/*
    * Copyright 2011-2012 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
    {
      Arguments.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
   {
     Arguments.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 --------------------------------------------------------
 
 }