/**
 * 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
 * <p>
 * http://www.apache.org/licenses/LICENSE-2.0
 * <p>
 * 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.hadoop.hdfs.server.datanode.metrics;

import org.apache.hadoop.test.GenericTestUtils;
import org.apache.log4j.Level;
import org.junit.Before;
import org.junit.Rule;
import org.junit.Test;
import org.junit.rules.Timeout;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.Map;
import java.util.Random;

import static org.hamcrest.core.Is.is;
import static org.junit.Assert.assertThat;
import static org.junit.Assert.assertTrue;


/**
 * Test that the {@link DataNodePeerMetrics} class is able to detect
 * outliers i.e. slow nodes via the metrics it maintains.
 */
public class TestDataNodeOutlierDetectionViaMetrics {
  public static final Logger LOG =
      LoggerFactory.getLogger(TestDataNodeOutlierDetectionViaMetrics.class);

  /**
   * Set a timeout for every test case.
   */
  @Rule
  public Timeout testTimeout = new Timeout(300_000);

  // A few constants to keep the test run time short.
  private static final int WINDOW_INTERVAL_SECONDS = 3;
  private static final int ROLLING_AVERAGE_WINDOWS = 10;
  private static final int SLOW_NODE_LATENCY_MS = 20_000;
  private static final int FAST_NODE_MAX_LATENCY_MS = 5;
  private static final long MIN_OUTLIER_DETECTION_PEERS = 10;

  private Random random = new Random(System.currentTimeMillis());

  @Before
  public void setup() {
    GenericTestUtils.setLogLevel(DataNodePeerMetrics.LOG, Level.ALL);
    GenericTestUtils.setLogLevel(OutlierDetector.LOG, Level.ALL);
  }

  /**
   * Test that a very slow peer is detected as an outlier.
   */
  @Test
  public void testOutlierIsDetected() throws Exception {
    final String slowNodeName = "SlowNode";

    DataNodePeerMetrics peerMetrics = new DataNodePeerMetrics(
        "PeerMetrics-For-Test", WINDOW_INTERVAL_SECONDS,
        ROLLING_AVERAGE_WINDOWS);

    injectFastNodesSamples(peerMetrics);
    injectSlowNodeSamples(peerMetrics, slowNodeName);

    // Trigger a snapshot.
    peerMetrics.dumpSendPacketDownstreamAvgInfoAsJson();

    final Map<String, Double> outliers = peerMetrics.getOutliers();
    LOG.info("Got back outlier nodes: {}", outliers);
    assertThat(outliers.size(), is(1));
    assertTrue(outliers.containsKey(slowNodeName));
  }

  /**
   * Test that when there are no outliers, we get back nothing.
   */
  @Test
  public void testWithNoOutliers() throws Exception {
    DataNodePeerMetrics peerMetrics = new DataNodePeerMetrics(
        "PeerMetrics-For-Test", WINDOW_INTERVAL_SECONDS,
        ROLLING_AVERAGE_WINDOWS);

    injectFastNodesSamples(peerMetrics);

    // Trigger a snapshot.
    peerMetrics.dumpSendPacketDownstreamAvgInfoAsJson();

    // Ensure that we get back the outlier.
    assertTrue(peerMetrics.getOutliers().isEmpty());
  }

  /**
   * Inject fake stats for MIN_OUTLIER_DETECTION_PEERS fast nodes.
   *
   * @param peerMetrics
   */
  public void injectFastNodesSamples(DataNodePeerMetrics peerMetrics) {
    for (int nodeIndex = 0;
         nodeIndex < MIN_OUTLIER_DETECTION_PEERS; ++nodeIndex) {
      final String nodeName = "FastNode-" + nodeIndex;
      LOG.info("Generating stats for node {}", nodeName);
      for (int i = 0;
           i < 2 * DataNodePeerMetrics.MIN_OUTLIER_DETECTION_SAMPLES;
           ++i) {
        peerMetrics.addSendPacketDownstream(
            nodeName, random.nextInt(FAST_NODE_MAX_LATENCY_MS));
      }
    }
  }

  /**
   * Inject fake stats for one extremely slow node.
   */
  public void injectSlowNodeSamples(
      DataNodePeerMetrics peerMetrics, String slowNodeName)
      throws InterruptedException {

    // And the one slow node.
    for (int i = 0;
         i < 2 * DataNodePeerMetrics.MIN_OUTLIER_DETECTION_SAMPLES;
         ++i) {
      peerMetrics.addSendPacketDownstream(
          slowNodeName, SLOW_NODE_LATENCY_MS);
    }
  }
}