/*
 * Copyright 2017 Valerii Vyshniak (val@val.one)
 * Copyright 2017 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.channel.Channel;
import org.jboss.netty.channel.ChannelHandlerContext;
import org.jboss.netty.handler.codec.frame.FrameDecoder;

public class Tk103FrameDecoder extends FrameDecoder {

    private static final int FRAME_MIN_SIZE = 2;
    private static final int FRAME_MAX_SIZE = 1024;
    private static final byte FRAME_START_SYMBOL = (byte) '(';
    private static final byte FRAME_END_SYMBOL = (byte) ')';
    private static final byte FRAME_FREE_TEXT_BLOCK_SYMBOL = (byte) '$';

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

        if (buf.readableBytes() < FRAME_MIN_SIZE) {
            return null;
        }

        int indexStart = buf.indexOf(buf.readerIndex(), buf.writerIndex(), FRAME_START_SYMBOL);
        if (indexStart == -1) {
            buf.clear();
            return null;
        }
        indexStart++;

        int index, cnt;
        for (index = indexStart, cnt = 0;; index++) {
            int i = index;
            index = buf.indexOf(index, buf.writerIndex(), FRAME_END_SYMBOL);
            if (index == -1) {
                break;
            }
            for (;; i++, cnt++) {
                i = buf.indexOf(i, index, FRAME_FREE_TEXT_BLOCK_SYMBOL);
                if (i == -1 || i >= index) {
                    break;
                }
            }
            if (cnt % 2 == 0) {
                break;
            }
        }

        if (index == -1) {
            while (buf.readableBytes() > FRAME_MAX_SIZE) {
                int i = buf.indexOf(buf.readerIndex() + 1, buf.writerIndex(), FRAME_START_SYMBOL);
                if (i == -1) {
                    buf.clear();
                } else {
                    buf.readerIndex(i);
                }
            }
            return null;
        }

        buf.readerIndex(indexStart);
        ChannelBuffer result = buf.readBytes(index - indexStart);
        buf.readerIndex(buf.readerIndex() + 1);

        return result;

    }

}