package com.atlassian.plugin.servlet.filter;
   
   import java.io.IOException;
   
   import javax.servlet.Filter;
   import javax.servlet.FilterChain;
   import javax.servlet.FilterConfig;
   import javax.servlet.ServletException;
   import javax.servlet.ServletRequest;
  import javax.servlet.ServletResponse;
  import javax.servlet.http.HttpServletRequest;
  
  import com.atlassian.plugin.servlet.PluginHttpRequestWrapper;
  import com.atlassian.plugin.servlet.descriptors.ServletFilterModuleDescriptor;
  import com.atlassian.plugin.servlet.util.ClassLoaderStack;
  
  /**
   * We wrap the plugins filter so that we can set some things up before the plugins filter is called. Currently we do 
   * the following:
   *      <ul>
   *        <li>set the Threads classloader to the plugins classloader)</li>
   *        <li>wrap the request so that path info is right for the filters</li>
   *      </ul>
   *      
   * @since 2.1.0
   */
  public class DelegatingPluginFilter implements Filter
  {
      private final ServletFilterModuleDescriptor descriptor;
      private final Filter filter;
      
      public DelegatingPluginFilter(ServletFilterModuleDescriptor descriptor)
      {
          this.descriptor = descriptor;
          this.filter = descriptor.getModule();
      }
  
      public void init(FilterConfig filterConfig) throws ServletException
      {
          ClassLoaderStack.push(descriptor.getPlugin().getClassLoader());
          try
          {
              filter.init(filterConfig);
          }
          finally
          {
              ClassLoaderStack.pop();
          }
      }
  
      public void doFilter(ServletRequest request, ServletResponse response, final FilterChain chain)
          throws IOException, ServletException
      {
          // Cache the class loader in case the chain below disabled the plugin making getClassLoader() inaccessible. This
          // is a bit dodgy, but it's a concession to the fact that web actions result in plugin disablement. The post
          // chain push only lasts until we exit back the outer push here.
          final ClassLoader pluginClassLoader = descriptor.getPlugin().getClassLoader();
          ClassLoaderStack.push(pluginClassLoader);
          try
          {
              // Reset the classloader during chain execution to prevent plugin's classloader being used for the duration
              // of the request
              FilterChain resetContextClassLoaderChain = new FilterChain()
              {
                  public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse) throws IOException, ServletException
                  {
                      ClassLoaderStack.pop();
                      try
                      {
                          chain.doFilter(servletRequest, servletResponse);
                      }
                      finally
                      {
                          ClassLoaderStack.push(pluginClassLoader);
                      }
                  }
              };
              filter.doFilter(new PluginHttpRequestWrapper((HttpServletRequest) request, descriptor), response, resetContextClassLoaderChain);
          }
          finally
          {
              ClassLoaderStack.pop();
          }
      }
      
      public void destroy()
      {
          ClassLoaderStack.push(descriptor.getPlugin().getClassLoader());
          try
          {
              filter.destroy();
          }
          finally
          {
              ClassLoaderStack.pop();
          }
      }
  
      public Filter getDelegatingFilter()
     {
         return filter;
     }
 }