#pragma once
 
#ifndef TCG_OBSERVER_NOTIFIER_H
#define TCG_OBSERVER_NOTIFIER_H
 
// tcg includes
#include "base.h"
 
// STD includes
#include <set>
 
/*!
  \file     tcg_observer_notifier.h
 
  \brief    This file contains the barebone of an elementary, classical
            implementation of the Observer pattern requiring derivation.
 
  \details  This is intended as a convenient and lightweight predefined
            implementation when hardwiring the Observer pattern in a
            known class using derivation.
 
            Observe that this implementation <I>does not deal with the
            actual notifications forwarding</I> - it just manages the
            set of observers/notifiers in a notifier/observer instance.
 
            No multithreading is taken into consideration.
 
  \remark   See elsewhere for more advanced implementations.
*/
 
namespace tcg
{
 
//************************************************************************
//    Observer/notifier  base polymorphic classes
//************************************************************************
 
class observer_base;
class notifier_base;
 
//------------------------------------------------------------
 
class observer_base
{
public:
	virtual ~observer_base() {}
 
	virtual void attach(notifier_base *notifier) = 0; //!< Adds the specified notifier to the internal set of notifiers.
	virtual void detach(notifier_base *notifier) = 0; //!< Removes the specified notifier from the internal set of notifiers.
};
 
//------------------------------------------------------------
 
class notifier_base
{
public:
	virtual ~notifier_base() {}
 
	virtual void attach(observer_base *observer) = 0; //!< Adds the specified observer to the internal set of observers.
	virtual void detach(observer_base *observer) = 0; //!< Removes the specified observer from the internal set of observers.
};
 
//************************************************************************
//    Observer/notifier  with a single interacting object
//************************************************************************
 
template <typename Notifier = notifier_base, typename Base = observer_base>
class observer_single : public noncopyable<Base>
{
	Notifier *m_notifier; // Not owned
 
public:
	typedef Notifier notifier_type;
 
public:
	observer_single() : m_notifier() {}
	~observer_single()
	{
		if (m_notifier)
			static_cast<notifier_base *>(m_notifier)->detach(this); // The detaching function is most probably \a private in
	}																// reimplemented notifier classes (like in this observer).
																	// Besides, it would be a virtual function call anyway.
	notifier_type *notifier() const { return m_notifier; }
 
private:
	void attach(notifier_base *notifier)
	{
		assert(notifier && !m_notifier);
		m_notifier = static_cast<Notifier *>(notifier);
	}
 
	void detach(notifier_base *notifier)
	{
		assert(m_notifier && m_notifier == static_cast<Notifier *>(notifier));
		m_notifier = 0;
	}
};
 
//------------------------------------------------------------
 
template <typename Observer = observer_base, typename Base = notifier_base>
class notifier_single : public noncopyable<Base>
{
	Observer *m_observer; // Not owned
 
public:
	typedef Observer observer_type;
 
public:
	notifier_single() : m_observer() {}
	~notifier_single()
	{
		if (m_observer)
			static_cast<observer_base *>(m_observer)->detach(this);
	}
 
	observer_type *observer() const { return m_observer; }
 
	void addObserver(observer_type *observer)
	{
		notifier_single::attach(observer);					  // No reason to go polymorphic here - it's this very class.
		static_cast<observer_base *>(observer)->attach(this); // However, here it's necessary - like above, downcast to
	}														  // the very base.
 
	void removeObserver(observer_type *observer)
	{
		static_cast<observer_base *>(observer)->detach(this);
		notifier_single::detach(observer);
	}
 
private:
	void attach(observer_base *observer)
	{
		assert(observer && !m_observer);
		m_observer = static_cast<Observer *>(observer);
	}
 
	void detach(observer_base *observer)
	{
		assert(m_observer && m_observer == static_cast<Observer *>(observer));
		m_observer = 0;
	}
};
 
//************************************************************************
//    Observer/notifier  with multiple interacting objects
//************************************************************************
 
template <typename Notifier = notifier_base, typename Base = observer_base,
		  typename Set = std::set<Notifier *>>
class observer : public noncopyable<Base>
{
	Set m_notifiers; // Not owned
 
public:
	typedef Notifier notifier_type;
	typedef Set notifiers_container;
 
public:
	~observer()
	{
		typename Set::iterator nt, nEnd = m_notifiers.end();
		for (nt = m_notifiers.begin(); nt != nEnd; ++nt)
			static_cast<notifier_base *>(*nt)->detach(this);
	}
 
	const notifiers_container &notifiers() const
	{
		return m_notifiers;
	}
 
private:
	void attach(notifier_base *notifier)
	{
		assert(notifier);
		m_notifiers.insert(static_cast<Notifier *>(notifier));
	}
 
	void detach(notifier_base *notifier)
	{
		assert(!m_notifiers.empty());
		m_notifiers.erase(static_cast<Notifier *>(notifier));
	}
};
 
//------------------------------------------------------------
 
template <typename Observer = observer_base, typename Base = notifier_base,
		  typename Set = std::set<Observer *>>
class notifier : public noncopyable<Base>
{
	Set m_observers; // Not owned
 
public:
	typedef Observer observer_type;
	typedef Set observers_container;
 
public:
	~notifier()
	{
		typename Set::iterator ot, oEnd = m_observers.end();
		for (ot = m_observers.begin(); ot != oEnd; ++ot)
			static_cast<observer_base *>(*ot)->detach(this);
	}
 
	const observers_container &observers() const
	{
		return m_observers;
	}
 
	void addObserver(observer_type *observer)
	{
		notifier::attach(observer);
		static_cast<observer_base *>(observer)->attach(this);
	}
 
	void removeObserver(observer_type *observer)
	{
		static_cast<observer_base *>(observer)->detach(this);
		notifier::detach(observer);
	}
 
private:
	void attach(observer_base *observer)
	{
		assert(observer);
		m_observers.insert(static_cast<Observer *>(observer));
	}
 
	void detach(observer_base *observer)
	{
		assert(!m_observers.empty());
		m_observers.erase(static_cast<Observer *>(observer));
	}
};
 
} // namespace tcg
 
#endif // TCG_OBSERVER_NOTIFIER_H