/*
    * ====================================================================
    * 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.util.Map;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.ConcurrentMap;
  
  import org.apache.http.annotation.Contract;
  import org.apache.http.annotation.ThreadingBehavior;
  
  /**
   * Implements a bounded failure cache. The oldest entries are discarded when
   * the maximum size is exceeded.
   *
   * @since 4.3
   */
  @Contract(threading = ThreadingBehavior.SAFE)
  public class DefaultFailureCache implements FailureCache {
  
      static final int DEFAULT_MAX_SIZE = 1000;
      static final int MAX_UPDATE_TRIES = 10;
  
      private final int maxSize;
      private final ConcurrentMap<String, FailureCacheValue> storage;
  
      /**
       * Create a new failure cache with the maximum size of
       * {@link #DEFAULT_MAX_SIZE}.
       */
      public DefaultFailureCache() {
          this(DEFAULT_MAX_SIZE);
      }
  
      /**
       * Creates a new failure cache with the specified maximum size.
       * @param maxSize the maximum number of entries the cache should store
       */
      public DefaultFailureCache(final int maxSize) {
          this.maxSize = maxSize;
          this.storage = new ConcurrentHashMap<String, FailureCacheValue>();
      }
  
      @Override
      public int getErrorCount(final String identifier) {
          if (identifier == null) {
              throw new IllegalArgumentException("identifier may not be null");
          }
          final FailureCacheValue storedErrorCode = storage.get(identifier);
          return storedErrorCode != null ? storedErrorCode.getErrorCount() : 0;
      }
  
      @Override
      public void resetErrorCount(final String identifier) {
          if (identifier == null) {
              throw new IllegalArgumentException("identifier may not be null");
          }
          storage.remove(identifier);
      }
  
      @Override
      public void increaseErrorCount(final String identifier) {
          if (identifier == null) {
              throw new IllegalArgumentException("identifier may not be null");
          }
          updateValue(identifier);
          removeOldestEntryIfMapSizeExceeded();
      }
  
      private void updateValue(final String identifier) {
          /**
           * Due to concurrency it is possible that someone else is modifying an
           * entry before we could write back our updated value. So we keep
           * trying until it is our turn.
           *
          * In case there is a lot of contention on that identifier, a thread
          * might starve. Thus it gives up after a certain number of failed
          * update tries.
          */
         for (int i = 0; i < MAX_UPDATE_TRIES; i++) {
             final FailureCacheValue oldValue = storage.get(identifier);
             if (oldValue == null) {
                 final FailureCacheValueailureCacheValue.html#FailureCacheValue">FailureCacheValue newValue = new FailureCacheValue(identifier, 1);
                 if (storage.putIfAbsent(identifier, newValue) == null) {
                     return;
                 }
             }
             else {
                 final int errorCount = oldValue.getErrorCount();
                 if (errorCount == Integer.MAX_VALUE) {
                     return;
                 }
                 final FailureCacheValueailureCacheValue.html#FailureCacheValue">FailureCacheValue newValue = new FailureCacheValue(identifier, errorCount + 1);
                 if (storage.replace(identifier, oldValue, newValue)) {
                     return;
                 }
             }
         }
     }
 
     private void removeOldestEntryIfMapSizeExceeded() {
         if (storage.size() > maxSize) {
             final FailureCacheValue valueWithOldestTimestamp = findValueWithOldestTimestamp();
             if (valueWithOldestTimestamp != null) {
                 storage.remove(valueWithOldestTimestamp.getKey(), valueWithOldestTimestamp);
             }
         }
     }
 
     private FailureCacheValue findValueWithOldestTimestamp() {
         long oldestTimestamp = Long.MAX_VALUE;
         FailureCacheValue oldestValue = null;
         for (final Map.Entry<String, FailureCacheValue> storageEntry : storage.entrySet()) {
             final FailureCacheValue value = storageEntry.getValue();
             final long creationTimeInNanos = value.getCreationTimeInNanos();
             if (creationTimeInNanos < oldestTimestamp) {
                 oldestTimestamp = creationTimeInNanos;
                 oldestValue = storageEntry.getValue();
             }
         }
         return oldestValue;
     }
 }