//
// AutoPtr.h
//
// $Id: //poco/1.4/Foundation/include/Poco/AutoPtr.h#1 $
//
// Library: Foundation
// Package: Core
// Module:  AutoPtr
//
// Definition of the AutoPtr template class.
//
// Copyright (c) 2004-2006, Applied Informatics Software Engineering GmbH.
// and Contributors.
//
// Permission is hereby granted, free of charge, to any person or organization
// obtaining a copy of the software and accompanying documentation covered by
// this license (the "Software") to use, reproduce, display, distribute,
// execute, and transmit the Software, and to prepare derivative works of the
// Software, and to permit third-parties to whom the Software is furnished to
// do so, all subject to the following:
// 
// The copyright notices in the Software and this entire statement, including
// the above license grant, this restriction and the following disclaimer,
// must be included in all copies of the Software, in whole or in part, and
// all derivative works of the Software, unless such copies or derivative
// works are solely in the form of machine-executable object code generated by
// a source language processor.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
// SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
// FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
// ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.
//


#ifndef Foundation_AutoPtr_INCLUDED
#define Foundation_AutoPtr_INCLUDED


#include "Poco/Foundation.h"
#include "Poco/Exception.h"
#include <algorithm>
#include <functional> // for std::less, greater, etc

namespace Poco {


template <class C>
class AutoPtr
	/// AutoPtr is a "smart" pointer for classes implementing
	/// reference counting based garbage collection.
	/// To be usable with the AutoPtr template, a class must
	/// implement the following behaviour:
	/// A class must maintain a reference count.
	/// The constructors of the object initialize the reference
	/// count to one.
	/// The class must implement a public duplicate() method:
	///     void duplicate();
	/// that increments the reference count by one.
	/// The class must implement a public release() method:
	///     void release()
	/// that decrements the reference count by one, and,
	/// if the reference count reaches zero, deletes the
	/// object.
	///
	/// AutoPtr works in the following way:
	/// If an AutoPtr is assigned an ordinary pointer to
	/// an object (via the constructor or the assignment operator),
	/// it takes ownership of the object and the object's reference 
	/// count remains unchanged.
	/// If the AutoPtr is assigned another AutoPtr, the
	/// object's reference count is incremented by one by
	/// calling duplicate() on its object.
	/// The destructor of AutoPtr calls release() on its
	/// object.
	/// AutoPtr supports dereferencing with both the ->
	/// and the * operator. An attempt to dereference a null
	/// AutoPtr results in a NullPointerException being thrown.
	/// AutoPtr also implements all relational operators.
	/// Note that AutoPtr allows casting of its encapsulated data types.
{
public:
	AutoPtr(): _ptr(0)
	{
	}

	AutoPtr(C* ptr): _ptr(ptr)
	{
	}

	AutoPtr(C* ptr, bool shared): _ptr(ptr)
	{
		if (shared && _ptr) _ptr->duplicate();
	}

	AutoPtr(const AutoPtr& ptr): _ptr(ptr._ptr)
	{
		if (_ptr) _ptr->duplicate();
	}

	template <class Other> 
	AutoPtr(const AutoPtr<Other>& ptr): _ptr(ptr.get())
	{
		if (_ptr) _ptr->duplicate();
	}

	~AutoPtr()
	{
		if (_ptr) _ptr->release();
	}
	
	AutoPtr& assign(C* ptr)
	{
		if (_ptr != ptr)
		{
			if (_ptr) _ptr->release();
			_ptr = ptr;
		}
		return *this;
	}

	AutoPtr& assign(C* ptr, bool shared)
	{
		if (_ptr != ptr)
		{
			if (_ptr) _ptr->release();
			_ptr = ptr;
			if (shared && _ptr) _ptr->duplicate();
		}
		return *this;
	}
	
	AutoPtr& assign(const AutoPtr& ptr)
	{
		if (&ptr != this)
		{
			if (_ptr) _ptr->release();
			_ptr = ptr._ptr;
			if (_ptr) _ptr->duplicate();
		}
		return *this;
	}
	
	template <class Other> 
	AutoPtr& assign(const AutoPtr<Other>& ptr)
	{
		if (ptr.get() != _ptr)
		{
			if (_ptr) _ptr->release();
			_ptr = ptr.get();
			if (_ptr) _ptr->duplicate();
		}
		return *this;
	}

	AutoPtr& operator = (C* ptr)
	{
		return assign(ptr);
	}

	AutoPtr& operator = (const AutoPtr& ptr)
	{
		return assign(ptr);
	}
	
	template <class Other> 
	AutoPtr& operator = (const AutoPtr<Other>& ptr)
	{
		return assign<Other>(ptr);
	}

	void swap(AutoPtr& ptr)
	{
		std::swap(_ptr, ptr._ptr);
	}
	
	template <class Other> 
	AutoPtr<Other> cast() const
		/// Casts the AutoPtr via a dynamic cast to the given type.
		/// Returns an AutoPtr containing NULL if the cast fails.
		/// Example: (assume class Sub: public Super)
		///    AutoPtr<Super> super(new Sub());
		///    AutoPtr<Sub> sub = super.cast<Sub>();
		///    poco_assert (sub.get());
	{
		Other* pOther = dynamic_cast<Other*>(_ptr);
		return AutoPtr<Other>(pOther, true);
	}

	template <class Other> 
	AutoPtr<Other> unsafeCast() const
		/// Casts the AutoPtr via a static cast to the given type.
		/// Example: (assume class Sub: public Super)
		///    AutoPtr<Super> super(new Sub());
		///    AutoPtr<Sub> sub = super.unsafeCast<Sub>();
		///    poco_assert (sub.get());
	{
		Other* pOther = static_cast<Other*>(_ptr);
		return AutoPtr<Other>(pOther, true);
	}

	C* operator -> () const
	{
		if (_ptr)
			return _ptr;
		else
			throw NullPointerException();
	}

	C& operator * () const
	{
		if (_ptr)
			return *_ptr;
		else
			throw NullPointerException();
	}

	C* get() const
	{
		return _ptr;
	}
	
	// This also serves as an safe implicit conversion to a boolean type
	operator C* () const
	{
		return _ptr;
	}
	
	bool operator ! () const
	{
		return _ptr == 0;
	}

	bool isNull() const
	{
		return _ptr == 0;
	}
	
	C* duplicate() const
	{
		if (_ptr) _ptr->duplicate();
		return _ptr;
	}
private:
	C* _ptr;
};

namespace Detail {
	// This class will generate a compilation error if the types T and U
	// can not be compared, i.e. they do not have a a composite
	// pointer type
	// Intentionaly complex to reduce the likeliness of warnings
	template <class T, class U>
	struct EnsureHasCompositePointerType
	{
		static void constraints(T* a, U* b, bool& x)
		{
			// If you get a compilation error here, then you have
			// tried to compare two smart pointers with
			// unrelated types.
			x = a < b;
		}
		typedef void f_type(T*, U*, bool&);
		void no_op(f_type)
		{
			// empty on purpose
		}
		EnsureHasCompositePointerType()
		{
			// This assignment should be optimized away by the compiler
			void (*p)(T*, U*, bool&) = constraints;
			// To get rid of the warning that we do not use the
			// variable
			no_op(p); 
		}
	};
	
	// The use of EnsureHasCompositePointerType, is done to ensure that
	// the pointers can be compared using the normal C++ language rules.
	// The reason the operators are not used directly is because
	// they are not required to give a total ordering for objects of any
	// type, however the predicates, eg. std::less, are required to give
	// a total ordering.

	template <class T, class U>
	bool pointerLess(T* a, U* b)
	{
		EnsureHasCompositePointerType<T, U>();
		return std::less<const void*>()(a, b);
	}
	template <class T, class U>
	bool pointerLessEq(T* a, U* b)
	{
		EnsureHasCompositePointerType<T, U>();
		return std::less_equal<const void*>()(a, b);
	}
	template <class T, class U>
	bool pointerGreater(T* a, U* b)
	{
		EnsureHasCompositePointerType<T, U>();
		return std::greater<const void*>()(a, b);
	}
	template <class T, class U>
	bool pointerGreaterEq(T* a, U* b)
	{
		EnsureHasCompositePointerType<T, U>();
		return std::greater_equal<const void*>()(a, b);
	}
}

template <class C>
inline void swap(AutoPtr<C>& p1, AutoPtr<C>& p2)
{
	p1.swap(p2);
}

template <class T, class U>
bool operator == (const AutoPtr<T>& a, const AutoPtr<U>& b)
{
	return a.get() == b.get();
}

template <class T, class U>
bool operator == (T* a, const AutoPtr<U>& b)
{
	return a == b.get();
}

template <class T, class U>
bool operator == (const AutoPtr<T>& a, U* b)
{
	return a.get() == b;
}


template <class T, class U>
bool operator != (const AutoPtr<T>& a, const AutoPtr<U>& b)
{
	return a.get() != b.get();
}

template <class T, class U>
bool operator != (T* a, const AutoPtr<U>& b)
{
	return a != b.get();
}

template <class T, class U>
bool operator != (const AutoPtr<T>& a, U* b)
{
	return a.get() != b;
}


template <class T, class U>
bool operator < (const AutoPtr<T>& a, const AutoPtr<U>& b)
{
	return Detail::pointerLess(a.get(), b.get());
}

template <class T, class U>
bool operator < (T* a, const AutoPtr<U>& b)
{
	return Detail::pointerLess(a, b.get());
}

template <class T, class U>
bool operator < (const AutoPtr<T>& a, U* b)
{
	return Detail::pointerLess(a.get(), b);
}


template <class T, class U>
bool operator <= (const AutoPtr<T>& a, const AutoPtr<U>& b)
{
	return Detail::pointerLessEq(a.get(), b.get());
}

template <class T, class U>
bool operator <= (T* a, const AutoPtr<U>& b)
{
	return Detail::pointerLessEq(a, b.get());
}

template <class T, class U>
bool operator <= (const AutoPtr<T>& a, U* b)
{
	return Detail::pointerLessEq(a.get(), b);
}


template <class T, class U>
bool operator > (const AutoPtr<T>& a, const AutoPtr<U>& b)
{
	return Detail::pointerGreater(a.get(), b.get());
}

template <class T, class U>
bool operator > (T* a, const AutoPtr<U>& b)
{
	return Detail::pointerGreater(a, b.get());
}

template <class T, class U>
bool operator > (const AutoPtr<T>& a, U* b)
{
	return Detail::pointerGreater(a.get(), b);
}


template <class T, class U>
bool operator >= (const AutoPtr<T>& a, const AutoPtr<U>& b)
{
	return Detail::pointerGreaterEq(a.get(), b.get());
}

template <class T, class U>
bool operator >= (T* a, const AutoPtr<U>& b)
{
	return Detail::pointerGreaterEq(a, b.get());
}

template <class T, class U>
bool operator >= (const AutoPtr<T>& a, U* b)
{
	return Detail::pointerGreaterEq(a.get(), b);
}

} // namespace Poco


#endif // Foundation_AutoPtr_INCLUDED