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/*
 * Copyright (c) 2015-2016, Ivan Sokolov. All rights reserved.
 * This code is licensed under MIT license (see LICENSE for details)
 */

package com.github.sirikid.iterators;

import java.util.ListIterator;
import java.util.NoSuchElementException;
import javax.annotation.Nullable;

/**
 * Iterator, that contains only one element.
 *
 * @author Ivan Sokolov
 * @version 1.1.0
 * @param  type of element
 * @see SingletonSpliterator
 * @since 1.0.0
 */

public class SingletonIterator implements ListIterator {
	@Nullable private final T value;
	private boolean alreadyUsed;

	/**
	 * Sole constructor.
	 *
	 * @param value the value to be in iterator
	 */
	public SingletonIterator(@Nullable T value) {
		this.value = value;
		alreadyUsed = false;
	}

	@Override
	public boolean hasNext() {
		return !alreadyUsed;
	}

	@Override
	public T next() {
		if (!hasNext()) throw new NoSuchElementException();
		alreadyUsed = true;
		return value;
	}

	@Override
	public boolean hasPrevious() {
		return alreadyUsed;
	}

	@Override
	public T previous() {
		if (!hasPrevious()) throw new NoSuchElementException();
		alreadyUsed = false;
		return value;
	}

	@Override
	public int nextIndex() {
		return alreadyUsed ? 1 : 0;
	}

	@Override
	public int previousIndex() {
		return alreadyUsed ? 0 : -1;
	}

	@Override
	public void remove() {
		throw new UnsupportedOperationException("remove");
	}

	@Override
	public void set(final T unused) {
		throw new UnsupportedOperationException("set");
	}

	@Override
	public void add(final T unused) {
		throw new UnsupportedOperationException("add");
	}
}