/**
    *
    * 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.wal;
  
  import java.io.IOException;
  import java.util.List;
  import java.util.concurrent.atomic.AtomicInteger;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.conf.Configuration;
  import org.apache.hadoop.hbase.regionserver.wal.FSHLog;
  // imports for classes still in regionserver.wal
  import org.apache.hadoop.hbase.regionserver.wal.WALActionsListener;
  
  /**
   * A WAL Provider that pre-creates N WALProviders and then limits our grouping strategy to them.
   * Control the number of delegate providers via "hbase.wal.regiongrouping.numgroups." Control
   * the choice of delegate provider implementation and the grouping strategy the same as
   * {@link RegionGroupingProvider}.
   */
  @InterfaceAudience.Private
  public class BoundedRegionGroupingProvider extends RegionGroupingProvider {
    private static final Log LOG = LogFactory.getLog(BoundedRegionGroupingProvider.class);
  
    static final String NUM_REGION_GROUPS = "hbase.wal.regiongrouping.numgroups";
    static final int DEFAULT_NUM_REGION_GROUPS = 2;
    private WALProvider[] delegates;
    private AtomicInteger counter = new AtomicInteger(0);
  
    @Override
    public void init(final WALFactory factory, final Configuration conf,
        final List<WALActionsListener> listeners, final String providerId) throws IOException {
      super.init(factory, conf, listeners, providerId);
      // no need to check for and close down old providers; our parent class will throw on re-invoke
      delegates = new WALProvider[Math.max(1, conf.getInt(NUM_REGION_GROUPS,
          DEFAULT_NUM_REGION_GROUPS))];
      for (int i = 0; i < delegates.length; i++) {
        delegates[i] = factory.getProvider(DELEGATE_PROVIDER, DEFAULT_DELEGATE_PROVIDER, listeners,
            providerId + i);
      }
      LOG.info("Configured to run with " + delegates.length + " delegate WAL providers.");
    }
  
    @Override
    WALProvider populateCache(final byte[] group) {
      final WALProvider temp = delegates[counter.getAndIncrement() % delegates.length];
      final WALProvider extant = cached.putIfAbsent(group, temp);
      // if someone else beat us to initializing, just take what they set.
      // note that in such a case we skew load away from the provider we picked at first
      return extant == null ? temp : extant;
    }
  
    @Override
    public void shutdown() throws IOException {
      // save the last exception and rethrow
      IOException failure = null;
      for (WALProvider provider : delegates) {
        try {
          provider.shutdown();
        } catch (IOException exception) {
          LOG.error("Problem shutting down provider '" + provider + "': " + exception.getMessage());
          LOG.debug("Details of problem shutting down provider '" + provider + "'", exception);
          failure = exception;
        }
      }
      if (failure != null) {
        throw failure;
      }
    }
  
    @Override
    public void close() throws IOException {
      // save the last exception and rethrow
      IOException failure = null;
      for (WALProvider provider : delegates) {
        try {
          provider.close();
        } catch (IOException exception) {
          LOG.error("Problem closing provider '" + provider + "': " + exception.getMessage());
          LOG.debug("Details of problem shutting down provider '" + provider + "'", exception);
          failure = exception;
       }
     }
     if (failure != null) {
       throw failure;
     }
   }
 
   /**
    * iff the given WALFactory is using the BoundedRegionGroupingProvider for meta and/or non-meta,
    * count the number of files (rolled and active). if either of them isn't, count 0
    * for that provider.
    * @param walFactory may not be null.
    */
   public static long getNumLogFiles(WALFactory walFactory) {
     long result = 0;
     if (walFactory.provider instanceof BoundedRegionGroupingProvider) {
       BoundedRegionGroupingProvider groupProviders =
           (BoundedRegionGroupingProvider)walFactory.provider;
       for (int i = 0; i < groupProviders.delegates.length; i++) {
         result +=
             ((FSHLog)((DefaultWALProvider)(groupProviders.delegates[i])).log).getNumLogFiles();
       }
     }
     WALProvider meta = walFactory.metaProvider.get();
     if (meta instanceof BoundedRegionGroupingProvider) {
       for (int i = 0; i < ((BoundedRegionGroupingProvider)meta).delegates.length; i++) {
         result += ((FSHLog)
             ((DefaultWALProvider)(((BoundedRegionGroupingProvider)meta).delegates[i])).log)
             .getNumLogFiles();      }
     }
     return result;
   }
 
   /**
    * iff the given WALFactory is using the BoundedRegionGroupingProvider for meta and/or non-meta,
    * count the size of files (rolled and active). if either of them isn't, count 0
    * for that provider.
    * @param walFactory may not be null.
    */
   public static long getLogFileSize(WALFactory walFactory) {
     long result = 0;
     if (walFactory.provider instanceof BoundedRegionGroupingProvider) {
       BoundedRegionGroupingProvider groupProviders =
           (BoundedRegionGroupingProvider)walFactory.provider;
       for (int i = 0; i < groupProviders.delegates.length; i++) {
         result +=
             ((FSHLog)((DefaultWALProvider)(groupProviders.delegates[i])).log).getLogFileSize();
       }
     }
     WALProvider meta = walFactory.metaProvider.get();
     if (meta instanceof BoundedRegionGroupingProvider) {
       for (int i = 0; i < ((BoundedRegionGroupingProvider)meta).delegates.length; i++) {
         result += ((FSHLog)
             ((DefaultWALProvider)(((BoundedRegionGroupingProvider)meta).delegates[i])).log)
             .getLogFileSize();
       }
     }
     return result;
   }
 }