/*
 * 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 com.ning.compress.BufferRecycler;
import com.ning.compress.lzf.ChunkDecoder;
import com.ning.compress.lzf.util.ChunkDecoderFactory;
import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.ByteToMessageDecoder;

import java.util.List;

import static com.ning.compress.lzf.LZFChunk.BLOCK_TYPE_COMPRESSED;
import static com.ning.compress.lzf.LZFChunk.BLOCK_TYPE_NON_COMPRESSED;
import static com.ning.compress.lzf.LZFChunk.BYTE_V;
import static com.ning.compress.lzf.LZFChunk.BYTE_Z;
import static com.ning.compress.lzf.LZFChunk.HEADER_LEN_NOT_COMPRESSED;

Uncompresses a ByteBuf encoded with the LZF format. See original LZF package
and LZF format for full description.
/**
 * Uncompresses a {@link ByteBuf} encoded with the LZF format.
 *
 * See original <a href="http://oldhome.schmorp.de/marc/liblzf.html">LZF package</a>
 * and <a href="https://github.com/ning/compress/wiki/LZFFormat">LZF format</a> for full description.
 */
public class LzfDecoder extends ByteToMessageDecoder {
    
Current state of decompression.
/**
     * Current state of decompression.
     */
    private enum State {
        INIT_BLOCK,
        INIT_ORIGINAL_LENGTH,
        DECOMPRESS_DATA,
        CORRUPTED
    }

    private State currentState = State.INIT_BLOCK;

    
Magic number of LZF chunk.
/**
     * Magic number of LZF chunk.
     */
    private static final short MAGIC_NUMBER = BYTE_Z << 8 | BYTE_V;

    
Underlying decoder in use.
/**
     * Underlying decoder in use.
     */
    private ChunkDecoder decoder;

    
Object that handles details of buffer recycling.
/**
     * Object that handles details of buffer recycling.
     */
    private BufferRecycler recycler;

    
Length of current received chunk of data.
/**
     * Length of current received chunk of data.
     */
    private int chunkLength;

    
Original length of current received chunk of data. It is equal to chunkLength for non compressed chunks. /**
     * Original length of current received chunk of data.
     * It is equal to {@link #chunkLength} for non compressed chunks.
     */
    private int originalLength;

    
Indicates is this chunk compressed or not.
/**
     * Indicates is this chunk compressed or not.
     */
    private boolean isCompressed;

    
Creates a new LZF decoder with the most optimal available methods for underlying data access. It will "unsafe" instance if one can be used on current JVM. It should be safe to call this constructor as implementations are dynamically loaded; however, on some non-standard platforms it may be necessary to use LzfDecoder(boolean) with true param. /**
     * Creates a new LZF decoder with the most optimal available methods for underlying data access.
     * It will "unsafe" instance if one can be used on current JVM.
     * It should be safe to call this constructor as implementations are dynamically loaded; however, on some
     * non-standard platforms it may be necessary to use {@link #LzfDecoder(boolean)} with {@code true} param.
     */
    public LzfDecoder() {
        this(false);
    }

    
Creates a new LZF decoder with specified decoding instance.
Params:
safeInstance –  If true decoder will use ChunkDecoder that only uses standard JDK access methods, and should work on all Java platforms and JVMs. Otherwise decoder will try to use highly optimized ChunkDecoder implementation that uses Sun JDK's Unsafe class (which may be included by other JDK's as well)./**
     * Creates a new LZF decoder with specified decoding instance.
     *
     * @param safeInstance
     *        If {@code true} decoder will use {@link ChunkDecoder} that only uses standard JDK access methods,
     *        and should work on all Java platforms and JVMs.
     *        Otherwise decoder will try to use highly optimized {@link ChunkDecoder} implementation that uses
     *        Sun JDK's {@link sun.misc.Unsafe} class (which may be included by other JDK's as well).
     */
    public LzfDecoder(boolean safeInstance) {
        decoder = safeInstance ?
                ChunkDecoderFactory.safeInstance()
              : ChunkDecoderFactory.optimalInstance();

        recycler = BufferRecycler.instance();
    }

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

                final int type = in.readByte();
                switch (type) {
                case BLOCK_TYPE_NON_COMPRESSED:
                    isCompressed = false;
                    currentState = State.DECOMPRESS_DATA;
                    break;
                case BLOCK_TYPE_COMPRESSED:
                    isCompressed = true;
                    currentState = State.INIT_ORIGINAL_LENGTH;
                    break;
                default:
                    throw new DecompressionException(String.format(
                            "unknown type of chunk: %d (expected: %d or %d)",
                            type, BLOCK_TYPE_NON_COMPRESSED, BLOCK_TYPE_COMPRESSED));
                }
                chunkLength = in.readUnsignedShort();

                if (type != BLOCK_TYPE_COMPRESSED) {
                    break;
                }
                // fall through
            case INIT_ORIGINAL_LENGTH:
                if (in.readableBytes() < 2) {
                    break;
                }
                originalLength = in.readUnsignedShort();

                currentState = State.DECOMPRESS_DATA;
                // fall through
            case DECOMPRESS_DATA:
                final int chunkLength = this.chunkLength;
                if (in.readableBytes() < chunkLength) {
                    break;
                }
                final int originalLength = this.originalLength;

                if (isCompressed) {
                    final int idx = in.readerIndex();

                    final byte[] inputArray;
                    final int inPos;
                    if (in.hasArray()) {
                        inputArray = in.array();
                        inPos = in.arrayOffset() + idx;
                    } else {
                        inputArray = recycler.allocInputBuffer(chunkLength);
                        in.getBytes(idx, inputArray, 0, chunkLength);
                        inPos = 0;
                    }

                    ByteBuf uncompressed = ctx.alloc().heapBuffer(originalLength, originalLength);
                    final byte[] outputArray = uncompressed.array();
                    final int outPos = uncompressed.arrayOffset() + uncompressed.writerIndex();

                    boolean success = false;
                    try {
                        decoder.decodeChunk(inputArray, inPos, outputArray, outPos, outPos + originalLength);
                        uncompressed.writerIndex(uncompressed.writerIndex() + originalLength);
                        out.add(uncompressed);
                        in.skipBytes(chunkLength);
                        success = true;
                    } finally {
                        if (!success) {
                            uncompressed.release();
                        }
                    }

                    if (!in.hasArray()) {
                        recycler.releaseInputBuffer(inputArray);
                    }
                } else if (chunkLength > 0) {
                    out.add(in.readRetainedSlice(chunkLength));
                }

                currentState = State.INIT_BLOCK;
                break;
            case CORRUPTED:
                in.skipBytes(in.readableBytes());
                break;
            default:
                throw new IllegalStateException();
            }
        } catch (Exception e) {
            currentState = State.CORRUPTED;
            decoder = null;
            recycler = null;
            throw e;
        }
    }
}