/**
 * Copyright (C) 2014-2016 LinkedIn Corp. (pinot-core@linkedin.com)
 *
 * 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.linkedin.pinot.core.util;

import it.unimi.dsi.fastutil.ints.Int2IntOpenHashMap;


/**
 * Abstract base class for IndexedPriorityQueue's.
 *
 */
public abstract class BaseIndexedPriorityQueue {

  protected boolean _minHeap;
  protected Int2IntOpenHashMap _keyToIndexMap;
  protected Int2IntOpenHashMap _indexToKeyMap;

  /**
   * Constructor for the class.
   *
   * @param initialCapacity Initial capacity for the priority queue
   * @param minHeap Min order, ie smallest element on top.
   */
  public BaseIndexedPriorityQueue(int initialCapacity, boolean minHeap) {
    _minHeap = minHeap;
    _keyToIndexMap = new Int2IntOpenHashMap(initialCapacity);
    _indexToKeyMap = new Int2IntOpenHashMap(initialCapacity);
  }

  /**
   * Helper method to update key/index mappings.
   *
   * @param key Key for position
   * @param position Position for key
   */
  protected void updateKeyIndexMap(int key, int position) {
    _keyToIndexMap.put(key, position);
    _indexToKeyMap.put(position, key);
  }

  /**
   * Helper method to swap keys for the specified indices.
   * @param index1 First index
   * @param index2 Second index
   */
  protected void swapKeys(int index1, int index2) {
    int key1 = _indexToKeyMap.get(index1);
    int key2 = _indexToKeyMap.get(index2);

    updateKeyIndexMap(key1, index2);
    updateKeyIndexMap(key2, index1);
  }

  /**
   * Returns index of left child of the specified index.
   * Does not check for actual existence of the child in the
   * priority queue.
   *
   * @param index Index for which to find the left child.
   * @return Index of the left.
   */
  protected int getLeftChildIndex(int index) {
    return ((2 * (index + 1)) - 1);
  }

  /**
   * Returns index of right child of the specified index.
   * Does not check for actual existence of the child in the
   * priority queue.
   *
   * @param index Index for which to find the right child.
   * @return Index of the right.
   */
  protected int getRightChildIndex(int index) {
    return (2 * (index + 1));
  }

  /**
   * Returns the index of parent for the specified node.
   * Returns -1 for root.
   *
   * @param index Index of node for which to identify the parent.
   * @return Index of parent.
   */
  protected int getParentIndex(int index) {
    return (((index + 1) / 2) - 1);
  }
}