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/*
 * Copyright 2011 Lincoln Baxter, III
 *
 * 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.ocpsoft.rewrite.servlet.config;

import java.net.MalformedURLException;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.Set;

import javax.servlet.Servlet;
import javax.servlet.ServletContext;

import org.ocpsoft.common.pattern.WeightedComparator;
import org.ocpsoft.common.services.ServiceLoader;
import org.ocpsoft.common.util.Iterators;
import org.ocpsoft.logging.Logger;
import org.ocpsoft.rewrite.config.Condition;
import org.ocpsoft.rewrite.config.ConfigurationRuleParameterBuilder;
import org.ocpsoft.rewrite.context.EvaluationContext;
import org.ocpsoft.rewrite.param.ParameterStore;
import org.ocpsoft.rewrite.param.Parameterized;
import org.ocpsoft.rewrite.param.ParameterizedPattern;
import org.ocpsoft.rewrite.param.ParameterizedPatternBuilder;
import org.ocpsoft.rewrite.param.RegexParameterizedPatternBuilder;
import org.ocpsoft.rewrite.servlet.ServletRegistration;
import org.ocpsoft.rewrite.servlet.http.event.HttpServletRewrite;
import org.ocpsoft.rewrite.servlet.spi.ServletRegistrationProvider;
import org.ocpsoft.rewrite.util.Transpositions;
import org.ocpsoft.urlbuilder.Address;

/**
 * A {@link Condition} responsible for comparing the current {@link Address} to Servlet Mappings defined in the current
 * {@link ServletContext}.
 * 
 * @author Lincoln Baxter, III
 */
public abstract class ServletMapping extends HttpCondition implements Parameterized
{
   private static final Logger log = Logger.getLogger(Resource.class);

   private final RegexParameterizedPatternBuilder resource;

   private List servletRegistrationProviders = null;

   private ServletMapping(final String resource)
   {
      this.resource = new RegexParameterizedPatternBuilder(resource);
   }

   /**
    * Create a {@link Condition} that returns true if the given resource is mapped by any {@link Servlet}
    * instances registered within the current application, and returns false if no {@link Servlet} will
    * handle the specified resource pattern.
    * 
    * 
    * The given resource path may be parameterized:
    * 

    * 
    *    /example/{param}.html 

    *    /css/{value}.css 

    *    ... 
    * 
    * 
    * 
    * @param location {@link ParameterizedPattern} specifying the {@link Address} of the internal resource.
    * 
    * @see {@link ConfigurationRuleParameterBuilder#where(String)}
    */
   public static ServletMapping includes(final String resource)
   {
      return new ServletMapping(resource) {
         @Override
         public String toString()
         {
            return "ServletMapping.includes(\"" + resource + "\")";
         }
      };
   }

   @Override
   public boolean evaluateHttp(final HttpServletRewrite event, final EvaluationContext context)
   {
      if (resource != null && resource.isParameterComplete(event, context))
      {
         String path = resource.build(event, context, Transpositions.encodePath());
         try
         {
            for (ServletRegistration registration : getServletRegistration(event.getServletContext()))
            {
               Collection mappings = registration.getMappings();

               for (String mapping : mappings)
               {
                  if (path.startsWith("/") && !mapping.startsWith("/"))
                  {
                     mapping = "/" + mapping;
                  }

                  if (mapping.contains("*"))
                  {
                     mapping = mapping.replaceAll("\\*", ".*");
                  }

                  if (path.matches(mapping))
                  {
                     return true;
                  }
               }
            }

            return event.getServletContext().getResource(path) != null;
         }
         catch (MalformedURLException e)
         {
            log.debug("Invalid file format [{}]", path);
         }
      }
      return false;
   }

   /**
    * Obtains the list of registered {@link Servlet} instances using the {@link ServletRegistrationProvider} SPI.
    */
   private List getServletRegistration(ServletContext context)
   {
      for (ServletRegistrationProvider provider : getServletRegistrationProviders())
      {
         List registrations = provider.getServletRegistrations(context);
         if (registrations != null)
         {
            return registrations;
         }
      }
      throw new IllegalStateException("Unable to find the Servlet registrations of the application");
   }

   /**
    * Returns the list of {@link ServletRegistrationProvider} implementations.
    */
   private List getServletRegistrationProviders()
   {
      if (servletRegistrationProviders == null)
      {
         servletRegistrationProviders = Iterators.asList(
                  ServiceLoader.loadTypesafe(ServletRegistrationProvider.class).iterator());
         Collections.sort(servletRegistrationProviders, new WeightedComparator());
      }
      return servletRegistrationProviders;
   }

   /**
    * Return the underlying {@link ParameterizedPatternBuilder} for this {@link ServletMapping}.
    */
   public ParameterizedPatternBuilder getResourceExpression()
   {
      return resource;
   }

   @Override
   public Set getRequiredParameterNames()
   {
      return resource.getRequiredParameterNames();
   }

   @Override
   public void setParameterStore(ParameterStore store)
   {
      resource.setParameterStore(store);
   }
}