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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 2011 David Jurgens
 *
 * 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.util;

import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;


/** 
 * A utility class for mapping a set of objects to unique indices based on
 * object equality.  The indices returned by this class will always being at
 * {@code 0}.
 *
 * @see HashIndexer
 */
public class ObjectIndexer implements Indexer, java.io.Serializable {

    private static final long serialVersionUID = 1L;

    /**
     * A mapping from each item to its index.
     */
    private final BiMap indices;

    /**
     * Creates an empty {@code ObjectIndexer} with no mappings.
     */
    public ObjectIndexer() {
        indices = new HashBiMap();
    }

    /**
     * Creates an {@code ObjectIndexer} with indices for all of the provided items.
     */
    public ObjectIndexer(Collection items) {
        this();
        for (T item : items)
            index(item);
    }

    /**
     * Creates an {@code ObjectIndexer} with indices for all of the provided items.
     */
    public ObjectIndexer(Indexer indexed) {
        this();
        for (Map.Entry e : indexed)
            indices.put(e.getKey(), e.getValue());
    }

    /**
     * {@inheritDoc}
     */
    public void clear() {
        indices.clear();
    }

    /**
     * {@inheritDoc}
     */
    public boolean contains(T item) {
        return indices.containsKey(item);
    }

    /**
     * {@inheritDoc}
     */
    public Set items() {
        return Collections.unmodifiableSet(indices.keySet());
    }

    /**
     * {@inheritDoc}
     */
    public int find(T item) {
        Integer i = indices.get(item);
        return (i == null) ? -1 : i;
    }

    /**
     * {@inheritDoc}
     */
    public int highestIndex() {
        return indices.size() - 1;
    }

    /**
     * {@inheritDoc}
     */
    public int index(T item) {
        Integer i = indices.get(item);
        if (i == null) {
            synchronized(indices) {                
                i = indices.get(item);
                if (i == null) {
                    i = indices.size();
                    indices.put(item, i);
                }
            }
        }
        return i;
    }

    /**
     * {@inheritDoc}
     */
    public boolean indexAll(Collection items) {
        boolean modified = false;
        for (T item : items) {
            Integer i = indices.get(item);
            if (i == null) {
                synchronized(indices) {                
                    i = indices.get(item);
                    if (i == null) {
                        i = indices.size();
                        indices.put(item, i);
                        modified = true;
                    }
                }
            }
        }
        return modified;
    }

    /**
     * {@inheritDoc} The returned iterator does not support {@code remove}.
     */
    public Iterator> iterator() {
        return Collections.unmodifiableSet(indices.entrySet()).iterator();
    }

    /**
     * {@inheritDoc}
     */
    public T lookup(int index) {
        return indices.inverse().get(index);
    }

    /**
     * {@inheritDoc}
     */
    public Map mapping() {
        return Collections.unmodifiableMap(indices.inverse());
    }
    
    /**
     * {@inheritDoc}
     */
    public int size() {
        return indices.size();
    }

    /**
     * {@inheritDoc}
     */
    public String toString() {
        return indices.toString();
    }
}