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package org.openjdk.jmh.util;

import java.io.Serializable;
import java.util.*;

Bounded variant of PriorityQueue. Note: elements are returned in reverse order. For instance, if "top N smallest elements" are required, use new BoundedPriorityQueue(N), and the elements would be returned in largest to smallest order. 
Type parameters:
<E> – type of the element/**
 * Bounded variant of {@link PriorityQueue}.
 * Note: elements are returned in reverse order.
 * For instance, if "top N smallest elements" are required, use {@code new BoundedPriorityQueue(N)},
 * and the elements would be returned in largest to smallest order.
 *
 * @param <E> type of the element
 */
public class BoundedPriorityQueue<E> extends AbstractQueue<E> implements Serializable {
    private static final long serialVersionUID = 7159618773497127413L;

    private final int maxSize;
    private final Comparator<? super E> comparator;
    private final Queue<E> queue;

    
Creates a bounded priority queue with the specified maximum size and default ordering. At most maxSize smallest elements would be kept in the queue. 
Params:
maxSize – maximum size of the queue/**
     * Creates a bounded priority queue with the specified maximum size and default ordering.
     * At most {@code maxSize} smallest elements would be kept in the queue.
     *
     * @param maxSize maximum size of the queue
     */
    public BoundedPriorityQueue(int maxSize) {
        this(maxSize, null);
    }

    
Creates a bounded priority queue with the specified maximum size. At most maxSize smallest elements would be kept in the queue. 
Params:
maxSize –    maximum size of the queue
comparator – comparator that orders the elements/**
     * Creates a bounded priority queue with the specified maximum size.
     * At most {@code maxSize} smallest elements would be kept in the queue.
     *
     * @param maxSize    maximum size of the queue
     * @param comparator comparator that orders the elements
     */
    public BoundedPriorityQueue(int maxSize, Comparator<? super E> comparator) {
        this.maxSize = maxSize;
        this.comparator = reverse(comparator);
        this.queue = new PriorityQueue<>(10, this.comparator);
    }

    
Internal queue should be in fact in reverse order.
By default, the queue aims for "top N smallest elements".
So peek() should return the biggest element, so it can be removed when adding smaller element
Params:
comparator – comparator that designates ordering of the entries or null for default ordering
Type parameters:
<E> –        type of the element
Returns:
reverse comparator/**
     * Internal queue should be in fact in reverse order.
     * By default, the queue aims for "top N smallest elements".
     * So peek() should return the biggest element, so it can be removed when adding smaller element
     *
     * @param comparator comparator that designates ordering of the entries or {@code null} for default ordering
     * @param <E>        type of the element
     * @return reverse comparator
     */
    private static <E> Comparator<? super E> reverse(Comparator<? super E> comparator) {
        if (comparator == null) {
            return Collections.reverseOrder();
        }
        return Collections.reverseOrder(comparator);
    }

    @Override
    public boolean add(E e) {
        return offer(e);
    }

    @Override
    public boolean offer(E e) {
        if (queue.size() >= maxSize) {
            E head = peek();
            if (comparator.compare(e, head) < 1) {
                return false;
            }
            poll();
        }
        return queue.offer(e);
    }

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

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

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

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