/*
 * Copyright 2019 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 io.netty.buffer.ByteBuf;
import io.netty.channel.Channel;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.TooLongFrameException;
import java.nio.charset.StandardCharsets;
import org.traccar.BaseFrameDecoder;

public class NavisFrameDecoder extends BaseFrameDecoder {

    private static final int NTCB_HEADER_LENGTH = 16;
    private static final int NTCB_LENGTH_OFFSET = 12;
    private static final int FLEX_HEADER_LENGTH = 2;
    private static final int MAX_FRAME_LENGTH = 65551;

    private final NavisProtocolDecoder protocolDecoder;

    public NavisFrameDecoder(NavisProtocolDecoder protocolDecoder) {
        this.protocolDecoder = protocolDecoder;
    }

    @Override
    protected Object decode(
            ChannelHandlerContext ctx, Channel channel, ByteBuf buf) throws Exception {

        // Check minimum length
        if (buf.readableBytes() < 1) {
            return null;
        }

        if (buf.getByte(buf.readerIndex()) == 0x7F) {
            // FLEX keep alive frame
            return buf.readRetainedSlice(1);
        }

        if (protocolDecoder.getFlexDataSize() > 0) {
            // FLEX frame
            if (buf.readableBytes() > MAX_FRAME_LENGTH) {
                throw new TooLongFrameException();
            }

            if (buf.readableBytes() > FLEX_HEADER_LENGTH) {
                int length = 0;
                String type = buf.toString(buf.readerIndex(), 2, StandardCharsets.US_ASCII);
                switch (type) {
                    // FLEX 1.0
                    case "~A":
                        length = protocolDecoder.getFlexDataSize()
                                * buf.getByte(buf.readerIndex() + FLEX_HEADER_LENGTH) + 1 + 1;
                        break;
                    case "~T":
                        length = protocolDecoder.getFlexDataSize() + 4 + 1;
                        break;
                    case "~C":
                        length = protocolDecoder.getFlexDataSize() + 1;
                        break;
                    // FLEX 2.0 (Extra packages)
                    case "~E":
                        length++;
                        for (int i = 0; i < buf.getByte(buf.readerIndex() + FLEX_HEADER_LENGTH); i++) {
                            if (buf.readableBytes() > FLEX_HEADER_LENGTH + length + 1) {
                                length += buf.getUnsignedShort(length + FLEX_HEADER_LENGTH) + 2;
                            } else {
                                return null;
                            }
                        }
                        length++;
                        break;
                    case "~X":
                        length = buf.getUnsignedShortLE(buf.readerIndex() + FLEX_HEADER_LENGTH) + 4 + 1;
                        break;
                    default:
                        return null;
                }

                if (buf.readableBytes() >= FLEX_HEADER_LENGTH + length) {
                    return buf.readRetainedSlice(buf.readableBytes());
                }
            }
        } else {
            // NTCB frame
            if (buf.readableBytes() < NTCB_HEADER_LENGTH) {
                return null;
            }

            int length = buf.getUnsignedShortLE(buf.readerIndex() + NTCB_LENGTH_OFFSET);
            if (buf.readableBytes() >= NTCB_HEADER_LENGTH + length) {
                if (buf.readableBytes() > MAX_FRAME_LENGTH) {
                    throw new TooLongFrameException();
                }
                return buf.readRetainedSlice(NTCB_HEADER_LENGTH + length);
            }
        }

        return null;
    }

}