/*
    *    Copyright 2009-2021 the original author or authors.
    *
    *    Licensed 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.
   */
  package org.apache.ibatis.cache.decorators;
  
  import java.util.HashMap;
  import java.util.HashSet;
  import java.util.Map;
  import java.util.Set;
  
  import org.apache.ibatis.cache.Cache;
  import org.apache.ibatis.logging.Log;
  import org.apache.ibatis.logging.LogFactory;
  
  /**
   * The 2nd level cache transactional buffer.
   * <p>
   * This class holds all cache entries that are to be added to the 2nd level cache during a Session.
   * Entries are sent to the cache when commit is called or discarded if the Session is rolled back.
   * Blocking cache support has been added. Therefore any get() that returns a cache miss
   * will be followed by a put() so any lock associated with the key can be released.
   *
   * @author Clinton Begin
   * @author Eduardo Macarron
   */
  public class TransactionalCache implements Cache {
  
    private static final Log log = LogFactory.getLog(TransactionalCache.class);
  
    private final Cache delegate;
    private boolean clearOnCommit;
    private final Map<Object, Object> entriesToAddOnCommit;
    private final Set<Object> entriesMissedInCache;
  
    public TransactionalCache(Cache delegate) {
      this.delegate = delegate;
      this.clearOnCommit = false;
      this.entriesToAddOnCommit = new HashMap<>();
      this.entriesMissedInCache = new HashSet<>();
    }
  
    @Override
    public String getId() {
      return delegate.getId();
    }
  
    @Override
    public int getSize() {
      return delegate.getSize();
    }
  
    @Override
    public Object getObject(Object key) {
      // issue #116
      Object object = delegate.getObject(key);
      if (object == null) {
        entriesMissedInCache.add(key);
      }
      // issue #146
      if (clearOnCommit) {
        return null;
      } else {
        return object;
      }
    }
  
    @Override
    public void putObject(Object key, Object object) {
      entriesToAddOnCommit.put(key, object);
    }
  
    @Override
    public Object removeObject(Object key) {
      return null;
    }
  
    @Override
    public void clear() {
      clearOnCommit = true;
      entriesToAddOnCommit.clear();
    }
  
    public void commit() {
      if (clearOnCommit) {
        delegate.clear();
      }
      flushPendingEntries();
     reset();
   }
 
   public void rollback() {
     unlockMissedEntries();
     reset();
   }
 
   private void reset() {
     clearOnCommit = false;
     entriesToAddOnCommit.clear();
     entriesMissedInCache.clear();
   }
 
   private void flushPendingEntries() {
     for (Map.Entry<Object, Object> entry : entriesToAddOnCommit.entrySet()) {
       delegate.putObject(entry.getKey(), entry.getValue());
     }
     for (Object entry : entriesMissedInCache) {
       if (!entriesToAddOnCommit.containsKey(entry)) {
         delegate.putObject(entry, null);
       }
     }
   }
 
   private void unlockMissedEntries() {
     for (Object entry : entriesMissedInCache) {
       try {
         delegate.removeObject(entry);
       } catch (Exception e) {
         log.warn("Unexpected exception while notifying a rollback to the cache adapter. "
             + "Consider upgrading your cache adapter to the latest version. Cause: " + e);
       }
     }
   }
 
 }