/*
    * Copyright 2012-2013 smartics, Kronseder & Reiner GmbH
    *
    * 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 de.smartics.properties.spi.core.registry;
  
  import java.io.Serializable;
  import java.util.HashMap;
  import java.util.Map;
  import java.util.Map.Entry;
  import java.util.concurrent.locks.Lock;
  import java.util.concurrent.locks.ReentrantReadWriteLock;
  
  import javax.annotation.CheckForNull;
  import javax.annotation.concurrent.ThreadSafe;
  
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import de.smartics.properties.api.core.domain.ConfigException;
  import de.smartics.properties.api.core.domain.PropertiesContext;
  import de.smartics.properties.api.core.domain.PropertyDescriptor;
  import de.smartics.properties.spi.core.context.DeclarationConfigParser;
  import de.smartics.properties.spi.core.util.ClassLoaderUtils;
  import de.smartics.util.lang.Arg;
  import de.smartics.util.lang.classpath.ClassPathContext;
  
  /**
   * Manages configurations for property descriptors. The configurations are
   * backed by <code>META-INF/property/config.xml</code> files. This registry
   * serves as a cache.
   */
  @ThreadSafe
  public final class ConfigurationRegistry implements Serializable
  {
    // ********************************* Fields *********************************
  
    // --- constants ------------------------------------------------------------
  
    /**
     * The class version identifier.
     */
    private static final long serialVersionUID = 1L;
  
    /**
     * Reference to the logger for this class.
     */
    private static final Logger LOG = LoggerFactory
        .getLogger(ConfigurationRegistry.class);
  
    // --- members --------------------------------------------------------------
  
    /**
     * The lock for synchronized access to the context cache.
     *
     * @serial
     */
    private final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
  
    /**
     * The read lock for synchronized access to the context cache.
     *
     * @serial
     */
    private final Lock readLock = lock.readLock();
  
    /**
     * The write lock for synchronized access to the context cache.
     *
     * @serial
     */
    private final Lock writeLock = lock.writeLock();
  
    /**
     * Maps the properties context configuration information keyed by their
     * archive path.
     */
    private final Map<String, PropertiesContext> contexts =
        new HashMap<String, PropertiesContext>();
  
    // ****************************** Initializer *******************************
  
    // ****************************** Constructors ******************************
  
    /**
     * Default constructor.
     */
    public ConfigurationRegistry()
   {
   }
 
   // ****************************** Inner Classes *****************************
 
   // ********************************* Methods ********************************
 
   // --- init -----------------------------------------------------------------
 
   // --- get&set --------------------------------------------------------------
 
   // --- business -------------------------------------------------------------
 
   /**
    * Returns the properties context for the given descriptor.
    *
    * @param descriptor the descriptor whose properties context is requested.
    * @return the context for the property provided by the descriptor. May return
    *         <code>null</code> if the {@code descriptor} is unknown.
    * @throws NullPointerException if {@code descriptor} is <code>null</code>.
    */
   @CheckForNull
   public PropertiesContext get(final PropertyDescriptor descriptor)
     throws NullPointerException
   {
     Arg.checkNotNull("descriptor", descriptor);
 
     final Class<?> declaringType = descriptor.getDeclaringType();
     return get(declaringType);
   }
 
   /**
    * Returns the properties context for the declaring type of a property set.
    *
    * @param declaringType the declaring type of a property set.
    * @return the context for the declared properties. May return
    *         <code>null</code> if the {@code declaringType} is unknown.
    * @throws NullPointerException if {@code declaringType} is <code>null</code>.
    */
   @CheckForNull
   public PropertiesContext get(final Class<?> declaringType)
     throws NullPointerException
   {
     Arg.checkNotNull("declaringType", declaringType);
 
     final ClassLoader loader = declaringType.getClassLoader();
     if (loader == null)
     {
       LOG.debug("Declaring type '{}' not registered as a property set.",
           declaringType.getName());
       return PropertiesContext.createEmptyContext();
     }
 
     try
     {
       final PropertiesContext context = load(declaringType);
       return context;
     }
     catch (final ConfigException e)
     {
       LOG.debug("Cannot load properties context for declaring type '"
                 + declaringType.getName() + "'.", e);
       return PropertiesContext.createEmptyContext();
     }
   }
 
   private PropertiesContext load(final Class<?> declaringType)
     throws ConfigException
   {
     final String archivePath = ClassLoaderUtils.calcArchivePath(declaringType);
     final ClassPathContext cpContext =
         new ClassPathContext(declaringType.getClassLoader(), archivePath);
 
     readLock.lock();
     try
     {
       PropertiesContext context = contexts.get(archivePath);
       if (context == null)
       {
         readLock.unlock();
         writeLock.lock();
         try
         {
           context = contexts.get(archivePath);
           if (context == null)
           {
             final DeclarationConfigParser parser =
                 new DeclarationConfigParser();
             context = parser.parse(cpContext);
 
             contexts.put(archivePath, context);
           }
         }
         finally
         {
           readLock.lock();
           writeLock.unlock();
         }
       }
       return context;
     }
     finally
     {
       readLock.unlock();
     }
   }
 
   // --- object basics --------------------------------------------------------
 
   /**
    * Returns the string representation of the object.
    *
    * @return the string representation of the object.
    */
   @Override
   public String toString()
   {
     final StringBuilder buffer = new StringBuilder();
 
     for (final Entry<String, PropertiesContext> entry : contexts.entrySet())
     {
       buffer.append(entry.getKey()).append('=')
           .append(entry.getValue().getHomePageUrl());
     }
 
     return buffer.toString();
   }
 }