/*
    *  Licensed to the Apache Software Foundation (ASF) under one
    *  or more contributor license agreements.  See the NOTICE file
    *  distributed with this work for additional information
    *  regarding copyright ownership.  The ASF licenses this file
    *  to you 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.apache.myfaces.trinidad.resource;
  
  import java.io.ByteArrayInputStream;
  import java.io.ByteArrayOutputStream;
  import java.io.File;
  import java.io.IOException;
  
  import java.io.InputStream;
  import java.net.URL;
  
  import java.net.UnknownServiceException;
  import java.net.URLConnection;
  import java.net.URLStreamHandler;
  import java.util.Map;
  import java.util.HashMap;
  
  
  
  /**
   * Base class for resource loaders.  Resource loaders can lookup resources
   * as URLs from arbitrary locations, including JAR files.
   *
   */
  public class CachingResourceLoader extends ResourceLoader
  {
    /**
     * Constructs a new CachingResourceLoader.
     *
     * @param parent  the parent resource loader
     */
    public CachingResourceLoader(
      ResourceLoader parent)
    {
      super(parent);
  
      _cache = new HashMap<String, URL>();
    }
  
    /**
     * Returns the cached resource url if previously requested.  Otherwise,
     * fully reads the resource contents stores in the cache.
     *
     * @param path  the resource path
     *
     * @return the cached resource url
     *
     * @throws java.io.IOException  if an I/O error occurs
     */
    @Override
    protected URL findResource(
      String path
      ) throws IOException
    {
      URL url = _cache.get(path);
  
      if (url == null)
      {
        url = getParent().getResource(path);
  
        if (url != null)
        {
          url = new URL("cache", null, -1, path, new URLStreamHandlerImpl(url));
          _cache.put(path, url);
        }
      }
  
      return url;
    }
  
    private final Map<String, URL> _cache;
  
    /**
     * URLStreamHandler to cache URL contents and URLConnection headers.
     */
    static private class URLStreamHandlerImpl extends URLStreamHandler
    {
      public URLStreamHandlerImpl(
        URL delegate)
      {
        _delegate = delegate;
      }
 
     @Override
     protected URLConnection openConnection(
       URL url
       ) throws IOException
     {
       return new URLConnectionImpl(url, _delegate.openConnection(), this);
     }
 
     protected InputStream getInputStream(
       URLConnection conn) throws IOException
     {
       long lastModified = _getLastModified(_delegate);
 
       if (_contents == null || _contentsModified < lastModified)
       {
         InputStream in = conn.getInputStream();
         ByteArrayOutputStream out = new ByteArrayOutputStream();
         try
         {
           byte[] buffer = new byte[2048];
           int length;
           while ((length = (in.read(buffer))) >= 0)
           {
             out.write(buffer, 0, length);
           }
         }
         finally
         {
           in.close();
         }
         _contents = out.toByteArray();
         _contentsModified = conn.getLastModified();
       }
 
       return new ByteArrayInputStream(_contents);
     }
 
     private final URL    _delegate;
     private       byte[] _contents;
     private       long   _contentsModified;
   }
 
   /**
    * URLConnection to cache URL contents and header fields.
    */
   static private class URLConnectionImpl extends URLConnection
   {
     /**
      * Creates a new URLConnectionImpl.
      *
      * @param url      the cached url
      * @param handler  the caching stream handler
      */
     public URLConnectionImpl(
       URL                  url,
       URLConnection        conn,
       URLStreamHandlerImpl handler)
     {
       super(url);
       _conn = conn;
       _handler = handler;
     }
 
     @Override
     public void connect() throws IOException
     {
       // cache: no-op
     }
 
     @Override
     public String getContentType()
     {
       return _conn.getContentType();
     }
 
     @Override
     public int getContentLength()
     {
       return _conn.getContentLength();
     }
 
     @Override
     public long getLastModified()
     {
       return _conn.getLastModified();
     }
 
     @Override
     public String getHeaderField(
       String name)
     {
       return _conn.getHeaderField(name);
     }
 
     @Override
     public InputStream getInputStream() throws IOException
     {
       return _handler.getInputStream(_conn);
     }
 
     private final URLConnection        _conn;
     private final URLStreamHandlerImpl _handler;
   }
 
   static private long _getLastModified(URL url) throws IOException
   {
     if ("file".equals(url.getProtocol()))
     {
       String externalForm = url.toExternalForm();
       // Remove the "file:"
       File file = new File(externalForm.substring(5));
 
       return file.lastModified();
     }
     else
     {
       URLConnection connection = url.openConnection();
       long modified = connection.getLastModified();
       try
       {
         InputStream is = connection.getInputStream();
         if (is != null)
           is.close();
       }
       catch (UnknownServiceException use)
       {
       }
 
       return modified;
     }
   }
 }