#include "SpecializedList.h"
struct NodeType
{
  NodeType* next;
  NodeType* back;
  int info;
};

SpecializedList::SpecializedList()
{
  length = 0;
  list = NULL;
}
  
void SpecializedList::ResetForward()
// Post: currentNextPos has been initialized for a forward 
//       traversal.
{
  currentNextPos = NULL;
}

void SpecializedList::GetNextItem(int& item, 
     bool& finished)
// Pre:  ResetForward has been called before the first call to 
//       this function.
// Post: item is a copy of the next item in the list.
//       finished is true if item is the last item in the list; 
//       false otherwise.
{
  if (currentNextPos == NULL)
    currentNextPos = list->next;
  else
    currentNextPos = currentNextPos->next;
  item = currentNextPos->info;
  finished = (currentNextPos == list);
}

void SpecializedList::ResetBackward()
// Post: currentBackPos has been initialized for a backward 
//       traversal.
{
  currentBackPos = NULL;
}

void SpecializedList::GetPriorItem(int& item, 
     bool& finished)
// Post: item is a copy of the previous item in the list.
//       finished is true if item is the first item in the list; 
//       false otherwise.
{
  if (currentBackPos == NULL)
    currentBackPos = list;
  else
    currentBackPos = currentBackPos->back;
  item = currentBackPos->info;
  finished = (currentBackPos == list->next);
}

void SpecializedList::PutFront(int item)
// Post: item has been inserted at the front of the list.
{
  NodeType* newNode;
 
  newNode = new NodeType;
  newNode->info = item;
  if (list == NULL)			
  { // list is empty.
    newNode->back = newNode;
    newNode->next = newNode;
    list = newNode;
  }
  else
  {
    newNode->back = list;
    newNode->next = list->next;
    list->next->back = newNode;
    list->next = newNode;
  }
  length++;
}

void SpecializedList::PutEnd(int item)
// Post: item has been inserted at the end of the list.
{
  PutFront(item);
  list = list->next;
}