/*

 * 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.

 *

 * 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.

 */

import java.io.ByteArrayOutputStream;

import java.io.Closeable;

import java.io.IOException;

import java.io.InputStream;

import java.io.OutputStream;

import java.net.InetAddress;

import java.net.ServerSocket;

import java.net.Socket;

import java.util.ArrayList;

import java.util.Arrays;

import java.util.HashSet;

import java.util.List;

import java.util.Objects;

import java.util.Set;

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors;

import java.util.concurrent.RejectedExecutionException;

import java.util.concurrent.ThreadFactory;

import java.util.concurrent.TimeUnit;

import java.util.stream.Stream;

import static java.lang.StackWalker.Option.RETAIN_CLASS_REFERENCE;

/**

 * A base dummy ldap server.

 *

 * For any ldap tests which required a simple dummy server to support the

 * test, may use this server directly with specifying ConnectionHandler,

 * SessionHandler/RequestHandler, or extends to build more complex server logic.

 *

 * This server already extends Thread and implements AutoCloseable, so it can

 * be started in thread and integrated with try-with-resources

 *

 * To initiate a instance of this server, valid ServerSocket could be supplied,

 * it will allow the flexibility for listening address/port customization

 * and SSL usage, for default no parameter constructor, a ServerSocket which

 * listen on loopback address will be created.

 *

 * To use this dummy server in test, user could customize the processing logic

 * in three level with below handler interface.

 *   -ConnectionHandler provide connection level handling, server will hand

 *                      over accepted socket and processing thread to handler.

 *                      By default, DefaultConnectionHandler will be used if no

 *                      specified, it reads full ldap request message then

 *                      pass it to RequestHandler instance which returned by

 *                      SessionHandler per session.

 *

 *   -SessionHandler    provide session level handling when DefaultConnectionHandler

 *                      been used, it's to retrieve RequestHandler instance of

 *                      current session.

 *                      For most of tests, only one session need to be handled

 *                      on server or all ldap request could be handled by same

 *                      logic whatever current session is, user can use

 *                      setCommonRequestHandler to setup one single session

 *                      handler which will always return given RequestHandler

 *                      instance.

 *

 *   -RequestHandler    provide ldap message request handling when

 *                      DefaultConnectionHandler been used.

 *

 * @see ConnectionHandler

 * @see SessionHandler

 * @see RequestHandler

 */

public class BaseLdapServer extends Thread implements AutoCloseable {

    private volatile boolean isRunning;

    private final List<Socket> socketList = new ArrayList<>();

    private ServerSocket serverSocket;

    private ExecutorService workingPool;

    private ConnectionHandler connectionHandler;

    private SessionHandler sessionHandler;

    enum DebugLevel {

        FULL,      // all debug message will be printed

        NONE,      // none of debug message will be printed

        CUSTOMIZE  // only specified class debug message will be printed

    }

    private StackWalker stackWalker = null;

    private DebugLevel debugLevel = DebugLevel.NONE;

    private Set<Class<?>> debugOptions = new HashSet<>();

    /**

     * BaseLdapServer overload default constructor.

     *

     * @throws IOException if an I/O error occurs when opening the socket.

     */

    public BaseLdapServer() throws IOException {

        this(new ServerSocket(0, 0, InetAddress.getLoopbackAddress()));

    }

    /**

     * BaseLdapServer constructor with given server socket and specify whether

     * use daemon for each accept connection handling thread.

     *

     * @param serverSocket    given server socket

     */

    public BaseLdapServer(ServerSocket serverSocket) {

        this.serverSocket = Objects.requireNonNull(serverSocket);

        workingPool = Executors.newCachedThreadPool();

        try {

            stackWalker = StackWalker.getInstance(RETAIN_CLASS_REFERENCE);

        } catch (SecurityException se) {

            // just ignore

        }

    }

    @Override

    public void run() {

        if (getConnectionHandler() == null) {

            debug("INFO: No connection handler been specified, try default.");

            connectionHandler = new DefaultConnectionHandler();

        }

        debug("INFO: Using connection handler : " + getConnectionHandler()

                .getClass().getName());

        debug("INFO: LdapServer running and listening on port " + getPort());

        try {

            while (isRunning) {

                Socket socket = serverSocket.accept();

                debug("INFO: Accept new connection " + socket);

                synchronized (socketList) {

                    socketList.add(socket);

                }

                workingPool.submit(() -> getConnectionHandler()

                        .handleConnection(socket));

            }

        } catch (IOException | RejectedExecutionException e) {

            if (isRunning) {

                throw new RuntimeException(e);

            } else {

                debug("INFO: Server exit.");

            }

        }

    }

    /*

     * Override Thread.start()

     */

    @Override

    public synchronized void start() {

        super.start();

    }

    /**

     * Start Server thread and return itself for method chaining

     *

     * @return current server instance

     */

    @SuppressWarnings("unchecked")

    public <T extends BaseLdapServer> T startServer() {

        start();

        return (T) this;

    }

    /**

     * Stop server.

     */

    public void stopServer() {

        debug("INFO: Stopping Server.");

        isRunning = false;

        workingPool.shutdown();

        cleanupClosableRes(serverSocket);

        // let's cleanup thread pool

        synchronized (socketList) {

            socketList.forEach(BaseLdapServer::cleanupClosableRes);

        }

        try {

            if (!workingPool.awaitTermination(10, TimeUnit.SECONDS)) {

                workingPool.shutdownNow();

            }

        } catch (InterruptedException e) {

            workingPool.shutdownNow();

            Thread.currentThread().interrupt();

        }

    }

    /**

     * Return local port which server is listening.

     *

     * @return port which server is listening

     */

    public int getPort() {

        if (serverSocket != null) {

            return serverSocket.getLocalPort();

        } else {

            return -1;

        }

    }

    /**

     * Return flag to indicate whether current server is running.

     *

     * @return <tt>true</tt> if current server is running.

     */

    public boolean isRunning() {

        return isRunning;

    }

    /**

     * Return ConnectionHandler instance

     *

     * @return ConnectionHandler instance

     * @see ConnectionHandler

     */

    ConnectionHandler getConnectionHandler() {

        return connectionHandler;

    }

    /**

     * Set ConnectionHandler when server is not running.

     *

     * @param connHandler ConnectionHandler instance

     * @return current server instance for method chaining

     */

    @SuppressWarnings("unchecked")

    public <T extends BaseLdapServer> T setConnectionHandler(

            ConnectionHandler connHandler) {

        if (!isRunning) {

            connectionHandler = connHandler;

        }

        return (T) this;

    }

    /**

     * Return SessionHandler instance

     *

     * @return SessionHandler instance

     * @see SessionHandler

     */

    SessionHandler getSessionHandler() {

        return sessionHandler;

    }

    /**

     * Set SessionHandler when server is not running.

     *

     * @param sessionHandler given SessionHandler

     * @return current server instance for method chaining

     */

    @SuppressWarnings("unchecked")

    public <T extends BaseLdapServer> T setSessionHandler(

            SessionHandler sessionHandler) {

        if (!isRunning) {

            this.sessionHandler = sessionHandler;

        }

        return (T) this;

    }

    /**

     * Set one common RequestHandler, it will be used to handle all requests

     * whatever current session is.

     *

     * For most of tests, server only need to handle one session, use this

     * method will create stateless session handler with given request handler.

     *

     * @param requestHandler RequestHandler instance

     * @return current server instance for method chaining

     */

    @SuppressWarnings("unchecked")

    public <T extends BaseLdapServer> T setCommonRequestHandler(

            RequestHandler requestHandler) {

        if (!isRunning) {

            // ignore any session, always return fixed request handler

            setSessionHandler(socket -> requestHandler);

        }

        return (T) this;

    }

    @Override

    public void close() {

        stopServer();

    }

    /**

     * Cleanup any given closable resource

     *

     * @param res given closable resource

     */

    static void cleanupClosableRes(Closeable res) {

        if (res != null) {

            try {

                res.close();

            } catch (IOException e) {

                // ignore

            }

        }

    }

    /**

     * Set debug level to specify which kinds of debug message will be printed.

     *

     * @param debugLevel given debug level

     * @param opts       given opts if debug level is DebugLevel.CUSTOMIZE

     * @return current server instance for method chaining

     */

    @SuppressWarnings("unchecked")

    public <T extends BaseLdapServer> T setDebugLevel(DebugLevel debugLevel,

            Class<?>... opts) {

        Objects.requireNonNull(debugLevel);

        if (!isRunning) {

            this.debugLevel = debugLevel;

            if (debugLevel == DebugLevel.CUSTOMIZE) {

                debugOptions.clear();

                Stream.of(opts).filter(Objects::nonNull)

                        .forEach(debugOptions::add);

            }

        }

        return (T) this;

    }

    /**

     * Print given message if debug enabled.

     *

     * @param message given message to print

     */

    void debug(String message) {

        switch (debugLevel) {

            case FULL:

                System.out.println((stackWalker != null ?

                        stackWalker.getCallerClass().getName() :

                        "") + ": " + message);

                break;

            case CUSTOMIZE:

                if (stackWalker != null) {

                    if (debugOptions.contains(stackWalker.getCallerClass())) {

                        System.out.println(

                                stackWalker.getCallerClass().getName() + ": "

                                        + message);

                    }

                }

                break;

            case NONE:

            default:

                break;

        }

    }

    /**

     * Default connection handler implementation.

     */

    class DefaultConnectionHandler implements ConnectionHandler {

        @Override

        public void handleConnection(Socket socket) {

            try (socket;

                    OutputStream out = socket.getOutputStream();

                    InputStream in = socket.getInputStream()) {

                byte[] inBuffer = new byte[1024];

                int count;

                byte[] request;

                ByteArrayOutputStream buffer = new ByteArrayOutputStream();

                int msgLen = -1;

                while ((count = in.read(inBuffer)) > 0) {

                    buffer.write(inBuffer, 0, count);

                    if (msgLen <= 0) {

                        msgLen = getMessageLength(buffer.toByteArray());

                    }

                    if (msgLen > 0 && buffer.size() >= msgLen) {

                        if (buffer.size() > msgLen) {

                            byte[] tmpBuffer = buffer.toByteArray();

                            request = Arrays.copyOf(tmpBuffer, msgLen);

                            buffer.reset();

                            buffer.write(tmpBuffer, msgLen,

                                    tmpBuffer.length - msgLen);

                        } else {

                            request = buffer.toByteArray();

                            buffer.reset();

                        }

                        msgLen = -1;

                    } else {

                        debug("INFO: request msg not complete, received "

                                + buffer.size() + ", expected " + msgLen);

                        continue;

                    }

                    if (getSessionHandler() != null) {

                        var handler = getSessionHandler()

                                .getRequestHandler(socket);

                        if (handler != null) {

                            debug("INFO: Process request. Session handler : "

                                    + getSessionHandler()

                                    + ", Request handler : " + handler);

                            handler.handleRequest(new LdapMessage(request),

                                    out);

                        } else {

                            debug("WARNING: no valid request handler returned from "

                                    + getSessionHandler() + ", " + socket);

                        }

                    } else {

                        debug("WARNING: no valid session handler been specified, discard request.");

                    }

                }

                debug("INFO: Connection Handler exit.");

            } catch (IOException e) {

                if (!isRunning()) {

                    debug("INFO: Connection Handler exit : " + e.getMessage());

                } else {

                    e.printStackTrace();

                }

            }

        }

        private int getMessageLength(byte[] encoding) {

            if (encoding.length < 2) {

                // no enough data to extract msg len, just return -1

                return -1;

            }

            if (encoding[0] != 0x30) {

                throw new RuntimeException("Error: bad LDAP encoding message: "

                        + "expected ASN.1 SEQUENCE tag (0x30), encountered "

                        + encoding[0]);

            }

            int len;

            int index = 1;

            int payloadLen = 0;

            if ((encoding[1] & 0x80) == 0x80) {

                len = (encoding[1] & 0x0F);

                index++;

            } else {

                len = 1;

            }

            if (len > 4) {

                throw new RuntimeException(

                        "Error: LDAP encoding message payload too large");

            }

            if (encoding.length < index + len) {

                // additional data required to extract payload len, return -1

                return -1;

            }

            for (byte b : Arrays.copyOfRange(encoding, index, index + len)) {

                payloadLen = payloadLen << 8 | (b & 0xFF);

            }

            if (payloadLen <= 0) {

                throw new RuntimeException(

                        "Error: invalid LDAP encoding message length or payload too large");

            }

            return index + len + payloadLen;

        }

    }

}