/*
    * 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.bcel.util;
  
  import java.io.Closeable;
  import java.io.File;
  import java.io.IOException;
  import java.net.URI;
  import java.net.URL;
  import java.net.URLClassLoader;
  import java.nio.file.DirectoryStream;
  import java.nio.file.FileSystem;
  import java.nio.file.FileSystems;
  import java.nio.file.Files;
  import java.nio.file.Path;
  import java.nio.file.Paths;
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.List;
  import java.util.Map;
  
  /**
   * Wraps a Java 9 JEP 220 modular runtime image. Requires the JRT NIO file system.
   *
   * @since 6.3
   */
  public class ModularRuntimeImage implements Closeable {
  
      static final String MODULES_PATH = File.separator + "modules";
      static final String PACKAGES_PATH = File.separator + "packages";
  
      private final URLClassLoader classLoader;
      private final FileSystem fileSystem;
  
      /**
       * Constructs a default instance.
       */
      @SuppressWarnings("resource") // See #close()
      public ModularRuntimeImage() {
          this(null, FileSystems.getFileSystem(URI.create("jrt:/")));
      }
  
      /**
       * Constructs an instance using the JRT file system implementation from a specific Java Home.
       *
       * @param javaHome Path to a Java 9 or greater home.
       *
       * @throws IOException an I/O error occurs accessing the file system
       */
      public ModularRuntimeImage(final String javaHome) throws IOException {
          final Map<String, ?> emptyMap = Collections.emptyMap();
          final Path jrePath = Paths.get(javaHome);
          final Path jrtFsPath = jrePath.resolve("lib").resolve("jrt-fs.jar");
          this.classLoader = URLClassLoader.newInstance(new URL[] {jrtFsPath.toUri().toURL()});
          this.fileSystem = FileSystems.newFileSystem(URI.create("jrt:/"), emptyMap, classLoader);
      }
  
      private ModularRuntimeImage(final URLClassLoader cl, final FileSystem fs) {
          this.classLoader = cl;
          this.fileSystem = fs;
      }
  
      @Override
      public void close() throws IOException {
          if (classLoader != null) {
              classLoader.close();
          }
          if (fileSystem != null) {
              fileSystem.close();
          }
      }
  
      public FileSystem getFileSystem() {
          return fileSystem;
      }
  
      /**
       * Lists all entries in the given directory.
       *
       * @param dirPath directory path.
       * @return a list of dir entries if an I/O error occurs
       * @throws IOException an I/O error occurs accessing the file system
       */
      public List<Path> list(final Path dirPath) throws IOException {
          final List<Path> list = new ArrayList<>();
         try (DirectoryStream<Path> ds = Files.newDirectoryStream(dirPath)) {
             ds.forEach(list::add);
         }
         return list;
     }
 
     /**
      * Lists all entries in the given directory.
      *
      * @param dirName directory path.
      * @return a list of dir entries if an I/O error occurs
      * @throws IOException an I/O error occurs accessing the file system
      */
     public List<Path> list(final String dirName) throws IOException {
         return list(fileSystem.getPath(dirName));
     }
 
     /**
      * Lists all modules.
      *
      * @return a list of modules
      * @throws IOException an I/O error occurs accessing the file system
      */
     public List<Path> modules() throws IOException {
         return list(MODULES_PATH);
     }
 
     /**
      * Lists all packages.
      *
      * @return a list of modules
      * @throws IOException an I/O error occurs accessing the file system
      */
     public List<Path> packages() throws IOException {
         return list(PACKAGES_PATH);
     }
 
 }