/**
    * 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.util.compaction;
  
  import com.google.common.base.Optional;
  import com.google.common.collect.Lists;
  import com.google.common.collect.Maps;
  import com.google.common.collect.Sets;
  import java.util.List;
  import java.util.Map;
  import java.util.Set;
  import java.util.concurrent.locks.ReadWriteLock;
  import java.util.concurrent.locks.ReentrantReadWriteLock;
  import org.apache.hadoop.hbase.ServerName;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  
  @InterfaceAudience.Private
  class ClusterCompactionQueues {
  
    private final Map<ServerName, List<MajorCompactionRequest>> compactionQueues;
    private final Set<ServerName> compactingServers;
    private final ReadWriteLock lock;
    private final int concurrentServers;
  
    ClusterCompactionQueues(int concurrentServers) {
      this.concurrentServers = concurrentServers;
  
      this.compactionQueues = Maps.newHashMap();
      this.lock = new ReentrantReadWriteLock();
      this.compactingServers = Sets.newHashSet();
    }
  
    void addToCompactionQueue(ServerName serverName, MajorCompactionRequest info) {
      this.lock.writeLock().lock();
      try {
        List<MajorCompactionRequest> result = this.compactionQueues.get(serverName);
        if (result == null) {
          result = Lists.newArrayList();
          compactionQueues.put(serverName, result);
        }
        result.add(info);
      } finally {
        this.lock.writeLock().unlock();
      }
    }
  
    boolean hasWorkItems() {
      lock.readLock().lock();
      try {
        for (List<MajorCompactionRequest> majorCompactionRequests : this.compactionQueues.values()) {
          if (!majorCompactionRequests.isEmpty()) {
            return true;
          }
        }
        return false;
      } finally {
        lock.readLock().unlock();
      }
    }
  
    int getCompactionRequestsLeftToFinish() {
      lock.readLock().lock();
      try {
        int size = 0;
        for (List<MajorCompactionRequest> queue : compactionQueues.values()) {
          size += queue.size();
        }
        return size;
      } finally {
        lock.readLock().unlock();
      }
    }
  
    List<MajorCompactionRequest> getQueue(ServerName serverName) {
      lock.readLock().lock();
      try {
        return compactionQueues.get(serverName);
      } finally {
        lock.readLock().unlock();
      }
    }
  
    MajorCompactionRequest reserveForCompaction(ServerName serverName) {
      lock.writeLock().lock();
     try {
       if (!compactionQueues.get(serverName).isEmpty()) {
         compactingServers.add(serverName);
         return compactionQueues.get(serverName).remove(0);
       }
       return null;
     } finally {
       lock.writeLock().unlock();
     }
   }
 
   void releaseCompaction(ServerName serverName) {
     lock.writeLock().lock();
     try {
       compactingServers.remove(serverName);
     } finally {
       lock.writeLock().unlock();
     }
   }
 
   boolean atCapacity() {
     lock.readLock().lock();
     try {
       return compactingServers.size() >= concurrentServers;
     } finally {
       lock.readLock().unlock();
     }
   }
 
   Optional<ServerName> getLargestQueueFromServersNotCompacting() {
     lock.readLock().lock();
     try {
       Sets.SetView<ServerName> difference =
           Sets.difference(compactionQueues.keySet(), compactingServers);
       ServerName serverName = null;
       int maxItems = 0;
       for (ServerName server : difference) {
         if (compactionQueues.get(server).size() > maxItems) {
           maxItems = compactionQueues.get(server).size();
           serverName = server;
         }
       }
       return Optional.fromNullable(serverName);
     } finally {
       lock.readLock().unlock();
     }
   }
 }