/*
**  ClanLib SDK
**  Copyright (c) 1997-2005 The ClanLib Team
**
**  This software is provided 'as-is', without any express or implied
**  warranty.  In no event will the authors be held liable for any damages
**  arising from the use of this software.
**
**  Permission is granted to anyone to use this software for any purpose,
**  including commercial applications, and to alter it and redistribute it
**  freely, subject to the following restrictions:
**
**  1. The origin of this software must not be misrepresented; you must not
**     claim that you wrote the original software. If you use this software
**     in a product, an acknowledgment in the product documentation would be
**     appreciated but is not required.
**  2. Altered source versions must be plainly marked as such, and must not be
**     misrepresented as being the original software.
**  3. This notice may not be removed or altered from any source distribution.
**
**  Note: Some of the libraries ClanLib may link to may have additional
**  requirements or restrictions.
**
**  File Author(s):
**
**    Magnus Norddahl
**    (if your name is missing here, please add it)
*/

//! clanCore="System"
//! header=core.h

#ifndef HEADER_SHAREDPTR_HPP
#define HEADER_SHAREDPTR_HPP

template <typename TEvil>
class SharedPtr_Generic
{
public:
	SharedPtr_Generic() : ptr(0), ref_count(1) { return; }

	virtual ~SharedPtr_Generic() { return; }

public:
	//: Pointer to new-allocated data, or else 0:
	TEvil *ptr;
	
	//: reference count:
	unsigned int ref_count;
};

template <typename T, typename TEvil>
class SharedPtr_Deleter : public SharedPtr_Generic<T>
{
public:
	SharedPtr_Deleter(TEvil *e) { this->ptr = e; }

	~SharedPtr_Deleter() { delete this->ptr; }
};

//: Shared pointer class (automatically deletes data when all SharedPtrs to data are gone).
//- !group=Core/System!
//- !header=core.h!
//- <p> Use SharedPtr when you have data that's intended to be shared between
//- multiple users without each user needing an individual copy. </p>
//- <p> Note that SharedPtr uses a very simple reference counting system, so is susecptible
//- to circular loop issues. </p>
template <typename T, typename U = T>
class SharedPtr
{
//! Construction:
public:
	//: Constructs a SharedPtr.
	//param t: A pointer which was the return value of a 'new' call.
	//- <p> After the SharedPtr has been constructed based on a passed pointer,
	//- the SharedPtr takes full control over that data. The original pointer shouldn't
	//- be used to access or delete the data anymore; instead, use the SharedPtr. </p>
	SharedPtr() : impl(0) { return; }

	SharedPtr(const SharedPtr<T, U>& other) : impl(other.impl) { increment(); }

	template <typename D>
	explicit SharedPtr(D* ptr) : impl(new SharedPtr_Deleter<T, D>(ptr)) { return; }

	explicit SharedPtr(SharedPtr_Generic<T> *impl) : impl(impl) { increment(); }
	
	~SharedPtr() { decrement(); }
	
//! Attributes:
public:
	//: Returns true if this SharedPtr is not dereferencable.
	bool is_null() const { return impl ? (impl->ptr == 0) : true; }

	//: Returns number of references (including this one) to the data cache.
	//- <p> Returns 0 if this pointer is null. </p>
	int get_ref_count() const { if (impl == 0) return 0; return impl->ref_count; }
	
	//: Gives access to the pointer itself.
	//- <p> Be careful not to keep the returned pointer around after doing any
	//- non-const operations on the SharedPtr; it could be invalid
	//- after that.</p>
	U* get() { return (U*) ((impl != 0) ? impl->ptr : 0); }

	U const* get() const { return (const U*) ((impl != 0) ? impl->ptr : 0); }

	//: Pointer equality check operator.
	//- <p> This will return true if the SharedPtrs point to the same data. It doesn't
	//- check the data itself for equality. </p>
	bool operator==(const T* other) const { return other == ((impl != 0) ? impl->ptr : 0); }

	bool operator==(const SharedPtr<T, U>& other) const { return other.impl == impl; }

	//: reelase the content of the SharedPtr
	//- <p> Decrements the reference count and sets the data pointer to null.
	//- This is usefull for solving circular references</p>
	void release (void) 
	{
		if (impl!= 0)
		{
			decrement ();
			impl = 0;
		}
	}
//! Operations:
public:
	//: Copy assignment operator.
	//param t: A pointer which was the return value of a 'new' call.
	//- <p> Once the assignment statement is finished when assigning a passed pointer,
	//- the SharedPtr takes full control over that data. The original pointer shouldn't
	//- be used to access or delete the data anymore; instead, use the SharedPtr. </p>
	SharedPtr<T, U>& operator=(const SharedPtr<T, U>& other)
	{
		if (other.impl != impl)
		{
			decrement();
			impl = other.impl;
			increment();
		}
		return *this;
	}

	template <typename D>
	SharedPtr<T, U>& operator=(D* t)
	{
		decrement();
		impl = new SharedPtr_Deleter<T, D>(t);
		return *this;
	}
	
	//: Dereferencing operator.
	U& operator*() { return *((U*) impl->ptr); }

	U const& operator*() const { return *((const U*) impl->ptr); }
	
	//: Indirect member access operator.
	U* operator->() { return (U*) impl->ptr; }

	U const* operator->() const { return (const U*) impl->ptr; }

	SharedPtr_Generic<T> *get_impl() { return impl; }

//! Implementation:
private:
	// Shared data:
	SharedPtr_Generic<T> *impl;
	
	//: Increases the ref count
	void increment()
	{
		if (impl != 0)
			++impl->ref_count;
	}
	
	//: Decreases the ref count, deletes entry and sets ptr to 0 if ptr_ref_count reaches zero
	void decrement()
	{
		if (impl != 0)
		{
			if (--impl->ref_count == 0)
			{
				delete impl;
				impl = 0;
			}
		}
	}
};

#endif