/*
 * Copyright (c) 2011-2022, The DART development contributors
 * All rights reserved.
 *
 * The list of contributors can be found at:
 *   https://github.com/dartsim/dart/blob/master/LICENSE
 *
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 *   without modification, are permitted provided that the following
 *   conditions are met:
 *   * Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *   * Redistributions in binary form must reproduce the above
 *     copyright notice, this list of conditions and the following
 *     disclaimer in the documentation and/or other materials provided
 *     with the distribution.
 *   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
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 *   INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 *   MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 *   DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
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 */

#ifndef DART_COMMON_SUBJECT_HPP_
#define DART_COMMON_SUBJECT_HPP_

#include <set>

namespace dart {
namespace common {

class Observer;

/// The Subject class is a base class for any object that wants to report when
/// it gets destroyed. This is useful for complex frameworks in which it is
/// difficult or impossible to know when an object or resource might destroyed
/// by some other part of the code, or when special cleanup might be needed
/// upon the destruction of an object. Simply by inheriting the Subject class,
/// any class can have the destruction notification feature.
///
/// Note that the Subject class should ALWAYS be virtually inherited. No other
/// special considerations are needed when virtually inheriting the Subject
/// class.
///
/// dart::sub_ptr is a templated smart pointer that will change itself into a
/// nullptr when its Subject is destroyed. It offers one of the easiest ways to
/// take advantage of the Subject/Observer pattern.
class Subject
{
public:
  friend class Observer;

  /// Destructor will notify all Observers that it is destructing
  virtual ~Subject();

protected:
  /// Send a destruction notification to all Observers. This will cause all
  /// Observers to behave as if this Subject has been permanently deleted, so it
  /// should only be called when that behavior is desired.
  void sendDestructionNotification() const;

  /// Add an Observer to the list of Observers
  void addObserver(Observer* _observer) const;

  /// Remove an Observer from the list of Observers
  void removeObserver(Observer* _observer) const;

  /// List of current Observers
  mutable std::set<Observer*> mObservers;
};

} // namespace common
} // namespace dart

#endif // DART_COMMON_SUBJECT_HPP_
