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/*
 * Copyright 2014 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 io.netty.handler.codec.compression;

import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.ByteToMessageDecoder;
import io.netty.util.internal.ObjectUtil;
import net.jpountz.lz4.LZ4Exception;
import net.jpountz.lz4.LZ4Factory;
import net.jpountz.lz4.LZ4FastDecompressor;

import java.util.List;
import java.util.zip.Checksum;

import static io.netty.handler.codec.compression.Lz4Constants.*;

/**
 * Uncompresses a {@link ByteBuf} encoded with the LZ4 format.
 *
 * See original LZ4 Github project
 * and LZ4 block format
 * for full description.
 *
 * Since the original LZ4 block format does not contains size of compressed block and size of original data
 * this encoder uses format like LZ4 Java library
 * written by Adrien Grand and approved by Yann Collet (author of original LZ4 library).
 *
 *  * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *     * * * * * * * * * *
 *  * Magic * Token *  Compressed *  Decompressed *  Checksum *  +  *  LZ4 compressed *
 *  *       *       *    length   *     length    *           *     *      block      *
 *  * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *     * * * * * * * * * *
 */
public class Lz4FrameDecoder extends ByteToMessageDecoder {
    /**
     * Current state of stream.
     */
    private enum State {
        INIT_BLOCK,
        DECOMPRESS_DATA,
        FINISHED,
        CORRUPTED
    }

    private State currentState = State.INIT_BLOCK;

    /**
     * Underlying decompressor in use.
     */
    private LZ4FastDecompressor decompressor;

    /**
     * Underlying checksum calculator in use.
     */
    private ByteBufChecksum checksum;

    /**
     * Type of current block.
     */
    private int blockType;

    /**
     * Compressed length of current incoming block.
     */
    private int compressedLength;

    /**
     * Decompressed length of current incoming block.
     */
    private int decompressedLength;

    /**
     * Checksum value of current incoming block.
     */
    private int currentChecksum;

    /**
     * Creates the fastest LZ4 decoder.
     *
     * Note that by default, validation of the checksum header in each chunk is
     * DISABLED for performance improvements. If performance is less of an issue,
     * or if you would prefer the safety that checksum validation brings, please
     * use the {@link #Lz4FrameDecoder(boolean)} constructor with the argument
     * set to {@code true}.
     */
    public Lz4FrameDecoder() {
        this(false);
    }

    /**
     * Creates a LZ4 decoder with fastest decoder instance available on your machine.
     *
     * @param validateChecksums  if {@code true}, the checksum field will be validated against the actual
     *                           uncompressed data, and if the checksums do not match, a suitable
     *                           {@link DecompressionException} will be thrown
     */
    public Lz4FrameDecoder(boolean validateChecksums) {
        this(LZ4Factory.fastestInstance(), validateChecksums);
    }

    /**
     * Creates a new LZ4 decoder with customizable implementation.
     *
     * @param factory            user customizable {@link LZ4Factory} instance
     *                           which may be JNI bindings to the original C implementation, a pure Java implementation
     *                           or a Java implementation that uses the {@link sun.misc.Unsafe}
     * @param validateChecksums  if {@code true}, the checksum field will be validated against the actual
     *                           uncompressed data, and if the checksums do not match, a suitable
     *                           {@link DecompressionException} will be thrown. In this case encoder will use
     *                           xxhash hashing for Java, based on Yann Collet's work available at
     *                           Github.
     */
    public Lz4FrameDecoder(LZ4Factory factory, boolean validateChecksums) {
        this(factory, validateChecksums ? new Lz4XXHash32(DEFAULT_SEED) : null);
    }

    /**
     * Creates a new customizable LZ4 decoder.
     *
     * @param factory   user customizable {@link LZ4Factory} instance
     *                  which may be JNI bindings to the original C implementation, a pure Java implementation
     *                  or a Java implementation that uses the {@link sun.misc.Unsafe}
     * @param checksum  the {@link Checksum} instance to use to check data for integrity.
     *                  You may set {@code null} if you do not want to validate checksum of each block
     */
    public Lz4FrameDecoder(LZ4Factory factory, Checksum checksum) {
        decompressor = ObjectUtil.checkNotNull(factory, "factory").fastDecompressor();
        this.checksum = checksum == null ? null : ByteBufChecksum.wrapChecksum(checksum);
    }

    @Override
    protected void decode(ChannelHandlerContext ctx, ByteBuf in, List