/*
 * 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 com.indeed.util.compress;

import java.io.IOException;
import java.io.InputStream;

/**
 * This interface is meant to be implemented by those compression codecs which are capable to
 * compress / de-compress a stream starting at any arbitrary position.
 *
 * <p>Especially the process of de-compressing a stream starting at some arbitrary position is
 * challenging. Most of the codecs are only able to successfully de-compress a stream, if they start
 * from the very beginning till the end. One of the reasons is the stored state at the beginning of
 * the stream which is crucial for de-compression.
 *
 * <p>Yet there are few codecs which do not save the whole state at the beginning of the stream and
 * hence can be used to de-compress stream starting at any arbitrary points. This interface is meant
 * to be used by such codecs. Such codecs are highly valuable, especially in the context of Hadoop,
 * because an input compressed file can be split and hence can be worked on by multiple machines in
 * parallel.
 */
public interface SplittableCompressionCodec extends CompressionCodec {

    /**
     * During decompression, data can be read off from the decompressor in two modes, namely
     * continuous and blocked. Few codecs (e.g. BZip2) are capable of compressing data in blocks and
     * then decompressing the blocks. In Blocked reading mode codecs inform 'end of block' events to
     * its caller. While in continuous mode, the caller of codecs is unaware about the blocks and
     * uncompressed data is spilled out like a continuous stream.
     */
    public enum READ_MODE {
        CONTINUOUS,
        BYBLOCK
    };

    /**
     * Create a stream as dictated by the readMode. This method is used when the codecs wants the
     * ability to work with the underlying stream positions.
     *
     * @param seekableIn The seekable input stream (seeks in compressed data)
     * @param start The start offset into the compressed stream. May be changed by the underlying
     *     codec.
     * @param end The end offset into the compressed stream. May be changed by the underlying codec.
     * @param readMode Controls whether stream position is reported continuously from the compressed
     *     stream only only at block boundaries.
     * @return a stream to read uncompressed bytes from
     */
    SplitCompressionInputStream createInputStream(
            InputStream seekableIn,
            Decompressor decompressor,
            long start,
            long end,
            READ_MODE readMode)
            throws IOException;
}
