/**
 * 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.bookkeeper.util;

import java.io.BufferedReader;
import java.io.File;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Arrays;
import java.util.Map;
import java.util.Timer;
import java.util.TimerTask;
import java.util.concurrent.atomic.AtomicBoolean;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import com.google.common.base.Charsets;

/**
 * A base class for running a Unix command.
 *
 * <code>Shell</code> can be used to run unix commands like <code>du</code> or
 * <code>df</code>. It also offers facilities to gate commands by
 * time-intervals.
 */
abstract public class Shell {

    public static final Log LOG = LogFactory.getLog(Shell.class);

    private static boolean IS_JAVA7_OR_ABOVE =
        System.getProperty("java.version").substring(0, 3).compareTo("1.7") >= 0;

    public static boolean isJava7OrAbove() {
        return IS_JAVA7_OR_ABOVE;
    }

    /** a Unix command to get the current user's name */
    public final static String USER_NAME_COMMAND = "whoami";

    /** Windows CreateProcess synchronization object */
    public static final Object WindowsProcessLaunchLock = new Object();

    /** a Unix command to get the current user's groups list */
    public static String[] getGroupsCommand() {
        return (WINDOWS) ? new String[] { "cmd", "/c", "groups" } : new String[] { "bash", "-c", "groups" };
    }

    /** a Unix command to get a given user's groups list */
    public static String[] getGroupsForUserCommand(final String user) {
        //'groups username' command return is non-consistent across different unixes
        return (WINDOWS) ? new String[] { WINUTILS, "groups", "-F", "\"" + user + "\"" } : new String[] { "bash", "-c",
                "id -Gn " + user };
    }

    /** a Unix command to get a given netgroup's user list */
    public static String[] getUsersForNetgroupCommand(final String netgroup) {
        //'groups username' command return is non-consistent across different unixes
        return (WINDOWS) ? new String[] { "cmd", "/c", "getent netgroup " + netgroup } : new String[] { "bash", "-c",
                "getent netgroup " + netgroup };
    }

    /** Return a command to get permission information. */
    public static String[] getGetPermissionCommand() {
        return (WINDOWS) ? new String[] { WINUTILS, "ls", "-F" } : new String[] { "/bin/ls", "-ld" };
    }

    /** Return a command to set permission */
    public static String[] getSetPermissionCommand(String perm, boolean recursive) {
        if (recursive) {
            return (WINDOWS) ? new String[] { WINUTILS, "chmod", "-R", perm } : new String[] { "chmod", "-R", perm };
        } else {
            return (WINDOWS) ? new String[] { WINUTILS, "chmod", perm } : new String[] { "chmod", perm };
        }
    }

    /**
     * Return a command to set permission for specific file.
     *
     * @param perm String permission to set
     * @param recursive boolean true to apply to all sub-directories recursively
     * @param file String file to set
     * @return String[] containing command and arguments
     */
    public static String[] getSetPermissionCommand(String perm, boolean recursive, String file) {
        String[] baseCmd = getSetPermissionCommand(perm, recursive);
        String[] cmdWithFile = Arrays.copyOf(baseCmd, baseCmd.length + 1);
        cmdWithFile[cmdWithFile.length - 1] = file;
        return cmdWithFile;
    }

    /** Return a command to set owner */
    public static String[] getSetOwnerCommand(String owner) {
        return (WINDOWS) ? new String[] { WINUTILS, "chown", "\"" + owner + "\"" } : new String[] { "chown", owner };
    }

    /** Return a command to create symbolic links */
    public static String[] getSymlinkCommand(String target, String link) {
        return WINDOWS ? new String[] { WINUTILS, "symlink", link, target } : new String[] { "ln", "-s", target, link };
    }

    /** Return a command for determining if process with specified pid is alive. */
    public static String[] getCheckProcessIsAliveCommand(String pid) {
        return Shell.WINDOWS ? new String[] { Shell.WINUTILS, "task", "isAlive", pid } : new String[] { "kill", "-0",
                isSetsidAvailable ? "-" + pid : pid };
    }

    /** Return a command to send a signal to a given pid */
    public static String[] getSignalKillCommand(int code, String pid) {
        return Shell.WINDOWS ? new String[] { Shell.WINUTILS, "task", "kill", pid } : new String[] { "kill",
                "-" + code, isSetsidAvailable ? "-" + pid : pid };
    }

    /**
     * Returns a File referencing a script with the given basename, inside the
     * given parent directory.  The file extension is inferred by platform: ".cmd"
     * on Windows, or ".sh" otherwise.
     *
     * @param parent File parent directory
     * @param basename String script file basename
     * @return File referencing the script in the directory
     */
    public static File appendScriptExtension(File parent, String basename) {
        return new File(parent, appendScriptExtension(basename));
    }

    /**
     * Returns a script file name with the given basename.  The file extension is
     * inferred by platform: ".cmd" on Windows, or ".sh" otherwise.
     *
     * @param basename String script file basename
     * @return String script file name
     */
    public static String appendScriptExtension(String basename) {
        return basename + (WINDOWS ? ".cmd" : ".sh");
    }

    /**
     * Returns a command to run the given script.  The script interpreter is
     * inferred by platform: cmd on Windows or bash otherwise.
     *
     * @param script File script to run
     * @return String[] command to run the script
     */
    public static String[] getRunScriptCommand(File script) {
        String absolutePath = script.getAbsolutePath();
        return WINDOWS ? new String[] { "cmd", "/c", absolutePath } : new String[] { "/bin/bash", absolutePath };
    }

    /** a Unix command to set permission */
    public static final String SET_PERMISSION_COMMAND = "chmod";
    /** a Unix command to set owner */
    public static final String SET_OWNER_COMMAND = "chown";

    /** a Unix command to set the change user's groups list */
    public static final String SET_GROUP_COMMAND = "chgrp";
    /** a Unix command to create a link */
    public static final String LINK_COMMAND = "ln";
    /** a Unix command to get a link target */
    public static final String READ_LINK_COMMAND = "readlink";

    /**Time after which the executing script would be timedout*/
    protected long timeOutInterval = 0L;
    /** If or not script timed out*/
    private AtomicBoolean timedOut;

    /** Centralized logic to discover and validate the sanity of the Hadoop
     *  home directory. Returns either NULL or a directory that exists and
     *  was specified via either -Dhadoop.home.dir or the HADOOP_HOME ENV
     *  variable.  This does a lot of work so it should only be called
     *  privately for initialization once per process.
     **/
    private static String checkHadoopHome() {

        // first check the Dflag hadoop.home.dir with JVM scope
        String home = System.getProperty("hadoop.home.dir");

        // fall back to the system/user-global env variable
        if (home == null) {
            home = System.getenv("HADOOP_HOME");
        }

        try {
            // couldn't find either setting for hadoop's home directory
            if (home == null) {
                throw new IOException("HADOOP_HOME or hadoop.home.dir are not set.");
            }

            if (home.startsWith("\"") && home.endsWith("\"")) {
                home = home.substring(1, home.length() - 1);
            }

            // check that the home setting is actually a directory that exists
            File homedir = new File(home);
            if (!homedir.isAbsolute() || !homedir.exists() || !homedir.isDirectory()) {
                throw new IOException("Hadoop home directory " + homedir
                        + " does not exist, is not a directory, or is not an absolute path.");
            }

            home = homedir.getCanonicalPath();

        } catch (IOException ioe) {
            LOG.error("Failed to detect a valid hadoop home directory", ioe);
            home = null;
        }

        return home;
    }

    private static String HADOOP_HOME_DIR = checkHadoopHome();

    // Public getter, throws an exception if HADOOP_HOME failed validation
    // checks and is being referenced downstream.
    public static final String getHadoopHome() throws IOException {
        if (HADOOP_HOME_DIR == null) {
            throw new IOException("Misconfigured HADOOP_HOME cannot be referenced.");
        }

        return HADOOP_HOME_DIR;
    }

    /** fully qualify the path to a binary that should be in a known hadoop
     *  bin location. This is primarily useful for disambiguating call-outs
     *  to executable sub-components of Hadoop to avoid clashes with other
     *  executables that may be in the path.  Caveat:  this call doesn't
     *  just format the path to the bin directory.  It also checks for file
     *  existence of the composed path. The output of this call should be
     *  cached by callers.
     * */
    public static final String getQualifiedBinPath(String executable) throws IOException {
        // construct hadoop bin path to the specified executable
        String fullExeName = HADOOP_HOME_DIR + File.separator + "bin" + File.separator + executable;

        File exeFile = new File(fullExeName);
        if (!exeFile.exists()) {
            throw new IOException("Could not locate executable " + fullExeName + " in the Hadoop binaries.");
        }

        return exeFile.getCanonicalPath();
    }

    /** Set to true on Windows platforms */
    public static final boolean WINDOWS /* borrowed from Path.WINDOWS */
    = System.getProperty("os.name").startsWith("Windows");

    public static final boolean LINUX = System.getProperty("os.name").startsWith("Linux");

    /** a Windows utility to emulate Unix commands */
    public static final String WINUTILS = getWinUtilsPath();

    public static final String getWinUtilsPath() {
        String winUtilsPath = null;

        try {
            if (WINDOWS) {
                winUtilsPath = getQualifiedBinPath("winutils.exe");
            }
        } catch (IOException ioe) {
            LOG.error("Failed to locate the winutils binary in the hadoop binary path", ioe);
        }

        return winUtilsPath;
    }

    public static final boolean isSetsidAvailable = isSetsidSupported();

    private static boolean isSetsidSupported() {
        if (Shell.WINDOWS) {
            return false;
        }
        ShellCommandExecutor shexec = null;
        boolean setsidSupported = true;
        try {
            String[] args = { "setsid", "bash", "-c", "echo $$" };
            shexec = new ShellCommandExecutor(args);
            shexec.execute();
        } catch (IOException ioe) {
            LOG.warn("setsid is not available on this machine. So not using it.");
            setsidSupported = false;
        } finally { // handle the exit code
            if (null != shexec) {
                LOG.info("setsid exited with exit code " + shexec.getExitCode());
            }
        }
        return setsidSupported;
    }

    /** Token separator regex used to parse Shell tool outputs */
    public static final String TOKEN_SEPARATOR_REGEX = WINDOWS ? "[|\n\r]" : "[ \t\n\r\f]";

    private long interval; // refresh interval in msec
    private long lastTime; // last time the command was performed
    private Map<String, String> environment; // env for the command execution
    private File dir;
    private Process process; // sub process used to execute the command
    private int exitCode;

    /**If or not script finished executing*/
    private volatile AtomicBoolean completed;

    public Shell() {
        this(0L);
    }

    /**
     * @param interval the minimum duration to wait before re-executing the
     *        command.
     */
    public Shell(long interval) {
        this.interval = interval;
        this.lastTime = (interval < 0) ? 0 : -interval;
    }

    /** set the environment for the command
     * @param env Mapping of environment variables
     */
    protected void setEnvironment(Map<String, String> env) {
        this.environment = env;
    }

    /** set the working directory
     * @param dir The directory where the command would be executed
     */
    protected void setWorkingDirectory(File dir) {
        this.dir = dir;
    }

    /** check to see if a command needs to be executed and execute if needed */
    protected void run() throws IOException {
        if (lastTime + interval > MathUtils.now())
            return;
        exitCode = 0; // reset for next run
        runCommand();
    }

    /** Run a command */
    private void runCommand() throws IOException {
        ProcessBuilder builder = new ProcessBuilder(getExecString());
        Timer timeOutTimer = null;
        ShellTimeoutTimerTask timeoutTimerTask = null;
        timedOut = new AtomicBoolean(false);
        completed = new AtomicBoolean(false);

        if (environment != null) {
            builder.environment().putAll(this.environment);
        }
        if (dir != null) {
            builder.directory(this.dir);
        }

        if (Shell.WINDOWS) {
            synchronized (WindowsProcessLaunchLock) {
                // To workaround the race condition issue with child processes
                // inheriting unintended handles during process launch that can
                // lead to hangs on reading output and error streams, we
                // serialize process creation. More info available at:
                // http://support.microsoft.com/kb/315939
                process = builder.start();
            }
        } else {
            process = builder.start();
        }

        if (timeOutInterval > 0) {
            timeOutTimer = new Timer("Shell command timeout");
            timeoutTimerTask = new ShellTimeoutTimerTask(this);
            //One time scheduling.
            timeOutTimer.schedule(timeoutTimerTask, timeOutInterval);
        }
        final BufferedReader errReader = new BufferedReader(new InputStreamReader(process.getErrorStream(),
                Charsets.UTF_8));
        BufferedReader inReader = new BufferedReader(new InputStreamReader(process.getInputStream(), Charsets.UTF_8));
        final StringBuffer errMsg = new StringBuffer();

        // read error and input streams as this would free up the buffers
        // free the error stream buffer
        Thread errThread = new Thread() {
            @Override
            public void run() {
                try {
                    String line = errReader.readLine();
                    while ((line != null) && !isInterrupted()) {
                        errMsg.append(line);
                        errMsg.append(System.getProperty("line.separator"));
                        line = errReader.readLine();
                    }
                } catch (IOException ioe) {
                    LOG.warn("Error reading the error stream", ioe);
                }
            }
        };
        try {
            errThread.start();
        } catch (IllegalStateException ise) {
        }
        try {
            parseExecResult(inReader); // parse the output
            // clear the input stream buffer
            String line = inReader.readLine();
            while (line != null) {
                line = inReader.readLine();
            }
            // wait for the process to finish and check the exit code
            exitCode = process.waitFor();
            try {
                // make sure that the error thread exits
                errThread.join();
            } catch (InterruptedException ie) {
                LOG.warn("Interrupted while reading the error stream", ie);
            }
            completed.set(true);
            //the timeout thread handling
            //taken care in finally block
            if (exitCode != 0) {
                throw new ExitCodeException(exitCode, errMsg.toString());
            }
        } catch (InterruptedException ie) {
            throw new IOException(ie.toString());
        } finally {
            if (timeOutTimer != null) {
                timeOutTimer.cancel();
            }
            // close the input stream
            try {
                inReader.close();
            } catch (IOException ioe) {
                LOG.warn("Error while closing the input stream", ioe);
            }
            if (!completed.get()) {
                errThread.interrupt();
            }
            try {
                errReader.close();
            } catch (IOException ioe) {
                LOG.warn("Error while closing the error stream", ioe);
            }
            process.destroy();
            lastTime = MathUtils.now();
        }
    }

    /** return an array containing the command name & its parameters */
    protected abstract String[] getExecString();

    /** Parse the execution result */
    protected abstract void parseExecResult(BufferedReader lines) throws IOException;

    /** get the current sub-process executing the given command
     * @return process executing the command
     */
    public Process getProcess() {
        return process;
    }

    /** get the exit code
     * @return the exit code of the process
     */
    public int getExitCode() {
        return exitCode;
    }

    /**
     * This is an IOException with exit code added.
     */
    public static class ExitCodeException extends IOException {
        private static final long serialVersionUID = 2241095121609500810L;

        int exitCode;

        public ExitCodeException(int exitCode, String message) {
            super(message);
            this.exitCode = exitCode;
        }

        public int getExitCode() {
            return exitCode;
        }
    }

    /**
     * A simple shell command executor.
     *
     * <code>ShellCommandExecutor</code>should be used in cases where the output
     * of the command needs no explicit parsing and where the command, working
     * directory and the environment remains unchanged. The output of the command
     * is stored as-is and is expected to be small.
     */
    public static class ShellCommandExecutor extends Shell {

        private String[] command;
        private StringBuffer output;

        public ShellCommandExecutor(String[] execString) {
            this(execString, null);
        }

        public ShellCommandExecutor(String[] execString, File dir) {
            this(execString, dir, null);
        }

        public ShellCommandExecutor(String[] execString, File dir, Map<String, String> env) {
            this(execString, dir, env, 0L);
        }

        /**
         * Create a new instance of the ShellCommandExecutor to execute a command.
         *
         * @param execString The command to execute with arguments
         * @param dir If not-null, specifies the directory which should be set
         *            as the current working directory for the command.
         *            If null, the current working directory is not modified.
         * @param env If not-null, environment of the command will include the
         *            key-value pairs specified in the map. If null, the current
         *            environment is not modified.
         * @param timeout Specifies the time in milliseconds, after which the
         *                command will be killed and the status marked as timedout.
         *                If 0, the command will not be timed out.
         */
        public ShellCommandExecutor(String[] execString, File dir, Map<String, String> env, long timeout) {
            command = execString.clone();
            if (dir != null) {
                setWorkingDirectory(dir);
            }
            if (env != null) {
                setEnvironment(env);
            }
            timeOutInterval = timeout;
        }

        /** Execute the shell command. */
        public void execute() throws IOException {
            this.run();
        }

        @Override
        public String[] getExecString() {
            return command.clone();
        }

        @Override
        protected void parseExecResult(BufferedReader lines) throws IOException {
            output = new StringBuffer();
            char[] buf = new char[512];
            int nRead;
            while ((nRead = lines.read(buf, 0, buf.length)) > 0) {
                output.append(buf, 0, nRead);
            }
        }

        /** Get the output of the shell command.*/
        public String getOutput() {
            return (output == null) ? "" : output.toString();
        }

        /**
         * Returns the commands of this instance.
         * Arguments with spaces in are presented with quotes round; other
         * arguments are presented raw
         *
         * @return a string representation of the object.
         */
        @Override
        public String toString() {
            StringBuilder builder = new StringBuilder();
            String[] args = getExecString();
            for (String s : args) {
                if (s.indexOf(' ') >= 0) {
                    builder.append('"').append(s).append('"');
                } else {
                    builder.append(s);
                }
                builder.append(' ');
            }
            return builder.toString();
        }
    }

    /**
     * To check if the passed script to shell command executor timed out or
     * not.
     *
     * @return if the script timed out.
     */
    public boolean isTimedOut() {
        return timedOut.get();
    }

    /**
     * Set if the command has timed out.
     *
     */
    private void setTimedOut() {
        this.timedOut.set(true);
    }

    /**
     * Static method to execute a shell command.
     * Covers most of the simple cases without requiring the user to implement
     * the <code>Shell</code> interface.
     * @param cmd shell command to execute.
     * @return the output of the executed command.
     */
    public static String execCommand(String... cmd) throws IOException {
        return execCommand(null, cmd, 0L);
    }

    /**
     * Static method to execute a shell command.
     * Covers most of the simple cases without requiring the user to implement
     * the <code>Shell</code> interface.
     * @param env the map of environment key=value
     * @param cmd shell command to execute.
     * @param timeout time in milliseconds after which script should be marked timeout
     * @return the output of the executed command.o
     */

    public static String execCommand(Map<String, String> env, String[] cmd, long timeout) throws IOException {
        ShellCommandExecutor exec = new ShellCommandExecutor(cmd, null, env, timeout);
        exec.execute();
        return exec.getOutput();
    }

    /**
     * Static method to execute a shell command.
     * Covers most of the simple cases without requiring the user to implement
     * the <code>Shell</code> interface.
     * @param env the map of environment key=value
     * @param cmd shell command to execute.
     * @return the output of the executed command.
     */
    public static String execCommand(Map<String, String> env, String... cmd) throws IOException {
        return execCommand(env, cmd, 0L);
    }

    /**
     * Timer which is used to timeout scripts spawned off by shell.
     */
    private static class ShellTimeoutTimerTask extends TimerTask {

        private Shell shell;

        public ShellTimeoutTimerTask(Shell shell) {
            this.shell = shell;
        }

        @Override
        public void run() {
            Process p = shell.getProcess();
            try {
                p.exitValue();
            } catch (Exception e) {
                //Process has not terminated.
                //So check if it has completed
                //if not just destroy it.
                if (p != null && !shell.completed.get()) {
                    shell.setTimedOut();
                    p.destroy();
                }
            }
        }
    }
}
