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The DSI utilities are a mishmash of classes accumulated during the last twenty years in projects developed at the DSI (Dipartimento di Scienze dell'Informazione, i.e., Information Sciences Department), now DI (Dipartimento di Informatica, i.e., Informatics Department), of the Universita` degli Studi di Milano.

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/*
 * DSI utilities
 *
 * Copyright (C) 2005-2020 Sebastiano Vigna
 *
 *  This library is free software; you can redistribute it and/or modify it
 *  under the terms of the GNU Lesser General Public License as published by the Free
 *  Software Foundation; either version 3 of the License, or (at your option)
 *  any later version.
 *
 *  This library is distributed in the hope that it will be useful, but
 *  WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 *  or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License
 *  for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public License
 *  along with this program; if not, see .
 *
 */

package it.unimi.dsi.io;

import java.io.Closeable;
import java.io.IOException;
import java.util.List;
import java.util.NoSuchElementException;

import it.unimi.dsi.fastutil.objects.ObjectArrayList;
import it.unimi.dsi.fastutil.objects.ObjectIterator;
import it.unimi.dsi.lang.MutableString;
import it.unimi.dsi.logging.ProgressLogger;

/** An adapter that exposes a fast buffered reader as an iterator
 * over the returned lines. Since we just actually read a line to know
 * whether {@link #hasNext()} should return true, the last line read
 * from the underlying fast buffered reader has to be cached.
 * Mixing calls to this adapter and to the underlying fast buffered
 * reader will not usually give the expected results.
 *
 * Since this class allocates no resource, it is not {@link Closeable} and
 * it will not close the underlying {@link FastBufferedReader} under any circumstances.
 * If you need resource handling, try {@link FileLinesCollection}.
 *
 * This class reuses the same mutable strings. As a result,
 * the comments for {@link FileLinesCollection}
 * apply here. If you want just get all the remaining lines, use {@link #allLines()}.
 */

public class LineIterator implements ObjectIterator {
	/** The underlying fast buffered reader. */
	private final FastBufferedReader fastBufferedReader;
	/** The mutable strings returned by this iterator. */
	private final MutableString[] s = { new MutableString(), new MutableString() };
	/** An optional progress meter. */
	private final ProgressLogger pl;
	/** Whether we must still advance to the next line. */
	private boolean toAdvance = true;
	/** In case {@link #toAdvance} is false, whether there is a next line. */
	private boolean hasNext;
	/** Which string in {@link #s} should be returned next. */
	private int k;

	/** Creates a new line iterator over a specified fast buffered reader.
	 *
	 * @param fastBufferedReader the underlying buffered reader.
	 * @param pl an optional progress logger, or {@code null}.
	 * */
	public LineIterator(final FastBufferedReader fastBufferedReader, final ProgressLogger pl) {
		this.fastBufferedReader = fastBufferedReader;
		this.pl = pl;
	}

	/** Creates a new line iterator over a specified fast buffered reader.
	 *
	 * @param fastBufferedReader the underlying buffered reader.
	 */
	public LineIterator(final FastBufferedReader fastBufferedReader) {
		this(fastBufferedReader, null);
	}


	@Override
	public boolean hasNext() {
		if (toAdvance) {
			try {
				k = 1 - k;
				hasNext = fastBufferedReader.readLine(s[k]) != null;
			} catch (final IOException e) {
				throw new RuntimeException(e);
			}
			toAdvance = false;
		}

		return hasNext;
	}

	@Override
	public MutableString next() {
		if (! hasNext()) throw new NoSuchElementException();
		toAdvance = true;
		if (pl != null) pl.update();
		return s[k];
	}

	/** Returns all lines remaining in this iterator as a list.
	 *
	 * @return all lines remaining in this iterator as a list.
	 */

	public List allLines() {
		final ObjectArrayList result = new ObjectArrayList<>();
		while(hasNext()) result.add(next().copy());
		return result;
	}
}