/*
    * Copyright 2015 The Netty Project
    *
    * The Netty Project 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:
    *
    *   https://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 io.netty.channel.pool;
  
  import io.netty.util.concurrent.Future;
  import io.netty.util.concurrent.GlobalEventExecutor;
  import io.netty.util.concurrent.Promise;
  import io.netty.util.internal.ReadOnlyIterator;
  
  import java.io.Closeable;
  import java.util.Iterator;
  import java.util.Map.Entry;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.ConcurrentMap;
  
  import static io.netty.util.internal.ObjectUtil.checkNotNull;
  
  /**
   * A skeletal {@link ChannelPoolMap} implementation. To find the right {@link ChannelPool}
   * the {@link Object#hashCode()} and {@link Object#equals(Object)} is used.
   */
  public abstract class AbstractChannelPoolMap<K, P extends ChannelPool>
          implements ChannelPoolMap<K, P>, Iterable<Entry<K, P>>, Closeable {
      private final ConcurrentMap<K, P> map = new ConcurrentHashMap<>();
  
      @Override
      public final P get(K key) {
          P pool = map.get(checkNotNull(key, "key"));
          if (pool == null) {
              pool = newPool(key);
              P old = map.putIfAbsent(key, pool);
              if (old != null) {
                  // We need to destroy the newly created pool as we not use it.
                  poolCloseAsyncIfSupported(pool);
                  pool = old;
              }
          }
          return pool;
      }
      /**
       * Remove the {@link ChannelPool} from this {@link AbstractChannelPoolMap}. Returns {@code true} if removed,
       * {@code false} otherwise.
       *
       * If the removed pool extends {@link SimpleChannelPool} it will be closed asynchronously to avoid blocking in
       * this method.
       *
       * Please note that {@code null} keys are not allowed.
       */
      public final boolean remove(K key) {
          P pool =  map.remove(checkNotNull(key, "key"));
          if (pool != null) {
              poolCloseAsyncIfSupported(pool);
              return true;
          }
          return false;
      }
  
      /**
       * Remove the {@link ChannelPool} from this {@link AbstractChannelPoolMap}. Returns a future that comletes with a
       * {@code true} result if the pool has been removed by this call, otherwise the result is {@code false}.
       *
       * If the removed pool extends {@link SimpleChannelPool} it will be closed asynchronously to avoid blocking in
       * this method. The returned future will be completed once this asynchronous pool close operation completes.
       */
      private Future<Boolean> removeAsyncIfSupported(K key) {
          P pool =  map.remove(checkNotNull(key, "key"));
          if (pool != null) {
              final Promise<Boolean> removePromise = GlobalEventExecutor.INSTANCE.newPromise();
              poolCloseAsyncIfSupported(pool).addListener(future -> {
                  if (future.isSuccess()) {
                      removePromise.setSuccess(Boolean.TRUE);
                  } else {
                      removePromise.setFailure(future.cause());
                  }
              });
              return removePromise;
          }
          return GlobalEventExecutor.INSTANCE.newSucceededFuture(Boolean.FALSE);
      }
  
      /**
       * If the pool implementation supports asynchronous close, then use it to avoid a blocking close call in case
       * the ChannelPoolMap operations are called from an EventLoop.
       *
       * @param pool the ChannelPool to be closed
       */
     private static Future<Void> poolCloseAsyncIfSupported(ChannelPool pool) {
         if (pool instanceof SimpleChannelPool) {
             return ((SimpleChannelPool) pool).closeAsync();
         } else {
             try {
                 pool.close();
                 return GlobalEventExecutor.INSTANCE.newSucceededFuture(null);
             } catch (Exception e) {
                 return GlobalEventExecutor.INSTANCE.newFailedFuture(e);
             }
         }
     }
 
     @Override
     public final Iterator<Entry<K, P>> iterator() {
         return new ReadOnlyIterator<Entry<K, P>>(map.entrySet().iterator());
     }
 
     /**
      * Returns the number of {@link ChannelPool}s currently in this {@link AbstractChannelPoolMap}.
      */
     public final int size() {
         return map.size();
     }
 
     /**
      * Returns {@code true} if the {@link AbstractChannelPoolMap} is empty, otherwise {@code false}.
      */
     public final boolean isEmpty() {
         return map.isEmpty();
     }
 
     @Override
     public final boolean contains(K key) {
         return map.containsKey(checkNotNull(key, "key"));
     }
 
     /**
      * Called once a new {@link ChannelPool} needs to be created as non exists yet for the {@code key}.
      */
     protected abstract P newPool(K key);
 
     @Override
     public final void close() {
         for (K key: map.keySet()) {
             // Wait for remove to finish to ensure that resources are released before returning from close
             removeAsyncIfSupported(key).syncUninterruptibly();
         }
     }
 }