/*
 * 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.commons.crypto.stream.input;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.ReadableByteChannel;

import org.apache.commons.crypto.stream.CryptoInputStream;

/**
 * The ChannelInput class takes a {@link ReadableByteChannel} object and
 * wraps it as {@link Input} object acceptable by
 * {@link CryptoInputStream}.
 */
public class ChannelInput implements Input {
    private static final int SKIP_BUFFER_SIZE = 2048;

    private ByteBuffer buf;
    private final ReadableByteChannel channel;

    /**
     * Constructs the
     * {@link org.apache.commons.crypto.stream.input.ChannelInput}.
     *
     * @param channel the ReadableByteChannel object.
     */
    public ChannelInput(final ReadableByteChannel channel) {
        this.channel = channel;
    }

    /**
     * Overrides the {@link Input#available()}. Returns an estimate of the
     * number of bytes that can be read (or skipped over) from this input stream
     * without blocking by the next invocation of a method for this input
     * stream. The next invocation might be the same thread or another thread. A
     * single read or skip of this many bytes will not block, but may read or
     * skip fewer bytes.
     *
     * @return an estimate of the number of bytes that can be read (or skipped
     *         over) from this input stream without blocking or {@code 0} when
     *         it reaches the end of the input stream.
     * @throws IOException if an I/O error occurs.
     */
    @Override
    public int available() throws IOException {
        return 0;
    }

    /**
     * Overrides the
     * {@link org.apache.commons.crypto.stream.input.Input#seek(long)}. Closes
     * this input and releases any system resources associated with the under
     * layer input.
     *
     * @throws IOException if an I/O error occurs.
     */
    @Override
    public void close() throws IOException {
        channel.close();
    }

    /**
     * Gets the skip buffer.
     *
     * @return the buffer.
     */
    private ByteBuffer getSkipBuf() {
        if (buf == null) {
            buf = ByteBuffer.allocate(SKIP_BUFFER_SIZE);
        }
        return buf;
    }

    /**
     * Overrides the
     * {@link org.apache.commons.crypto.stream.input.Input#read(ByteBuffer)}.
     * Reads a sequence of bytes from input into the given buffer.
     *
     * @param dst The buffer into which bytes are to be transferred.
     * @return the total number of bytes read into the buffer, or
     *         {@code -1} if there is no more data because the end of the
     *         stream has been reached.
     * @throws IOException if an I/O error occurs.
     */
    @Override
    public int read(final ByteBuffer dst) throws IOException {
        return channel.read(dst);
    }

    /**
     * Overrides the
     * {@link org.apache.commons.crypto.stream.input.Input#read(long, byte[], int, int)}
     * . Reads up to {@code len} bytes of data from the input stream into
     * an array of bytes. An attempt is made to read as many as {@code len}
     * bytes, but a smaller number may be read. The number of bytes actually
     * read is returned as an integer.
     *
     * @param position the given position within a stream.
     * @param buffer the buffer into which the data is read.
     * @param offset the start offset in array buffer.
     * @param length the maximum number of bytes to read.
     * @return the total number of bytes read into the buffer, or
     *         {@code -1} if there is no more data because the end of the
     *         stream has been reached.
     * @throws IOException if an I/O error occurs.
     */
    @Override
    public int read(final long position, final byte[] buffer, final int offset, final int length)
            throws IOException {
        throw new UnsupportedOperationException(
                "Positioned read is not supported by this implementation");
    }

    /**
     * Overrides the
     * {@link org.apache.commons.crypto.stream.input.Input#seek(long)}. Seeks to
     * the given offset from the start of the stream. The next read() will be
     * from that location.
     *
     * @param position the offset from the start of the stream.
     * @throws IOException if an I/O error occurs.
     */
    @Override
    public void seek(final long position) throws IOException {
        throw new UnsupportedOperationException(
                "Seek is not supported by this implementation");
    }

    /**
     * Overrides the
     * {@link org.apache.commons.crypto.stream.input.Input#skip(long)}. Skips
     * over and discards {@code n} bytes of data from this input stream.
     *
     * @param n the number of bytes to be skipped.
     * @return the actual number of bytes skipped.
     * @throws IOException if an I/O error occurs.
     */
    @Override
    public long skip(final long n) throws IOException {
        long remaining = n;
        int nr;

        if (n <= 0) {
            return 0;
        }

        final int size = (int) Math.min(SKIP_BUFFER_SIZE, remaining);
        final ByteBuffer skipBuffer = getSkipBuf();
        while (remaining > 0) {
            skipBuffer.clear();
            skipBuffer.limit((int) Math.min(size, remaining));
            nr = read(skipBuffer);
            if (nr < 0) {
                break;
            }
            remaining -= nr;
        }

        return n - remaining;
    }
}