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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 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.text;

import java.io.BufferedReader;
import java.io.IOError;
import java.io.IOException;
import java.io.StringReader;

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

/**
 * An iterator over all the tokens in a stream, which supports arbitrary
 * look-ahead into the stream by buffering the tokens.
 *
 * @author David Jurgens
 */
public class BufferedIterator implements Iterator {

    /**
     * The backing iterator that will tokenize the stream
     */
    private final Iterator tokenizer;

    /**
     * A buffer of tokens to return.  This is intentionally a {@code List} and
     * not a {@code Queue} so that we can take advantage of the {@link
     * List#subList(int,int)} functionality for {@link #peek(int)}.
     */
    private final List buffer;

    /**
     * Tokenizes the string and buffers to the tokens to allow arbitrary
     * look-ahead.
     */
    public BufferedIterator(String str) {
	this(new BufferedReader(new StringReader(str)));
    }

    /**
     * Tokenizes the string contents on the reader and buffers to the tokens to
     * allow arbitrary look-ahead.
     */
    public BufferedIterator(BufferedReader br) {
	this(new WordIterator(br));
    }

    /**
     * Buffers the tokens in the provided iterator to allow arbitrarily
     * look-ahead.  The state of the provided iterator is updated by calls to
     * this iterator.
     */
    public BufferedIterator(Iterator tokens) {
        this.tokenizer = tokens;
	buffer = new LinkedList();
    }
    
    /**
     * Advances the specified number of tokens in the stream and places them in
     * the buffer.
     *
     * @param tokens the number of tokens to advance
     *
     * @return {@true} if the stream contained at least that many tokens, {@code
     *         false} if the stream contained fewer
     */
    private boolean advance(int tokens) {
	while (buffer.size() < tokens && tokenizer.hasNext())
	    buffer.add(tokenizer.next());
	return buffer.size() >= tokens;
    }

    /**
     * Returns {@code true} if the stream contains another token to return.
     */
    public boolean hasNext() {
	return buffer.size() > 0 || advance(1);
    }

    /**
     * Returns the next token in the stream.
     */
    public String next() {
	if (!hasNext()) {
	    throw new NoSuchElementException();
	}
	return buffer.remove(0);
    }

    /**
     * Returns an list of the next tokens in the stream based on the requested
     * amount.  If the stream did not contain as many tokens as was requested,
     * list will contain the remaining tokens, but will not throw an {@code
     * NoSuchElementException}.
     *
     * @param tokens the number of tokens to access in the stream
     * 
     * @return a list of the requested tokens or the remaining tokens in the
     *         stream, whichever is fewer
     */
    public List peek(int tokens) {
	advance(tokens);
	return new ArrayList(
	    buffer.subList(0, Math.min(tokens, buffer.size())));
    }
    
    /**
     * Throws an {@link UnsupportedOperationException} if called.
     */ 
    public void remove() {
	throw new UnsupportedOperationException("remove is not supported");
    }
}