/*

  * 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.File;

 import java.io.IOException;

 import java.net.URISyntaxException;

 import java.net.URL;

 import java.net.URLDecoder;

 import java.util.ArrayList;

 import java.util.Arrays;

 import java.util.Enumeration;

 import java.util.List;

 import java.util.jar.JarEntry;

 import java.util.jar.JarFile;

 import org.apache.commons.lang.StringUtils;

 /**

  * Lists the content of a directory on the class path.

  * <p>

  * Currently only the protocols

  * </p>

  * <ol>

  * <li>file system (<code>file</code>) and</li>

  * <li>JAR files (<code>jar</code>)</li>

  * </ol>

  * <p>

  * are supported.

  * </p>

  */

 public class ClassPathDirectoryListing

 {

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

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

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

   /**

    * The context to load the directory listings.

    */

   private final ClassPathContext context;

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

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

   /**

    * Default constructor.

    *

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

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

    */

   public ClassPathDirectoryListing(final ClassLoader classLoader)

     throws NullPointerException

   {

     this(new ClassPathContext(classLoader, null));

   }

   /**

    * Default constructor.

    *

    * @param context the context to load the directory listings.

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

    */

   public ClassPathDirectoryListing(final ClassPathContext context)

     throws NullPointerException

   {

     Arg.checkNotNull("context", context);

     this.context = context;

   }

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

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

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

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

   /**

    * Returns the context to load the directory listings.

    *

    * @return the context to load the directory listings.

    */

   public final ClassPathContext getClassPathContext()

   {

     return context;

   }

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

   /**

    * Lists the contents of the resource path.

    *

    * @param resourcePath the path to the resource whose contents is to be

    *          listed. The empty string returns the contents of the class

    *          loader's root directory (which is usually the parent class

    *          loader's root).

    * @return the contents of the resource as names. The list may be empty, but

    *         is never <code>null</code>.

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

    * @throws IllegalArgumentException if resource path cannot be resolved to

    *           determine the contents. Either the protocol is unknown or there

    *           is a problem to access the resource's content physically.

    * @impl Sub classes may override this method to add additional protocol

    *       handlers. Call this method, if the derived handler does not handle

    *       the protocol.

    */

   public List<String> list(final String resourcePath)

     throws NullPointerException, IllegalArgumentException

   {

     Arg.checkNotNull("resourcePath", resourcePath);

     final URL resourcePathUrl = context.getResource(resourcePath);

     if (resourcePathUrl == null)

     {

       throw new IllegalArgumentException("Cannot find resource '"

                                          + resourcePath + "' on class path.");

     }

     final String protocol = resourcePathUrl.getProtocol();

     if ("file".equals(protocol))

     {

       return handleFile(resourcePath, resourcePathUrl);

     }

     else if ("jar".equals(protocol))

     {

       return handleJar(resourcePath, resourcePathUrl);

     }

     throw new IllegalArgumentException(

         "Protocol '" + protocol + "' is not supported to resolve resource '"

             + resourcePath + "'.");

   }

   private List<String> handleFile(final String resourcePath,

       final URL resourcePathUrl) throws IllegalArgumentException

   {

     try

     {

       final String[] contentsArray = new File(resourcePathUrl.toURI()).list();

       return Arrays.asList(contentsArray);

     }

     catch (final URISyntaxException e)

     {

       throw new IllegalArgumentException(

           "Cannot read URL derived from resource '" + resourcePath

               + "' on the class path.", e);

     }

   }

   private List<String> handleJar(final String resourcePath,

       final URL resourcePathUrl) throws IllegalArgumentException

   {

     try

     {

       final List<String> contents = new ArrayList<String>();

       final int separatorIndex = resourcePathUrl.getPath().indexOf('!');

       final String jarPath =

           resourcePathUrl.getPath().substring(5, separatorIndex);

       final JarFile jar = new JarFile(URLDecoder.decode(jarPath, "UTF-8"));

       traverseJarEntries(resourcePath, contents, jar);

       return contents;

     }

     catch (final IOException e)

     {

       throw new IllegalArgumentException("Read from JAR '" + resourcePath

                                          + "'.", e);

     }

   }

   private void traverseJarEntries(final String resourcePath,

       final List<String> contents, final JarFile jar)

   {

     final int resourcePathLength = resourcePath.length();

     final Enumeration<JarEntry> entries = jar.entries();

     while (entries.hasMoreElements())

     {

       final String name = entries.nextElement().getName();

       if (name.startsWith(resourcePath))

       {

         final String entry = name.substring(resourcePathLength);

         final String normalized = normalize(entry);

         if (normalized != null && !contents.contains(normalized))

         {

           contents.add(normalized);

         }

       }

     }

   }

   private static String normalize(final String entry)

   {

     if (StringUtils.isBlank(entry))

     {

       return null;

     }

     String normalized = entry;

     if (normalized.charAt(0) == '/')

     {

       if (entry.length() == 1)

       {

         return null;

       }

       normalized = normalized.substring(1);

     }

     final int subDirIndex = normalized.indexOf('/');

     if (subDirIndex != -1)

     {

       normalized = normalized.substring(0, subDirIndex);

     }

     return normalized;

   }

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

 }