/*

 * Copyright (c) 2019, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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 */

package sun.tools;

import java.io.IOException;

import java.io.UncheckedIOException;

import java.nio.file.Files;

import java.nio.file.Paths;

import java.util.jar.Attributes;

import java.util.jar.JarFile;

import java.util.jar.Manifest;

import java.util.stream.Stream;

/**

 * A helper class that retrieves the main class name for

 * a running Java process using the proc filesystem (procfs)

 */

public class ProcessHelper implements sun.tools.common.ProcessHelper {

    private static final String CMD_PREFIX = "cmd:";

    private static final ProcessHelper INSTANCE = new ProcessHelper();

    public static ProcessHelper getInstance() {

        return INSTANCE;

    }

    /**

     * Gets the main class name for the given Java process by parsing the

     * process command line.

     * @param pid - process ID (pid)

     * @return main class name or null if the process no longer exists or

     * was started with a native launcher (e.g. jcmd etc)

     */

    public String getMainClass(String pid) {

        String cmdLine = getCommandLine(pid);

        if (cmdLine == null) {

            return null;

        }

        if (cmdLine.startsWith(CMD_PREFIX)) {

            cmdLine = cmdLine.substring(CMD_PREFIX.length());

        }

        String[] parts = cmdLine.split(" ");

        String mainClass = null;

        if(parts.length == 0) {

            return null;

        }

        // Check the executable

        String[] executablePath = parts[0].split("/");

        if (executablePath.length > 0) {

            String binaryName = executablePath[executablePath.length - 1];

            if (!"java".equals(binaryName)) {

                // Skip the process if it is not started with java launcher

                return null;

            }

        }

        // If -jar option is used then read the main class name from the manifest file.

        // Otherwise, the main class name is either specified in -m or --module options or it

        // is the first part that is not a Java option (doesn't start with '-' and is not a

        // classpath or a module path).

        for (int i = 1; i < parts.length && mainClass == null; i++) {

            if (i < parts.length - 1) {

                // Check if the module is executed with explicitly specified main class

                if ((parts[i].equals("-m") || parts[i].equals("--module"))) {

                    return getMainClassFromModuleArg(parts[i + 1]);

                }

                // Check if the main class needs to be read from the manifest.mf in a JAR file

                if (parts[i].equals("-jar")) {

                    return getMainClassFromJar(parts[i + 1], pid);

                }

            }

            // If this is a classpath or a module path option then skip the next part

            // (the classpath or the module path itself)

            if (parts[i].equals("-cp") || parts[i].equals("-classpath") ||  parts[i].equals("--class-path") ||

                    parts[i].equals("-p") || parts[i].equals("--module-path")) {

                i++;

                continue;

            }

            // Skip all other Java options

            if (parts[i].startsWith("-")) {

                continue;

            }

            mainClass = parts[i];

        }

        return mainClass;

    }

    private String getMainClassFromModuleArg(String moduleArg) {

        int pos = moduleArg.lastIndexOf("/");

        return (pos > 0 && pos < moduleArg.length()-1) ? moduleArg.substring(pos + 1) : null;

    }

    private String getMainClassFromJar(String jar, String pid) {

        if (!jar.startsWith("/")) {

            String cwd = getCurrentWorkingDir(pid);

            if (cwd != null) {

                jar = cwd + "/" + jar;

            }

        }

        try (JarFile jarFile = new JarFile(jar)) {

            Manifest mf = jarFile.getManifest();

            if (mf != null) {

                Attributes mainAttributes = mf.getMainAttributes();

                return mainAttributes.getValue("Main-Class");

            }

        } catch (IOException e) {

            return null;

        }

        return null;

    }

    private static String getCurrentWorkingDir(String pid) {

        return ("/proc/" + pid + "/cwd");

    }

    private static String getCommandLine(String pid) {

        try (Stream<String> lines =

                     Files.lines(Paths.get("/proc/" + pid + "/cmdline"))) {

            return lines.map(x -> x.replaceAll("\0", " ")).findFirst().orElse(null);

        } catch (IOException | UncheckedIOException e) {

            return null;

        }

    }

}