package lrs;

/**
 * Represents the non-empty state of a LStruct.
 * @author Dung X. Nguyen  Copyright 2000 - All rights reserved.
 * @since 02/15/00
 */
class NonNullNode extends ANode
{
    private Object _dat;
    /** @SBGen Variable (,rest,,64)   */
    private LRStruct _tail;

    /**
     * Initializes this NonNullNode to contain dat and an empty tail list.
     * @param dat the data object to be stored in this NonNullNode.
     */
    NonNullNode(Object dat)
    {
	_dat = dat;
	_tail = new LRStruct();
    }

    /**
     * Initializes this NonNullNode to contain dat and a given tail list.
     * @param dat the data object to be stored in this NonNullNode.
     * @param tail the LRStruct tail of this NonNullNode.
     */
    NonNullNode(Object dat, LRStruct tail)
    {
	_dat = dat;
	_tail = tail;
    }

    LRStruct getRest(LRStruct owner)
    {
	return _tail;
    }

    Object getFirst(LRStruct owner)
    {
	return _dat;
    }

    void setRest(LRStruct tail, LRStruct owner)
    {
	_tail = tail;
    }

    void setFirst(Object first, LRStruct owner)
    {
	_dat = first;
    }

    /**
     * Inserts a data object at the front of the LRStruct owner.
     * @param dat the object to be inserted at the front.
     * @param owner the LRS referencing this NonNullNode.
     */
    void insertFront(Object dat, LRStruct owner)
    {
	owner.setHead (new NonNullNode (dat, new LRStruct (this)));
	/* Details:
	   LRStruct coOwner = new LRStruct (this);
	   NonNullNode newNode = new NonNullNode (dat, coOwner);
	   owner.setHead (newNode); // "old" style: owner._head = newNode - cannot be done here.
	 */
    }

    Object removeFront(LRStruct owner)
    {
    	owner.setHead (_tail.getHead()); // owner._head = _tail._head
    	return _dat;
    }

    /**
     * Calls the visitor's non-null case.
     */
    Object execute (IAlgo visitor, Object input, LRStruct owner)
    {
	return visitor.nonNullCase (owner, input);
    }
}