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The S-Space Package is a collection of algorithms for building Semantic Spaces as well as a highly-scalable library for designing new distributional semantics algorithms. Distributional algorithms process text corpora and represent the semantic for words as high dimensional feature vectors. This package also includes matrices, vectors, and numerous clustering algorithms. These approaches are known by many names, such as word spaces, semantic spaces, or distributed semantics and rest upon the Distributional Hypothesis: words that appear in similar contexts have similar meanings.
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/*
 * Copyright 2010 Keith Stevens
 *
 * This file is part of the S-Space package and is covered under the terms and
 * conditions therein.
 *
 * The S-Space package is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as published
 * by the Free Software Foundation and distributed hereunder to you.
 *
 * THIS SOFTWARE IS PROVIDED "AS IS" AND NO REPRESENTATIONS OR WARRANTIES,
 * EXPRESS OR IMPLIED ARE MADE.  BY WAY OF EXAMPLE, BUT NOT LIMITATION, WE MAKE
 * NO REPRESENTATIONS OR WARRANTIES OF MERCHANT- ABILITY OR FITNESS FOR ANY
 * PARTICULAR PURPOSE OR THAT THE USE OF THE LICENSED SOFTWARE OR DOCUMENTATION
 * WILL NOT INFRINGE ANY THIRD PARTY PATENTS, COPYRIGHTS, TRADEMARKS OR OTHER
 * RIGHTS.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program. If not, see .
 */

package edu.ucla.sspace.dependency;


import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Iterator;

/**
 * A {@link DependencyPath} that supports constant time access to the nodes and
 * relations that make up its sequence.
 */
public class SimpleDependencyPath implements DependencyPath {
    
    /**
     * The list of terms and relations.
     */
    final List path;

    /**
     * The list of terms and relations.
     */
    final List nodes;

    /**
     * Creates a {@link SimpleDependencyPath} starting at the head node of the
     * first relation in the list.
     */
    public SimpleDependencyPath(List path) {
        this(path, true);
    }

    /**
     * Creates a {@link SimpleDependencyPath} that starts at either the head
     * node or dependent node of the first relation in the list.
     */
    public SimpleDependencyPath(List path, 
                                boolean isHeadFirst) {
        if (path == null || path.size() == 0)
            throw new IllegalArgumentException("Cannot provide empty path");
        this.path = new ArrayList(path);        
        this.nodes = new ArrayList(path.size() + 1);
        DependencyTreeNode cur = (isHeadFirst)
            ? path.get(0).headNode() : path.get(0).dependentNode();
        nodes.add(cur);
        for (DependencyRelation r : path) {
            DependencyTreeNode next = r.headNode();
            // If the head node is the last node we saw, then the dependent node
            // must be the next node in the path
            if (next.equals(cur)) 
                next = r.dependentNode();
            nodes.add(next);
            cur = next;
        }
    }

    /**
     * Creates new {@link SimpleDependencyPath} as a copy of the provided path.
     */
    public SimpleDependencyPath(DependencyPath path) {
        if (path == null || path.length() == 0)
            throw new IllegalArgumentException("Cannot provide empty path");

        int size = path.length();
        this.path = new ArrayList(size);
        this.nodes = new ArrayList(size + 1);
        DependencyTreeNode cur = path.first();
        nodes.add(cur);
        for (DependencyRelation r : path) {
            this.path.add(r);
            DependencyTreeNode next = r.headNode();
            // If the head node is the last node we saw, then the dependent node
            // must be the next node in the path
            if (next.equals(cur)) 
                next = r.dependentNode();
            nodes.add(next);
            next = cur;
        }
    }       

    /**
     * Creates a {@link SimpleDependencyPath} from a single relation, optionally
     * starting at the head node of the relation.
     */
    public SimpleDependencyPath(DependencyRelation relation, 
                                boolean startFromHead) {
        this();
        if (relation == null)
            throw new IllegalArgumentException("Cannot provide empty path");
        path.add(relation);
        if (startFromHead) {
            nodes.add(relation.headNode());
            nodes.add(relation.dependentNode());
        }
        else {
            nodes.add(relation.dependentNode());
            nodes.add(relation.headNode());           
        }
    }

    /**
     * Creates an empty dependency path
     */
    public SimpleDependencyPath() { 
        path = new ArrayList();
        nodes = new ArrayList();
    }

    /**
     * Returns a copy of this dependency path
     */
    public SimpleDependencyPath copy() {
        SimpleDependencyPath copy = new SimpleDependencyPath();
        copy.path.addAll(path);
        copy.nodes.addAll(nodes);
        return copy;
    }

    /**
     * Returns a copy of this dependency path that has the provided related
     * appended to the end of its path sequence.
     */
    public SimpleDependencyPath extend(DependencyRelation relation) {
        SimpleDependencyPath copy = copy();
        // Figure out which node is at the end of our path, and then add the new
        // node to the end of our nodes
        DependencyTreeNode last = last(); 
        copy.nodes.add((relation.headNode().equals(last)) 
                       ? relation.dependentNode() : relation.headNode());
        copy.path.add(relation);
        return copy;
    }

    public boolean equals(Object o) {
        if (o instanceof DependencyPath) {
            DependencyPath p = (DependencyPath)o;
            if (p.length() != length())
                return false;
            DependencyTreeNode f = p.first();
            DependencyTreeNode n = first();
            if (!(f == n || (f != null && f.equals(n))))
                return false;
            Iterator it1 = iterator();
            Iterator it2 = p.iterator();
            while (it1.hasNext())
                if (!(it1.next().equals(it2.next())))
                    return false;
            return true;
        }
        return false;
    }

    /**
     * {@inheritDoc}
     */
    public DependencyTreeNode first() {
        return (nodes.isEmpty()) ? null : nodes.get(0);
    }

    /**
     * {@inheritDoc}
     */
    public DependencyRelation firstRelation() {
        return (path.isEmpty()) ? null : path.get(0);
    }    

    /**
     * {@inheritDoc}
     */
    public DependencyTreeNode getNode(int position) {
        if (position < 0 || position >= nodes.size())
            throw new IndexOutOfBoundsException("Invalid node: " + position);
        return nodes.get(position);
    }

    /**
     * {@inheritDoc}
     */
    public String getRelation(int position) {
        if (position < 0 || position >= path.size())
            throw new IndexOutOfBoundsException("Invalid relation: " +position);
        DependencyRelation r = path.get(position);
        return r.relation();
    }

    /**
     * {@inheritDoc}
     */
    public Iterator iterator() {
        return path.iterator();
    }

    /**
     * {@inheritDoc}
     */
    public DependencyTreeNode last() {
        return nodes.get(nodes.size() - 1);
    }

    /**
     * {@inheritDoc}
     */
    public DependencyRelation lastRelation() {
        return path.get(path.size() - 1);
    }    
    
    /**
     * {@inheritDoc}
     */
    public int length() {
        return path.size();
    }

    /**
     * Returns the path in order with words and relations space delimited.
     */
    public String toString() {
         int size = nodes.size();
         StringBuilder sb = new StringBuilder(8 * size);
         sb.append(nodes.get(0).word());
         for (int i = 1; i < size; ++i)
             sb.append(' ')
                 .append(path.get(i-1).relation())
                 .append(' ').append(nodes.get(i).word());
         return sb.toString();
    }
}