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BitTorrent Client Library (Core)
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/*
 * Copyright (c) 2016—2017 Andrei Tomashpolskiy and individual contributors.
 *
 * 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 bt.protocol.handler;

import bt.protocol.EncodingContext;
import bt.protocol.InvalidMessageException;
import bt.protocol.DecodingContext;
import bt.protocol.Piece;

import java.nio.ByteBuffer;
import java.util.Objects;

import static bt.protocol.Protocols.readInt;

public final class PieceHandler extends UniqueMessageHandler {

    public PieceHandler() {
        super(Piece.class);
    }

    @Override
    public int doDecode(DecodingContext context, ByteBuffer buffer) {
        return decodePiece(context, buffer, buffer.remaining());
    }

    @Override
    public boolean doEncode(EncodingContext context, Piece message, ByteBuffer buffer) {
        return writePiece(message.getPieceIndex(), message.getOffset(), message.getBlock(), buffer);
    }

    // piece: 
    private static boolean writePiece(int pieceIndex, int offset, byte[] block, ByteBuffer buffer) {

        if (pieceIndex < 0 || offset < 0) {
            throw new InvalidMessageException("Invalid arguments: pieceIndex (" + pieceIndex
                    + "), offset (" + offset + ")");
        }
        if (block.length == 0) {
            throw new InvalidMessageException("Invalid block: empty");
        }
        if (buffer.remaining() < Integer.BYTES * 2 + block.length) {
            return false;
        }

        buffer.putInt(pieceIndex);
        buffer.putInt(offset);
        buffer.put(block);

        return true;
    }

    private static int decodePiece(DecodingContext context, ByteBuffer buffer, int length) {

        int consumed = 0;

        if (buffer.remaining() >= length) {

            int pieceIndex = Objects.requireNonNull(readInt(buffer));
            int blockOffset = Objects.requireNonNull(readInt(buffer));
            byte[] block = new byte[length - Integer.BYTES * 2];
            buffer.get(block);

            context.setMessage(new Piece(pieceIndex, blockOffset, block));
            consumed = length;
        }

        return consumed;
    }
}