/*
    * 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:
    *
    *   https://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 java.util.List;
  
  import static io.netty.handler.codec.compression.Bzip2Constants.BASE_BLOCK_SIZE;
  import static io.netty.handler.codec.compression.Bzip2Constants.BLOCK_HEADER_MAGIC_1;
  import static io.netty.handler.codec.compression.Bzip2Constants.BLOCK_HEADER_MAGIC_2;
  import static io.netty.handler.codec.compression.Bzip2Constants.END_OF_STREAM_MAGIC_1;
  import static io.netty.handler.codec.compression.Bzip2Constants.END_OF_STREAM_MAGIC_2;
  import static io.netty.handler.codec.compression.Bzip2Constants.HUFFMAN_MAXIMUM_TABLES;
  import static io.netty.handler.codec.compression.Bzip2Constants.HUFFMAN_MAX_ALPHABET_SIZE;
  import static io.netty.handler.codec.compression.Bzip2Constants.HUFFMAN_MINIMUM_TABLES;
  import static io.netty.handler.codec.compression.Bzip2Constants.HUFFMAN_SELECTOR_LIST_MAX_LENGTH;
  import static io.netty.handler.codec.compression.Bzip2Constants.HUFFMAN_SYMBOL_RANGE_SIZE;
  import static io.netty.handler.codec.compression.Bzip2Constants.MAGIC_NUMBER;
  import static io.netty.handler.codec.compression.Bzip2Constants.MAX_BLOCK_SIZE;
  import static io.netty.handler.codec.compression.Bzip2Constants.MAX_SELECTORS;
  import static io.netty.handler.codec.compression.Bzip2Constants.MIN_BLOCK_SIZE;
  
  /**
   * Uncompresses a {@link ByteBuf} encoded with the Bzip2 format.
   *
   * See <a href="https://en.wikipedia.org/wiki/Bzip2">Bzip2</a>.
   */
  public class Bzip2Decoder extends ByteToMessageDecoder {
      /**
       * Current state of stream.
       */
      private enum State {
          INIT,
          INIT_BLOCK,
          INIT_BLOCK_PARAMS,
          RECEIVE_HUFFMAN_USED_MAP,
          RECEIVE_HUFFMAN_USED_BITMAPS,
          RECEIVE_SELECTORS_NUMBER,
          RECEIVE_SELECTORS,
          RECEIVE_HUFFMAN_LENGTH,
          DECODE_HUFFMAN_DATA,
          EOF
      }
      private State currentState = State.INIT;
  
      /**
       * A reader that provides bit-level reads.
       */
      private final Bzip2BitReader reader = new Bzip2BitReader();
  
      /**
       * The decompressor for the current block.
       */
      private Bzip2BlockDecompressor blockDecompressor;
  
      /**
       * Bzip2 Huffman coding stage.
       */
      private Bzip2HuffmanStageDecoder huffmanStageDecoder;
  
      /**
       * Always: in the range 0 .. 9. The current block size is 100000 * this number.
       */
      private int blockSize;
  
      /**
       * The CRC of the current block as read from the block header.
       */
      private int blockCRC;
  
      /**
       * The merged CRC of all blocks decompressed so far.
       */
      private int streamCRC;
  
      @Override
      protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
          if (!in.isReadable()) {
              return;
          }
  
          final Bzip2BitReader reader = this.reader;
          reader.setByteBuf(in);
 
         for (;;) {
             switch (currentState) {
             case INIT:
                 if (in.readableBytes() < 4) {
                     return;
                 }
                 int magicNumber = in.readUnsignedMedium();
                 if (magicNumber != MAGIC_NUMBER) {
                     throw new DecompressionException("Unexpected stream identifier contents. Mismatched bzip2 " +
                             "protocol version?");
                 }
                 int blockSize = in.readByte() - '0';
                 if (blockSize < MIN_BLOCK_SIZE || blockSize > MAX_BLOCK_SIZE) {
                     throw new DecompressionException("block size is invalid");
                 }
                 this.blockSize = blockSize * BASE_BLOCK_SIZE;
 
                 streamCRC = 0;
                 currentState = State.INIT_BLOCK;
                  // fall through
             case INIT_BLOCK:
                 if (!reader.hasReadableBytes(10)) {
                     return;
                 }
                 // Get the block magic bytes.
                 final int magic1 = reader.readBits(24);
                 final int magic2 = reader.readBits(24);
                 if (magic1 == END_OF_STREAM_MAGIC_1 && magic2 == END_OF_STREAM_MAGIC_2) {
                     // End of stream was reached. Check the combined CRC.
                     final int storedCombinedCRC = reader.readInt();
                     if (storedCombinedCRC != streamCRC) {
                         throw new DecompressionException("stream CRC error");
                     }
                     currentState = State.EOF;
                     break;
                 }
                 if (magic1 != BLOCK_HEADER_MAGIC_1 || magic2 != BLOCK_HEADER_MAGIC_2) {
                     throw new DecompressionException("bad block header");
                 }
                 blockCRC = reader.readInt();
                 currentState = State.INIT_BLOCK_PARAMS;
                 // fall through
             case INIT_BLOCK_PARAMS:
                 if (!reader.hasReadableBits(25)) {
                     return;
                 }
                 final boolean blockRandomised = reader.readBoolean();
                 final int bwtStartPointer = reader.readBits(24);
 
                 blockDecompressor = new Bzip2BlockDecompressor(this.blockSize, blockCRC,
                                                                 blockRandomised, bwtStartPointer, reader);
                 currentState = State.RECEIVE_HUFFMAN_USED_MAP;
                 // fall through
             case RECEIVE_HUFFMAN_USED_MAP:
                 if (!reader.hasReadableBits(16)) {
                     return;
                 }
                 blockDecompressor.huffmanInUse16 = reader.readBits(16);
                 currentState = State.RECEIVE_HUFFMAN_USED_BITMAPS;
                 // fall through
             case RECEIVE_HUFFMAN_USED_BITMAPS:
                 Bzip2BlockDecompressor blockDecompressor = this.blockDecompressor;
                 final int inUse16 = blockDecompressor.huffmanInUse16;
                 final int bitNumber = Integer.bitCount(inUse16);
                 final byte[] huffmanSymbolMap = blockDecompressor.huffmanSymbolMap;
 
                 if (!reader.hasReadableBits(bitNumber * HUFFMAN_SYMBOL_RANGE_SIZE + 3)) {
                     return;
                 }
 
                 int huffmanSymbolCount = 0;
                 if (bitNumber > 0) {
                     for (int i = 0; i < 16; i++) {
                         if ((inUse16 & 1 << 15 >>> i) != 0) {
                             for (int j = 0, k = i << 4; j < HUFFMAN_SYMBOL_RANGE_SIZE; j++, k++) {
                                 if (reader.readBoolean()) {
                                     huffmanSymbolMap[huffmanSymbolCount++] = (byte) k;
                                 }
                             }
                         }
                     }
                 }
                 blockDecompressor.huffmanEndOfBlockSymbol = huffmanSymbolCount + 1;
 
                 int totalTables = reader.readBits(3);
                 if (totalTables < HUFFMAN_MINIMUM_TABLES || totalTables > HUFFMAN_MAXIMUM_TABLES) {
                     throw new DecompressionException("incorrect huffman groups number");
                 }
                 int alphaSize = huffmanSymbolCount + 2;
                 if (alphaSize > HUFFMAN_MAX_ALPHABET_SIZE) {
                     throw new DecompressionException("incorrect alphabet size");
                 }
                 huffmanStageDecoder = new Bzip2HuffmanStageDecoder(reader, totalTables, alphaSize);
                 currentState = State.RECEIVE_SELECTORS_NUMBER;
                 // fall through
             case RECEIVE_SELECTORS_NUMBER:
                 if (!reader.hasReadableBits(15)) {
                     return;
                 }
                 int totalSelectors = reader.readBits(15);
                 if (totalSelectors < 1 || totalSelectors > MAX_SELECTORS) {
                     throw new DecompressionException("incorrect selectors number");
                 }
                 huffmanStageDecoder.selectors = new byte[totalSelectors];
 
                 currentState = State.RECEIVE_SELECTORS;
                 // fall through
             case RECEIVE_SELECTORS:
                 Bzip2HuffmanStageDecoder huffmanStageDecoder = this.huffmanStageDecoder;
                 byte[] selectors = huffmanStageDecoder.selectors;
                 totalSelectors = selectors.length;
                 final Bzip2MoveToFrontTable tableMtf = huffmanStageDecoder.tableMTF;
 
                 int currSelector;
                 // Get zero-terminated bit runs (0..62) of MTF'ed Huffman table. length = 1..6
                 for (currSelector = huffmanStageDecoder.currentSelector;
                             currSelector < totalSelectors; currSelector++) {
                     if (!reader.hasReadableBits(HUFFMAN_SELECTOR_LIST_MAX_LENGTH)) {
                         // Save state if end of current ByteBuf was reached
                         huffmanStageDecoder.currentSelector = currSelector;
                         return;
                     }
                     int index = 0;
                     while (reader.readBoolean()) {
                         index++;
                         if (index >= huffmanStageDecoder.totalTables) {
                             throw new DecompressionException("incorrect selector index " + index);
                         }
                     }
                     selectors[currSelector] = tableMtf.indexToFront(index);
                 }
 
                 currentState = State.RECEIVE_HUFFMAN_LENGTH;
                 // fall through
             case RECEIVE_HUFFMAN_LENGTH:
                 huffmanStageDecoder = this.huffmanStageDecoder;
                 totalTables = huffmanStageDecoder.totalTables;
                 final byte[][] codeLength = huffmanStageDecoder.tableCodeLengths;
                 alphaSize = huffmanStageDecoder.alphabetSize;
 
                 /* Now the coding tables */
                 int currGroup;
                 int currLength = huffmanStageDecoder.currentLength;
                 int currAlpha = 0;
                 boolean modifyLength = huffmanStageDecoder.modifyLength;
                 boolean saveStateAndReturn = false;
                 loop: for (currGroup = huffmanStageDecoder.currentGroup; currGroup < totalTables; currGroup++) {
                     // start_huffman_length
                     if (!reader.hasReadableBits(5)) {
                         saveStateAndReturn = true;
                         break;
                     }
                     if (currLength < 0) {
                         currLength = reader.readBits(5);
                     }
                     for (currAlpha = huffmanStageDecoder.currentAlpha; currAlpha < alphaSize; currAlpha++) {
                         // delta_bit_length: 1..40
                         if (!reader.isReadable()) {
                             saveStateAndReturn = true;
                             break loop;
                         }
                         while (modifyLength || reader.readBoolean()) {  // 0=>next symbol; 1=>alter length
                             if (!reader.isReadable()) {
                                 modifyLength = true;
                                 saveStateAndReturn = true;
                                 break loop;
                             }
                             // 1=>decrement length;  0=>increment length
                             currLength += reader.readBoolean() ? -1 : 1;
                             modifyLength = false;
                             if (!reader.isReadable()) {
                                 saveStateAndReturn = true;
                                 break loop;
                             }
                         }
                         codeLength[currGroup][currAlpha] = (byte) currLength;
                     }
                     currLength = -1;
                     currAlpha = huffmanStageDecoder.currentAlpha = 0;
                     modifyLength = false;
                 }
                 if (saveStateAndReturn) {
                     // Save state if end of current ByteBuf was reached
                     huffmanStageDecoder.currentGroup = currGroup;
                     huffmanStageDecoder.currentLength = currLength;
                     huffmanStageDecoder.currentAlpha = currAlpha;
                     huffmanStageDecoder.modifyLength = modifyLength;
                     return;
                 }
 
                 // Finally create the Huffman tables
                 huffmanStageDecoder.createHuffmanDecodingTables();
                 currentState = State.DECODE_HUFFMAN_DATA;
                 // fall through
             case DECODE_HUFFMAN_DATA:
                 blockDecompressor = this.blockDecompressor;
                 final int oldReaderIndex = in.readerIndex();
                 final boolean decoded = blockDecompressor.decodeHuffmanData(this.huffmanStageDecoder);
                 if (!decoded) {
                     return;
                 }
                 // It used to avoid "Bzip2Decoder.decode() did not read anything but decoded a message" exception.
                 // Because previous operation may read only a few bits from Bzip2BitReader.bitBuffer and
                 // don't read incoming ByteBuf.
                 if (in.readerIndex() == oldReaderIndex && in.isReadable()) {
                     reader.refill();
                 }
 
                 final int blockLength = blockDecompressor.blockLength();
                 ByteBuf uncompressed = ctx.alloc().buffer(blockLength);
                 try {
                     int uncByte;
                     while ((uncByte = blockDecompressor.read()) >= 0) {
                         uncompressed.writeByte(uncByte);
                     }
                     // We did read all the data, lets reset the state and do the CRC check.
                     currentState = State.INIT_BLOCK;
                     int currentBlockCRC = blockDecompressor.checkCRC();
                     streamCRC = (streamCRC << 1 | streamCRC >>> 31) ^ currentBlockCRC;
 
                     out.add(uncompressed);
                     uncompressed = null;
                 } finally {
                     if (uncompressed != null) {
                         uncompressed.release();
                     }
                 }
                 // Return here so the ByteBuf that was put in the List will be forwarded to the user and so can be
                 // released as soon as possible.
                 return;
             case EOF:
                 in.skipBytes(in.readableBytes());
                 return;
             default:
                 throw new IllegalStateException();
             }
         }
     }
 
     /**
      * Returns {@code true} if and only if the end of the compressed stream
      * has been reached.
      */
     public boolean isClosed() {
         return currentState == State.EOF;
     }
 }