/*
 * (c) Copyright 2018 Palantir Technologies Inc. All rights reserved.
 *
 * 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.palantir.common.collect;

import com.google.common.collect.ImmutableSet;
import java.util.AbstractQueue;
import java.util.Iterator;

/**
 * This queue is empty and will neither return nor accept any elements
 * @author carrino
 */
public final class EmptyQueue<E> extends AbstractQueue<E> {
    private static final EmptyQueue<?> INSTANCE = new EmptyQueue<Object>();

    @SuppressWarnings("unchecked")
    public static <E> EmptyQueue<E> of() {
        return (EmptyQueue<E>) INSTANCE;
    }

    private EmptyQueue() {
        /* */
    }

    @Override
    public boolean offer(E o) {
        return false;
    }

    @Override
    public Iterator<E> iterator() {
        return ImmutableSet.<E>of().iterator();
    }

    @Override
    public int size() {
        return 0;
    }

    @Override
    public E peek() {
        return null;
    }

    @Override
    public E poll() {
        return null;
    }
}
