/*
 * 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 org.apache.datasketches.kll;

import org.apache.datasketches.quantilescommon.QuantilesSketchIteratorAPI;

/**
 * The base implementation for the KLL sketch iterator hierarchy used for viewing the
 * non-ordered quantiles retained by a sketch.
 *
 * <p>Prototype example of the recommended iteration loop:</p>
 * <pre>{@code
 *   SketchIterator itr = sketch.iterator();
 *   while (itr.next()) {
 *     ...get*();
 *   }
 * }</pre>
 *
 * @author Lee Rhodes
 */
public class KllSketchIterator implements QuantilesSketchIteratorAPI {
  protected final int[] levelsArr;
  protected final int numLevels;
  protected int level;
  protected int index;
  protected long weight;
  protected boolean isInitialized_;

  KllSketchIterator(final int[] levelsArr, final int numLevels) {
    this.levelsArr = levelsArr;
    this.numLevels = numLevels;
    this.isInitialized_ = false;
  }

  @Override
  public long getWeight() {
    return weight;
  }

  @Override
  public boolean next() {
    if (!isInitialized_) {
      level = 0;
      index = levelsArr[level];
      weight = 1;
      isInitialized_ = true;
    } else {
      index++;
    }
    if (index < levelsArr[level + 1]) {
      return true;
    }
    // go to the next non-empty level
    do {
      level++;
      if (level == numLevels) {
        return false; // run out of levels
      }
      weight *= 2;
    } while (levelsArr[level] == levelsArr[level + 1]);
    index = levelsArr[level];
    return true;
  }

}
