/*

  * Copyright 2002-2004 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.

  * 

  * Code obtained from http://opensource.atlassian.com/confluence/spring/display/DISC/Caching+the+result+of+methods+using+Spring+and+EHCache

  * and modified for use within Kuali

  */

 // begin Kuali Foundation modification

 package org.kuali.rice.kns.util.cache;

 // Kuali Foundation modification: changed some imports

 import java.io.Serializable;

 import org.aopalliance.intercept.MethodInterceptor;

 import org.aopalliance.intercept.MethodInvocation;

 import org.apache.commons.logging.Log;

 import org.apache.commons.logging.LogFactory;

 import org.springframework.beans.factory.InitializingBean;

 import org.springframework.util.Assert;

 import com.opensymphony.oscache.base.Cache;

 import com.opensymphony.oscache.base.NeedsRefreshException;

 /**

  * begin Kuali Foundation modification

  * This class implements org.aopalliance.intercept.MethodInterceptor. This interceptor builds the cache key for the method and

  * checks if an earlier result was cached with that key. If so, the cached result is returned; otherwise, the intercepted method is

  * called and the result cached for future use.

  * end Kuali Foundation modification

  * 

  * @author Kuali Rice Team (rice.collab@kuali.org)

  * @since 2004.10.07

  */

 public class MethodCacheInterceptor implements MethodInterceptor, InitializingBean {

     private static final Log LOG = LogFactory.getLog(MethodCacheInterceptor.class);

     private Cache cache;

     // begin Kuali Foundation modification

     private int expirationTimeInSeconds = 1000;

     private long maxEntrySizeInBytes = 0;

     // end Kuali Foundation modification

     /**

      * begin Kuali Foundation modification

      * @param cache name of cache to be used

      * end Kuali Foundation modification

      */

     public void setCache(Cache cache) {

         this.cache = cache;

     }

     // begin Kuali Foundation modification

     /**

      * Entries older than this will have their contents replaced by the return value from a call to the appropriate method

      * 

      * @param expirationTimeInSeconds

      */

     public void setExpirationTimeInSeconds(int expirationTimeInSeconds) {

         this.expirationTimeInSeconds = expirationTimeInSeconds;

     }

     /**

      * Entries whose size is larger than the current value will not be cached. If the maxEntrySizeInBytes <= 0, no size limit will

      * be applied.

      * 

      * @param maxEntrySizeInBytes

      */

     public void setMaxEntrySizeInBytes(long maxEntrySizeInBytes) {

         this.maxEntrySizeInBytes = maxEntrySizeInBytes;

     }

     // end Kuali Foundation modification

     /**

      * Checks if required attributes are provided.

      * 

      * begin Kuali Foundation modification

      * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet()

      * end Kuali Foundation modification

      */

     public void afterPropertiesSet() throws Exception {

         Assert.notNull(cache, "A cache is required. Use setCache(Cache) to provide one.");

     }

     /**

      * begin Kuali Foundation modification

      * Caches method results, if possible.

      * <p>

      * Results must be Serializable to be cached. Method with unSerializable results will never have their results cached, and will

      * log error messages complaining about that fact.

      * 

      * @see org.aopalliance.intercept.MethodInterceptor#invoke(org.aopalliance.intercept.MethodInvocation)

      * end Kuali Foundation modification

      */

     public Object invoke(MethodInvocation invocation) throws Throwable {

         // begin Kuali Foundation modification

         boolean cancelUpdate = true;

         Object methodResult = null;

         String cacheKey = buildCacheKey(invocation);

         // lookup result in cache

         if (LOG.isTraceEnabled()) {

             LOG.trace("looking for method result for invocation '" + cacheKey + "'");

         }

         try {

             CopiedObject cachedEntry = (CopiedObject) cache.getFromCache(cacheKey, expirationTimeInSeconds);

             if (LOG.isDebugEnabled()) {

                 LOG.debug("using cached result deepCopy for invocation '" + cacheKey + "'");

             }

             // really expensive hack to try to keep from returning direct references to modifiable cached values

             // because if you return a direct reference to a cached value to someone, and it is of a mutable type, any changes they

             // make to what seems like "their copy" will also be reflected in the cached value, which is a Really Bad Thing

             methodResult = cachedEntry.getContent(); // getContent returns a copy

             cancelUpdate = false;

         }

         catch (NeedsRefreshException e) {

             // call intercepted method

             try {

                 if (LOG.isTraceEnabled()) {

                     LOG.trace("calling intercepted method for invocation '" + cacheKey + "'");

                 }

                 methodResult = invocation.proceed();

             }

             catch (Exception invocationException) {

                 LOG.warn("unable to cache methodResult: caught exception invoking intercepted method: '" + invocationException);

                 throw invocationException;

             }

             // cache method result, if possible

             // there's no way to tell whether a result is cacheable until after the method gets called,

             // since methods may hand back a Serializable object even if the method is declared to return

             // a more general nonSerializable type (e.g. List is not Serializable, but if the method

             // actually returns ArrayList instances, they are)

             //

             // nulls are a special case, since isAssignableFrom will never return true, yet they are

             // Serializable (at least for this kind of use)

             //

             // caching a deepCopy of the methodResult to prevent someone changing the cached value directly,

             // through a shared reference

             if ((methodResult == null) || (Serializable.class.isAssignableFrom(methodResult.getClass()))) {

                 try {

                     CopiedObject oldContent = (CopiedObject) e.getCacheContent();

                     CopiedObject newContent = oldContent;

                     if ( newContent == null ) {

                     newContent = new CopiedObject();

                     }

                     newContent.setContent((Serializable)methodResult);

                     // if no size limit, or under size limit, add to cache

                     if ((maxEntrySizeInBytes <= 0) || (newContent.getSize() <= maxEntrySizeInBytes)) {

                         if (LOG.isTraceEnabled()) {

                             LOG.trace("caching results for invocation '" + cacheKey + "'");

                         }

                         cache.putInCache(cacheKey, newContent);

                         // adding, not updating

                         cancelUpdate = false;

                     }

                     else {

                         if (LOG.isTraceEnabled()) {

                             LOG.trace("rejecting oversized methodResult (" + newContent.getSize() + " bytes) for invocation '" + cacheKey + "'");

                         }

                         // size limit exceeded: remove existing (expired) cache entry, if any

                         if (oldContent != null) {

                             if (LOG.isTraceEnabled()) {

                                 LOG.trace("flushing previous value for oversized invocation '" + cacheKey + "'");

                             }

                             cache.cancelUpdate(cacheKey);

                             cache.flushEntry(cacheKey);

                             // already canceled the update, don't need to cancel the update again

                             cancelUpdate = false;

                         }

                     }

                 }

                 catch (Exception cacheException) {

                     LOG.error("unable to cache methodResult: caught exception invoking putInCache: '" + cacheException);

                     throw cacheException;

                 }

             }

             else {

                 LOG.error("unable to cache nonSerializable result type for invocation '" + cacheKey + "'");

             }

         }

         finally {

             // it is imperative that you call cancelUpdate if you aren't going to update the cache entry

             if (cancelUpdate) {

                 cache.cancelUpdate(cacheKey);

             }

         }

         return methodResult;

         // end Kuali Foundation modification

     }

     // begin Kuali Foundation modification

     /**

      * @param invocation MethodInvocation being handled

      * @return cache key: className.methodName(paramClass=argValue[,paramClass=argValue...])

      */

     private String buildCacheKey(MethodInvocation invocation) {

         return buildCacheKey(invocation.getStaticPart().toString(), invocation.getArguments());

     }

     /**

      * @param className

      * @param methodName

      * @param paramTypes

      * @param argValues

      * @return cache key: className.methodName(paramClass=argValue[,paramClass=argValue...])

      */

     public String buildCacheKey(String methodSignature, Object[] argValues) {

         StringBuffer cacheKey = new StringBuffer(methodSignature);

         cacheKey.append(": ");

         if (argValues != null) {

             for (int i = 0; i < argValues.length; i++) {

                 if (i > 0) {

                     cacheKey.append(",");

                 }

                 // handle weird cache bug:

                 // if you call a one-arg method foo with a null arg i.e. foo(null),

                 // and then call it with an argument whose toString evaluates to "null",

                 // OSCache gets stuck in an infinite wait() call because it somehow thinks

                 // another thread is already updating this cache entry

                 //

                 // workaround: change so that args which are actually null literal have

                 // some weird, unlikely-to-be-encountered String representation

                 if (argValues[i] == null) {

                     cacheKey.append("<literal null>");

                 }

                 else {

                     cacheKey.append(argValues[i]);

                 }

             }

         }

         return cacheKey.toString();

     }

     /**

      * @param key

      * @return true if the cache contains an entry with the given key

      */

     public boolean containsCacheKey(String key) {

         boolean contains = false;

         try {

             cache.getFromCache(key);

             contains = true;

         }

         catch (NeedsRefreshException e) {

             // it is imperative that you call cancelUpdate if you aren't going to update the cache entry that caused the

             // NeedsRefreshException above

             cache.cancelUpdate(key);

             contains = false;

         }

         return contains;

     }

     /** 

      * Removes a method cache if one exists for the given key.

      * @param cacheKey - key for method signature and parameters - see buildCacheKey

      */

     public void removeCacheKey(String cacheKey) {

             if (!containsCacheKey(cacheKey)) {

                     return;

               }

                 if ( LOG.isDebugEnabled() ) {

                         LOG.debug("removing method cache for key: " + cacheKey);

                 }

                 cache.cancelUpdate(cacheKey);

                 cache.flushEntry(cacheKey);

     }

     // Kuali Foundation modification: removed getCacheKey(String, String, Object[])

     // end Kuali Foundation modification

 }