#ifndef DLIST_H
#define DLIST_H

#include <cassert>

template<class T>
class Node
{
public:
    T data;
    Node<T> *prior;
    Node<T> *next;
    Node() : data(T()), prior(0), next(0) {}
    Node(const T &initdata) : data(initdata), prior(0), next(0) {}
};

template<class T>
class DList
{
protected:
    int m_nCount;
    Node<T> *m_pNodeHead;
    Node<T> *m_pNodeTail;

public:
    DList();
    DList(const T &initdata);
    ~DList();

public:
    int     IsEmpty() const;
    int     GetCount() const;
    int     InsertBefore(const int pos, const T data);
    int     InsertAfter(const int pos, const T data);
    int     AddHead(const T data);
    int     AddTail(const T data);
    void    RemoveAt(const int pos);
    void    RemoveHead();
    void    RemoveTail();
    void    RemoveAll();
    T&      GetTail();
    T       GetTail() const;
    T&      GetHead();
    T       GetHead() const;
    T&      GetAt(const int pos);
    T       GetAt(const int pos) const;
    void    SetAt(const int pos, T data);
    int     Find(const T data) const;
    T&      GetPrev(int &pos);
    T&      GetNext(int &pos);
};

template<class T>
inline DList<T>::DList() : m_nCount(0), m_pNodeHead(0), m_pNodeTail(0)
{
}

template<class T>
inline DList<T>::DList(const T &initdata)
                 : m_nCount(0), m_pNodeHead(0), m_pNodeTail(0)
{
    AddHead(initdata);
}

template<class T>
inline DList<T>::~DList()
{
    RemoveAll();
}

template<class T>
inline T& DList<T>::GetNext(int &pos)
{
    assert(0 != m_nCount);
    assert(1 <= pos && pos <= m_nCount);

    int i;
    Node<T> *pTmpNode = m_pNodeHead;

    for (i = 1; i < pos; ++i)
    {
        pTmpNode = pTmpNode->next;
    }

    ++pos;

    return pTmpNode->data;
}

template<class T>
inline T& DList<T>::GetPrev(int &pos)
{
    assert(0 != m_nCount);
    assert(1 <= pos && pos <= m_nCount);

    int i;
    Node<T> *pTmpNode = m_pNodeHead;

    for (i = 1; i < pos; ++i)
    {
        pTmpNode = pTmpNode->next;
    }

    --pos;

    return pTmpNode->data;
}

template<class T>
inline int DList<T>::InsertBefore(const int pos, const T data)
{
    int i;
    int nRetPos;
    Node<T> *pTmpNode;
    Node<T> *pNewNode;

    pNewNode = new Node<T>;
    if (0 == pNewNode)
    {
        nRetPos = 0;
    	return nRetPos;
    }

    pNewNode->data = data;

    // if the list is empty, replace the head node with the new node.
    if (0 == m_pNodeHead)
    {
        pNewNode->prior = 0;
        pNewNode->next = 0;
        m_pNodeHead = pNewNode;
        m_pNodeTail = pNewNode;
        nRetPos = 1;
		m_nCount++;
		return nRetPos;
    }

    // is pos range valid?
    assert(1 <= pos && pos <= m_nCount);

    // insert before head node?
    if (1 == pos)
    {
        pNewNode->prior = 0;
        pNewNode->next = m_pNodeHead;
        m_pNodeHead->prior = pNewNode;
        m_pNodeHead = pNewNode;
        nRetPos = 1;
		m_nCount++;
		return nRetPos;
    }

    // if the list is not empty and is not inserted before head node,
    // seek to the pos of the list and insert the new node before it.
    pTmpNode = m_pNodeHead;
    for (i = 1; i < pos; ++i)
    {
        pTmpNode = pTmpNode->next;
    }
    pNewNode->next = pTmpNode;
    pNewNode->prior = pTmpNode->prior;

    pTmpNode->prior->next = pNewNode;
    pTmpNode->prior = pNewNode;

    // if tail node, must update m_pNodeTail
    if (0 == pNewNode->next)
    {
        m_pNodeTail = pNewNode;
    }

    nRetPos = pos;

    ++m_nCount;
    return nRetPos;
}

template<class T>
inline int DList<T>::InsertAfter(const int pos, const T data)
{
    int i;
    int nRetPos;
    Node<T> *pNewNode;
    Node<T> *pTmpNode;

    pNewNode = new Node<T>;
    if (0 == pNewNode)
    {
        nRetPos = 0;
		return nRetPos;
    }

    pNewNode->data = data;

    // if the list is empty, replace the head node with the new node.
    if (0 == m_pNodeHead)
    {
        pNewNode->prior = 0;
        pNewNode->next = 0;
        m_pNodeHead = pNewNode;
        m_pNodeTail = pNewNode;
        nRetPos = 1;
		m_nCount++;
		return nRetPos;
    }

    // is pos range valid?
    assert(1 <= pos && pos <= m_nCount);
    
    // if the list is not empty,
    // seek to the pos of the list and insert the new node after it.
    pTmpNode = m_pNodeHead;
    for (i = 1; i < pos; ++i)
    {
        pTmpNode = pTmpNode->next;
    }

    pNewNode->next = pTmpNode->next;
    pNewNode->prior = pTmpNode;

    // if NewNode's position is m_pNodeTail, update m_pNodeTail
    if (pTmpNode->next == m_pNodeTail)
    {
        m_pNodeTail->prior = pNewNode;
    }

    pTmpNode->next = pNewNode;

    // if tail node, must update m_pNodeTail
    if (0 == pNewNode->next)
    {
        m_pNodeTail = pNewNode;
    }

    nRetPos = pos + 1;

    ++m_nCount;
    return nRetPos;
}

template<class T>
inline T& DList<T>::GetAt(const int pos)
{
    assert(1 <= pos && pos <= m_nCount);

    int i;
    Node<T> *pTmpNode = m_pNodeHead;

    for (i = 1; i < pos; ++i)
    {
        pTmpNode = pTmpNode->next;
    }

    return pTmpNode->data;
}

template<class T>
inline T DList<T>::GetAt(const int pos) const
{
    assert(1 <= pos && pos <= m_nCount);

    int i;
    Node<T> *pTmpNode = m_pNodeHead;

    for (i = 1; i < pos; ++i)
    {
        pTmpNode = pTmpNode->next;
    }

    return pTmpNode->data;
}

template<class T>
inline int DList<T>::AddHead(const T data)
{
    return InsertBefore(1, data);
}

template<class T>
inline int DList<T>::AddTail(const T data)
{
    return InsertAfter(GetCount(), data);
}

template<class T>
inline int DList<T>::IsEmpty() const
{
    return 0 == m_nCount;
}

template<class T>
inline int DList<T>::GetCount() const
{
    return m_nCount;
}

template<class T>
inline T& DList<T>::GetTail()
{
    assert(0 != m_nCount);
    return m_pNodeTail->data;
}

template<class T>
inline T DList<T>::GetTail() const
{
    assert(0 != m_nCount);
    return m_pNodeTail->data;
}

template<class T>
inline T& DList<T>::GetHead()
{
    assert(0 != m_nCount);
    return m_pNodeHead->data;
}

template<class T>
inline T DList<T>::GetHead() const
{
    assert(0 != m_nCount);
    return m_pNodeHead->data;
}

template<class T>
inline void DList<T>::RemoveAt(const int pos)
{
    assert(1 <= pos && pos <= m_nCount);

    int i;
    Node<T> *pTmpNode = m_pNodeHead;

    // head node?
    if (1 == pos)
    {
        m_pNodeHead = m_pNodeHead->next;
    }
	else
	{
		for (i = 1; i < pos; ++i)
		{
			pTmpNode = pTmpNode->next;
		}
		pTmpNode->prior->next = pTmpNode->next;
	}


    delete pTmpNode;
    --m_nCount;
    if (0 == m_nCount)
    {
        m_pNodeTail = 0;
    }
}

template<class T>
inline void DList<T>::RemoveHead()
{
    assert(0 != m_nCount);
    RemoveAt(1);
}

template<class T>
inline void DList<T>::RemoveTail()
{
    assert(0 != m_nCount);
    RemoveAt(m_nCount);
}

template<class T>
inline void DList<T>::RemoveAll()
{
    int i;
    int nCount;
    Node<T> *pTmpNode;

    nCount = m_nCount;
    for (i = 0; i < nCount; ++i)
    {
        pTmpNode = m_pNodeHead->next;
        delete m_pNodeHead;
        m_pNodeHead = pTmpNode;
    }

    m_nCount = 0;
}

template<class T>
inline void DList<T>::SetAt(const int pos, T data)
{
    assert(1 <= pos && pos <= m_nCount);

    int i;
    Node<T> *pTmpNode = m_pNodeHead;

    for (i = 1; i < pos; ++i)
    {
        pTmpNode = pTmpNode->next;
    }
    pTmpNode->data = data;
}

template<class T>
inline int DList<T>::Find(const T data) const
{
    int i;
    int nCount;
    Node<T> *pTmpNode = m_pNodeHead;

    nCount = m_nCount;
    for (i = 0; i < nCount; ++i)
    {
        if (data == pTmpNode->data)
            return i + 1;
        pTmpNode = pTmpNode->next;
    }

    return 0;
}

#endif//DLIST_H