#include <iostream>
using namespace std;


struct Node
{
	int data;
	Node* previous;
	Node* next;
};

Node* g_firstNode = 0;
Node* g_currentNode = 0;


//
// print all the nodes
//
void PrintAllNodes()
{
	// is list empty?
	if (g_firstNode == 0)
	{	// print empty message
		cout << "List is empty." << endl;
	}
	else
	{	// traverse list
		Node* p = g_firstNode;
		while (p != 0)
		{
			cout << p->data;
			p = p->next;
			if (p != 0)
			{
				cout << ", ";
			}
		}
		cout << endl << endl;
	}
}


//
// deletes the current node
//
void Delete()
{
	// if currentNode is 0, then there are no nodes in the list
	if (g_currentNode == 0)
	{
		cout << "There are no nodes in the list." << endl;
		return;
	}

	// delete this node
	
	// if there is a previous node, then link it to the next node
	// (works even if the next node is 0)
	if (g_currentNode->previous != 0)
	{
		g_currentNode->previous->next = g_currentNode->next;
	}
	else
	{	// else, set the first node to the next node
		g_firstNode = g_currentNode->next;
	}

	// if there is a next node, then link it to the previous node
	// also, move the current node to the next node, and delete the current
	// (works even if the previous node is 0)
	if (g_currentNode->next != 0)
	{
		g_currentNode->next->previous = g_currentNode->previous;
		Node* next = g_currentNode->next;
		delete g_currentNode;
		g_currentNode = next;

	}
	else
	{	// else, move the current node to the previous one, and delete the current
		Node* previous = g_currentNode->previous;
		delete g_currentNode;
		g_currentNode = previous;
	}

	cout << "Node deleted." << endl;

}


//
// insert a node after current
//
void Insert()
{
	// create the node and get the data from the user
	Node* newNode = new Node;
	cout << "Enter an integer value for the new node : " << flush;
	cin >> newNode->data;

	// if current node is 0, then the list is empty
	if (g_currentNode == 0)
	{	// add node the first item, and set current to new node
		newNode->previous = 0;					// no links after
		newNode->next = 0;						// no links before
		g_firstNode = newNode;
		g_currentNode = newNode;
	}
	else
	{	// add the node after this item, and increment current to the new item
		newNode->previous = g_currentNode;		// new node links back to current
		newNode->next = g_currentNode->next;	// new node links forward to the next node
		if (g_currentNode->next != 0)			// link next node backwards
		{	// there exists a next node, so link is backwards to new node
			g_currentNode->next->previous = newNode;
		}
		g_currentNode->next = newNode;			// current links forward to new node
		g_currentNode = newNode;				// set current node to new node
	}
}


//
// move to the next node
//
void Next()
{
	// list empty?
	if (g_currentNode == 0)
	{
		cout << "List is empty." << endl;
		return;
	}

	// is there a next node?
	if (g_currentNode->next != 0)
	{	// there is, move to it
		g_currentNode = g_currentNode->next;
	}
	else
	{	// else, display message
		cout << "Can't move to the next node, because I am at the end of the list." << endl;
	}
}

//
// move to the previous node
//
void Previous()
{
	// list emtpy?
	if (g_currentNode == 0)
	{
		cout << "List is empty." << endl;
		return;
	}

	// is there a previous node?
	if (g_currentNode->previous != 0)
	{	// there is, move to it
		g_currentNode = g_currentNode->previous;
	}
	else
	{	// else, display message
		cout << "Can't move to the previous node, because I am at the beginning of the list." << endl;
	}
}


//
// prints the console controls
//
void PrintHelp()
{
	cout << "HELP" << endl;
	cout << "? - help" << endl;
	cout << "l - List all node data" << endl;
	cout << "d - Delete current node" << endl;
	cout << "i - Insert a node after current" << endl;
	cout << "n - move current node to Next node" << endl;
	cout << "p - move current node to Previous node" << endl;
	cout << "x - eXit" << endl;
}


//
// program entry
//
int main()
{
	cout << "Doubly linked list test console." << endl;
	cout << "Hit '?' for a list of options." << endl; 
	
	char option = '\0';
	do
	{
		// print command prompt and get option
		cout << endl;
		if (g_currentNode != 0)
		{	// if the list isn't empty, print the current node
			cout << "Current node value : " << g_currentNode->data << endl;
		}
		cout << "Command : " << flush;
		cin >> option;
		cout << endl;

		// make lowercase is uppercase
		if ((option >= 'A') && (option <='Z'))
		{
			option += 'a' - 'A';
		}

		// dispatch to appropriate routines based on option
		switch (option)
		{
			case '?': PrintHelp(); break;
			case 'l': PrintAllNodes(); break;
			case 'd': Delete(); break;
			case 'i': Insert(); break;
			case 'n': Next(); break;
			case 'p': Previous(); break;
			case 'x': break;
			default: cout << "Unrecognized option.  Hit '?' for a list of options." << endl; break;
		}

	} while (option != 'x');

	return 0;
}