/*
    * ====================================================================
    * 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.http.impl.client.cache;
  
  import java.io.Closeable;
  import java.io.IOException;
  import java.lang.ref.PhantomReference;
  import java.lang.ref.ReferenceQueue;
  import java.util.HashSet;
  import java.util.Set;
  
  import org.apache.http.annotation.ThreadSafe;
  import org.apache.http.client.cache.HttpCacheEntry;
  import org.apache.http.client.cache.HttpCacheStorage;
  import org.apache.http.client.cache.HttpCacheUpdateCallback;
  import org.apache.http.client.cache.Resource;
  import org.apache.http.util.Args;
  
  /**
   * {@link HttpCacheStorage} implementation capable of deallocating resources associated with
   * the cache entries. This cache keeps track of cache entries using {@link PhantomReference}
   * and maintains a collection of all resources that are no longer in use. The cache, however,
   * does not automatically deallocates associated resources by invoking {@link Resource#dispose()}
   * method. The consumer MUST periodically call {@link #cleanResources()} method to trigger
   * resource deallocation. The cache can be permanently shut down using {@link #shutdown()}
   * method. All resources associated with the entries used by the cache will be deallocated.
   *
   * This {@link HttpCacheStorage} implementation is intended for use with {@link FileResource}
   * and similar.
   *
   * @since 4.1
   */
  @ThreadSafe
  public class ManagedHttpCacheStorage implements HttpCacheStorage, Closeable {
  
      private final CacheMap entries;
      private final ReferenceQueue<HttpCacheEntry> morque;
      private final Set<ResourceReference> resources;
  
      private volatile boolean shutdown;
  
      public ManagedHttpCacheStorage(final CacheConfig config) {
          super();
          this.entries = new CacheMap(config.getMaxCacheEntries());
          this.morque = new ReferenceQueue<HttpCacheEntry>();
          this.resources = new HashSet<ResourceReference>();
      }
  
      private void ensureValidState() throws IllegalStateException {
          if (this.shutdown) {
              throw new IllegalStateException("Cache has been shut down");
          }
      }
  
      private void keepResourceReference(final HttpCacheEntry entry) {
          final Resource resource = entry.getResource();
          if (resource != null) {
              // Must deallocate the resource when the entry is no longer in used
              final ResourceReference ref = new ResourceReference(entry, this.morque);
              this.resources.add(ref);
          }
      }
  
      public void putEntry(final String url, final HttpCacheEntry entry) throws IOException {
          Args.notNull(url, "URL");
          Args.notNull(entry, "Cache entry");
          ensureValidState();
          synchronized (this) {
              this.entries.put(url, entry);
              keepResourceReference(entry);
          }
      }
  
      public HttpCacheEntry getEntry(final String url) throws IOException {
          Args.notNull(url, "URL");
         ensureValidState();
         synchronized (this) {
             return this.entries.get(url);
         }
     }
 
     public void removeEntry(final String url) throws IOException {
         Args.notNull(url, "URL");
         ensureValidState();
         synchronized (this) {
             // Cannot deallocate the associated resources immediately as the
             // cache entry may still be in use
             this.entries.remove(url);
         }
     }
 
     public void updateEntry(
             final String url,
             final HttpCacheUpdateCallback callback) throws IOException {
         Args.notNull(url, "URL");
         Args.notNull(callback, "Callback");
         ensureValidState();
         synchronized (this) {
             final HttpCacheEntry existing = this.entries.get(url);
             final HttpCacheEntry updated = callback.update(existing);
             this.entries.put(url, updated);
             if (existing != updated) {
                 keepResourceReference(updated);
             }
         }
     }
 
     public void cleanResources() {
         if (this.shutdown) {
             return;
         }
         ResourceReference ref;
         while ((ref = (ResourceReference) this.morque.poll()) != null) {
             synchronized (this) {
                 this.resources.remove(ref);
             }
             ref.getResource().dispose();
         }
     }
 
     public void shutdown() {
         if (this.shutdown) {
             return;
         }
         this.shutdown = true;
         synchronized (this) {
             this.entries.clear();
             for (final ResourceReference ref: this.resources) {
                 ref.getResource().dispose();
             }
             this.resources.clear();
             while (this.morque.poll() != null) {
             }
         }
     }
 
     public void close() {
         shutdown();
     }
 
 }