/*
 * Copyright 2011 The Netty Project
 *
 * The Netty Project 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.jboss.netty.example.factorial;

import java.math.BigInteger;

import org.jboss.netty.buffer.ChannelBuffer;
import org.jboss.netty.buffer.ChannelBuffers;
import org.jboss.netty.channel.Channel;
import org.jboss.netty.channel.ChannelHandlerContext;
import org.jboss.netty.handler.codec.oneone.OneToOneEncoder;

/**
 * Encodes a {@link Number} into the binary representation prepended with
 * a magic number ('F' or 0x46) and a 32-bit length prefix.  For example, 42
 * will be encoded to { 'F', 0, 0, 0, 1, 42 }.
 */
public class NumberEncoder extends OneToOneEncoder {

    @Override
    protected Object encode(
            ChannelHandlerContext ctx, Channel channel, Object msg) throws Exception {
        if (!(msg instanceof Number)) {
            // Ignore what this encoder can't encode.
            return msg;
        }

        // Convert to a BigInteger first for easier implementation.
        BigInteger v;
        if (msg instanceof BigInteger) {
            v = (BigInteger) msg;
        } else {
            v = new BigInteger(String.valueOf(msg));
        }

        // Convert the number into a byte array.
        byte[] data = v.toByteArray();
        int dataLength = data.length;

        // Construct a message.
        ChannelBuffer buf = ChannelBuffers.dynamicBuffer();
        buf.writeByte((byte) 'F'); // magic number
        buf.writeInt(dataLength);  // data length
        buf.writeBytes(data);      // data

        // Return the constructed message.
        return buf;
    }
}