/* 
    * Copyright (c) 2005-2011, Fraunhofer-Gesellschaft
    * All rights reserved.
    * 
    * Redistribution and use in source and binary forms, with or without
    * modification, are permitted provided that the following conditions are
    * met:
    * 
    * (1) Redistributions of source code must retain the above copyright
   *     notice, this list of conditions and the disclaimer at the end.
   *     Redistributions in binary form must reproduce the above copyright
   *     notice, this list of conditions and the following disclaimer in
   *     the documentation and/or other materials provided with the
   *     distribution.
   * 
   * (2) Neither the name of Fraunhofer nor the names of its
   *     contributors may be used to endorse or promote products derived
   *     from this software without specific prior written permission.
   * 
   * DISCLAIMER
   * 
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
   * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
   * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
   * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
   * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
   * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
   * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   *  
   */
  package org.ogf.graap.wsag.client.api;
  
  import java.io.InputStream;
  import java.util.Properties;
  
  import javax.security.auth.login.LoginContext;
  
  import org.w3.x2005.x08.addressing.EndpointReferenceType;
  
  /*
   * AgreementFactoryLocator
   */
  
  /**
   * The Locator returns a new wsag4j client instances. The lookup mechanism for a client implementation class
   * is as follows:
   * <ol>
   * <li>load the class specified in the system property <code>client interface class name</code>, for example
   * {@linkplain org.ogf.graap.wsag.client.api.AgreementFactoryRegistryClient}</li>
   * <li>load the class specified in the {@value #APP_CONFIG_FILENAME} file</li>
   * <li>load the class specified in the {@value #IMPLEMENTATION_CONFIG_FILENAME} file</li>
   * </ol>
   * 
   * The key used in the configuration (system property) corresponds to the name of the client interface.
   * 
   * 
   * @param <T>
   *            the type of the client
   * 
   * @author Oliver Waeldrich
   * 
   */
  public class ClientLocator<T>
  {
      /**
       * client implementation configuration
       */
      private static final String IMPLEMENTATION_CONFIG_FILENAME = "/META-INF"
          + ClientFactory.DEFAULT_CONFIGURATION_FILE;
  
      /**
       * application configuration
       */
      private static final String APP_CONFIG_FILENAME = ClientFactory.DEFAULT_CONFIGURATION_FILE;
  
      /**
       * The name of the client interface class.
       */
      private final String configurationKey;
  
      private final String implementationClassFromConfig;
  
      /**
       * Instantiates a new client locator.
       * 
       * @param clazz
       *            the client class
       */
      protected ClientLocator( Class<T> clazz )
      {
          configurationKey = clazz.getName();
          implementationClassFromConfig = readClassFromConfig();
      }
  
      private synchronized ClientFactory<T> newClientFactoryInstance()
     {
         return newClientFactoryInstance( null );
     }
 
     private synchronized ClientFactory<T> newClientFactoryInstance( String alternativeConfiguration )
     {
         //
         // read from system properties
         //
         String clazzName =
             System.getProperties().getProperty( configurationKey, implementationClassFromConfig );
 
         if ( alternativeConfiguration != null )
         {
             clazzName = readClassFromConfigFile( alternativeConfiguration, clazzName );
         }
 
         if ( ( clazzName == null ) || "".equals( clazzName ) )
         {
             throw new RuntimeException( "failed to lookup client factory implementation for interface"
                 + configurationKey );
         }
 
         //
         // instantiate locator class
         //
         try
         {
             @SuppressWarnings( "unchecked" )
             Class<ClientFactory<T>> clazz =
                 (Class<ClientFactory<T>>) Class.forName( clazzName, true,
                     ClientLocator.class.getClassLoader() );
 
             ClientFactory<T> instance = clazz.newInstance();
             return instance;
         }
         catch ( Exception e )
         {
             throw new RuntimeException( "failed to instantiate client factory implementation for interface "
                 + configurationKey );
         }
         catch ( Error e )
         {
             System.err.println( "failed to instantiate client factory implementation for interface "
                 + configurationKey );
             System.err.println( e.getMessage() );
             throw e;
         }
     }
 
     private String readClassFromConfig()
     {
         //
         // read from client implementation configuration, no default value
         //
         String clientImplConfig = readClassFromConfigFile( IMPLEMENTATION_CONFIG_FILENAME, null );
 
         //
         // read from application configuration, default value from client impl configuration
         //
         String appConfig = readClassFromConfigFile( APP_CONFIG_FILENAME, clientImplConfig );
         return appConfig;
     }
 
     /**
      * Returns the locator class name form the wsag4j-client.config file at he specified path. If the property
      * does not exist the default value is returned.
      * 
      * @return the locator class name
      */
     private String readClassFromConfigFile( String fileName, String defaultValue )
     {
         Properties properties = new Properties();
         try
         {
             InputStream inputStream = ClientLocator.class.getResourceAsStream( fileName );
             properties.load( inputStream );
         }
         catch ( Exception e )
         {
             // failed to lookup config file
         }
 
         String fromConfig = properties.getProperty( configurationKey, defaultValue );
 
         return fromConfig;
     }
 
     /**
      * Returns a new client instance.
      * 
      * @param epr
      *            the client epr
      * 
      * @return the new client
      * 
      * @throws Exception
      *             client instantiation error
      */
     public T newInstance( EndpointReferenceType epr ) throws Exception
     {
         return newClientFactoryInstance().newInstance( epr );
     }
 
     /**
      * Returns a new client instance.
      * 
      * @param epr
      *            the client epr
      * 
      * @param context
      *            client login context
      * 
      * @return the new client
      * 
      * @throws Exception
      *             client instantiation error
      */
     public T newInstance( EndpointReferenceType epr, LoginContext context ) throws Exception
     {
         return newClientFactoryInstance().newInstance( epr, context );
     }
 
     /**
      * Returns a new client instance providing an alternative client configuration file.
      * 
      * @param epr
      *            the client epr
      * 
      * @param altConfig
      *            alternative client factory implementation
      * 
      * @return the new client
      * 
      * @throws Exception
      *             client instantiation error
      */
     protected T newInstance( EndpointReferenceType epr, String altConfig ) throws Exception
     {
         return newClientFactoryInstance( altConfig ).newInstance( epr );
     }
 
     /**
      * Returns a new client instance providing an alternative client configuration file.
      * 
      * @param epr
      *            the client epr
      * 
      * @param context
      *            client login context
      * 
      * @param altConfig
      *            alternative client factory implementation
      * 
      * @return the new client
      * 
      * @throws Exception
      *             client instantiation error
      */
     protected T newInstance( EndpointReferenceType epr, LoginContext context, String altConfig )
         throws Exception
     {
         return newClientFactoryInstance( altConfig ).newInstance( epr, context );
     }
 }