/*
 * Copyright 2018-present Open Networking Foundation
 *
 * 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 io.atomix.storage.journal.index;

import java.util.Map;
import java.util.TreeMap;

/**
 * Sparse index.
 */
public class SparseJournalIndex implements JournalIndex {
  private static final int MIN_DENSITY = 1000;
  private final int density;
  private final TreeMap<Long, Integer> positions = new TreeMap<>();

  public SparseJournalIndex(double density) {
    this.density = (int) Math.ceil(MIN_DENSITY / (density * MIN_DENSITY));
  }

  @Override
  public void index(long index, int position) {
    if (index % density == 0) {
      positions.put(index, position);
    }
  }

  @Override
  public Position lookup(long index) {
    Map.Entry<Long, Integer> entry = positions.floorEntry(index);
    return entry != null ? new Position(entry.getKey(), entry.getValue()) : null;
  }

  @Override
  public void truncate(long index) {
    positions.tailMap(index, false).clear();
  }
}