/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 hivemall.utils.collections;

import java.util.Comparator;
import java.util.PriorityQueue;

import javax.annotation.Nonnegative;
import javax.annotation.Nonnull;
import javax.annotation.Nullable;

public final class BoundedPriorityQueue<E> {

    @Nonnegative
    private final int maxSize;
    @Nonnull
    private final Comparator<E> comparator;
    @Nonnull
    private final PriorityQueue<E> queue;

    public BoundedPriorityQueue(int size, @Nonnull Comparator<E> comparator) {
        if (size < 1) {
            throw new IllegalArgumentException("Illegal queue size: " + size);
        }
        if (comparator == null) {
            throw new IllegalArgumentException("comparator should not be null");
        }
        this.maxSize = size;
        this.comparator = comparator;
        this.queue = new PriorityQueue<E>(size + 10, comparator);
    }

    public boolean offer(@Nonnull E e) {
        if (e == null) {
            throw new IllegalArgumentException("Null argument is not permitted");
        }
        final int numElem = queue.size();
        if (numElem >= maxSize) {
            E smallest = queue.peek();
            final int cmp = comparator.compare(e, smallest);
            if (cmp < 0) {
                return false;
            }
            queue.poll();
        }
        queue.offer(e);
        return true;
    }

    @Nullable
    public E poll() {
        return queue.poll();
    }

    @Nullable
    public E peek() {
        return queue.peek();
    }

    public int size() {
        return queue.size();
    }

    public void clear() {
        queue.clear();
    }

}