//======= Copyright � 1996-2005, Valve Corporation, All rights reserved. ======//
//
// Purpose: Linked list container class 
//
// $Revision: $
// $NoKeywords: $
//=============================================================================//

#ifndef UTLLINKEDLIST_H
#define UTLLINKEDLIST_H

#ifdef _WIN32
#pragma once
#endif

#include "tier0/basetypes.h"
#include "utlmemory.h"
#include "utlfixedmemory.h"
#include "utlblockmemory.h"
#include "tier0/dbg.h"

// define to enable asserts griping about things you shouldn't be doing with multilists
// #define MULTILIST_PEDANTIC_ASSERTS 1 

// This is a useful macro to iterate from head to tail in a linked list.
#define FOR_EACH_LL( listName, iteratorName ) \
	for( int iteratorName=listName.Head(); iteratorName != listName.InvalidIndex(); iteratorName = listName.Next( iteratorName ) )

//-----------------------------------------------------------------------------
// class CUtlLinkedList:
// description:
//		A lovely index-based linked list! T is the class type, I is the index
//		type, which usually should be an unsigned short or smaller. However,
//		you must avoid using 16- or 8-bit arithmetic on PowerPC architectures; 
//		therefore you should not use UtlLinkedListElem_t::I as the type of 
//		a local variable... ever. PowerPC integer arithmetic must be 32- or 
//		64-bit only; otherwise performance plummets.
//-----------------------------------------------------------------------------

template <class T, class I>
struct UtlLinkedListElem_t
{
	T  m_Element;
	I  m_Previous;
	I  m_Next;

private:
	// No copy constructor for these...
	UtlLinkedListElem_t(const UtlLinkedListElem_t&);
};


// Class S is the storage type; the type you can use to save off indices in 
// persistent memory. Class I is the iterator type, which is what should be used
// in local scopes. I defaults to be S, but be aware that on the 360, 16-bit 
// arithmetic is catastrophically slow. Therefore you should try to save shorts
// in memory, but always operate on 32's or 64's in local scope.
// The ideal parameter order would be TSMI (you are more likely to override M than I)
// but since M depends on I we can't have the defaults in that order, alas.
template <class T, class S = unsigned short, bool ML = false, class I = S, class M = CUtlMemory< UtlLinkedListElem_t<T, S>, I > >
class CUtlLinkedList
{
public:
	typedef T ElemType_t;
	typedef S IndexType_t; // should really be called IndexStorageType_t, but that would be a huge change
	typedef I IndexLocalType_t;
	typedef M MemoryAllocator_t;

	// constructor, destructor
	CUtlLinkedList(ssize_t growSize = 0, ssize_t initSize = 0);
	~CUtlLinkedList();

	// gets particular elements
	T& Element(I i);
	T const& Element(I i) const;
	T& operator[](I i);
	T const& operator[](I i) const;

	// Make sure we have a particular amount of memory
	void EnsureCapacity(int num);

	void SetGrowSize(int growSize);

	// Memory deallocation
	void Purge();

	// Delete all the elements then call Purge.
	void PurgeAndDeleteElements();

	// Insertion methods....
	I	InsertBefore(I before);
	I	InsertAfter(I after);
	I	AddToHead();
	I	AddToTail();

	I	InsertBefore(I before, T const& src);
	I	InsertAfter(I after, T const& src);
	I	AddToHead(T const& src);
	I	AddToTail(T const& src);

	// Find an element and return its index or InvalidIndex() if it couldn't be found.
	I		Find(const T& src) const;

	// Look for the element. If it exists, remove it and return true. Otherwise, return false.
	bool	FindAndRemove(const T& src);

	// Removal methods
	void	Remove(I elem);
	void	RemoveAll();

	// Allocation/deallocation methods
	// If multilist == true, then list list may contain many
	// non-connected lists, and IsInList and Head + Tail are meaningless...
	I		Alloc(bool multilist = false);
	void	Free(I elem);

	// Identify the owner of this linked list's memory:
	void	SetAllocOwner(const char* pszAllocOwner);

	// list modification
	void	LinkBefore(I before, I elem);
	void	LinkAfter(I after, I elem);
	void	Unlink(I elem);
	void	LinkToHead(I elem);
	void	LinkToTail(I elem);

	// invalid index (M will never allocate an element at this index)
	inline static S  InvalidIndex() { return (S)M::InvalidIndex(); }

	// Is a given index valid to use? (representable by S and not the invalid index)
	static bool IndexInRange(I index);

	inline static size_t ElementSize() { return sizeof(ListElem_t); }

	// list statistics
	int	Count() const;
	I	MaxElementIndex() const;
	I	NumAllocated(void) const { return m_NumAlloced; }

	// Traversing the list
	I  Head() const;
	I  Tail() const;
	I  Previous(I i) const;
	I  Next(I i) const;

	// Are nodes in the list or valid?
	bool  IsValidIndex(I i) const;
	bool  IsInList(I i) const;

protected:

	// What the linked list element looks like
	typedef UtlLinkedListElem_t<T, S>  ListElem_t;

	// constructs the class
	I		AllocInternal(bool multilist = false);
	void ConstructList();

	// Gets at the list element....
	ListElem_t& InternalElement(I i) { return m_Memory[i]; }
	ListElem_t const& InternalElement(I i) const { return m_Memory[i]; }

	// copy constructors not allowed
	CUtlLinkedList(CUtlLinkedList<T, S, ML, I, M> const& list) { Assert(0); }

	M	m_Memory;
	I	m_Head;
	I	m_Tail;
	I	m_FirstFree;
	I	m_ElementCount;		// The number actually in the list
	I	m_NumAlloced;		// The number of allocated elements
	typename M::Iterator_t	m_LastAlloc; // the last index allocated

	// For debugging purposes; 
	// it's in release builds so this can be used in libraries correctly
	ListElem_t* m_pElements;

	FORCEINLINE M const& Memory(void) const
	{
		return m_Memory;
	}

	void ResetDbgInfo()
	{
		m_pElements = m_Memory.Base();
	}
};


// this is kind of ugly, but until C++ gets templatized typedefs in C++0x, it's our only choice
template < class T >
class CUtlFixedLinkedList : public CUtlLinkedList< T, intptr_t, true, intptr_t, CUtlFixedMemory< UtlLinkedListElem_t< T, intptr_t > > >
{
public:
	CUtlFixedLinkedList(ssize_t growSize = 0, ssize_t initSize = 0)
		: CUtlLinkedList< T, intptr_t, true, intptr_t, CUtlFixedMemory< UtlLinkedListElem_t< T, intptr_t > > >(growSize, initSize) {}

	bool IsValidIndex(intptr_t i) const
	{
		if (!this->Memory().IsIdxValid(i))
			return false;

#ifdef _DEBUG // it's safe to skip this here, since the only way to get indices after m_LastAlloc is to use MaxElementIndex
		if (this->Memory().IsIdxAfter(i, this->m_LastAlloc))
		{
			Assert(0);
			return false; // don't read values that have been allocated, but not constructed
		}
#endif

		return (this->Memory()[i].m_Previous != i) || (this->Memory()[i].m_Next == i);
	}

private:
	int	MaxElementIndex() const { Assert(0); return this->InvalidIndex(); } // fixedmemory containers don't support iteration from 0..maxelements-1
	void ResetDbgInfo() {}
};

// this is kind of ugly, but until C++ gets templatized typedefs in C++0x, it's our only choice
template < class T, class I = unsigned short >
class CUtlBlockLinkedList : public CUtlLinkedList< T, I, true, I, CUtlBlockMemory< UtlLinkedListElem_t< T, I >, I > >
{
public:
	CUtlBlockLinkedList(int growSize = 0, int initSize = 0)
		: CUtlLinkedList< T, I, true, I, CUtlBlockMemory< UtlLinkedListElem_t< T, I >, I > >(growSize, initSize) {}
protected:
	void ResetDbgInfo() {}
};


//-----------------------------------------------------------------------------
// constructor, destructor
//-----------------------------------------------------------------------------

template <class T, class S, bool ML, class I, class M>
CUtlLinkedList<T, S, ML, I, M>::CUtlLinkedList(ssize_t growSize, ssize_t initSize) :
	m_Memory(growSize, initSize), m_LastAlloc(m_Memory.InvalidIterator())
{
	// Prevent signed non-int datatypes
	COMPILE_TIME_ASSERT(sizeof(S) == 8 || (((S)-1) > 0));
	ConstructList();
	ResetDbgInfo();
}

template <class T, class S, bool ML, class I, class M>
CUtlLinkedList<T, S, ML, I, M>::~CUtlLinkedList()
{
	RemoveAll();
}

template <class T, class S, bool ML, class I, class M>
void CUtlLinkedList<T, S, ML, I, M>::ConstructList()
{
	m_Head = InvalidIndex();
	m_Tail = InvalidIndex();
	m_FirstFree = InvalidIndex();
	m_ElementCount = 0;
	m_NumAlloced = 0;
}


//-----------------------------------------------------------------------------
// gets particular elements
//-----------------------------------------------------------------------------

template <class T, class S, bool ML, class I, class M>
inline T& CUtlLinkedList<T, S, ML, I, M>::Element(I i)
{
	return m_Memory[i].m_Element;
}

template <class T, class S, bool ML, class I, class M>
inline T const& CUtlLinkedList<T, S, ML, I, M>::Element(I i) const
{
	return m_Memory[i].m_Element;
}

template <class T, class S, bool ML, class I, class M>
inline T& CUtlLinkedList<T, S, ML, I, M>::operator[](I i)
{
	return m_Memory[i].m_Element;
}

template <class T, class S, bool ML, class I, class M>
inline T const& CUtlLinkedList<T, S, ML, I, M>::operator[](I i) const
{
	return m_Memory[i].m_Element;
}

//-----------------------------------------------------------------------------
// list statistics
//-----------------------------------------------------------------------------

template <class T, class S, bool ML, class I, class M>
inline int CUtlLinkedList<T, S, ML, I, M>::Count() const
{
#ifdef MULTILIST_PEDANTIC_ASSERTS
	AssertMsg(!ML, "CUtlLinkedList::Count() is meaningless for linked lists.");
#endif
	return m_ElementCount;
}

template <class T, class S, bool ML, class I, class M>
inline I CUtlLinkedList<T, S, ML, I, M>::MaxElementIndex() const
{
	return m_Memory.NumAllocated();
}


//-----------------------------------------------------------------------------
// Traversing the list
//-----------------------------------------------------------------------------

template <class T, class S, bool ML, class I, class M>
inline I  CUtlLinkedList<T, S, ML, I, M>::Head() const
{
	return m_Head;
}

template <class T, class S, bool ML, class I, class M>
inline I  CUtlLinkedList<T, S, ML, I, M>::Tail() const
{
	return m_Tail;
}

template <class T, class S, bool ML, class I, class M>
inline I  CUtlLinkedList<T, S, ML, I, M>::Previous(I i) const
{
	Assert(IsValidIndex(i));
	return InternalElement(i).m_Previous;
}

template <class T, class S, bool ML, class I, class M>
inline I  CUtlLinkedList<T, S, ML, I, M>::Next(I i) const
{
	Assert(IsValidIndex(i));
	return InternalElement(i).m_Next;
}


//-----------------------------------------------------------------------------
// Are nodes in the list or valid?
//-----------------------------------------------------------------------------

#pragma warning(push)
#pragma warning( disable: 4310 ) // Allows "(I)(S)M::INVALID_INDEX" below
template <class T, class S, bool ML, class I, class M>
inline bool CUtlLinkedList<T, S, ML, I, M>::IndexInRange(I index) // Static method
{
	// Since S is not necessarily the type returned by M, we need to check that M returns indices
	// which are representable by S. A common case is 'S === unsigned short', 'I == int', in which
	// case CUtlMemory will have 'InvalidIndex == (int)-1' (which casts to 65535 in S), and will
	// happily return elements at index 65535 and above.

	// Do some static checks here:
	//  'I' needs to be able to store 'S'
	COMPILE_TIME_ASSERT(sizeof(I) >= sizeof(S));
	//  'S' should be unsigned (to avoid signed arithmetic errors for plausibly exhaustible ranges)
	COMPILE_TIME_ASSERT((sizeof(S) > 2) || (((S)-1) > 0));
	//  M::INVALID_INDEX should be storable in S to avoid ambiguities (e.g. with 65536)
	COMPILE_TIME_ASSERT((M::INVALID_INDEX == -1) || (M::INVALID_INDEX == (S)M::INVALID_INDEX));

	return (((S)index == index) && ((S)index != InvalidIndex()));
}
#pragma warning(pop)

template <class T, class S, bool ML, class I, class M>
inline bool CUtlLinkedList<T, S, ML, I, M>::IsValidIndex(I i) const
{
	if (!m_Memory.IsIdxValid(i))
		return false;

	if (m_Memory.IsIdxAfter(i, m_LastAlloc))
		return false; // don't read values that have been allocated, but not constructed

	return (m_Memory[i].m_Previous != i) || (m_Memory[i].m_Next == i);
}

template <class T, class S, bool ML, class I, class M>
inline bool CUtlLinkedList<T, S, ML, I, M>::IsInList(I i) const
{
	if (!m_Memory.IsIdxValid(i) || m_Memory.IsIdxAfter(i, m_LastAlloc))
		return false; // don't read values that have been allocated, but not constructed

	return Previous(i) != i;
}

/*
template <class T>
inline bool CUtlFixedLinkedList<T>::IsInList( int i ) const
{
	return m_Memory.IsIdxValid( i ) && (Previous( i ) != i);
}
*/

//-----------------------------------------------------------------------------
// Makes sure we have enough memory allocated to store a requested # of elements
//-----------------------------------------------------------------------------

template< class T, class S, bool ML, class I, class M >
void CUtlLinkedList<T, S, ML, I, M>::EnsureCapacity(int num)
{
	MEM_ALLOC_CREDIT_CLASS();
	m_Memory.EnsureCapacity(num);
	ResetDbgInfo();
}

template< class T, class S, bool ML, class I, class M >
void CUtlLinkedList<T, S, ML, I, M>::SetGrowSize(int growSize)
{
	RemoveAll();
	m_Memory.Init(growSize);
	ResetDbgInfo();
}

template< class T, class S, bool ML, class I, class M >
void CUtlLinkedList<T, S, ML, I, M>::SetAllocOwner(const char* pszAllocOwner)
{
	m_Memory.SetAllocOwner(pszAllocOwner);
}


//-----------------------------------------------------------------------------
// Deallocate memory
//-----------------------------------------------------------------------------

template <class T, class S, bool ML, class I, class M>
void  CUtlLinkedList<T, S, ML, I, M>::Purge()
{
	RemoveAll();

	m_Memory.Purge();
	m_FirstFree = InvalidIndex();
	m_NumAlloced = 0;

	//Routing "m_LastAlloc = m_Memory.InvalidIterator();" through a local const to sidestep an internal compiler error on 360 builds
	const typename M::Iterator_t scInvalidIterator = m_Memory.InvalidIterator();
	m_LastAlloc = scInvalidIterator;
	ResetDbgInfo();
}


template<class T, class S, bool ML, class I, class M>
void CUtlLinkedList<T, S, ML, I, M>::PurgeAndDeleteElements()
{
	I iNext;
	for (I i = Head(); i != InvalidIndex(); i = iNext)
	{
		iNext = Next(i);
		MemAllocSingleton()->Free(Element(i));
	}

	Purge();
}

//-----------------------------------------------------------------------------
// Node allocation/deallocation
//-----------------------------------------------------------------------------
template <class T, class S, bool ML, class I, class M>
I CUtlLinkedList<T, S, ML, I, M>::AllocInternal(bool multilist)
{
	Assert(!multilist || ML);
#ifdef MULTILIST_PEDANTIC_ASSERTS
	Assert(multilist == ML);
#endif
	I elem;
	if (m_FirstFree == InvalidIndex())
	{
		Assert(m_Memory.IsValidIterator(m_LastAlloc) || m_ElementCount == 0);

		typename M::Iterator_t it = m_Memory.IsValidIterator(m_LastAlloc) ? m_Memory.Next(m_LastAlloc) : m_Memory.First();

		if (!m_Memory.IsValidIterator(it))
		{
			MEM_ALLOC_CREDIT_CLASS();
			m_Memory.Grow();
			ResetDbgInfo();

			it = m_Memory.IsValidIterator(m_LastAlloc) ? m_Memory.Next(m_LastAlloc) : m_Memory.First();

			Assert(m_Memory.IsValidIterator(it));
			if (!m_Memory.IsValidIterator(it))
			{
				ExecuteNTimes(10, Warning(eDLL_T::COMMON, "CUtlLinkedList overflow! (exhausted memory allocator)\n"));
				return InvalidIndex();
			}
		}

		// We can overflow before the utlmemory overflows, since S != I
		if (!IndexInRange(m_Memory.GetIndex(it)))
		{
			ExecuteNTimes(10, Warning(eDLL_T::COMMON, "CUtlLinkedList overflow! (exhausted index range)\n"));
			return InvalidIndex();
		}

		m_LastAlloc = it;
		elem = m_Memory.GetIndex(m_LastAlloc);
		m_NumAlloced++;
	}
	else
	{
		elem = m_FirstFree;
		m_FirstFree = InternalElement(m_FirstFree).m_Next;
	}

	if (!multilist)
	{
		InternalElement(elem).m_Next = elem;
		InternalElement(elem).m_Previous = elem;
	}
	else
	{
		InternalElement(elem).m_Next = InvalidIndex();
		InternalElement(elem).m_Previous = InvalidIndex();
	}

	return elem;
}

template <class T, class S, bool ML, class I, class M>
I CUtlLinkedList<T, S, ML, I, M>::Alloc(bool multilist)
{
	I elem = AllocInternal(multilist);
	if (elem == InvalidIndex())
		return elem;

	Construct(&Element(elem));

	return elem;
}

template <class T, class S, bool ML, class I, class M>
void  CUtlLinkedList<T, S, ML, I, M>::Free(I elem)
{
	Assert(IsValidIndex(elem) && IndexInRange(elem));
	Unlink(elem);

	ListElem_t& internalElem = InternalElement(elem);
	Destruct(&internalElem.m_Element);
	internalElem.m_Next = m_FirstFree;
	m_FirstFree = elem;
}

//-----------------------------------------------------------------------------
// Insertion methods; allocates and links (uses default constructor)
//-----------------------------------------------------------------------------

template <class T, class S, bool ML, class I, class M>
I CUtlLinkedList<T, S, ML, I, M>::InsertBefore(I before)
{
	// Make a new node
	I   newNode = AllocInternal();
	if (newNode == InvalidIndex())
		return newNode;

	// Link it in
	LinkBefore(before, newNode);

	// Construct the data
	Construct(&Element(newNode));

	return newNode;
}

template <class T, class S, bool ML, class I, class M>
I CUtlLinkedList<T, S, ML, I, M>::InsertAfter(I after)
{
	// Make a new node
	I   newNode = AllocInternal();
	if (newNode == InvalidIndex())
		return newNode;

	// Link it in
	LinkAfter(after, newNode);

	// Construct the data
	Construct(&Element(newNode));

	return newNode;
}

template <class T, class S, bool ML, class I, class M>
inline I CUtlLinkedList<T, S, ML, I, M>::AddToHead()
{
	return InsertAfter(InvalidIndex());
}

template <class T, class S, bool ML, class I, class M>
inline I CUtlLinkedList<T, S, ML, I, M>::AddToTail()
{
	return InsertBefore(InvalidIndex());
}


//-----------------------------------------------------------------------------
// Insertion methods; allocates and links (uses copy constructor)
//-----------------------------------------------------------------------------

template <class T, class S, bool ML, class I, class M>
I CUtlLinkedList<T, S, ML, I, M>::InsertBefore(I before, T const& src)
{
	// Make a new node
	I   newNode = AllocInternal();
	if (newNode == InvalidIndex())
		return newNode;

	// Link it in
	LinkBefore(before, newNode);

	// Construct the data
	CopyConstruct(&Element(newNode), src);

	return newNode;
}

template <class T, class S, bool ML, class I, class M>
I CUtlLinkedList<T, S, ML, I, M>::InsertAfter(I after, T const& src)
{
	// Make a new node
	I   newNode = AllocInternal();
	if (newNode == InvalidIndex())
		return newNode;

	// Link it in
	LinkAfter(after, newNode);

	// Construct the data
	CopyConstruct(&Element(newNode), src);

	return newNode;
}

template <class T, class S, bool ML, class I, class M>
inline I CUtlLinkedList<T, S, ML, I, M>::AddToHead(T const& src)
{
	return InsertAfter(InvalidIndex(), src);
}

template <class T, class S, bool ML, class I, class M>
inline I CUtlLinkedList<T, S, ML, I, M>::AddToTail(T const& src)
{
	return InsertBefore(InvalidIndex(), src);
}


//-----------------------------------------------------------------------------
// Removal methods
//-----------------------------------------------------------------------------

template<class T, class S, bool ML, class I, class M>
I CUtlLinkedList<T, S, ML, I, M>::Find(const T& src) const
{
	for (I i = Head(); i != InvalidIndex(); i = Next(i))
	{
		if (Element(i) == src)
			return i;
	}
	return InvalidIndex();
}


template<class T, class S, bool ML, class I, class M>
bool CUtlLinkedList<T, S, ML, I, M>::FindAndRemove(const T& src)
{
	I i = Find(src);
	if (i == InvalidIndex())
	{
		return false;
	}
	else
	{
		Remove(i);
		return true;
	}
}


template <class T, class S, bool ML, class I, class M>
void  CUtlLinkedList<T, S, ML, I, M>::Remove(I elem)
{
	Free(elem);
}

template <class T, class S, bool ML, class I, class M>
void  CUtlLinkedList<T, S, ML, I, M>::RemoveAll()
{
	// Have to do some convoluted stuff to invoke the destructor on all
	// valid elements for the multilist case (since we don't have all elements
	// connected to each other in a list).

	if (m_LastAlloc == m_Memory.InvalidIterator())
	{
		Assert(m_Head == InvalidIndex());
		Assert(m_Tail == InvalidIndex());
		Assert(m_FirstFree == InvalidIndex());
		Assert(m_ElementCount == 0);
		return;
	}

	if (ML)
	{
		for (typename M::Iterator_t it = m_Memory.First(); it != m_Memory.InvalidIterator(); it = m_Memory.Next(it))
		{
			I i = m_Memory.GetIndex(it);
			if (IsValidIndex(i)) // skip elements already in the free list
			{
				ListElem_t& internalElem = InternalElement(i);
				Destruct(&internalElem.m_Element);
				internalElem.m_Previous = i;
				internalElem.m_Next = m_FirstFree;
				m_FirstFree = i;
			}

			if (it == m_LastAlloc)
				break; // don't destruct elements that haven't ever been constructed
		}
	}
	else
	{
		I i = Head();
		I next;
		while (i != InvalidIndex())
		{
			next = Next(i);
			ListElem_t& internalElem = InternalElement(i);
			Destruct(&internalElem.m_Element);
			internalElem.m_Previous = i;
			internalElem.m_Next = next == InvalidIndex() ? m_FirstFree : next;
			i = next;
		}
		if (Head() != InvalidIndex())
		{
			m_FirstFree = Head();
		}
	}

	// Clear everything else out
	m_Head = InvalidIndex();
	m_Tail = InvalidIndex();
	m_ElementCount = 0;
}


//-----------------------------------------------------------------------------
// list modification
//-----------------------------------------------------------------------------

template <class T, class S, bool ML, class I, class M>
void  CUtlLinkedList<T, S, ML, I, M>::LinkBefore(I before, I elem)
{
	Assert(IsValidIndex(elem));

	// Unlink it if it's in the list at the moment
	Unlink(elem);

	ListElem_t* pNewElem = &InternalElement(elem);

	// The element *after* our newly linked one is the one we linked before.
	pNewElem->m_Next = before;

	S newElem_mPrevious; // we need to hang on to this for the comparison against InvalidIndex()
					// below; otherwise we get a a load-hit-store on pNewElem->m_Previous, even
					// with
	if (before == InvalidIndex())
	{
		// In this case, we're linking to the end of the list, so reset the tail
		newElem_mPrevious = m_Tail;
		pNewElem->m_Previous = m_Tail;
		m_Tail = elem;
	}
	else
	{
		// Here, we're not linking to the end. Set the prev pointer to point to
		// the element we're linking.
		Assert(IsInList(before));
		ListElem_t* beforeElem = &InternalElement(before);
		pNewElem->m_Previous = newElem_mPrevious = beforeElem->m_Previous;
		beforeElem->m_Previous = elem;
	}

	// Reset the head if we linked to the head of the list
	if (newElem_mPrevious == InvalidIndex())
		m_Head = elem;
	else
		InternalElement(newElem_mPrevious).m_Next = elem;

	// one more element baby
	++m_ElementCount;
}

template <class T, class S, bool ML, class I, class M>
void  CUtlLinkedList<T, S, ML, I, M>::LinkAfter(I after, I elem)
{
	Assert(IsValidIndex(elem));

	// Unlink it if it's in the list at the moment
	if (IsInList(elem))
		Unlink(elem);

	ListElem_t& newElem = InternalElement(elem);

	// The element *before* our newly linked one is the one we linked after
	newElem.m_Previous = after;
	if (after == InvalidIndex())
	{
		// In this case, we're linking to the head of the list, reset the head
		newElem.m_Next = m_Head;
		m_Head = elem;
	}
	else
	{
		// Here, we're not linking to the end. Set the next pointer to point to
		// the element we're linking.
		Assert(IsInList(after));
		ListElem_t& afterElem = InternalElement(after);
		newElem.m_Next = afterElem.m_Next;
		afterElem.m_Next = elem;
	}

	// Reset the tail if we linked to the tail of the list
	if (newElem.m_Next == InvalidIndex())
		m_Tail = elem;
	else
		InternalElement(newElem.m_Next).m_Previous = elem;

	// one more element baby
	++m_ElementCount;
}

template <class T, class S, bool ML, class I, class M>
void  CUtlLinkedList<T, S, ML, I, M>::Unlink(I elem)
{
	Assert(IsValidIndex(elem));
	if (IsInList(elem))
	{
		ListElem_t* pOldElem = &m_Memory[elem];

		// If we're the first guy, reset the head
		// otherwise, make our previous node's next pointer = our next
		if (pOldElem->m_Previous != InvalidIndex())
		{
			m_Memory[pOldElem->m_Previous].m_Next = pOldElem->m_Next;
		}
		else
		{
			m_Head = pOldElem->m_Next;
		}

		// If we're the last guy, reset the tail
		// otherwise, make our next node's prev pointer = our prev
		if (pOldElem->m_Next != InvalidIndex())
		{
			m_Memory[pOldElem->m_Next].m_Previous = pOldElem->m_Previous;
		}
		else
		{
			m_Tail = pOldElem->m_Previous;
		}

		// This marks this node as not in the list, 
		// but not in the free list either
		pOldElem->m_Previous = pOldElem->m_Next = elem;

		// One less puppy
		--m_ElementCount;
	}
}

template <class T, class S, bool ML, class I, class M>
inline void CUtlLinkedList<T, S, ML, I, M>::LinkToHead(I elem)
{
	LinkAfter(InvalidIndex(), elem);
}

template <class T, class S, bool ML, class I, class M>
inline void CUtlLinkedList<T, S, ML, I, M>::LinkToTail(I elem)
{
	LinkBefore(InvalidIndex(), elem);
}


//-----------------------------------------------------------------------------
// Class to drop in to replace a CUtlLinkedList that needs to be more memory aggressive
//-----------------------------------------------------------------------------

DECLARE_POINTER_HANDLE(UtlPtrLinkedListIndex_t); // to enforce correct usage

template < typename T >
class CUtlPtrLinkedList
{
public:
	CUtlPtrLinkedList()
		: m_pFirst(NULL),
		m_nElems(0)
	{
		COMPILE_TIME_ASSERT(sizeof(IndexType_t) == sizeof(Node_t*));
	}

	~CUtlPtrLinkedList()
	{
		RemoveAll();
	}

	typedef UtlPtrLinkedListIndex_t IndexType_t;

	T& operator[](IndexType_t i)
	{
		return ((Node_t*)i)->elem;
	}

	const T& operator[](IndexType_t i) const
	{
		return ((Node_t*)i)->elem;
	}

	IndexType_t	AddToTail()
	{
		return DoInsertBefore((IndexType_t)m_pFirst, NULL);
	}

	IndexType_t	AddToTail(T const& src)
	{
		return DoInsertBefore((IndexType_t)m_pFirst, &src);
	}

	IndexType_t	AddToHead()
	{
		IndexType_t result = DoInsertBefore((IndexType_t)m_pFirst, NULL);
		m_pFirst = ((Node_t*)result);
		return result;
	}

	IndexType_t	AddToHead(T const& src)
	{
		IndexType_t result = DoInsertBefore((IndexType_t)m_pFirst, &src);
		m_pFirst = ((Node_t*)result);
		return result;
	}

	IndexType_t InsertBefore(IndexType_t before)
	{
		return DoInsertBefore(before, NULL);
	}

	IndexType_t InsertAfter(IndexType_t after)
	{
		Node_t* pBefore = ((Node_t*)after)->next;
		return DoInsertBefore(pBefore, NULL);
	}

	IndexType_t InsertBefore(IndexType_t before, T const& src)
	{
		return DoInsertBefore(before, &src);
	}

	IndexType_t InsertAfter(IndexType_t after, T const& src)
	{
		Node_t* pBefore = ((Node_t*)after)->next;
		return DoInsertBefore(pBefore, &src);
	}

	void Remove(IndexType_t elem)
	{
		Node_t* p = (Node_t*)elem;

		if (p->pNext == p)
		{
			m_pFirst = NULL;
		}
		else
		{
			if (m_pFirst == p)
			{
				m_pFirst = p->pNext;
			}
			p->pNext->pPrev = p->pPrev;
			p->pPrev->pNext = p->pNext;
		}

		delete p;
		m_nElems--;
	}

	void RemoveAll()
	{
		Node_t* p = m_pFirst;
		if (p)
		{
			do
			{
				Node_t* pNext = p->pNext;
				delete p;
				p = pNext;
			} while (p != m_pFirst);
		}

		m_pFirst = NULL;
		m_nElems = 0;
	}

	int	Count() const
	{
		return m_nElems;
	}

	IndexType_t Head() const
	{
		return (IndexType_t)m_pFirst;
	}

	IndexType_t Next(IndexType_t i) const
	{
		Node_t* p = ((Node_t*)i)->pNext;
		if (p != m_pFirst)
		{
			return (IndexType_t)p;
		}
		return NULL;
	}

	bool IsValidIndex(IndexType_t i) const
	{
		Node_t* p = ((Node_t*)i);
		return (p && p->pNext && p->pPrev);
	}

	inline static IndexType_t  InvalidIndex()
	{
		return NULL;
	}
private:

	struct Node_t
	{
		Node_t() {}
		Node_t(const T& _elem) : elem(_elem) {}

		// Have to do it like this instead of 'new' because we have to use the internal memalloc singleton!
		static Node_t* Alloc(const T* _elem)
		{
			Node_t* pNode = MemAllocSingleton()->Alloc<Node_t>(sizeof(Node_t));
			pNode->elem(_elem);

			return pNode;
		}

		T elem;
		Node_t* pPrev, * pNext;
	};

	Node_t* AllocNode(const T* pCopyFrom)
	{
		MEM_ALLOC_CREDIT_CLASS();
		Node_t* p;

		if (!pCopyFrom)
		{
			p = MemAllocSingleton()->Alloc<Node_t>(sizeof(Node_t));
		}
		else
		{
			p = Node_t::Alloc(*pCopyFrom);
		}

		return p;
	}

	IndexType_t DoInsertBefore(IndexType_t before, const T* pCopyFrom)
	{
		Node_t* p = AllocNode(pCopyFrom);
		Node_t* pBefore = (Node_t*)before;
		if (pBefore)
		{
			p->pNext = pBefore;
			p->pPrev = pBefore->pPrev;
			pBefore->pPrev = p;
			p->pPrev->pNext = p;
		}
		else
		{
			Assert(!m_pFirst);
			m_pFirst = p->pNext = p->pPrev = p;
		}

		m_nElems++;
		return (IndexType_t)p;
	}

	Node_t* m_pFirst;
	unsigned m_nElems;
};

//-----------------------------------------------------------------------------

#endif // UTLLINKEDLIST_H