/*
    * 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.commons.vfs2.impl;
  
  import java.io.IOException;
  import java.net.URL;
  import java.security.CodeSource;
  import java.security.Permission;
  import java.security.PermissionCollection;
  import java.security.Permissions;
  import java.security.SecureClassLoader;
  import java.security.cert.Certificate;
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.Enumeration;
  import java.util.List;
  import java.util.jar.Attributes;
  import java.util.jar.Attributes.Name;
  
  import org.apache.commons.vfs2.FileObject;
  import org.apache.commons.vfs2.FileSystemException;
  import org.apache.commons.vfs2.FileSystemManager;
  import org.apache.commons.vfs2.NameScope;
  import org.apache.commons.vfs2.util.FileObjectUtils;
  
  /**
   * A class loader that can load classes and resources from a search path.
   * <p>
   * The search path can consist of VFS FileObjects referring both to folders and JAR files. Any FileObject of type
   * FileType.FILE is assumed to be a JAR and is opened by creating a layered file system with the "jar" scheme.
   * </p>
   * <p>
   * TODO - Test this with signed Jars and a SecurityManager.
   * </p>
   *
   * @see FileSystemManager#createFileSystem
   */
  public class VFSClassLoader extends SecureClassLoader {
      private final ArrayList<FileObject> resources = new ArrayList<>();
  
      /**
       * Constructors a new VFSClassLoader for the given file.
       *
       * @param file the file to load the classes and resources from.
       * @param manager the FileManager to use when trying create a layered Jar file system.
       * @throws FileSystemException if an error occurs.
       */
      public VFSClassLoader(final FileObject file, final FileSystemManager manager) throws FileSystemException {
          this(new FileObject[] { file }, manager, null);
      }
  
      /**
       * Constructors a new VFSClassLoader for the given file.
       *
       * @param file the file to load the classes and resources from.
       * @param manager the FileManager to use when trying create a layered Jar file system.
       * @param parent the parent class loader for delegation.
       * @throws FileSystemException if an error occurs.
       */
      public VFSClassLoader(final FileObject file, final FileSystemManager manager, final ClassLoader parent)
              throws FileSystemException {
          this(new FileObject[] { file }, manager, parent);
      }
  
      /**
       * Constructors a new VFSClassLoader for the given files. The files will be searched in the order specified.
       *
       * @param files the files to load the classes and resources from.
       * @param manager the FileManager to use when trying create a layered Jar file system.
       * @throws FileSystemException if an error occurs.
       */
      public VFSClassLoader(final FileObject[] files, final FileSystemManager manager) throws FileSystemException {
          this(files, manager, null);
      }
  
      /**
       * Constructors a new VFSClassLoader for the given FileObjects. The FileObjects will be searched in the order
       * specified.
       *
       * @param files the FileObjects to load the classes and resources from.
       * @param manager the FileManager to use when trying create a layered Jar file system.
       * @param parent the parent class loader for delegation.
       * @throws FileSystemException if an error occurs.
       */
      public VFSClassLoader(final FileObject[] files, final FileSystemManager manager, final ClassLoader parent)
             throws FileSystemException {
         super(parent);
         addFileObjects(manager, files);
     }
 
     /**
      * Provide access to the file objects this class loader represents.
      *
      * @return An array of FileObjects.
      * @since 2.0
      */
     public FileObject[] getFileObjects() {
         return resources.toArray(FileObject.EMPTY_ARRAY);
     }
 
     /**
      * Appends the specified FileObjects to the list of FileObjects to search for classes and resources.
      *
      * @param manager The FileSystemManager.
      * @param files the FileObjects to append to the search path.
      * @throws FileSystemException if an error occurs.
      */
     private void addFileObjects(final FileSystemManager manager, final FileObject[] files) throws FileSystemException {
         for (FileObject file : files) {
             if (!FileObjectUtils.exists(file)) {
                 // Does not exist - skip
                 continue;
             }
 
             // TODO - use federation instead
             if (manager.canCreateFileSystem(file)) {
                 // Use contents of the file
                 file = manager.createFileSystem(file);
             }
 
             resources.add(file);
         }
     }
 
     /**
      * Finds and loads the class with the specified name from the search path.
      *
      * @throws ClassNotFoundException if the class is not found.
      */
     @Override
     protected Class<?> findClass(final String name) throws ClassNotFoundException {
         try {
             final String path = name.replace('.', '/').concat(".class");
             final Resource res = loadResource(path);
             if (res == null) {
                 throw new ClassNotFoundException(name);
             }
             return defineClass(name, res);
         } catch (final IOException ioe) {
             throw new ClassNotFoundException(name, ioe);
         }
     }
 
     /**
      * Loads and verifies the class with name and located with res.
      */
     private Class<?> defineClass(final String name, final Resource res) throws IOException {
         final URL url = res.getCodeSourceURL();
         final String pkgName = res.getPackageName();
         if (pkgName != null) {
             final Package pkg = getPackage(pkgName);
             if (pkg != null) {
                 if (pkg.isSealed()) {
                     if (!pkg.isSealed(url)) {
                         throw new FileSystemException("vfs.impl/pkg-sealed-other-url", pkgName);
                     }
                 } else if (isSealed(res)) {
                     throw new FileSystemException("vfs.impl/pkg-sealing-unsealed", pkgName);
                 }
             } else {
                 definePackage(pkgName, res);
             }
         }
 
         final byte[] bytes = res.getBytes();
         final Certificate[] certs = res.getFileObject().getContent().getCertificates();
         final CodeSource cs = new CodeSource(url, certs);
         return defineClass(name, bytes, 0, bytes.length, cs);
     }
 
     /**
      * Returns true if the we should seal the package where res resides.
      */
     private boolean isSealed(final Resource res) throws FileSystemException {
         final String sealed = res.getPackageAttribute(Attributes.Name.SEALED);
         return "true".equalsIgnoreCase(sealed);
     }
 
     /**
      * Reads attributes for the package and defines it.
      */
     private Package definePackage(final String name, final Resource res) throws FileSystemException {
         // TODO - check for MANIFEST_ATTRIBUTES capability first
         final String specTitle = res.getPackageAttribute(Name.SPECIFICATION_TITLE);
         final String specVendor = res.getPackageAttribute(Attributes.Name.SPECIFICATION_VENDOR);
         final String specVersion = res.getPackageAttribute(Name.SPECIFICATION_VERSION);
         final String implTitle = res.getPackageAttribute(Name.IMPLEMENTATION_TITLE);
         final String implVendor = res.getPackageAttribute(Name.IMPLEMENTATION_VENDOR);
         final String implVersion = res.getPackageAttribute(Name.IMPLEMENTATION_VERSION);
 
         final URL sealBase;
         if (isSealed(res)) {
             sealBase = res.getCodeSourceURL();
         } else {
             sealBase = null;
         }
 
         return definePackage(name, specTitle, specVersion, specVendor, implTitle, implVersion, implVendor, sealBase);
     }
 
     /**
      * Calls super.getPermissions both for the code source and also adds the permissions granted to the parent layers.
      *
      * @param cs the CodeSource.
      * @return The PermissionCollections.
      */
     @Override
     protected PermissionCollection getPermissions(final CodeSource cs) {
         try {
             final String url = cs.getLocation().toString();
             final FileObject file = lookupFileObject(url);
             if (file == null) {
                 return super.getPermissions(cs);
             }
 
             final FileObject parentLayer = file.getFileSystem().getParentLayer();
             if (parentLayer == null) {
                 return super.getPermissions(cs);
             }
 
             final Permissions combi = new Permissions();
             PermissionCollection permCollect = super.getPermissions(cs);
             copyPermissions(permCollect, combi);
 
             for (FileObject parent = parentLayer; parent != null; parent = parent.getFileSystem().getParentLayer()) {
                 final CodeSource parentcs = new CodeSource(parent.getURL(), parent.getContent().getCertificates());
                 permCollect = super.getPermissions(parentcs);
                 copyPermissions(permCollect, combi);
             }
 
             return combi;
         } catch (final FileSystemException fse) {
             throw new SecurityException(fse.getMessage());
         }
     }
 
     /**
      * Copies the permissions from src to dest.
      *
      * @param src The source PermissionCollection.
      * @param dest The destination PermissionCollection.
      */
     protected void copyPermissions(final PermissionCollection src, final PermissionCollection dest) {
         for (final Enumeration<Permission> elem = src.elements(); elem.hasMoreElements();) {
             final Permission permission = elem.nextElement();
             dest.add(permission);
         }
     }
 
     /**
      * Does a reverse lookup to find the FileObject when we only have the URL.
      */
     private FileObject lookupFileObject(final String name) {
         for (final FileObject object : resources) {
             if (name.equals(object.getName().getURI())) {
                 return object;
             }
         }
         return null;
     }
 
     /**
      * Finds the resource with the specified name from the search path. This returns null if the resource is not found.
      *
      * @param name The resource name.
      * @return The URL that matches the resource.
      */
     @Override
     protected URL findResource(final String name) {
         try {
             final Resource res = loadResource(name);
             if (res != null) {
                 return res.getURL();
             }
             return null;
         } catch (final Exception ignored) {
             return null; // TODO: report?
         }
     }
 
     /**
      * Returns an Enumeration of all the resources in the search path with the specified name.
      * <p>
      * Gets called from {@link ClassLoader#getResources(String)} after parent class loader was questioned.
      *
      * @param name The resources to find.
      * @return An Enumeration of the resources associated with the name.
      * @throws FileSystemException if an error occurs.
      */
     @Override
     protected Enumeration<URL> findResources(final String name) throws IOException {
         final List<URL> result = new ArrayList<>(2);
 
         for (final FileObject baseFile : resources) {
             try (final FileObject file = baseFile.resolveFile(name, NameScope.DESCENDENT_OR_SELF)) {
                 if (FileObjectUtils.exists(file)) {
                     result.add(new Resource(name, baseFile, file).getURL());
                 }
             }
         }
 
         return Collections.enumeration(result);
     }
 
     /**
      * Searches through the search path of for the first class or resource with specified name.
      *
      * @param name The resource to load.
      * @return The Resource.
      * @throws FileSystemException if an error occurs.
      */
     private Resource loadResource(final String name) throws FileSystemException {
         for (final FileObject baseFile : resources) {
             try (final FileObject file = baseFile.resolveFile(name, NameScope.DESCENDENT_OR_SELF)) {
                 if (FileObjectUtils.exists(file)) {
                     return new Resource(name, baseFile, file);
                 }
             }
         }
         return null;
     }
 }