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The Apache Cassandra Project develops a highly scalable second-generation distributed database, bringing together Dynamo's fully distributed design and Bigtable's ColumnFamily-based data model.

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/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.apache.cassandra.transport;

import java.lang.reflect.Array;
import java.util.EnumMap;
import java.util.Map;

import io.netty.buffer.ByteBuf;

import io.netty.buffer.Unpooled;
import org.apache.cassandra.utils.Pair;

public class OptionCodec & OptionCodec.Codecable>
{
    public interface Codecable>
    {
        public int getId(int version);

        public Object readValue(ByteBuf cb, int version);
        public void writeValue(Object value, ByteBuf cb, int version);
        public int serializedValueSize(Object obj, int version);
    }

    private final Class klass;
    private final T[] ids;

    @SuppressWarnings({"unchecked"})
    public OptionCodec(Class klass)
    {
        this.klass = klass;

        T[] values = klass.getEnumConstants();
        int maxId = -1;
        for (T opt : values)
            maxId = Math.max(maxId, opt.getId(Server.CURRENT_VERSION));
        ids = (T[])Array.newInstance(klass, maxId + 1);
        for (T opt : values)
        {
            if (ids[opt.getId(Server.CURRENT_VERSION)] != null)
                throw new IllegalStateException(String.format("Duplicate option id %d", opt.getId(Server.CURRENT_VERSION)));
            ids[opt.getId(Server.CURRENT_VERSION)] = opt;
        }
    }

    private T fromId(int id)
    {
        T opt = ids[id];
        if (opt == null)
            throw new ProtocolException(String.format("Unknown option id %d", id));
        return opt;
    }

    public Map decode(ByteBuf body, int version)
    {
        EnumMap options = new EnumMap(klass);
        int n = body.readUnsignedShort();
        for (int i = 0; i < n; i++)
        {
            T opt = fromId(body.readUnsignedShort());
            Object value = opt.readValue(body, version);
            if (options.containsKey(opt))
                throw new ProtocolException(String.format("Duplicate option %s in message", opt.name()));
            options.put(opt, value);
        }
        return options;
    }

    public ByteBuf encode(Map options, int version)
    {
        int optLength = 2;
        for (Map.Entry entry : options.entrySet())
            optLength += 2 + entry.getKey().serializedValueSize(entry.getValue(), version);
        ByteBuf cb = Unpooled.buffer(optLength);
        cb.writeShort(options.size());
        for (Map.Entry entry : options.entrySet())
        {
            T opt = entry.getKey();
            cb.writeShort(opt.getId(version));
            opt.writeValue(entry.getValue(), cb, version);
        }
        return cb;
    }

    public Pair decodeOne(ByteBuf body, int version)
    {
        T opt = fromId(body.readUnsignedShort());
        Object value = opt.readValue(body, version);
        return Pair.create(opt, value);
    }

    public void writeOne(Pair option, ByteBuf dest, int version)
    {
        T opt = option.left;
        Object obj = option.right;
        dest.writeShort(opt.getId(version));
        opt.writeValue(obj, dest, version);
    }

    public int oneSerializedSize(Pair option, int version)
    {
        T opt = option.left;
        Object obj = option.right;
        return 2 + opt.serializedValueSize(obj, version);
    }
}