/*
 * 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 net.jpountz.lz4.LZ4Exception;
import net.jpountz.lz4.LZ4Factory;
import net.jpountz.lz4.LZ4FastDecompressor;
import net.jpountz.xxhash.XXHashFactory;

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

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

Uncompresses a 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      *
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *     * * * * * * * * * *
/**
 * Uncompresses a {@link ByteBuf} encoded with the LZ4 format.
 *
 * See original <a href="https://github.com/Cyan4973/lz4">LZ4 Github project</a>
 * and <a href="http://fastcompression.blogspot.ru/2011/05/lz4-explained.html">LZ4 block format</a>
 * 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 <a href="https://github.com/idelpivnitskiy/lz4-java">LZ4 Java</a> 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.
/**
     * Current state of stream.
     */
    private enum State {
        INIT_BLOCK,
        DECOMPRESS_DATA,
        FINISHED,
        CORRUPTED
    }

    private State currentState = State.INIT_BLOCK;

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

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

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

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

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

    
Checksum value of current incoming block.
/**
     * 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 Lz4FrameDecoder(boolean) constructor with the argument set to true. /**
     * 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.
Params:
validateChecksums –  if true, the checksum field will be validated against the actual uncompressed data, and if the checksums do not match, a suitable DecompressionException will be thrown/**
     * 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.
Params:
factory –  user customizable LZ4Factory instance which may be JNI bindings to the original C implementation, a pure Java implementation or a Java implementation that uses the Unsafe
validateChecksums –  if true, the checksum field will be validated against the actual uncompressed data, and if the checksums do not match, a suitable DecompressionException will be thrown. In this case encoder will use xxhash hashing for Java, based on Yann Collet's work available at Github./**
     * 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
     *                           <a href="https://github.com/Cyan4973/xxHash">Github</a>.
     */
    public Lz4FrameDecoder(LZ4Factory factory, boolean validateChecksums) {
        this(factory, validateChecksums ?
                XXHashFactory.fastestInstance().newStreamingHash32(DEFAULT_SEED).asChecksum()
              : null);
    }

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

    @Override
    protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
        try {
            switch (currentState) {
            case INIT_BLOCK:
                if (in.readableBytes() < HEADER_LENGTH) {
                    break;
                }
                final long magic = in.readLong();
                if (magic != MAGIC_NUMBER) {
                    throw new DecompressionException("unexpected block identifier");
                }

                final int token = in.readByte();
                final int compressionLevel = (token & 0x0F) + COMPRESSION_LEVEL_BASE;
                int blockType = token & 0xF0;

                int compressedLength = Integer.reverseBytes(in.readInt());
                if (compressedLength < 0 || compressedLength > MAX_BLOCK_SIZE) {
                    throw new DecompressionException(String.format(
                            "invalid compressedLength: %d (expected: 0-%d)",
                            compressedLength, MAX_BLOCK_SIZE));
                }

                int decompressedLength = Integer.reverseBytes(in.readInt());
                final int maxDecompressedLength = 1 << compressionLevel;
                if (decompressedLength < 0 || decompressedLength > maxDecompressedLength) {
                    throw new DecompressionException(String.format(
                            "invalid decompressedLength: %d (expected: 0-%d)",
                            decompressedLength, maxDecompressedLength));
                }
                if (decompressedLength == 0 && compressedLength != 0
                        || decompressedLength != 0 && compressedLength == 0
                        || blockType == BLOCK_TYPE_NON_COMPRESSED && decompressedLength != compressedLength) {
                    throw new DecompressionException(String.format(
                            "stream corrupted: compressedLength(%d) and decompressedLength(%d) mismatch",
                            compressedLength, decompressedLength));
                }

                int currentChecksum = Integer.reverseBytes(in.readInt());
                if (decompressedLength == 0 && compressedLength == 0) {
                    if (currentChecksum != 0) {
                        throw new DecompressionException("stream corrupted: checksum error");
                    }
                    currentState = State.FINISHED;
                    decompressor = null;
                    checksum = null;
                    break;
                }

                this.blockType = blockType;
                this.compressedLength = compressedLength;
                this.decompressedLength = decompressedLength;
                this.currentChecksum = currentChecksum;

                currentState = State.DECOMPRESS_DATA;
                // fall through
            case DECOMPRESS_DATA:
                blockType = this.blockType;
                compressedLength = this.compressedLength;
                decompressedLength = this.decompressedLength;
                currentChecksum = this.currentChecksum;

                if (in.readableBytes() < compressedLength) {
                    break;
                }

                final ByteBufChecksum checksum = this.checksum;
                ByteBuf uncompressed = null;

                try {
                    switch (blockType) {
                        case BLOCK_TYPE_NON_COMPRESSED:
                            // Just pass through, we not update the readerIndex yet as we do this outside of the
                            // switch statement.
                            uncompressed = in.retainedSlice(in.readerIndex(), decompressedLength);
                            break;
                        case BLOCK_TYPE_COMPRESSED:
                            uncompressed = ctx.alloc().buffer(decompressedLength, decompressedLength);

                            decompressor.decompress(CompressionUtil.safeNioBuffer(in),
                                    uncompressed.internalNioBuffer(uncompressed.writerIndex(), decompressedLength));
                            // Update the writerIndex now to reflect what we decompressed.
                            uncompressed.writerIndex(uncompressed.writerIndex() + decompressedLength);
                            break;
                        default:
                            throw new DecompressionException(String.format(
                                    "unexpected blockType: %d (expected: %d or %d)",
                                    blockType, BLOCK_TYPE_NON_COMPRESSED, BLOCK_TYPE_COMPRESSED));
                    }
                    // Skip inbound bytes after we processed them.
                    in.skipBytes(compressedLength);

                    if (checksum != null) {
                        CompressionUtil.checkChecksum(checksum, uncompressed, currentChecksum);
                    }
                    out.add(uncompressed);
                    uncompressed = null;
                    currentState = State.INIT_BLOCK;
                } catch (LZ4Exception e) {
                    throw new DecompressionException(e);
                } finally {
                    if (uncompressed != null) {
                        uncompressed.release();
                    }
                }
                break;
            case FINISHED:
            case CORRUPTED:
                in.skipBytes(in.readableBytes());
                break;
            default:
                throw new IllegalStateException();
            }
        } catch (Exception e) {
            currentState = State.CORRUPTED;
            throw e;
        }
    }

    
Returns true if and only if the end of the compressed stream has been reached. /**
     * Returns {@code true} if and only if the end of the compressed stream
     * has been reached.
     */
    public boolean isClosed() {
        return currentState == State.FINISHED;
    }
}