/*
 * Copyright (c) 2011-2015 EPFL DATA Laboratory
 * Copyright (c) 2014-2015 The Squall Collaboration (see NOTICE)
 *
 * 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 ch.epfl.data.squall.ewh.data_structures;

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

public class FixedSizePriorityQueue<T> extends PriorityQueue<T> {
    private final int _maxSize;

    /**
     * Constructs a {@link FixedSizePriorityQueue} with the specified
     * {@code maxSize} and {@code comparator}.
     *
     * @param maxSize
     *            - The maximum size the queue can reach, must be a positive
     *            integer.
     * @param comparator
     *            - The comparator to be used to compare the elements in the
     *            queue, must be non-null.
     */
    public FixedSizePriorityQueue(final int maxSize,
	    final Comparator<? super T> comparator) {
	super(maxSize, comparator); // initialCapacity is set to maxSize, as it
				    // will always reach this size
	if (maxSize <= 0) {
	    throw new IllegalArgumentException("maxSize = " + maxSize
		    + "; expected a positive integer.");
	}
	if (comparator == null) {
	    throw new NullPointerException("Comparator is null.");
	}
	_maxSize = maxSize;
    }

    /**
     * Adds an element to the queue. If the queue contains {@code maxSize}
     * elements, {@code e} will be compared to the lowest element in the queue
     * using {@code comparator}. If {@code e} is greater than or equal to the
     * lowest element, that element will be removed and {@code e} will be added
     * instead. Otherwise, the queue will not be modified and {@code e} will not
     * be added.
     *
     * @param e
     *            - Element to be added, must be non-null.
     */
    @Override
    public boolean add(final T e) {
	if (e == null) {
	    throw new NullPointerException("e is null.");
	}
	if (_maxSize <= size()) {
	    final T firstElm = peek();
	    if (super.comparator().compare(e, firstElm) < 1) {
		// e.priority is less than the smallest priority in the queue;
		// not added
		return false;
	    } else {
		// remove the element with the smallest priority to provide
		// space for the new element
		poll();
	    }
	}
	super.add(e);
	return true;
    }
}