/*******************************************************************************
 *
 * Copyright (c) 2004-2009 Oracle Corporation.
 *
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *
 *    Kohsuke Kawaguchi
 *
 *******************************************************************************/ 

package hudson.os;

import java.io.ByteArrayOutputStream;
import java.io.EOFException;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.List;
import java.util.ArrayList;
import java.util.Collection;
import java.util.logging.Logger;

/**
 * Encapsulates the process launch through <tt>su</tt> (embedded_su(1M) to be
 * exact)
 *
 * @author Kohsuke Kawaguchi
 */
public class EmbeddedSu {

    /**
     * Not meant to be instantiated.
     */
    private EmbeddedSu() {
    }

    /**
     * Launches a process as configured by {@link ProcessBuilder}, but under a
     * separate user priviledge by using <tt>su</tt> functionality.
     *
     * @param user The user name in which the new process runs.
     * @param pwd The password of the user.
     */
    public static Process startWithSu(String user, String pwd, ProcessBuilder pb) throws IOException {
        if (user == null || pwd == null) {
            throw new IllegalArgumentException();
        }

        // su only invokes a shell, so the argument has to be packed into the -c option
        StringBuilder buf = new StringBuilder("exec ");
        for (String cmd : pb.command()) {
            buf.append(' ');
            // to prevent shell from interfering with characters like '$' and '`',
            // put everything in single-quotes. When we do this, single-quotes in
            // arguments have to be escaped.
            buf.append('\'').append(cmd.replaceAll("\'", "'\''")).append('\'');
        }

        List<String> cmds = pb.command();
        cmds.clear();
        cmds.addAll(Arrays.asList("/usr/lib/embedded_su", user, "-c", buf.toString()));

        // now the command line massage is ready. start a process
        Process proc = pb.start();

        PrintWriter out = new PrintWriter(proc.getOutputStream(), true);
        InputStream in = proc.getInputStream();
        // send initialization block
        LOGGER.fine("Initiating embedded_su conversation");
        out.println(".");

        /*
         embedded_su often sends us PAM_ERROR_MSG that's useful, so capture them.
         alice@opensolaris:~$ /usr/lib/embedded_su root
         .
         CONV 1
         PAM_PROMPT_ECHO_OFF
         Password:
         .
         root
         CONV 1
         PAM_ERROR_MSG
         Roles can only be assumed by authorized users
         .
         ERROR
         embedded_su: Sorry
         .
         */
        List<String> errorMessages = new ArrayList<String>();

        while (true) {
            String line = readLine(in);
            if (line.startsWith("CONV")) {
                // how many blocks do we expect?
                int n = Integer.parseInt(line.substring(5));
                for (int i = 0; i < n; i++) {
                    String header = readLine(in);
                    String textBlock = readTextBlock(in);
                    LOGGER.fine("Got " + header + " : " + textBlock);
                    if (header.startsWith("PAM_PROMPT_ECHO_OFF")) {
                        // this is where we want to send the password
                        // if we are asked the password for the 2nd time, it's rather unlikely that
                        // the same value is expected --- instead, its' probably a retry.
                        out.println(pwd);
                        pwd = null;
                    }
                    if (header.startsWith("PAM_PROMPT_ECHO_ON")) {
                        // embedded_su expects some value but this is probably not where we want to send the password
                        out.println();
                    }
                    if (header.startsWith("PAM_ERROR_MSG")) {
                        errorMessages.add(textBlock);
                    }
                    // ignore the rest
                }
                continue;
            }
            if (line.startsWith("SUCCESS")) {
                LOGGER.fine("Authentication successful: " + line);
                return proc;
            }
            if (line.startsWith("ERROR")) {
                LOGGER.fine("Authentication faied: " + line);
                throw new SuAuthenticationFailureException(readTextBlock(in) + join(errorMessages));
            }

            LOGGER.fine("Unrecognized response: " + line);
            throw new IOException("Unrecognized response from embedded_su " + line);
        }
    }

    private static String join(Collection<String> col) {
        StringBuilder buf = new StringBuilder();
        for (String a : col) {
            buf.append(a);
        }
        return buf.toString();
    }

    /**
     * Reads a line from the given input stream, without any read ahead.
     *
     * Line end is '\n', as this is for Solaris.
     */
    private static String readLine(InputStream in) throws IOException {
        ByteArrayOutputStream buf = new ByteArrayOutputStream();
        int ch;

        while ((ch = in.read()) != -1) {
            if (ch == '\n') {
                return buf.toString();
            }
            buf.write(ch);
        }
        throw new EOFException();
    }

    /**
     * Reads the text block.
     */
    private static String readTextBlock(InputStream in) throws IOException {
        StringBuilder buf = new StringBuilder();

        while (true) {
            String line = readLine(in);
            if (line.equals(".")) {
                return buf.toString(); // end of it
            }
            if (line.startsWith("..")) {
                buf.append(line.substring(1));
            } else {
                buf.append(line);
            }
            buf.append('\n');
        }
    }
    private static final Logger LOGGER = Logger.getLogger(EmbeddedSu.class.getName());
}