/*
 * 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.solr.store.hdfs;

import java.io.IOException;
import java.lang.invoke.MethodHandles;
import java.util.Arrays;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

import com.codahale.metrics.MetricRegistry;
import org.apache.hadoop.fs.BlockLocation;
import org.apache.hadoop.fs.FileStatus;
import org.apache.hadoop.fs.FileSystem;
import org.apache.solr.core.SolrInfoBean;
import org.apache.solr.metrics.MetricsMap;
import org.apache.solr.metrics.SolrMetricProducer;
import org.apache.solr.metrics.SolrMetricsContext;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class HdfsLocalityReporter implements SolrInfoBean, SolrMetricProducer {
  public static final String LOCALITY_BYTES_TOTAL = "locality.bytes.total";
  public static final String LOCALITY_BYTES_LOCAL = "locality.bytes.local";
  public static final String LOCALITY_BYTES_RATIO = "locality.bytes.ratio";
  public static final String LOCALITY_BLOCKS_TOTAL = "locality.blocks.total";
  public static final String LOCALITY_BLOCKS_LOCAL = "locality.blocks.local";
  public static final String LOCALITY_BLOCKS_RATIO = "locality.blocks.ratio";

  private static final Logger log = LoggerFactory.getLogger(MethodHandles.lookup().lookupClass());

  private String hostname;
  private final ConcurrentMap<HdfsDirectory,ConcurrentMap<FileStatus,BlockLocation[]>> cache;

  private final Set<String> metricNames = ConcurrentHashMap.newKeySet();
  private SolrMetricsContext solrMetricsContext;

  public HdfsLocalityReporter() {
    cache = new ConcurrentHashMap<>();
  }

  /**
   * Set the host name to use when determining locality
   * @param hostname The name of this host; should correspond to what HDFS Data Nodes think this is.
   */
  public void setHost(String hostname) {
    this.hostname = hostname;
  }
  
  @Override
  public String getName() {
    return "hdfs-locality";
  }

  @Override
  public String getDescription() {
    return "Provides metrics for HDFS data locality.";
  }

  @Override
  public Category getCategory() {
    return Category.OTHER;
  }

  @Override
  public Set<String> getMetricNames() {
    return metricNames;
  }

  @Override
  public MetricRegistry getMetricRegistry() {
    return solrMetricsContext != null ? solrMetricsContext.getMetricRegistry() : null;
  }

  @Override
  public SolrMetricsContext getSolrMetricsContext() {
    return solrMetricsContext;
  }

  /**
   * Provide statistics on HDFS block locality, both in terms of bytes and block counts.
   */
  @Override
  public void initializeMetrics(SolrMetricsContext parentContext, String scope) {
    solrMetricsContext = parentContext.getChildContext(this);
    MetricsMap metricsMap = new MetricsMap((detailed, map) -> {
      long totalBytes = 0;
      long localBytes = 0;
      int totalCount = 0;
      int localCount = 0;

      for (Iterator<HdfsDirectory> iterator = cache.keySet().iterator(); iterator.hasNext();) {
        HdfsDirectory hdfsDirectory = iterator.next();

        if (hdfsDirectory.isClosed()) {
          iterator.remove();
        } else {
          try {
            refreshDirectory(hdfsDirectory);
            Map<FileStatus,BlockLocation[]> blockMap = cache.get(hdfsDirectory);

            // For every block in every file in this directory, count it
            for (BlockLocation[] locations : blockMap.values()) {
              for (BlockLocation bl : locations) {
                totalBytes += bl.getLength();
                totalCount++;

                if (Arrays.asList(bl.getHosts()).contains(hostname)) {
                  localBytes += bl.getLength();
                  localCount++;
                }
              }
            }
          } catch (IOException e) {
            log.warn("Could not retrieve locality information for {} due to exception: {}",
                hdfsDirectory.getHdfsDirPath(), e);
          }
        }
      }
      map.put(LOCALITY_BYTES_TOTAL, totalBytes);
      map.put(LOCALITY_BYTES_LOCAL, localBytes);
      if (localBytes == 0) {
        map.put(LOCALITY_BYTES_RATIO, 0);
      } else {
        map.put(LOCALITY_BYTES_RATIO, localBytes / (double) totalBytes);
      }
      map.put(LOCALITY_BLOCKS_TOTAL, totalCount);
      map.put(LOCALITY_BLOCKS_LOCAL, localCount);
      if (localCount == 0) {
        map.put(LOCALITY_BLOCKS_RATIO, 0);
      } else {
        map.put(LOCALITY_BLOCKS_RATIO, localCount / (double) totalCount);
      }
    });
    solrMetricsContext.gauge(this, metricsMap, true, "hdfsLocality", getCategory().toString(), scope);
  }

  /**
   * Add a directory for block locality reporting. This directory will continue to be checked until its close method has
   * been called.
   * 
   * @param dir
   *          The directory to keep metrics on.
   */
  public void registerDirectory(HdfsDirectory dir) {
    log.info("Registering direcotry {} for locality metrics.", dir.getHdfsDirPath().toString());
    cache.put(dir, new ConcurrentHashMap<FileStatus, BlockLocation[]>());
  }

  /**
   * Update the cached block locations for the given directory. This includes deleting any files that no longer exist in
   * the file system and adding any new files that have shown up.
   * 
   * @param dir
   *          The directory to refresh
   * @throws IOException
   *           If there is a problem getting info from HDFS
   */
  private void refreshDirectory(HdfsDirectory dir) throws IOException {
    Map<FileStatus,BlockLocation[]> directoryCache = cache.get(dir);
    Set<FileStatus> cachedStatuses = directoryCache.keySet();

    FileSystem fs = dir.getFileSystem();
    FileStatus[] statuses = fs.listStatus(dir.getHdfsDirPath());
    List<FileStatus> statusList = Arrays.asList(statuses);

    log.debug("Updating locality information for: {}", statusList);

    // Keep only the files that still exist
    cachedStatuses.retainAll(statusList);

    // Fill in missing entries in the cache
    for (FileStatus status : statusList) {
      if (!status.isDirectory() && !directoryCache.containsKey(status)) {
        BlockLocation[] locations = fs.getFileBlockLocations(status, 0, status.getLen());
        directoryCache.put(status, locations);
      }
    }
  }

}