/*
 * 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
 *
 *   https://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;

import org.apache.commons.io.IOUtils;

/**
 * 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 {
        IOUtils.close(classLoader);
        if (fileSystem != null) {
            try {
                fileSystem.close();
            } catch (final UnsupportedOperationException e) {
                // do nothing
            }
        }
    }

    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);
    }

}
