+	 * \param log The event log being committed to the undo stack.
+	 */
+	void notifyUndoCommitEvent(Event* log) override;
+
+	void notifyClearUndoEvent() override;
+	void notifyClearRedoEvent() override;
+
+private:
+	// Remove an observer from a given list
+	bool _remove_one(UndoObserverRecordList& list, UndoStackObserver& rec);
+
+	// Mark an observer for removal from a given list
+	bool _mark_one(UndoObserverRecordList& list, UndoStackObserver& rec);
+
+	// Keep track of whether or not we are notifying observers
+	unsigned int _iterating;
+
+	// Observers in the active list
+	UndoObserverRecordList _active;
+
+	// Observers to be added
+	UndoObserverRecordList _pending;
+
+	// Prevents the observer vector from modifications during 
+	// iteration through the vector
+	void _lock() { this->_iterating++; }
+	void _unlock();
+};
+
+}
+
+#endif // SEEN_COMPOSITE_UNDO_COMMIT_OBSERVER_H