/*

  * Copyright 2011-2013 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.util.lang;

 import java.io.IOException;

 import java.io.InputStream;

 import java.net.MalformedURLException;

 import java.net.URL;

 import java.util.Enumeration;

 import org.apache.commons.lang.ObjectUtils;

 /**

  * A constraint on resources to be loaded from the class path.

  */

 public final class ClassPathContext

 {

   // ********************************* Fields *********************************

   // --- constants ------------------------------------------------------------

   // --- members --------------------------------------------------------------

   /**

    * The class loader to load the directory listings.

    */

   private final ClassLoader classLoader;

   /**

    * Selects the archive root to load from.

    */

   private final String archiveRoot;

   // ****************************** Initializer *******************************

   // ****************************** Constructors ******************************

   /**

    * Default constructor.

    *

    * @param classLoader the class loader to load the directory listings.

    * @param archiveRoot the value for archiveRoot.

    * @throws NullPointerException if {@code classLoader} is <code>null</code>.

    */

   public ClassPathContext(final ClassLoader classLoader,

       final String archiveRoot) throws NullPointerException

   {

     Arg.checkNotNull("classLoader", classLoader);

     this.classLoader = classLoader;

     this.archiveRoot = archiveRoot;

   }

   // ****************************** Inner Classes *****************************

   // ********************************* Methods ********************************

   // --- init -----------------------------------------------------------------

   // --- get&set --------------------------------------------------------------

   // --- business -------------------------------------------------------------

   /**

    * Constructs the URL to the resource.

    *

    * @param resource the resource whose URL is requested.

    * @return the URL to the resource or <code>null</code> if the resource cannot

    *         be found on the class path.

    */

   public URL getResource(final String resource)

   {

     if (archiveRoot == null)

     {

       return classLoader.getResource(resource);

     }

     // TODO: maybe we should simply construct the URL?

     try

     {

       for (final Enumeration<URL> en = classLoader.getResources(resource); en

           .hasMoreElements();)

       {

         final URL current = en.nextElement();

         final String urlString = current.toExternalForm();

         if (urlString.startsWith(archiveRoot))

         {

           return current;

         }

       }

     }

     catch (final IOException e)

     {

       // return null

     }

     return null;

   }

   /**

    * Opens the stream to the resource.

    *

    * @param resource the resource whose stream is requested.

    * @return the stream to the resource or <code>null</code> if the resource

    *         cannot be found on the class path. If a stream is returned, the

    *         client is responsible to close that stream.

    */

   public InputStream getResourceAsStream(final String resource)

   {

     final URL url = getResource(resource);

     if (url != null)

     {

       try

       {

         return url.openStream();

       }

       catch (final IOException e)

       {

         // return null;

       }

     }

     return null;

   }

   /**

    * Constructs the URL to the resource.

    *

    * @param resource the resource whose URL is requested.

    * @return the constructed URL.

    * @throws IllegalArgumentException if the URL to the resource cannot be

    *           constructed.

    */

   public URL createUrl(final String resource) throws IllegalArgumentException

   {

     try

     {

       final String urlString =

           (archiveRoot != null ? archiveRoot : "") + resource;

       return new URL(urlString);

     }

     catch (final MalformedURLException e)

     {

       throw new IllegalArgumentException("Cannot construct URL with resource '"

                                          + resource + "'.", e);

     }

   }

   // --- object basics --------------------------------------------------------

   /**

    * Returns the hash code of the object.

    *

    * @return the hash code.

    */

   @Override

   public int hashCode()

   {

     return ObjectUtils.hashCode(archiveRoot);

   }

   /**

    * Returns <code>true</code> if the given object is semantically equal to the

    * given object, <code>false</code> otherwise.

    *

    * @param object the instance to compare to.

    * @return <code>true</code> if the given object is semantically equal to the

    *         given object, <code>false</code> otherwise.

    */

   @Override

   public boolean equals(final Object object)

   {

     if (this == object)

     {

       return true;

     }

     else if (object == null || getClass() != object.getClass())

     {

       return false;

     }

     final ClassPathContext other = (ClassPathContext) object;

     return ObjectUtils.equals(archiveRoot, other.archiveRoot);

   }

   @Override

   public String toString()

   {

     return archiveRoot != null ? archiveRoot : "<unspecified archive root>";

   }

 }