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/*
 * Original Guava code is copyright (C) 2015 The Guava Authors.
 * Modifications from Guava are copyright (C) 2015 DiffPlug.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.google.common.base;

import static com.google.common.base.Preconditions.checkState;

import java.util.Iterator;
import java.util.NoSuchElementException;

import com.google.common.annotations.GwtCompatible;

/**
 * Note this class is a copy of
 * {@link com.google.common.collect.AbstractIterator} (for dependency reasons).
 */
@GwtCompatible
abstract class AbstractIterator implements Iterator {
	private State state = State.NOT_READY;

	protected AbstractIterator() {}

	private enum State {
		READY, NOT_READY, DONE, FAILED,
	}

	private T next;

	protected abstract T computeNext();

	protected final T endOfData() {
		state = State.DONE;
		return null;
	}

	@Override
	public final boolean hasNext() {
		checkState(state != State.FAILED);
		switch (state) {
		case READY:
			return true;
		case DONE:
			return false;
		default:
		}
		return tryToComputeNext();
	}

	private boolean tryToComputeNext() {
		state = State.FAILED; // temporary pessimism
		next = computeNext();
		if (state != State.DONE) {
			state = State.READY;
			return true;
		}
		return false;
	}

	@Override
	public final T next() {
		if (!hasNext()) {
			throw new NoSuchElementException();
		}
		state = State.NOT_READY;
		T result = next;
		next = null;
		return result;
	}

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