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/*
 * Copyright (c) 2016—2021 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.net.crypto;

import javax.crypto.Cipher;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.ByteChannel;

/**
 * Decorates a byte channel with encryption
 *
 * @since 1.2
 */
public class EncryptedChannel implements ByteChannel {

    private final ByteChannel delegate;
    private final Cipher cipherIn;
    private final Cipher cipherOut;

    /**
     * Create an encrypted byte channel.
     *
     * @param delegate Delegate byte channel
     * @param cipherIn Cipher for decrypting incoming data
     * @param cipherOut Cipher for encrypting outgoing data
     * @since 1.2
     */
    public EncryptedChannel(ByteChannel delegate, Cipher cipherIn, Cipher cipherOut) {
        this.delegate = delegate;
        this.cipherIn = cipherIn;
        this.cipherOut = cipherOut;
    }

    @Override
    public int read(ByteBuffer dst) throws IOException {
        int read = 0;
        if (dst.hasRemaining()) {
            int position = dst.position();
            int limit = dst.limit();
            read = delegate.read(dst);
            if (read > 0) {
                dst.limit(dst.position());
                dst.position(position);
                byte[] bytes = new byte[dst.remaining()];
                dst.get(bytes);
                dst.limit(limit);
                dst.position(position);
                try {
                    bytes = cipherIn.update(bytes);
                } catch (Exception e) {
                    throw new RuntimeException(e);
                }
                dst.put(bytes);
            }
        }
        return read;
    }

    @Override
    public int write(ByteBuffer src) throws IOException {
        int written = 0;
        if (src.hasRemaining()) {
            int position = src.position();
            byte[] bytes = new byte[src.remaining()];
            src.get(bytes);
            src.position(position);
            try {
                bytes = cipherOut.update(bytes);
            } catch (Exception e) {
                throw new RuntimeException(e);
            }
            src.put(bytes);
            src.position(position);
            while (src.hasRemaining()) {
                // write fully
                written += delegate.write(src);
            }
        }
        return written;
    }

    @Override
    public boolean isOpen() {
        return delegate.isOpen();
    }

    @Override
    public void close() throws IOException {
        delegate.close();
    }
}