/*
 * 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.phoenix.query;

import org.apache.phoenix.schema.stats.GuidePostsInfo;
import org.apache.phoenix.schema.stats.GuidePostsKey;

/**
 * The interface for talking to underneath layers to load stats from stats table for a given key
 */
public interface PhoenixStatsLoader {
  /**
   * Use to check whether this is the time to load stats from stats table. There are two cases: a.
   * After a specified duration has passed b. The stats on server side (e.g. in stats table) has
   * been updated
   * @return boolean indicates whether we need to load stats or not
   */
  boolean needsLoad();

  /**
   * Called by client stats cache to load stats from underneath layers
   * @param statsKey the stats key used to search the stats on server side (in stats table)
   * @return GuidePostsInfo retrieved from sever side
   */
  GuidePostsInfo loadStats(GuidePostsKey statsKey) throws Exception;

  /**
   * Called by client stats cache to load stats from underneath layers
   * @param statsKey          the stats key used to search the stats on server side (in stats table)
   * @param prevGuidepostInfo the existing stats cached on the client side or
   *                          GuidePostsInfo.NO_GUIDEPOST
   * @return GuidePostsInfo retrieved from sever side
   */
  GuidePostsInfo loadStats(GuidePostsKey statsKey, GuidePostsInfo prevGuidepostInfo)
    throws Exception;
}
