/*
    * ====================================================================
    * 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;
  
  import java.io.Closeable;
  import java.lang.ref.ReferenceQueue;
  import java.util.Collection;
  import java.util.HashMap;
  import java.util.HashSet;
  import java.util.Map;
  import java.util.Set;
  import java.util.concurrent.atomic.AtomicBoolean;
  
  import org.apache.hc.client5.http.cache.HttpCacheCASOperation;
  import org.apache.hc.client5.http.cache.HttpCacheEntry;
  import org.apache.hc.client5.http.cache.HttpCacheStorage;
  import org.apache.hc.client5.http.cache.Resource;
  import org.apache.hc.client5.http.cache.ResourceIOException;
  import org.apache.hc.core5.annotation.Contract;
  import org.apache.hc.core5.annotation.ThreadingBehavior;
  import org.apache.hc.core5.util.Args;
  
  /**
   * <p>
   * {@link HttpCacheStorage} implementation capable of deallocating resources associated with
   * the cache entries.
   * <p>
   * This cache keeps track of cache entries using
   * {@link java.lang.ref.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.
   * </p>
   * <p>
   * This {@link HttpCacheStorage} implementation is intended for use with {@link FileResource}
   * and similar.
   * </p>
   * <p>
   * Compatibility note. Prior to version 4.4 this storage implementation used to dispose of
   * all resource entries upon {@link #close()}. As of version 4.4 the {@link #close()} method
   * disposes only of those resources that have been explicitly removed from the cache with
   * {@link #removeEntry(String)} method.
   * </p>
   * <p>
   * The {@link #shutdown()} ()} method can still be used to shut down the storage and dispose of
   * all resources currently managed by it.
   * </p>
   *
   * @since 4.1
   */
  @Contract(threading = ThreadingBehavior.SAFE)
  public class ManagedHttpCacheStorage implements HttpCacheStorage, Closeable {
  
      private final CacheMap entries;
      private final ReferenceQueue<HttpCacheEntry> morque;
      private final Set<ResourceReference> resources;
      private final AtomicBoolean active;
  
      public ManagedHttpCacheStorage(final CacheConfig config) {
          super();
          this.entries = new CacheMap(config.getMaxCacheEntries());
          this.morque = new ReferenceQueue<>();
          this.resources = new HashSet<>();
          this.active = new AtomicBoolean(true);
      }
  
      private void ensureValidState() {
          if (!isActive()) {
              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);
         }
     }
 
     @Override
     public void putEntry(final String url, final HttpCacheEntry entry) throws ResourceIOException {
         Args.notNull(url, "URL");
         Args.notNull(entry, "Cache entry");
         ensureValidState();
         synchronized (this) {
             this.entries.put(url, entry);
             keepResourceReference(entry);
         }
     }
 
     @Override
     public HttpCacheEntry getEntry(final String url) throws ResourceIOException {
         Args.notNull(url, "URL");
         ensureValidState();
         synchronized (this) {
             return this.entries.get(url);
         }
     }
 
     @Override
     public void removeEntry(final String url) throws ResourceIOException {
         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);
         }
     }
 
     @Override
     public void updateEntry(
             final String url,
             final HttpCacheCASOperation casOperation) throws ResourceIOException {
         Args.notNull(url, "URL");
         Args.notNull(casOperation, "CAS operation");
         ensureValidState();
         synchronized (this) {
             final HttpCacheEntry existing = this.entries.get(url);
             final HttpCacheEntry updated = casOperation.execute(existing);
             this.entries.put(url, updated);
             if (existing != updated) {
                 keepResourceReference(updated);
             }
         }
     }
 
     @Override
     public Map<String, HttpCacheEntry> getEntries(final Collection<String> keys) throws ResourceIOException {
         Args.notNull(keys, "Key");
         final Map<String, HttpCacheEntry> resultMap = new HashMap<>(keys.size());
         for (final String key: keys) {
             final HttpCacheEntry entry = getEntry(key);
             if (entry != null) {
                 resultMap.put(key, entry);
             }
         }
         return resultMap;
     }
 
     public void cleanResources() {
         if (isActive()) {
             ResourceReference ref;
             while ((ref = (ResourceReference) this.morque.poll()) != null) {
                 synchronized (this) {
                     this.resources.remove(ref);
                 }
                 ref.getResource().dispose();
             }
         }
     }
 
     public void shutdown() {
         if (compareAndSet()) {
             synchronized (this) {
                 this.entries.clear();
                 for (final ResourceReference ref: this.resources) {
                     ref.getResource().dispose();
                 }
                 this.resources.clear();
                 while (this.morque.poll() != null) {
                 }
             }
         }
     }
 
     @Override
     public void close() {
         if (compareAndSet()) {
             synchronized (this) {
                 ResourceReference ref;
                 while ((ref = (ResourceReference) this.morque.poll()) != null) {
                     this.resources.remove(ref);
                     ref.getResource().dispose();
                 }
             }
         }
     }
 
     /**
      * Check if the cache is still active and has not shut down.
      *
      * @return {@code true} if the cache is active, otherwise return {@code false}.
      * @since 5.2
      */
     public boolean isActive() {
         return active.get();
     }
 
     private boolean compareAndSet(){
         return this.active.compareAndSet(true, false);
     }
 }