package u6;

import utils.*;
import java.util.*;

/**
 * Heap implementation of the PriorityQueue.
 * Stores elements of the key-element pair type in a Heap structure.
 *
 * @author V.Boutchkova
 */
public class HeapPriorityQueue implements PriorityQueue {
  
  private Heap container;
  
  public HeapPriorityQueue(Heap emptyHeap) {
    container = emptyHeap;
  }  
  
  public HeapPriorityQueue(Comparator cmp) {
    container = new ArrayHeap(cmp);
  }  
  
  /**
   * Inserts an element with priority key in this priority queue.
   * @param key the priority value; smaller keys represent greater priority.
   * @param element the element value;
   */
  public void insert(Object key, Object element) {
    container.add(key, element);
  }
  
  
  /**
   * Extracts the element with greater priority, i.e. with minimal key.
   * @return the element with minimal key
   */
  public synchronized Object extract() {
    Object result = container.readMinElement();
    container.extractItem();
    return result;
  }
  
  /**
   * Gets the number of entries in this priority queue.
   * @return the number of elements
   */
  public int size() {
    return container.size();
  }
  
  /**
   * Checks whether this priority queue is empty. 
   * @return  true iff this priority queue is empty
   */
  public boolean isEmpty() {
    return container.size() == 0;
  }
  
  /**
   * Reads the minimal key in this priority queue, 
   * without removing the element.
   */
  public Object minKey() {
    return container.readMinKey();
  }
  
  /**
   * Reads the element with minimal key.
   */
  public Object minKeyElement() {
    return container.readMinElement();
  }
}