/*
    * ====================================================================
    * 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.
   * ====================================================================
   *
   * This software consists of voluntary contributions made by many
   * individuals on behalf of the Apache Software Foundation.  For more
   * information on the Apache Software Foundation, please see
   * <http://www.apache.org/>.
   *
   */
  package org.apache.hc.client5.http.impl.cache.memcached;
  
  import java.io.IOException;
  import java.net.InetSocketAddress;
  import java.util.Collection;
  import java.util.HashMap;
  import java.util.Map;
  import java.util.concurrent.CancellationException;
  import java.util.concurrent.ExecutionException;
  
  import org.apache.hc.client5.http.cache.HttpCacheEntrySerializer;
  import org.apache.hc.client5.http.cache.ResourceIOException;
  import org.apache.hc.client5.http.impl.Operations;
  import org.apache.hc.client5.http.impl.cache.AbstractBinaryAsyncCacheStorage;
  import org.apache.hc.client5.http.impl.cache.CacheConfig;
  import org.apache.hc.client5.http.impl.cache.HttpByteArrayCacheEntrySerializer;
  import org.apache.hc.core5.concurrent.Cancellable;
  import org.apache.hc.core5.concurrent.FutureCallback;
  import org.apache.hc.core5.util.Args;
  
  import net.spy.memcached.CASResponse;
  import net.spy.memcached.CASValue;
  import net.spy.memcached.MemcachedClient;
  import net.spy.memcached.internal.BulkFuture;
  import net.spy.memcached.internal.GetFuture;
  import net.spy.memcached.internal.OperationFuture;
  
  /**
   * <p>
   * This class is a storage backend that uses an external <i>memcached</i>
   * for storing cached origin responses. This storage option provides a
   * couple of interesting advantages over the default in-memory storage
   * backend:
   * </p>
   * <ol>
   * <li>in-memory cached objects can survive an application restart since
   * they are held in a separate process</li>
   * <li>it becomes possible for several cooperating applications to share
   * a large <i>memcached</i> farm together</li>
   * </ol>
   * <p>
   * Note that in a shared memcached pool setting you may wish to make use
   * of the Ketama consistent hashing algorithm to reduce the number of
   * cache misses that might result if one of the memcached cluster members
   * fails (see the <a href="http://dustin.github.com/java-memcached-client/apidocs/net/spy/memcached/KetamaConnectionFactory.html">
   * KetamaConnectionFactory</a>).
   * </p>
   * <p>
   * Because memcached places limits on the size of its keys, we need to
   * introduce a key hashing scheme to map the annotated URLs the higher-level
   * caching HTTP client wants to use as keys onto ones that are suitable
   * for use with memcached. Please see {@link KeyHashingScheme} if you would
   * like to use something other than the provided {@link SHA256KeyHashingScheme}.
   * </p>
   *
   * <p>
   * Please refer to the <a href="http://code.google.com/p/memcached/wiki/NewStart">
   * memcached documentation</a> and in particular to the documentation for
   * the <a href="http://code.google.com/p/spymemcached/">spymemcached
   * documentation</a> for details about how to set up and configure memcached
   * and the Java client used here, respectively.
   * </p>
   *
   * @since 5.0
   */
  public class MemcachedHttpAsyncCacheStorage extends AbstractBinaryAsyncCacheStorage<CASValue<Object>> {
  
      private final MemcachedClient client;
      private final KeyHashingScheme keyHashingScheme;
  
      /**
       * Create a storage backend talking to a <i>memcached</i> instance
       * listening on the specified host and port. This is useful if you
      * just have a single local memcached instance running on the same
      * machine as your application, for example.
      * @param address where the <i>memcached</i> daemon is running
      * @throws IOException in case of an error
      */
     public MemcachedHttpAsyncCacheStorage(final InetSocketAddress address) throws IOException {
         this(new MemcachedClient(address));
     }
 
     /**
      * Create a storage backend using the pre-configured given
      * <i>memcached</i> client.
      * @param cache client to use for communicating with <i>memcached</i>
      */
     public MemcachedHttpAsyncCacheStorage(final MemcachedClient cache) {
         this(cache, CacheConfig.DEFAULT, HttpByteArrayCacheEntrySerializer.INSTANCE, SHA256KeyHashingScheme.INSTANCE);
     }
 
     /**
      * Create a storage backend using the given <i>memcached</i> client and
      * applying the given cache configuration, serialization, and hashing
      * mechanisms.
      * @param client how to talk to <i>memcached</i>
      * @param config apply HTTP cache-related options
      * @param serializer alternative serialization mechanism
      * @param keyHashingScheme how to map higher-level logical "storage keys"
      *   onto "cache keys" suitable for use with memcached
      */
     public MemcachedHttpAsyncCacheStorage(
             final MemcachedClient client,
             final CacheConfig config,
             final HttpCacheEntrySerializer<byte[]> serializer,
             final KeyHashingScheme keyHashingScheme) {
         super((config != null ? config : CacheConfig.DEFAULT).getMaxUpdateRetries(),
                 serializer != null ? serializer : HttpByteArrayCacheEntrySerializer.INSTANCE);
         this.client = Args.notNull(client, "Memcached client");
         this.keyHashingScheme = keyHashingScheme;
     }
 
     @Override
     protected String digestToStorageKey(final String key) {
         return keyHashingScheme.hash(key);
     }
 
     private byte[] castAsByteArray(final Object storageObject) throws ResourceIOException {
         if (storageObject == null) {
             return null;
         }
         if (storageObject instanceof byte[]) {
             return (byte[]) storageObject;
         }
         throw new ResourceIOException("Unexpected cache content: " + storageObject.getClass());
     }
 
     @Override
     protected byte[] getStorageObject(final CASValue<Object> casValue) throws ResourceIOException {
         return castAsByteArray(casValue.getValue());
     }
 
     private <T> Cancellable operation(final OperationFuture<T> operationFuture, final FutureCallback<T> callback) {
         operationFuture.addListener(future -> {
             try {
                 callback.completed(operationFuture.get());
             } catch (final ExecutionException ex) {
                 if (ex.getCause() instanceof Exception) {
                     if (ex.getCause() instanceof CancellationException) {
                         callback.failed(new MemcachedOperationCancellationException(ex.getCause()));
                     } else {
                         callback.failed((Exception) ex.getCause());
                     }
                 } else {
                     callback.failed(ex);
                 }
             }
         });
         return Operations.cancellable(operationFuture);
     }
 
     @Override
     protected Cancellable store(final String storageKey, final byte[] storageObject, final FutureCallback<Boolean> callback) {
         return operation(client.set(storageKey, 0, storageObject), callback);
     }
 
     @Override
     protected Cancellable restore(final String storageKey, final FutureCallback<byte[]> callback) {
         final GetFuture<Object> getFuture = client.asyncGet(storageKey);
         getFuture.addListener(future -> {
             try {
                 callback.completed(castAsByteArray(getFuture.get()));
             } catch (final ExecutionException ex) {
                 if (ex.getCause() instanceof Exception) {
                     if (ex.getCause() instanceof CancellationException) {
                         callback.failed(new MemcachedOperationCancellationException(ex.getCause()));
                     } else {
                         callback.failed((Exception) ex.getCause());
                     }
                 } else {
                     callback.failed(ex);
                 }
             }
         });
         return Operations.cancellable(getFuture);
     }
 
     @Override
     protected Cancellable getForUpdateCAS(final String storageKey, final FutureCallback<CASValue<Object>> callback) {
         return operation(client.asyncGets(storageKey), callback);
     }
 
     @Override
     protected Cancellable updateCAS(
             final String storageKey, final CASValue<Object> casValue, final byte[] storageObject, final FutureCallback<Boolean> callback) {
         return operation(client.asyncCAS(storageKey, casValue.getCas(), storageObject), new FutureCallback<CASResponse>() {
 
             @Override
             public void completed(final CASResponse result) {
                 callback.completed(result == CASResponse.OK);
             }
 
             @Override
             public void failed(final Exception ex) {
                 callback.failed(ex);
             }
 
             @Override
             public void cancelled() {
                 callback.cancelled();
             }
 
         });
     }
 
     @Override
     protected Cancellable delete(final String storageKey, final FutureCallback<Boolean> callback) {
         return operation(client.delete(storageKey), callback);
     }
 
     @Override
     protected Cancellable bulkRestore(final Collection<String> storageKeys, final FutureCallback<Map<String, byte[]>> callback) {
         final BulkFuture<Map<String, Object>> future = client.asyncGetBulk(storageKeys);
         future.addListener(future1 -> {
             final Map<String, ?> storageObjectMap = future1.get();
             final Map<String, byte[]> resultMap = new HashMap<>(storageObjectMap.size());
             for (final Map.Entry<String, ?> resultEntry: storageObjectMap.entrySet()) {
                 resultMap.put(resultEntry.getKey(), castAsByteArray(resultEntry.getValue()));
             }
             callback.completed(resultMap);
         });
         return Operations.cancellable(future);
     }
 
 }