/*
 * 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 static org.junit.Assert.assertFalse;
import static org.junit.Assert.assertTrue;

import java.util.Collections;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hbase.io.ImmutableBytesWritable;
import org.apache.phoenix.schema.stats.GuidePostsInfo;
import org.apache.phoenix.schema.stats.GuidePostsKey;
import org.apache.phoenix.util.ByteUtil;
import org.junit.Test;

import org.apache.phoenix.thirdparty.com.google.common.cache.CacheBuilder;
import org.apache.phoenix.thirdparty.com.google.common.cache.LoadingCache;
import org.apache.phoenix.thirdparty.com.google.common.cache.Weigher;

/**
 * Test class around the PhoenixStatsCacheLoader.
 */
public class PhoenixStatsCacheLoaderTest {
  /**
   * {@link PhoenixStatsLoader} test implementation for the Stats Loader.
   */
  protected class TestStatsLoaderImpl implements PhoenixStatsLoader {
    private int maxLength = 1;
    private final CountDownLatch firstTimeRefreshedSignal;
    private final CountDownLatch secondTimeRefreshedSignal;

    public TestStatsLoaderImpl(CountDownLatch firstTimeRefreshedSignal,
      CountDownLatch secondTimeRefreshedSignal) {
      this.firstTimeRefreshedSignal = firstTimeRefreshedSignal;
      this.secondTimeRefreshedSignal = secondTimeRefreshedSignal;
    }

    @Override
    public boolean needsLoad() {
      // Whenever it's called, we try to load stats from stats table
      // no matter it has been updated or not.
      return true;
    }

    @Override
    public GuidePostsInfo loadStats(GuidePostsKey statsKey) throws Exception {
      return new GuidePostsInfo(Collections.<Long> emptyList(),
        new ImmutableBytesWritable(ByteUtil.EMPTY_BYTE_ARRAY), Collections.<Long> emptyList(),
        maxLength++, 0, Collections.<Long> emptyList());
    }

    @Override
    public GuidePostsInfo loadStats(GuidePostsKey statsKey, GuidePostsInfo prevGuidepostInfo)
      throws Exception {
      firstTimeRefreshedSignal.countDown();
      secondTimeRefreshedSignal.countDown();

      return new GuidePostsInfo(Collections.<Long> emptyList(),
        new ImmutableBytesWritable(ByteUtil.EMPTY_BYTE_ARRAY), Collections.<Long> emptyList(),
        maxLength++, 0, Collections.<Long> emptyList());
    }
  }

  GuidePostsInfo getStats(LoadingCache<GuidePostsKey, GuidePostsInfo> cache,
    GuidePostsKey guidePostsKey) {
    GuidePostsInfo guidePostsInfo;
    try {
      guidePostsInfo = cache.get(guidePostsKey);
    } catch (ExecutionException e) {
      assertFalse(true);
      return GuidePostsInfo.NO_GUIDEPOST;
    }

    return guidePostsInfo;
  }

  void sleep(int x) {
    try {
      Thread.sleep(x);
    } catch (InterruptedException e) {
      assertFalse(true);
    }
  }

  @Test
  public void testStatsBeingAutomaticallyRefreshed() {
    ExecutorService executor = Executors.newFixedThreadPool(4);

    CountDownLatch firstTimeRefreshedSignal = new CountDownLatch(1);
    CountDownLatch secondTimeRefreshedSignal = new CountDownLatch(2);

    Configuration config = HBaseFactoryProvider.getConfigurationFactory().getConfiguration();

    LoadingCache<GuidePostsKey, GuidePostsInfo> cache = CacheBuilder.newBuilder()
      // Refresh entries a given amount of time after they were written
      .refreshAfterWrite(100, TimeUnit.MILLISECONDS)
      // Maximum total weight (size in bytes) of stats entries
      .maximumWeight(QueryServicesOptions.DEFAULT_STATS_MAX_CACHE_SIZE)
      // Defer actual size to the PTableStats.getEstimatedSize()
      .weigher(new Weigher<GuidePostsKey, GuidePostsInfo>() {
        @Override
        public int weigh(GuidePostsKey key, GuidePostsInfo info) {
          return info.getEstimatedSize();
        }
      })
      // Log removals at TRACE for debugging
      .removalListener(new GuidePostsCacheImpl.PhoenixStatsCacheRemovalListener())
      // Automatically load the cache when entries are missing
      .build(new PhoenixStatsCacheLoader(
        new TestStatsLoaderImpl(firstTimeRefreshedSignal, secondTimeRefreshedSignal), config));

    try {
      GuidePostsKey guidePostsKey = new GuidePostsKey(new byte[4], new byte[4]);
      GuidePostsInfo guidePostsInfo = getStats(cache, guidePostsKey);
      assertTrue(guidePostsInfo.getMaxLength() == 1);

      // Note: With Guava cache, automatic refreshes are performed when the first stale request for
      // an entry occurs.

      // After we sleep here for any time which is larger than the refresh cycle, the refresh of
      // cache entry will be
      // triggered for its first time by the call of getStats(). This is deterministic behavior, and
      // it won't cause
      // randomized test failures.
      sleep(150);
      guidePostsInfo = getStats(cache, guidePostsKey);
      // Refresh has been triggered for its first time, but still could get the old value
      assertTrue(guidePostsInfo.getMaxLength() >= 1);
      firstTimeRefreshedSignal.await();

      sleep(150);
      guidePostsInfo = getStats(cache, guidePostsKey);
      // Now the second time refresh has been triggered by the above getStats() call, the first time
      // Refresh has completed
      // and the cache entry has been updated for sure.
      assertTrue(guidePostsInfo.getMaxLength() >= 2);
      secondTimeRefreshedSignal.await();
    } catch (InterruptedException e) {
      assertFalse(true);
    }
  }
}
