package lrs;

/**
 * Mutable linear recursive structure.  Serves as a host to algorithms that conform
 * to the visitor pattern.
 * @author Dung X. Nguyen  Copyright 2000 - All rights reserved.
 * @since 02/15/00
 * @dependency lrs.IAlgo 
 */
public class LRStruct
{
    /** @SBGen Variable (,state,,64)   */
    private ANode _head;

    /**
     * Initializes this LRStruct to an empty state.
     */
    public LRStruct ()
    {
	_head = NullNode.singleton;
    }

    /**
     * Inserts dat to the front of this LRStruct.
     * @param dat data to insert at this node
     */
    public final void insertFront (Object dat)
    {
	_head.insertFront (dat, this);
    }

    /**
     * Returns this node's first
     */
    public final Object removeFront ()
    {
	return _head.removeFront (this);
    }

    /**
     * Gets the data from this node
     */
    public final Object getFirst()
    {
	return _head.getFirst (this);
    }

    /**
     * Sets first data element to a new value.
     * @param dat new data for this node
     * @throws NoSuchElementException if this LRStruct is empty.
     */
    public final void setFirst (Object dat)
    {
	_head.setFirst (dat, this);
    }

    /**
     * Gets the rest of the structure
     * @throws NoSuchElementException if this LRStruct is empty.
     */
    public final LRStruct getRest ()
    {
	return _head.getRest (this);
    }

    /**
     * Sets a new tail for this node
     * @throws NoSuchElementException if this LRStruct is empty.
     */
    public final void setRest (LRStruct tail)
    {
	_head.setRest (tail, this);
    }

    /**
     * Serves as a host to execute an algorithm with a given input and return an appropriate
     * output object.
     * @param visitor an algorithm (!= null) that operates on LRStruct.
     * @param input input object needed by visitor.
     * @return output object resulting from the execution of visitor.
     */
    public final Object execute (IAlgo visitor, Object input)
    {
	return _head.execute (visitor, input, this);
    }

// Package access only:

    /**
     * Initiazes this LRStruct with a given head node.
     * @param node null != node.
     */
    LRStruct(ANode node)
    {
	_head = node;
    }

    /**
     * Changes the head node (i.e. state) of this LRStruct.
     * @param head
     */
    final void setHead (ANode head)
    {
	_head = head;
    }

    /**
     * Gets the head node (i.e. state) of this LRStruct.
     * @return the head node.
     */
    final ANode getHead ()
    {
	return _head;
    }
}