/**
    * 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.hadoop.hbase.master.balancer;
  
  import java.io.FileNotFoundException;
  import java.io.IOException;
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.HashMap;
  import java.util.LinkedList;
  import java.util.List;
  import java.util.concurrent.ExecutionException;
  import java.util.concurrent.TimeUnit;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.conf.Configuration;
  import org.apache.hadoop.hbase.ClusterStatus;
  import org.apache.hadoop.hbase.TableName;
  import org.apache.hadoop.hbase.HDFSBlocksDistribution;
  import org.apache.hadoop.hbase.HRegionInfo;
  import org.apache.hadoop.hbase.HTableDescriptor;
  import org.apache.hadoop.hbase.ServerName;
  import org.apache.hadoop.hbase.master.MasterServices;
  import org.apache.hadoop.hbase.regionserver.HRegion;
  
  import com.google.common.cache.CacheBuilder;
  import com.google.common.cache.CacheLoader;
  import com.google.common.cache.LoadingCache;
  
  /**
   * This will find where data for a region is located in HDFS. It ranks
   * {@link ServerName}'s by the size of the store files they are holding for a
   * given region.
   *
   */
  class RegionLocationFinder {
  
    private static Log LOG = LogFactory.getLog(RegionLocationFinder.class);
  
    private Configuration conf;
    private ClusterStatus status;
    private MasterServices services;
  
    private CacheLoader<HRegionInfo, List<ServerName>> loader =
        new CacheLoader<HRegionInfo, List<ServerName>>() {
  
          @Override
          public List<ServerName> load(HRegionInfo key) throws Exception {
            List<ServerName> servers = internalGetTopBlockLocation(key);
            if (servers == null) {
              return new LinkedList<ServerName>();
            }
            return servers;
          }
        };
  
    // The cache for where regions are located.
    private LoadingCache<HRegionInfo, List<ServerName>> cache = null;
  
    /**
     * Create a cache for region to list of servers
     * @param mins Number of mins to cache
     * @return A new Cache.
     */
    private LoadingCache<HRegionInfo, List<ServerName>> createCache(int mins) {
      return CacheBuilder.newBuilder().expireAfterAccess(mins, TimeUnit.MINUTES).build(loader);
    }
  
    public Configuration getConf() {
      return conf;
    }
  
    public void setConf(Configuration conf) {
      this.conf = conf;
      cache = createCache(conf.getInt("hbase.master.balancer.regionLocationCacheTime", 30));
    }
  
    public void setServices(MasterServices services) {
      this.services = services;
    }
  
    public void setClusterStatus(ClusterStatus status) {
      this.status = status;
   }
 
   protected List<ServerName> getTopBlockLocations(HRegionInfo region) {
     List<ServerName> servers = null;
     try {
       servers = cache.get(region);
     } catch (ExecutionException ex) {
       servers = new LinkedList<ServerName>();
     }
     return servers;
 
   }
 
   /**
    * Returns an ordered list of hosts that are hosting the blocks for this
    * region. The weight of each host is the sum of the block lengths of all
    * files on that host, so the first host in the list is the server which holds
    * the most bytes of the given region's HFiles.
    *
    * @param region region
    * @return ordered list of hosts holding blocks of the specified region
    */
   protected List<ServerName> internalGetTopBlockLocation(HRegionInfo region) {
     List<ServerName> topServerNames = null;
     try {
       HTableDescriptor tableDescriptor = getTableDescriptor(region.getTable());
       if (tableDescriptor != null) {
         HDFSBlocksDistribution blocksDistribution =
             HRegion.computeHDFSBlocksDistribution(getConf(), tableDescriptor, region);
         List<String> topHosts = blocksDistribution.getTopHosts();
         topServerNames = mapHostNameToServerName(topHosts);
       }
     } catch (IOException ioe) {
       LOG.debug("IOException during HDFSBlocksDistribution computation. for " + "region = "
           + region.getEncodedName(), ioe);
     }
 
     return topServerNames;
   }
 
   /**
    * return HTableDescriptor for a given tableName
    *
    * @param tableName the table name
    * @return HTableDescriptor
    * @throws IOException
    */
   protected HTableDescriptor getTableDescriptor(TableName tableName) throws IOException {
     HTableDescriptor tableDescriptor = null;
     try {
       if (this.services != null && this.services.getTableDescriptors() != null) {
         tableDescriptor = this.services.getTableDescriptors().get(tableName);
       }
     } catch (FileNotFoundException fnfe) {
       LOG.debug("FileNotFoundException during getTableDescriptors." + " Current table name = "
           + tableName, fnfe);
     }
 
     return tableDescriptor;
   }
 
   /**
    * Map hostname to ServerName, The output ServerName list will have the same
    * order as input hosts.
    *
    * @param hosts the list of hosts
    * @return ServerName list
    */
   protected List<ServerName> mapHostNameToServerName(List<String> hosts) {
     if (hosts == null || status == null) {
       return null;
     }
 
     List<ServerName> topServerNames = new ArrayList<ServerName>();
     Collection<ServerName> regionServers = status.getServers();
 
     // create a mapping from hostname to ServerName for fast lookup
     HashMap<String, List<ServerName>> hostToServerName = new HashMap<String, List<ServerName>>();
     for (ServerName sn : regionServers) {
       String host = sn.getHostname();
       if (!hostToServerName.containsKey(host)) {
         hostToServerName.put(host, new ArrayList<ServerName>());
       }
       hostToServerName.get(host).add(sn);
     }
 
     for (String host : hosts) {
       if (!hostToServerName.containsKey(host)) {
         continue;
       }
       for (ServerName sn : hostToServerName.get(host)) {
         // it is possible that HDFS is up ( thus host is valid ),
         // but RS is down ( thus sn is null )
         if (sn != null) {
           topServerNames.add(sn);
         }
       }
     }
     return topServerNames;
   }
 }