/**

  * Copyright (C) 2013 Matthias Langer

  *

  * 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 at.ipsquare.commons.core.util;

 import java.io.File;

 import java.io.FileNotFoundException;

 import java.io.IOException;

 import java.io.InputStream;

 import java.net.URL;

 import java.net.URLClassLoader;

 import java.net.URLDecoder;

 import java.util.Collection;

 import java.util.HashSet;

 import java.util.List;

 import java.util.Set;

 import java.util.TreeSet;

 import org.apache.commons.collections.EnumerationUtils;

 /**

  * For loading local resources from the classpath.

  * 

  * @author Matthias Langer

  * @since 2.0.0

  */

 public final class LocalResources

 {

   /**

    * Returns a file object for the given path.

    * 

    * Please note that this method does not work for resources that lie within JAR files. Use either {@link #getStream(String)}

    * or {@link #getUrl(String)} for these.

    * 

    * @param path a path relative to the current classpath.

    * @return an appropriate file object.

    */

   public static File getFile(String path) throws IOException

   {

     URL url = getUrl(path);

     if("jar".equals(url.getProtocol()))

         throw new IOException(url + " points to a file that lies within a JAR file. Please use getUrl() or getStream() instead.");

     File file = new File(URLDecoder.decode(url.getFile(), "UTF-8"));

     if(!file.canRead())

       throw new IOException("Not readable: '" + file + "'.");

     return file;

   }

   /**

    * Returns an {@link InputStream} for the given path.

    * 

    * @see #getFile(String)

    */

   public static InputStream getStream(String path) throws IOException

   {

     return getUrl(path).openStream();

   }

   /**

    * See {@link #getFile(String)} and {@link #getStream(String)}.

    */

   public static URL getUrl(String path) throws IOException

   {

     Set<ClassLoader> classLoaders = ClassLoaders.get();

     Set<String> urls = new HashSet<String>(2);

     for(ClassLoader cl : classLoaders)

     {

       URL url = getUrl(path, cl);

       if(url != null)

         urls.add(url.toExternalForm());

     }

     if(urls.isEmpty())

     {

       StringBuilder sb = new StringBuilder("'");

       sb.append(path).append("'");

       if(path.startsWith("/"))

         sb.append("; try ommiting the leading '/'.");

       sb.append("\n").append(classLoaderInfo(classLoaders));

       throw new FileNotFoundException(sb.toString());

     }

     if(urls.size() > 1)

       throw new IOException("'" + path + "' : Ambiguous path.");

     return new URL(urls.iterator().next());

   }

   private static String classLoaderInfo(Collection<ClassLoader> classLoaders)

   {

     StringBuilder sb = new StringBuilder("ClassLoaders involved:");

     for(ClassLoader cl : classLoaders)

       sb.append("\n").append(classLoaderInfo(cl));

     return sb.toString();

   }

   private static String classLoaderInfo(ClassLoader cl)

   {

     StringBuilder sb = new StringBuilder("** ");

     if(cl instanceof URLClassLoader)

     {

       URLClassLoader urlCl = (URLClassLoader) cl;

       sb.append("URLClassLoader -- ").append(collectClassLoaderUrls(urlCl));

     }

     else

       sb.append(cl);

     return sb.toString();

   }

   private static URL getUrl(String path, ClassLoader cl) throws IOException

   {

     @SuppressWarnings("unchecked")

     List<URL> urls = EnumerationUtils.toList(cl.getResources(path));

     if(urls.isEmpty())

       return null;

     if(urls.size() > 1)

       throw new IOException("'" + path + "' : Ambiguous path; URLs: " + urls);

     return urls.get(0);

   }

   private static Set<String> collectClassLoaderUrls(URLClassLoader cl)

   {

     Set<String> urls = new TreeSet<String>();

     collectClassLoaderUrls(cl, urls);

     return urls;

   }

   private static void collectClassLoaderUrls(URLClassLoader cl, Set<String> accumulator)

   {

     for(URL url : cl.getURLs())

       accumulator.add(url.toString());

     ClassLoader parent = cl.getParent();

     if(parent instanceof URLClassLoader)

       collectClassLoaderUrls((URLClassLoader) parent, accumulator);

   }

   private LocalResources()

   {

   }

 }