/*
 * Copyright 2016 Anton Tananaev (anton@traccar.org)
 *
 * Licensed 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.traccar.protocol;

import org.jboss.netty.buffer.ChannelBuffer;
import org.jboss.netty.buffer.ChannelBuffers;
import org.jboss.netty.channel.Channel;
import org.traccar.BaseProtocolDecoder;
import org.traccar.DeviceSession;
import org.traccar.helper.UnitsConverter;
import org.traccar.model.Position;

import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import javax.xml.bind.DatatypeConverter;
import java.net.SocketAddress;
import java.nio.ByteOrder;
import java.nio.charset.StandardCharsets;
import java.util.Date;

public class At2000ProtocolDecoder extends BaseProtocolDecoder {

    private static final int BLOCK_LENGTH = 16;

    public At2000ProtocolDecoder(At2000Protocol protocol) {
        super(protocol);
    }

    public static final int MSG_ACKNOWLEDGEMENT = 0x00;
    public static final int MSG_DEVICE_ID = 0x01;
    public static final int MSG_TRACK_REQUEST = 0x88;
    public static final int MSG_TRACK_RESPONSE = 0x89;
    public static final int MSG_SESSION_END = 0x0c;

    private Cipher cipher;

    private static void sendResponse(Channel channel) {
        if (channel != null) {
            ChannelBuffer response = ChannelBuffers.directBuffer(ByteOrder.LITTLE_ENDIAN, BLOCK_LENGTH);
            response.writeByte(MSG_ACKNOWLEDGEMENT);
            response.writeMedium(1);
            response.writeByte(0x00); // success
            response.writerIndex(BLOCK_LENGTH);
            channel.write(response);
        }
    }

    @Override
    protected Object decode(
            Channel channel, SocketAddress remoteAddress, Object msg) throws Exception {

        ChannelBuffer buf = (ChannelBuffer) msg;

        if (buf.getUnsignedByte(buf.readerIndex()) == 0x01) {
            buf.readUnsignedByte(); // codec id
        }

        int type = buf.readUnsignedByte();
        buf.readUnsignedMedium(); // length
        buf.skipBytes(BLOCK_LENGTH - 1 - 3);

        if (type == MSG_DEVICE_ID) {

            String imei = buf.readBytes(15).toString(StandardCharsets.US_ASCII);
            if (getDeviceSession(channel, remoteAddress, imei) != null) {

                byte[] iv = new byte[BLOCK_LENGTH];
                buf.readBytes(iv);
                IvParameterSpec ivSpec = new IvParameterSpec(iv);

                SecretKeySpec keySpec = new SecretKeySpec(
                        DatatypeConverter.parseHexBinary("000102030405060708090a0b0c0d0e0f"), "AES");

                cipher = Cipher.getInstance("AES/CBC/NoPadding");
                cipher.init(Cipher.DECRYPT_MODE, keySpec, ivSpec);

                byte[] data = new byte[BLOCK_LENGTH];
                buf.readBytes(data);
                cipher.update(data);

            }

        } else if (type == MSG_TRACK_RESPONSE) {

            DeviceSession deviceSession = getDeviceSession(channel, remoteAddress);
            if (deviceSession == null) {
                return null;
            }

            Position position = new Position();
            position.setProtocol(getProtocolName());
            position.setDeviceId(deviceSession.getDeviceId());

            byte[] data = new byte[buf.capacity() - BLOCK_LENGTH];
            buf.readBytes(data);
            buf = ChannelBuffers.wrappedBuffer(ByteOrder.LITTLE_ENDIAN, cipher.update(data));

            buf.readUnsignedShort(); // index
            buf.readUnsignedShort(); // reserved

            position.setValid(true);

            position.setTime(new Date(buf.readLong() * 1000));

            position.setLatitude(buf.readFloat());
            position.setLongitude(buf.readFloat());
            position.setAltitude(buf.readFloat());
            position.setSpeed(UnitsConverter.knotsFromKph(buf.readFloat()));
            position.setCourse(buf.readFloat());

            return position;

        }

        sendResponse(channel);

        return null;
    }

}

@@ -1879,16 +1879,20 @@
 _ENDIAN,
+ 2 *
  BLOCK_L
@@ -1891,32 +1891,32 @@
  BLOCK_LENGTH);%0A
-
             resp
@@ -1985,17 +1985,44 @@
 eMedium(
-1
+ChannelBuffers.swapMedium(1)
 );%0A     
@@ -2065,16 +2065,16 @@
 success%0A
-
         
@@ -2098,16 +2098,20 @@
 erIndex(
+2 * 
 BLOCK_LE

Fix AT2000 response (fix #2662)