// Copyright (C) 2010 Mike Linden
// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License
// as published by the Free Software Foundation; either version 2
// of the License, or (at your option) any later version.
//
// This program 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 for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.

package org.ex.ws.net.codec;

import java.security.SecureRandom;
import java.util.logging.Logger;

import org.ex.constants.GlobalConstants;
import org.ex.core.util.ChannelBufferUtils;
import org.ex.ws.model.World;
import org.ex.ws.model.player.PlayerDetails;
import org.ex.ws.net.ISAACCipher;
import org.ex.ws.net.codec.game.GamePacketBuilder;
import org.ex.ws.net.ondemand.OnDemandPool;
import org.ex.ws.net.ondemand.OnDemandRequest;
import org.ex.ws.util.NameUtils;
import org.jboss.netty.buffer.ChannelBuffer;
import org.jboss.netty.channel.Channel;
import org.jboss.netty.channel.ChannelHandlerContext;
import org.jboss.netty.handler.codec.replay.ReplayingDecoder;

/**
 * Login protocol decoding class.
 *
 * @author Mike
 *
 */
public final class RS2LoginDecoder extends ReplayingDecoder<RS2LoginStage> {

    /**
     * Logger instance.
     */
    private static final Logger logger = Logger.getLogger(RS2LoginDecoder.class
            .getName());

    /**
     * Packet opcode for game requests.
     */
    public static final int OPCODE_GAME = 14;

    /**
     * Packet opcode for update requests.
     */
    public static final int OPCODE_UPDATE = 15;

    /**
     * The secured random number generator.
     */
    private static final SecureRandom random = new SecureRandom();

    /**
     * The initial login response data.
     */
    private static final byte[] INITIAL_RESPONSE = new byte[] { 0x0, 0x0, 0x0,
            0x0, 0x0, 0x0, 0x0, 0x0 };

    @Override
    protected Object decode(ChannelHandlerContext ctx, Channel channel,
            ChannelBuffer buffer, RS2LoginStage stage) throws Exception {
        switch (stage) {
        case UPDATE:
            /*
             * Here we read the cache id (idx file), file id and priority.
             */
            int cacheId = buffer.readUnsignedByte();
            int fileId = (buffer.readUnsignedByte() << 8)
                    | buffer.readUnsignedByte();
            int priority = buffer.readUnsignedByte();

            /*
             * We push the request into the on-demand pool so it can be served.
             */
            OnDemandPool.getOnDemandPool().pushRequest(
                    new OnDemandRequest(channel, cacheId, fileId, priority));

            break;
        case OPCODE:
            /*
             * Here we read the first opcode which indicates the type of
             * connection.
             *
             * 14 = game, 15 = update.
             *
             * Updating is disabled in the vast majority of 317 clients.
             */
            int opcode = buffer.readUnsignedByte();
            switch (opcode) {
            case OPCODE_GAME:
                checkpoint(RS2LoginStage.LOGIN);
                return null;
            case OPCODE_UPDATE:
                checkpoint(RS2LoginStage.UPDATE);
                channel.write(new GamePacketBuilder().put(INITIAL_RESPONSE)
                        .toGamePacket());
                return null;
            }

            break;
        case LOGIN:
            /*
             * The name hash is a simple hash of the name which is suspected to
             * be used to select the appropiate login server.
             */
            @SuppressWarnings("unused")
            int nameHash = buffer.readUnsignedByte();

            /*
             * We generated the server session key using a SecureRandom class
             * for security.
             */
            long serverKey = random.nextLong();

            /*
             * The initial response is just 0s which the client is set to ignore
             * (probably some sort of modification).
             */
            channel.write(new GamePacketBuilder().put(INITIAL_RESPONSE)
                    .put((byte) 0).putLong(serverKey).toGamePacket());
            checkpoint(RS2LoginStage.PRECRYPTED);
            RS2ChannelAttributes.SERVER_KEY.set(channel, serverKey);
            return null;

        case PRECRYPTED:
            /*
             * Read the type of login.
             *
             * 16 = normal, 18 = reconnection.
             */
            int loginOpcode = buffer.readUnsignedByte();
            if (loginOpcode != 16 && loginOpcode != 18) {
                logger.info("Invalid login opcode : " + loginOpcode);
                channel.close();
                return null;
            }

            /*
             * Read the size of the login packet.
             */
            int loginSize = buffer.readUnsignedByte();

            /*
             * And calculate how long the encrypted block will be.
             */
            int loginEncryptSize = loginSize - (36 + 1 + 1 + 2);

            /*
             * This could be invalid, if so, ignore it.
             */
            if (loginEncryptSize <= 0) {
                logger.info("Encrypted packet size zero or negative : "
                        + loginEncryptSize);
                channel.close();
                return null;
            }
            checkpoint(RS2LoginStage.CRYPTED);
            RS2ChannelAttributes.LOGIN_SIZE.set(channel, loginSize);
            RS2ChannelAttributes.LOGIN_SIZE_ENCRYPTED.set(channel,
                    loginEncryptSize);
            return null;
        case CRYPTED:
            int size = RS2ChannelAttributes.LOGIN_SIZE.get(channel);
            int encryptSize = RS2ChannelAttributes.LOGIN_SIZE_ENCRYPTED
                    .get(channel);
            if (super.actualReadableBytes() >= size) {
                /*
                 * Read the magic ID which is 255 (0xFF) which indicates this is
                 * the real login packet.
                 */
                final int magicId = buffer.readUnsignedByte();
                if (magicId != 255) {
                    logger.info("Incorrect magic id : " + magicId);
                    channel.close();
                    return null;
                }

                /*
                 * Now read a short which is the client version and check if it
                 * equals the server version.
                 */
                final int version = buffer.readUnsignedShort();
                if (version != GlobalConstants.VERSION) {
                    logger.info("Incorrect version : " + version);
                    channel.close();
                    return null;
                }

                /*
                 * The following byte indicates if the client is on low or high
                 * memory.
                 */
                @SuppressWarnings("unused")
                final boolean lowMemoryVersion = buffer.readUnsignedByte() == 1;

                /*
                 * Read the cache indices.
                 */
                for (int i = 0; i < 9; i++) {
                    buffer.readInt();
                }

                /*
                 * The encrypted size includes the size byte which is not
                 * needed.
                 */
                encryptSize--;

                /*
                 * Check if there is a mismatch in the sizing.
                 */
                final int reportedSize = buffer.readUnsignedByte();
                if (reportedSize != encryptSize) {
                    logger.info("Packet size mismatch (expected : "
                            + encryptSize + ", reported : " + reportedSize
                            + ")");
                    channel.close();
                    return null;
                }

                /*
                 * Now read the encrypted block opcode (although in most 317
                 * clients and this server the RSA is disabled) and check if it
                 * is equal to 10.
                 */
                int blockOpcode = buffer.readUnsignedByte();
                if (blockOpcode != 10) {
                    logger.info("Invalid login block opcode : " + blockOpcode);
                    channel.close();
                    return null;
                }

                /*
                 * Read the client's session key.
                 */
                long clientKey = buffer.readLong();

                /*
                 * And verifiy it has the correct server session key.
                 */
                long servKey = RS2ChannelAttributes.SERVER_KEY.get(channel);
                long reportedServerKey = buffer.readLong();
                if (reportedServerKey != servKey) {
                    logger.info("Server key mismatch (expected : " + servKey
                            + ", reported : " + reportedServerKey + ").");
                    channel.close();
                    return null;
                }

                /*
                 * The UID, found in random.dat in newer clients and uid.dat in
                 * older clients, is a way of identifying a computer.
                 *
                 * However, some clients send a hardcoded or random UID, making
                 * it useless in the private server scene.
                 *
                 * Excellia no longer uses any form of UID identification.
                 * Instead, a specific long is used which must match the server
                 * sided copy or the channel will close.
                 */
                // int uid = buffer.readInt();
                final long verification = buffer.readLong();
                if (verification != 839527L) {
                    logger.info("Invalid security verification (expected : 839527L, reported : "
                            + verification + ").");
                    channel.close();
                    return null;
                }

                /*
                 * Read and format the name and password.
                 */
                String name = NameUtils.formatName(ChannelBufferUtils
                        .getRS2String(buffer));
                String pass = ChannelBufferUtils.getRS2String(buffer);
                logger.info("Login request : username=" + name + " password="
                        + pass);

                /*
                 * Setup the ISAAC cipher which is used to encrypt and decrypt
                 * opcodes.
                 *
                 * However, without RSA, this is rendered useless anyway.
                 */
                int[] sessionKey = new int[4];
                sessionKey[0] = (int) (clientKey >> 32);
                sessionKey[1] = (int) clientKey;
                sessionKey[2] = (int) (servKey >> 32);
                sessionKey[3] = (int) servKey;

                this.setState(null);
                RS2ChannelAttributes.SERVER_KEY.remove(channel);
                RS2ChannelAttributes.LOGIN_SIZE.remove(channel);
                RS2ChannelAttributes.LOGIN_SIZE_ENCRYPTED.remove(channel);

                ISAACCipher inCipher = new ISAACCipher(sessionKey);
                for (int i = 0; i < 4; i++) {
                    sessionKey[i] += 50;
                }
                ISAACCipher outCipher = new ISAACCipher(sessionKey);

                /*
                 * The login has successfully completed, do the appropiate
                 * things to fire orr the chain of events which will load and
                 * check saved games, etc.
                 */
                channel.getPipeline().remove("protocol");
                channel.getPipeline()
                        .addFirst("protocol", RS2CodecFactory.GAME);

                PlayerDetails pd = new PlayerDetails(channel, name, pass,
                        inCipher, outCipher);
                World.getWorld().load(pd);
            }
        }
        return null;
    }

}