/*
 * Copyright (c) 2011-2019, 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
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 *   * 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
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 *     disclaimer in the documentation and/or other materials provided
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 */

#ifndef DART_COMMON_OBSERVER_HPP_
#define DART_COMMON_OBSERVER_HPP_

#include <set>

namespace dart {
namespace common {

class Subject;

/// The Observer class should be inherited by any class that wants to respond
/// in a customized way to the destruction of a Subject. Simply override the
/// Observer::handleDestructionNotification() function to customize how your
/// class responds to the destruction of a Subject.
///
/// 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 Observer
{
public:
  friend class Subject;

  /// Destructor will notify all Subjects that it is destructing
  virtual ~Observer();

protected:
  /// Called whenever a Subject is destroyed (or sends out a destruction
  /// notification). Override handleDestructionNotification() in order to
  /// customize your class's response to destruction notifications.
  void receiveDestructionNotification(const Subject* _subject);

  /// Called by receiveDestructionNotification(). Override this function to
  /// customize your class's response to destruction notifications.
  virtual void handleDestructionNotification(const Subject* _subject);

  /// Add a Subject for this Observer
  void addSubject(const Subject* _subject);

  /// Remove a Subject from this Observer
  void removeSubject(const Subject* _subject);

  /// Remove all Subjects from this Observer
  void removeAllSubjects();

  /// List of current Subjects for this Observer
  std::set<const Subject*> mSubjects;
};

} // namespace common
} // namespace dart

#endif // DART_COMMON_OBSERVER_HPP_
