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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 2009 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.util;

import java.io.Serializable;

import java.util.Collection;
import java.util.Map;
import java.util.Set;

import java.util.concurrent.ConcurrentHashMap;


/**
 * A Mapping from Strings to object instances created by a {@link Generator}.
 * If a value does not exist for a given string, one will be automatically
 * generated using a provided {@code Generator}.
 *
 * @author Keith Stevens
 */
public class GeneratorMap implements Map, Serializable {

    private static final long serialVersionUID = 1L;

    /**
     * The {@code Generator} for generating new map values.
     */
    private final Generator generator;

    /**
     * A mapping from terms to their instance
     */
    private final Map termToItem;

    /**
     * Creates a new {@link GeneratorMap} using a {@code ConcurrentHashMap}.
     * Items will be using the provided {@link Generator}.
     */
    public GeneratorMap(Generator generator) {
        this(generator, new ConcurrentHashMap());
    }

    /**
     * Creates a new {@link GeneratorMap} using a the provided map}.  Items will
     * be using the provided {@link Generator}.
     */
    public GeneratorMap(Generator generator, Map map) {
        termToItem = map;
        this.generator = generator;
    }

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

    /**
     * {@inheritDoc}
     */
    public boolean containsKey(Object key) {
        return termToItem.containsKey(key);
    }

    /**
     * {@inheritDoc}
     */
    public boolean containsValue(Object value) {
        return termToItem.containsValue(value);
    }

    /**
     * {@inheritDoc}
     */
    public Set> entrySet() {
        return termToItem.entrySet();
    }

    /**
     * {@inheritDoc}
     */
    public boolean equals(Object o) {
        return termToItem.equals(o);
    }

    /**
     * Returns a {@code T} for the given term, if no mapping for
     * {@code term} then a new vaue is generated, stored, and returned.
     *
     * @param term The term specifying the item to return.
     *
     * @return A generated item corresponding to {@code term}.
     */
    public T get(Object term) {
        // Check that an index vector does not already exist.
        T v = termToItem.get(term);
        if (v == null) {
            synchronized (this) {
                // Confirm that some other thread has not created an index
                // vector for this term.
                v = termToItem.get(term);
                if (v == null) {
                    // Generate the index vector for this term and store it.
                    v = generator.generate();
                    termToItem.put((String) term, v);
                }
            }
        }
        return v;
    }

    /**
     * {@inheritDoc}
     */
    public int hashCode() {
        return termToItem.hashCode();
    }

    /**
     * {@inheritDoc}
     */
    public boolean isEmpty() {
        return termToItem.isEmpty();
    }
    
    /**
     * {@inheritDoc}
     */
    public Set keySet() {
        return termToItem.keySet();
    }

    /**
     * Unsupported.
     */
    public T put(String key, T vector) {
        throw new UnsupportedOperationException(
                "Items may not be inserted into this GeneratorMap.");
    }

    /**
     * Unsupported.
     */
    public void putAll(Map m) {
        throw new UnsupportedOperationException(
                "Items may not be inserted into this GeneratorMap.");
    }

    /**
     * {@inheritDoc}
     */
    public int size() {
        return termToItem.size();
    }

    /**
     * {@inheritDoc}
     */
    public Collection values() {
        return termToItem.values();
    }

    /**
     * {@inheritDoc}
     */
    public T remove(Object key) {
        return termToItem.remove(key);
    }
}