package lrs;

/**
 * Represents the non-empty state of a LStruct.
 * @author Dung X. Nguyen  Copyright 2000 - All rights reserved.
 * @author Alan L. Cox
 * @since 02/13/01
 */
class NonEmptyNode extends ANode
{
    private Object _data;
    private LRStruct _tail;

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

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

    /**
     * Returns the first data object of the referencing LRStruct.
     *
     * @param owner the LRStruct referencing this NonEmptyNode.
     * @return the tail LRStruct of owner.
     */
    Object getFirst(LRStruct owner)
    {
	return _data;
    }

    /**
     * Sets a new first data object for the referencing LRStruct.
     *
     * @param data the new data object for this NonEmptyNode.
     * @param owner the LRS referencing this NonEmptyNode.
     */
    void setFirst(Object first, LRStruct owner)
    {
	_data = first;
    }

    /**
     * Returns the tail LRStruct of the referencing LRStruct.
     *
     * @param owner the LRStruct referencing this NonEmptyNode.
     * @return the tail LRStruct of owner.
     */
    LRStruct getRest(LRStruct owner)
    {
	return _tail;
    }

    /**
     * Sets a new tail for the referencing LRStruct.
     *
     * @param tail the new tail for the owner LRStruct.
     * @param owner the LRS referencing this NonEmptyNode.
     */
    void setRest(LRStruct tail, LRStruct owner)
    {
	_tail = tail;
    }

    /**
     * Inserts a data object at the front of the LRStruct owner.
     *
     * @param data the object to be inserted at the front.
     * @param owner the LRS referencing this NonNullNode.
     */
    void insertFront(Object data, LRStruct owner)
    {
	owner.setHead(new NonEmptyNode(data, 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.
	 */
    }

    /**
     * Removes and returns the first data object for the referencing LRStruct.
     *
     * @param owner the LRStruct referencing this NonEmptyNode.
     * @return the front data of the LRStruct owner.
     */
    Object removeFront(LRStruct owner)
    {
    	owner.setHead(_tail.getHead()); // owner._head = _tail._head
    	return _data;
    }

    /**
     * Executes the visitor's non-empty case and returns the output.
     *
     * @param visitor the algorithm to be executed.
     * @param input the input needed by the algorithm.
     * @param owner the LRStruct referencing this NonEmptyNode.
     */
    Object execute(IAlgo visitor, Object input, LRStruct owner)
    {
	return visitor.nonEmptyCase(owner, input);
    }
}