// Copyright 2007, 2008 The Apache Software Foundation

 //

 // 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.tapestry5.internal.services;

 import static org.apache.tapestry5.ioc.internal.util.CollectionFactory.newList;

 import static org.apache.tapestry5.ioc.internal.util.Defense.notBlank;

 import org.apache.tapestry5.services.PersistentFieldChange;

 import org.apache.tapestry5.services.PersistentFieldStrategy;

 import org.apache.tapestry5.services.Request;

 import org.apache.tapestry5.services.Session;

 import java.util.Collection;

 import java.util.Collections;

 import java.util.List;

 /**

  * Base class for strategies that store their values as keys in the session. Implements a uniform format for the keys,

  * based on a prefix to identify the particular strategy.

  */

 public abstract class AbstractSessionPersistentFieldStrategy implements PersistentFieldStrategy

 {

     private final String prefix;

     private final Request request;

     protected AbstractSessionPersistentFieldStrategy(String prefix, Request request)

     {

         this.prefix = prefix;

         this.request = request;

     }

     public final Collection<PersistentFieldChange> gatherFieldChanges(String pageName)

     {

         Session session = request.getSession(false);

         if (session == null) return Collections.emptyList();

         List<PersistentFieldChange> result = newList();

         String fullPrefix = prefix + pageName + ":";

         for (String name : session.getAttributeNames(fullPrefix))

         {

             Object persistedValue = session.getAttribute(name);

             Object applicationValue = persistedValue == null ? null : convertPersistedToApplicationValue(

                     persistedValue);

             PersistentFieldChange change = buildChange(name, applicationValue);

             result.add(change);

             didReadChange(session, name);

         }

         return result;

     }

     public void discardChanges(String pageName)

     {

         Session session = request.getSession(false);

         if (session == null) return;

         String fullPrefix = prefix + pageName + ":";

         for (String name : session.getAttributeNames(fullPrefix))

         {

             session.setAttribute(name, null);

         }

     }

     /**

      * Called after each key is read by {@link #gatherFieldChanges(String)}. This implementation does nothing,

      * subclasses may override.

      *

      * @param session       the session from which a value was just read

      * @param attributeName the name of the attribute used to read a value

      */

     protected void didReadChange(Session session, String attributeName)

     {

     }

     private PersistentFieldChange buildChange(String name, Object newValue)

     {

         String[] chunks = name.split(":");

         // Will be empty string for the root component

         String componentId = chunks[2];

         String fieldName = chunks[3];

         return new PersistentFieldChangeImpl(componentId, fieldName, newValue);

     }

     public final void postChange(String pageName, String componentId, String fieldName,

                                  Object newValue)

     {

         notBlank(pageName, "pageName");

         notBlank(fieldName, "fieldName");

         Object persistedValue = newValue == null ? null : convertApplicationValueToPersisted(newValue);

         StringBuilder builder = new StringBuilder(prefix);

         builder.append(pageName);

         builder.append(':');

         if (componentId != null) builder.append(componentId);

         builder.append(':');

         builder.append(fieldName);

         Session session = request.getSession(persistedValue != null);

         // TAPESTRY-2308: The session will be false when newValue is null and the session

         // does not already exist.

         if (session != null)

         {

             session.setAttribute(builder.toString(), persistedValue);

         }

     }

     /**

      * Hook that allows a value to be converted as it is written to the session. Passed the new value provided by the

      * application, returns the object to be stored in the session. This implementation simply returns the provided

      * value.

      *

      * @param newValue non-null value

      * @return persisted value

      * @see #convertPersistedToApplicationValue(Object)

      */

     protected Object convertApplicationValueToPersisted(Object newValue)

     {

         return newValue;

     }

     /**

      * Converts a persisted value stored in the session back into an application value.   This implementation returns

      * the persisted value as is.

      *

      * @param persistedValue non-null persisted value

      * @return application value

      * @see #convertPersistedToApplicationValue(Object)

      */

     protected Object convertPersistedToApplicationValue(Object persistedValue)

     {

         return persistedValue;

     }

 }