/*

 * 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

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package sun.tools.common;

import java.io.IOException;

import java.io.UncheckedIOException;

import java.nio.file.Files;

import java.nio.file.Paths;

import java.util.stream.Stream;

/**

 * A helper class that retrieves the main class name for

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

 */

final class ProcessHelper {

    private static final String CMD_PREFIX = "cmd:";

    /**

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

     * process command line. If the application was started with the <em>-jar</em>

     * option this method returns the name of the jar file. If the application

     * was started with <em>-m</em> or <em>--module</em> option, the method returns

     * the module name and the main class name.

     * @param pid - process ID (pid)

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

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

     */

    static 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("\0");

        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;

            }

        }

        // To be consistent with the behavior on other platforms, if -jar, -m, or --module

        // options are used then just return the value (the path to the jar file or module

        // name with a main class). Otherwise, the main class name is the first part that

        // is not a Java option (doesn't start with '-' and is not a classpath or a module

        // whitespace option).

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

            if (i < parts.length - 1) {

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

                    return parts[i + 1];

                }

            }

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

                return parts[i].substring("--module=".length());

            }

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

            // (the classpath or the option value itself)

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

                    isModuleWhiteSpaceOption(parts[i])) {

                i++;

                continue;

            }

            // Skip all other Java options

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

                continue;

            }

            // If it is a source-file mode then return null

            if (parts[i].endsWith(".java")) {

                return null;

            }

            mainClass = parts[i];

        }

        return mainClass;

    }

    private static String getCommandLine(String pid) {

        try (Stream<String> lines =

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

            return lines.findFirst().orElse(null);

        } catch (IOException | UncheckedIOException e) {

            return null;

        }

    }

    private static boolean isModuleWhiteSpaceOption(String option) {

        return option.equals("-p") ||

               option.equals("--module-path") ||

               option.equals("--upgrade-module-path") ||

               option.equals("--add-modules") ||

               option.equals("--limit-modules") ||

               option.equals("--add-exports") ||

               option.equals("--add-opens") ||

               option.equals("--add-reads") ||

               option.equals("--patch-module");

    }

}