//
   //  ========================================================================
   //  Copyright (c) 1995-2014 Mort Bay Consulting Pty. Ltd.
   //  ------------------------------------------------------------------------
   //  All rights reserved. This program and the accompanying materials
   //  are made available under the terms of the Eclipse Public License v1.0
   //  and Apache License v2.0 which accompanies this distribution.
   //
   //      The Eclipse Public License is available at
  //      http://www.eclipse.org/legal/epl-v10.html
  //
  //      The Apache License v2.0 is available at
  //      http://www.opensource.org/licenses/apache2.0.php
  //
  //  You may elect to redistribute this code under either of these licenses.
  //  ========================================================================
  //
  
  package org.eclipse.jetty.webapp;
  
  import java.io.File;
  import java.io.IOException;
  import java.io.InputStream;
  import java.lang.instrument.ClassFileTransformer;
  import java.lang.instrument.IllegalClassFormatException;
  import java.lang.instrument.Instrumentation;
  import java.net.URL;
  import java.net.URLClassLoader;
  import java.security.CodeSource;
  import java.security.PermissionCollection;
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.Enumeration;
  import java.util.HashSet;
  import java.util.List;
  import java.util.Locale;
  import java.util.Set;
  import java.util.StringTokenizer;
  import java.util.concurrent.CopyOnWriteArrayList;
  
  import org.eclipse.jetty.util.IO;
  import org.eclipse.jetty.util.StringUtil;
  import org.eclipse.jetty.util.log.Log;
  import org.eclipse.jetty.util.log.Logger;
  import org.eclipse.jetty.util.resource.Resource;
  import org.eclipse.jetty.util.resource.ResourceCollection;
  
  
  /* ------------------------------------------------------------ */
  /** ClassLoader for HttpContext.
   * Specializes URLClassLoader with some utility and file mapping
   * methods.
   *
   * This loader defaults to the 2.3 servlet spec behavior where non
   * system classes are loaded from the classpath in preference to the
   * parent loader.  Java2 compliant loading, where the parent loader
   * always has priority, can be selected with the 
   * {@link org.eclipse.jetty.webapp.WebAppContext#setParentLoaderPriority(boolean)} 
   * method and influenced with {@link WebAppContext#isServerClass(String)} and 
   * {@link WebAppContext#isSystemClass(String)}.
   *
   * If no parent class loader is provided, then the current thread 
   * context classloader will be used.  If that is null then the 
   * classloader that loaded this class is used as the parent.
   * 
   */
  public class WebAppClassLoader extends URLClassLoader
  {
      private static final Logger LOG = Log.getLogger(WebAppClassLoader.class);
  
      private final Context _context;
      private final ClassLoader _parent;
      private final Set<String> _extensions=new HashSet<String>();
      private String _name=String.valueOf(hashCode());
      private final List<ClassFileTransformer> _transformers = new CopyOnWriteArrayList<>();
      
      /* ------------------------------------------------------------ */
      /** The Context in which the classloader operates.
       */
      public interface Context
      {
          /* ------------------------------------------------------------ */
          /** Convert a URL or path to a Resource.
           * The default implementation
           * is a wrapper for {@link Resource#newResource(String)}.
           * @param urlOrPath The URL or path to convert
           * @return The Resource for the URL/path
           * @throws IOException The Resource could not be created.
           */
          Resource newResource(String urlOrPath) throws IOException;
  
          /* ------------------------------------------------------------ */
          /**
           * @return Returns the permissions.
           */
          PermissionCollection getPermissions();
  
          /* ------------------------------------------------------------ */
          /** Is the class a System Class.
          * A System class is a class that is visible to a webapplication,
          * but that cannot be overridden by the contents of WEB-INF/lib or
          * WEB-INF/classes 
          * @param clazz The fully qualified name of the class.
          * @return True if the class is a system class.
          */
         boolean isSystemClass(String clazz);
 
         /* ------------------------------------------------------------ */
         /** Is the class a Server Class.
          * A Server class is a class that is part of the implementation of 
          * the server and is NIT visible to a webapplication. The web
          * application may provide it's own implementation of the class,
          * to be loaded from WEB-INF/lib or WEB-INF/classes 
          * @param clazz The fully qualified name of the class.
          * @return True if the class is a server class.
          */
         boolean isServerClass(String clazz);
 
         /* ------------------------------------------------------------ */
         /**
          * @return True if the classloader should delegate first to the parent 
          * classloader (standard java behaviour) or false if the classloader 
          * should first try to load from WEB-INF/lib or WEB-INF/classes (servlet 
          * spec recommendation).
          */
         boolean isParentLoaderPriority();
         
         /* ------------------------------------------------------------ */
         String getExtraClasspath();
         
     }
     
     /* ------------------------------------------------------------ */
     /** Constructor.
      */
     public WebAppClassLoader(Context context)
         throws IOException
     {
         this(null,context);
     }
     
     /* ------------------------------------------------------------ */
     /** Constructor.
      */
     public WebAppClassLoader(ClassLoader parent, Context context)
         throws IOException
     {
         super(new URL[]{},parent!=null?parent
                 :(Thread.currentThread().getContextClassLoader()!=null?Thread.currentThread().getContextClassLoader()
                         :(WebAppClassLoader.class.getClassLoader()!=null?WebAppClassLoader.class.getClassLoader()
                                 :ClassLoader.getSystemClassLoader())));
         _parent=getParent();
         _context=context;
         if (_parent==null)
             throw new IllegalArgumentException("no parent classloader!");
         
         _extensions.add(".jar");
         _extensions.add(".zip");
         
         // TODO remove this system property
         String extensions = System.getProperty(WebAppClassLoader.class.getName() + ".extensions");
         if(extensions!=null)
         {
             StringTokenizer tokenizer = new StringTokenizer(extensions, ",;");
             while(tokenizer.hasMoreTokens())
                 _extensions.add(tokenizer.nextToken().trim());
         }
         
         if (context.getExtraClasspath()!=null)
             addClassPath(context.getExtraClasspath());
     }
     
     /* ------------------------------------------------------------ */
     /**
      * @return the name of the classloader
      */
     public String getName()
     {
         return _name;
     }
 
     /* ------------------------------------------------------------ */
     /**
      * @param name the name of the classloader
      */
     public void setName(String name)
     {
         _name=name;
     }
     
 
     /* ------------------------------------------------------------ */
     public Context getContext()
     {
         return _context;
     }
 
     /* ------------------------------------------------------------ */
     /**
      * @param resource Comma or semicolon separated path of filenames or URLs
      * pointing to directories or jar files. Directories should end
      * with '/'.
      */
     public void addClassPath(Resource resource)
         throws IOException
     {
         if (resource instanceof ResourceCollection)
         {
             for (Resource r : ((ResourceCollection)resource).getResources())
                 addClassPath(r);
         }
         else
         {
             addClassPath(resource.toString());
         }
     }
     
     /* ------------------------------------------------------------ */
     /**
      * @param classPath Comma or semicolon separated path of filenames or URLs
      * pointing to directories or jar files. Directories should end
      * with '/'.
      */
     public void addClassPath(String classPath)
         throws IOException
     {
         if (classPath == null)
             return;
             
         StringTokenizer tokenizer= new StringTokenizer(classPath, ",;");
         while (tokenizer.hasMoreTokens())
         {
             Resource resource= _context.newResource(tokenizer.nextToken().trim());
             if (LOG.isDebugEnabled())
                 LOG.debug("Path resource=" + resource);
 
             // Add the resource
             if (resource.isDirectory() && resource instanceof ResourceCollection)
                 addClassPath(resource);
             else
             {
                 // Resolve file path if possible
                 File file= resource.getFile();
                 if (file != null)
                 {
                     URL url= resource.getURL();
                     addURL(url);
                 }
                 else if (resource.isDirectory())
                     addURL(resource.getURL());
                 else
                 {
                     if (LOG.isDebugEnabled())
                         LOG.debug("Check file exists and is not nested jar: "+resource);
                     throw new IllegalArgumentException("File not resolvable or incompatible with URLClassloader: "+resource);
                 }
             }
         }
     }
 
     /* ------------------------------------------------------------ */
     /**
      * @param file Checks if this file type can be added to the classpath.
      */
     private boolean isFileSupported(String file)
     {
         int dot = file.lastIndexOf('.');
         return dot!=-1 && _extensions.contains(file.substring(dot));
     }
     
     /* ------------------------------------------------------------ */
     /** Add elements to the class path for the context from the jar and zip files found
      *  in the specified resource.
      * @param lib the resource that contains the jar and/or zip files.
      */
     public void addJars(Resource lib)
     {
         if (lib.exists() && lib.isDirectory())
         {
             String[] files=lib.list();
             for (int f=0;files!=null && f<files.length;f++)
             {
                 try 
                 {
                     Resource fn=lib.addPath(files[f]);
                     String fnlc=fn.getName().toLowerCase(Locale.ENGLISH);
                     // don't check if this is a directory, see Bug 353165
                     if (isFileSupported(fnlc))
                     {
                         String jar=fn.toString();
                         jar=StringUtil.replace(jar, ",", "%2C");
                         jar=StringUtil.replace(jar, ";", "%3B");
                         addClassPath(jar);
                     }
                 }
                 catch (Exception ex)
                 {
                     LOG.warn(Log.EXCEPTION,ex);
                 }
             }
         }
     }
 
     /* ------------------------------------------------------------ */
     @Override
     public PermissionCollection getPermissions(CodeSource cs)
     {
         PermissionCollection permissions=_context.getPermissions();
         PermissionCollection pc= (permissions == null) ? super.getPermissions(cs) : permissions;
         return pc;
     }
 
     /* ------------------------------------------------------------ */
     @Override
     public Enumeration<URL> getResources(String name) throws IOException
     {
         boolean system_class=_context.isSystemClass(name);
         boolean server_class=_context.isServerClass(name);
         
         List<URL> from_parent = toList(server_class?null:_parent.getResources(name));
         List<URL> from_webapp = toList((system_class&&!from_parent.isEmpty())?null:this.findResources(name));
             
         if (_context.isParentLoaderPriority())
         {
             from_parent.addAll(from_webapp);
             return Collections.enumeration(from_parent);
         }
         from_webapp.addAll(from_parent);
         return Collections.enumeration(from_webapp);
     }
 
     /* ------------------------------------------------------------ */
     private List<URL> toList(Enumeration<URL> e)
     {
         if (e==null)
             return new ArrayList<URL>();
         return Collections.list(e);
     }
     
     /* ------------------------------------------------------------ */
     /**
      * Get a resource from the classloader
      * 
      * NOTE: this method provides a convenience of hacking off a leading /
      * should one be present. This is non-standard and it is recommended 
      * to not rely on this behavior
      */
     @Override
     public URL getResource(String name)
     {
         URL url= null;
         boolean tried_parent= false;
 
         //If the resource is a class name with .class suffix, strip it off before comparison
         //as the server and system patterns are specified without a .class suffix
         String tmp = name;
         if (tmp != null && tmp.endsWith(".class"))
             tmp = tmp.substring(0, tmp.length()-6);
       
         boolean system_class=_context.isSystemClass(tmp);
         boolean server_class=_context.isServerClass(tmp);
         
         if (system_class && server_class)
             return null;
         
         if (_parent!=null &&(_context.isParentLoaderPriority() || system_class ) && !server_class)
         {
             tried_parent= true;
             
             if (_parent!=null)
                 url= _parent.getResource(name);
         }
 
         if (url == null)
         {
             url= this.findResource(name);
 
             if (url == null && name.startsWith("/"))
             {
                 if (LOG.isDebugEnabled())
                     LOG.debug("HACK leading / off " + name);
                 url= this.findResource(name.substring(1));
             }
         }
 
         if (url == null && !tried_parent && !server_class )
         {
             if (_parent!=null)
                 url= _parent.getResource(name);
         }
 
         if (url != null)
             if (LOG.isDebugEnabled())
                 LOG.debug("getResource("+name+")=" + url);
 
         return url;
     }
 
     /* ------------------------------------------------------------ */
     @Override
     public Class<?> loadClass(String name) throws ClassNotFoundException
     {
         return loadClass(name, false);
     }
 
     /* ------------------------------------------------------------ */
     @Override
     protected synchronized Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException
     {
         Class<?> c= findLoadedClass(name);
         ClassNotFoundException ex= null;
         boolean tried_parent= false;
         
         boolean system_class=_context.isSystemClass(name);
         boolean server_class=_context.isServerClass(name);
         
         if (system_class && server_class)
         {
             return null;
         }
         
         if (c == null && _parent!=null && (_context.isParentLoaderPriority() || system_class) && !server_class)
         {
             tried_parent= true;
             try
             {
                 c= _parent.loadClass(name);
                 if (LOG.isDebugEnabled())
                     LOG.debug("loaded " + c);
             }
             catch (ClassNotFoundException e)
             {
                 ex= e;
             }
         }
 
         if (c == null)
         {
             try
             {
                 c= this.findClass(name);
             }
             catch (ClassNotFoundException e)
             {
                 ex= e;
             }
         }
 
         if (c == null && _parent!=null && !tried_parent && !server_class )
             c= _parent.loadClass(name);
 
         if (c == null && ex!=null)
             throw ex;
 
         if (resolve)
             resolveClass(c);
 
         if (LOG.isDebugEnabled())
             LOG.debug("loaded {} from {}",c,c==null?null:c.getClassLoader());
         
         return c;
     }
 
     /* ------------------------------------------------------------ */
     /**
      * @see addTransformer
      * @deprecated
      */
     public void addClassFileTransformer(ClassFileTransformer transformer)
     {
         _transformers.add(transformer);
     }
     
     /* ------------------------------------------------------------ */
     /**
      * @see removeTransformer
      * @deprecated
      */
     public boolean removeClassFileTransformer(ClassFileTransformer transformer)
     {
         return _transformers.remove(transformer);
     }
 
     /* ------------------------------------------------------------ */
     /**
      * @see addClassFileTransformer
      */
     public void addTransformer(ClassFileTransformer transformer)
     {
         _transformers.add(transformer);
     }
     
     /* ------------------------------------------------------------ */
     /**
      * @see removeClassFileTransformer
      */
     public boolean removeTransformer(ClassFileTransformer transformer)
     {
         return _transformers.remove(transformer);
     }
     
     
     /* ------------------------------------------------------------ */
     @Override
     protected Class<?> findClass(final String name) throws ClassNotFoundException
     {
         Class<?> clazz=null;
 
         if (_transformers.isEmpty())
             clazz = super.findClass(name);
         else
         {
             String path = name.replace('.', '/').concat(".class");
             URL url = getResource(path);
             if (url==null)
                 throw new ClassNotFoundException(name);
 
             InputStream content=null;
             try
             {
                 content = url.openStream();
                 byte[] bytes =IO.readBytes(content);
                     
                 for (ClassFileTransformer transformer : _transformers)
                     bytes=transformer.transform(this,name,null,null,bytes);
                 
                 clazz=defineClass(name,bytes,0,bytes.length);
             }
             catch (IOException e)
             {
                 throw new ClassNotFoundException(name,e);
             }
             catch (IllegalClassFormatException e)
             {
                 throw new ClassNotFoundException(name,e);
             }
             finally
             {
                 if (content!=null)
                 {
                     try
                     {
                         content.close(); 
                     }
                     catch (IOException e)
                     {
                         throw new ClassNotFoundException(name,e);
                     }
                 }
             }
         }
 
         return clazz;
     }
     
     /* ------------------------------------------------------------ */
     @Override
     public String toString()
     {
         return "WebAppClassLoader=" + _name+"@"+Long.toHexString(hashCode());
     }
 }