/*
 * Copyright (c) 2006-2011 Christian Plattner. All rights reserved.
 * Please refer to the LICENSE.txt for licensing details.
 */
package ch.ethz.ssh2;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.security.SecureRandom;

import ch.ethz.ssh2.channel.Channel;
import ch.ethz.ssh2.channel.ChannelManager;
import ch.ethz.ssh2.channel.X11ServerData;

/**
 * A <code>Session</code> is a remote execution of a program. "Program" means
 * in this context either a shell, an application or a system command. The
 * program may or may not have a tty. Only one single program can be started on
 * a session. However, multiple sessions can be active simultaneously.
 *
 * @author Christian Plattner
 * @version $Id: Session.java 96 2014-04-08 15:14:37Z dkocher@sudo.ch $
 */
public class Session {
    private ChannelManager cm;
    private Channel cn;

    private boolean flag_pty_requested = false;
    private boolean flag_x11_requested = false;
    private boolean flag_execution_started = false;
    private boolean flag_closed = false;

    private String x11FakeCookie = null;

    private final SecureRandom rnd;

    protected Session(ChannelManager cm, SecureRandom rnd) throws IOException {
        this.cm = cm;
        this.cn = cm.openSessionChannel();
        this.rnd = rnd;
    }

    /**
     * Basically just a wrapper for lazy people - identical to calling
     * <code>requestPTY("dumb", 0, 0, 0, 0, null)</code>.
     *
     * @throws IOException
     */
    public void requestDumbPTY() throws IOException {
        requestPTY("dumb", 0, 0, 0, 0, null);
    }

    /**
     * Basically just another wrapper for lazy people - identical to calling
     * <code>requestPTY(term, 0, 0, 0, 0, null)</code>.
     *
     * @throws IOException
     */
    public void requestPTY(String term) throws IOException {
        requestPTY(term, 0, 0, 0, 0, null);
    }

    /**
     * Allocate a pseudo-terminal for this session.
     * <p/>
     * This method may only be called before a program or shell is started in
     * this session.
     * <p/>
     * Different aspects can be specified:
     * <p/>
     * <ul>
     * <li>The TERM environment variable value (e.g., vt100)</li>
     * <li>The terminal's dimensions.</li>
     * <li>The encoded terminal modes.</li>
     * </ul>
     * Zero dimension parameters are ignored. The character/row dimensions
     * override the pixel dimensions (when nonzero). Pixel dimensions refer to
     * the drawable area of the window. The dimension parameters are only
     * informational. The encoding of terminal modes (parameter
     * <code>terminal_modes</code>) is described in RFC4254.
     *
     * @param term The TERM environment variable value (e.g., vt100)
     * @param term_width_characters terminal width, characters (e.g., 80)
     * @param term_height_characters terminal height, rows (e.g., 24)
     * @param term_width_pixels terminal width, pixels (e.g., 640)
     * @param term_height_pixels terminal height, pixels (e.g., 480)
     * @param terminal_modes encoded terminal modes (may be <code>null</code>)
     * @throws IOException
     */
    public void requestPTY(String term, int term_width_characters, int term_height_characters, int term_width_pixels,
                           int term_height_pixels, byte[] terminal_modes) throws IOException {
        if (term == null)
            throw new IllegalArgumentException("TERM cannot be null.");

        if ((terminal_modes != null) && (terminal_modes.length > 0)) {
            if (terminal_modes[terminal_modes.length - 1] != 0)
                throw new IOException("Illegal terminal modes description, does not end in zero byte");
        }
        else
            terminal_modes = new byte[] {0};

        synchronized (this) {
            /* The following is just a nicer error, we would catch it anyway later in the channel code */
            if (flag_closed)
                throw new IOException("This session is closed.");

            if (flag_pty_requested)
                throw new IOException("A PTY was already requested.");

            if (flag_execution_started)
                throw new IOException(
                    "Cannot request PTY at this stage anymore, a remote execution has already started.");

            flag_pty_requested = true;
        }

        cm.requestPTY(cn, term, term_width_characters, term_height_characters, term_width_pixels, term_height_pixels,
                      terminal_modes);
    }

    /**
     * Tells the server that the size of the terminal has changed.
     *
     * See {@link #requestPTY(String, int, int, int, int, byte[])} for more details about how parameters are interpreted.
     *
     * @param term_width_characters
     *            terminal width, characters (e.g., 80)
     * @param term_height_characters
     *            terminal height, rows (e.g., 24)
     * @param term_width_pixels
     *            terminal width, pixels (e.g., 640)
     * @param term_height_pixels
     *            terminal height, pixels (e.g., 480)
     * @throws IOException
     */
    public void resizePTY(int term_width_characters, int term_height_characters, int term_width_pixels, int term_height_pixels) throws IOException {
        requestWindowChange(term_width_characters, term_height_characters, term_width_pixels, term_height_pixels);
    }

    public void requestWindowChange(int term_width_characters, int term_height_characters, int term_width_pixels,
                                    int term_height_pixels) throws IOException {
        synchronized (this) {
            /* The following is just a nicer error, we would catch it anyway later in the channel code */
            if (flag_closed)
                throw new IOException("This session is closed.");

            if (!flag_pty_requested)
                throw new IOException("A PTY was not requested.");
        }

        cm.requestWindowChange(cn, term_width_characters, term_height_characters, term_width_pixels, term_height_pixels);
    }

    /**
     * Request X11 forwarding for the current session.
     * <p/>
     * You have to supply the name and port of your X-server.
     * <p/>
     * This method may only be called before a program or shell is started in
     * this session.
     *
     * @param hostname the hostname of the real (target) X11 server (e.g., 127.0.0.1)
     * @param port the port of the real (target) X11 server (e.g., 6010)
     * @param cookie if non-null, then present this cookie to the real X11 server
     * @param singleConnection if true, then the server is instructed to only forward one single
     * connection, no more connections shall be forwarded after first, or after the session
     * channel has been closed
     * @throws IOException
     */
    public void requestX11Forwarding(String hostname, int port, byte[] cookie, boolean singleConnection)
    throws IOException {
        if (hostname == null)
            throw new IllegalArgumentException("hostname argument may not be null");

        synchronized (this) {
            /* The following is just a nicer error, we would catch it anyway later in the channel code */
            if (flag_closed)
                throw new IOException("This session is closed.");

            if (flag_x11_requested)
                throw new IOException("X11 forwarding was already requested.");

            if (flag_execution_started)
                throw new IOException(
                    "Cannot request X11 forwarding at this stage anymore, a remote execution has already started.");

            flag_x11_requested = true;
        }

        /* X11ServerData - used to store data about the target X11 server */
        X11ServerData x11data = new X11ServerData();
        x11data.hostname = hostname;
        x11data.port = port;
        x11data.x11_magic_cookie = cookie; /* if non-null, then present this cookie to the real X11 server */
        /* Generate fake cookie - this one is used between remote clients and the ganymed proxy */
        byte[] fakeCookie = new byte[16];
        String hexEncodedFakeCookie;

        /* Make sure that this fake cookie is unique for this connection */

        while (true) {
            rnd.nextBytes(fakeCookie);
            /* Generate also hex representation of fake cookie */
            StringBuilder tmp = new StringBuilder(32);

            for (int i = 0; i < fakeCookie.length; i++) {
                String digit2 = Integer.toHexString(fakeCookie[i] & 0xff);
                tmp.append((digit2.length() == 2) ? digit2 : "0" + digit2);
            }

            hexEncodedFakeCookie = tmp.toString();

            /* Well, yes, chances are low, but we want to be on the safe side */

            if (cm.checkX11Cookie(hexEncodedFakeCookie) == null)
                break;
        }

        /* Ask for X11 forwarding */
        cm.requestX11(cn, singleConnection, "MIT-MAGIC-COOKIE-1", hexEncodedFakeCookie, 0);

        /* OK, that went fine, get ready to accept X11 connections... */
        /* ... but only if the user has not called close() in the meantime =) */

        synchronized (this) {
            if (flag_closed == false) {
                this.x11FakeCookie = hexEncodedFakeCookie;
                cm.registerX11Cookie(hexEncodedFakeCookie, x11data);
            }
        }

        /* Now it is safe to start remote X11 programs */
    }

    /**
     * Execute a command on the remote machine.
     *
     * @param cmd The command to execute on the remote host.
     * @throws IOException
     */
    public void execCommand(String cmd) throws IOException {
        this.execCommand(cmd, null);
    }

    /**
     * Execute a command on the remote machine.
     *
     * @param cmd The command to execute on the remote host.
     * @param charsetName The charset used to convert between Java Unicode Strings and byte encodings
     * @throws IOException
     */
    public void execCommand(String cmd, String charsetName) throws IOException {
        if (cmd == null)
            throw new IllegalArgumentException("cmd argument may not be null");

        synchronized (this) {
            /* The following is just a nicer error, we would catch it anyway later in the channel code */
            if (flag_closed)
                throw new IOException("This session is closed.");

            if (flag_execution_started)
                throw new IOException("A remote execution has already started.");

            flag_execution_started = true;
        }

        cm.requestExecCommand(cn, cmd, charsetName);
    }

    /**
     * Start a shell on the remote machine.
     *
     * @throws IOException
     */
    public void startShell() throws IOException {
        synchronized (this) {
            /* The following is just a nicer error, we would catch it anyway later in the channel code */
            if (flag_closed)
                throw new IOException("This session is closed.");

            if (flag_execution_started)
                throw new IOException("A remote execution has already started.");

            flag_execution_started = true;
        }

        cm.requestShell(cn);
    }

    /**
     * Start a subsystem on the remote machine.
     * Unless you know what you are doing, you will never need this.
     *
     * @param name the name of the subsystem.
     * @throws IOException
     */
    public void startSubSystem(String name) throws IOException {
        if (name == null)
            throw new IllegalArgumentException("name argument may not be null");

        synchronized (this) {
            /* The following is just a nicer error, we would catch it anyway later in the channel code */
            if (flag_closed)
                throw new IOException("This session is closed.");

            if (flag_execution_started)
                throw new IOException("A remote execution has already started.");

            flag_execution_started = true;
        }

        cm.requestSubSystem(cn, name);
    }

    /**
     * Request authentication agent forwarding.
     * @param agent object that implements the callbacks
     *
     * @throws IOException in case of any problem or when the session is closed
     */

    public synchronized void requestAuthAgentForwarding(AuthAgentCallback agent) throws IOException {
        synchronized (this) {
            /*
             * The following is just a nicer error, we would catch it anyway
             * later in the channel code
             */
            if (flag_closed)
                throw new IOException("This session is closed.");
        }

        cm.requestChannelAgentForwarding(cn, agent);
    }

    public int getState() {
        return cn.getState();
    }

    public InputStream getStdout() {
        return cn.getStdoutStream();
    }

    public InputStream getStderr() {
        return cn.getStderrStream();
    }

    public OutputStream getStdin() {
        return cn.getStdinStream();
    }

    /**
     * This method blocks until there is more data available on either the
     * stdout or stderr InputStream of this <code>Session</code>. Very useful
     * if you do not want to use two parallel threads for reading from the two
     * InputStreams. One can also specify a timeout. NOTE: do NOT call this
     * method if you use concurrent threads that operate on either of the two
     * InputStreams of this <code>Session</code> (otherwise this method may
     * block, even though more data is available).
     *
     * @param timeout The (non-negative) timeout in <code>ms</code>. <code>0</code> means no
     * timeout, the call may block forever.
     * @return <ul>
     *         <li><code>0</code> if no more data will arrive.</li>
     *         <li><code>1</code> if more data is available.</li>
     *         <li><code>-1</code> if a timeout occurred.</li>
     *         </ul>
     * @throws IOException
     * @deprecated This method has been replaced with a much more powerful wait-for-condition
     *             interface and therefore acts only as a wrapper.
     */
    public int waitUntilDataAvailable(long timeout) throws IOException {
        if (timeout < 0)
            throw new IllegalArgumentException("timeout must not be negative!");

        int conditions = cm.waitForCondition(cn, timeout, ChannelCondition.STDOUT_DATA | ChannelCondition.STDERR_DATA
                                             | ChannelCondition.EOF);

        if ((conditions & ChannelCondition.TIMEOUT) != 0)
            return -1;

        if ((conditions & (ChannelCondition.STDOUT_DATA | ChannelCondition.STDERR_DATA)) != 0)
            return 1;

        /* Here we do not need to check separately for CLOSED, since CLOSED implies EOF */

        if ((conditions & ChannelCondition.EOF) != 0)
            return 0;

        throw new IllegalStateException("Unexpected condition result (" + conditions + ")");
    }

    /**
     * This method blocks until certain conditions hold true on the underlying SSH-2 channel.
     * <p/>
     * This method returns as soon as one of the following happens:
     * <ul>
     * <li>at least of the specified conditions (see {@link ChannelCondition}) holds true</li>
     * <li>timeout > 0 and a timeout occured (TIMEOUT will be set in result conditions)</a>
     * <li>the underlying channel was closed (CLOSED will be set in result conditions)</a>
     * </ul>
     * <p/>
     * In any case, the result value contains ALL current conditions, which may be more
     * than the specified condition set (i.e., never use the "==" operator to test for conditions
     * in the bitmask, see also comments in {@link ChannelCondition}).
     * <p/>
     * Note: do NOT call this method if you want to wait for STDOUT_DATA or STDERR_DATA and
     * there are concurrent threads (e.g., StreamGobblers) that operate on either of the two
     * InputStreams of this <code>Session</code> (otherwise this method may
     * block, even though more data is available in the StreamGobblers).
     *
     * @param condition_set a bitmask based on {@link ChannelCondition} values
     * @param timeout non-negative timeout in ms, <code>0</code> means no timeout
     * @return all bitmask specifying all current conditions that are true
     */

    public int waitForCondition(int condition_set, long timeout) throws IOException {
        if (timeout < 0)
            throw new IllegalArgumentException("timeout must be non-negative!");

        return cm.waitForCondition(cn, timeout, condition_set);
    }

    /**
     * Get the exit code/status from the remote command - if available. Be
     * careful - not all server implementations return this value. It is
     * generally a good idea to call this method only when all data from the
     * remote side has been consumed (see also the <code<WaitForCondition</code> method).
     *
     * @return An <code>Integer</code> holding the exit code, or
     *         <code>null</code> if no exit code is (yet) available.
     */
    public Integer getExitStatus() {
        return cn.getExitStatus();
    }

    /**
     * Get the name of the signal by which the process on the remote side was
     * stopped - if available and applicable. Be careful - not all server
     * implementations return this value.
     *
     * @return An <code>String</code> holding the name of the signal, or
     *         <code>null</code> if the process exited normally or is still
     *         running (or if the server forgot to send this information).
     */
    public String getExitSignal() {
        return cn.getExitSignal();
    }

    /**
     * Close this session. NEVER forget to call this method to free up resources -
     * even if you got an exception from one of the other methods (or when
     * getting an Exception on the Input- or OutputStreams). Sometimes these other
     * methods may throw an exception, saying that the underlying channel is
     * closed (this can happen, e.g., if the other server sent a close message.)
     * However, as long as you have not called the <code>close()</code>
     * method, you may be wasting (local) resources.
     */
    public void close() {
        synchronized (this) {
            if (flag_closed)
                return;

            flag_closed = true;

            if (x11FakeCookie != null)
                cm.unRegisterX11Cookie(x11FakeCookie, true);

            try {
                cm.closeChannel(cn, "Closed due to user request", true);
            }
            catch (IOException ignored) {
            }
        }
    }
}