/*
    * 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 org.apache.commons.compress.compressors.snappy;
  
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.PushbackInputStream;
  import java.util.Arrays;
  
  import org.apache.commons.codec.digest.PureJavaCrc32C;
  import org.apache.commons.compress.compressors.CompressorInputStream;
  import org.apache.commons.compress.utils.BoundedInputStream;
  import org.apache.commons.compress.utils.ByteUtils;
  import org.apache.commons.compress.utils.IOUtils;
  import org.apache.commons.compress.utils.InputStreamStatistics;
  import org.apache.commons.io.input.CountingInputStream;
  
  /**
   * CompressorInputStream for the framing Snappy format.
   *
   * <p>
   * Based on the "spec" in the version "Last revised: 2013-10-25"
   * </p>
   *
   * @see <a href="https://github.com/google/snappy/blob/master/framing_format.txt">Snappy framing format description</a>
   * @since 1.7
   */
  public class FramedSnappyCompressorInputStream extends CompressorInputStream implements InputStreamStatistics {
  
      /**
       * package private for tests only.
       */
      static final long MASK_OFFSET = 0xa282ead8L;
  
      private static final int STREAM_IDENTIFIER_TYPE = 0xff;
      static final int COMPRESSED_CHUNK_TYPE = 0;
      private static final int UNCOMPRESSED_CHUNK_TYPE = 1;
      private static final int PADDING_CHUNK_TYPE = 0xfe;
      private static final int MIN_UNSKIPPABLE_TYPE = 2;
      private static final int MAX_UNSKIPPABLE_TYPE = 0x7f;
      private static final int MAX_SKIPPABLE_TYPE = 0xfd;
  
      // used by FramedSnappyCompressorOutputStream as well
      static final byte[] SZ_SIGNATURE = { // NOSONAR
              (byte) STREAM_IDENTIFIER_TYPE, // tag
              6, 0, 0, // length
              's', 'N', 'a', 'P', 'p', 'Y' };
  
      /**
       * Checks if the signature matches what is expected for a .sz file.
       *
       * <p>
       * .sz files start with a chunk with tag 0xff and content sNaPpY.
       * </p>
       *
       * @param signature the bytes to check
       * @param length    the number of bytes to check
       * @return true if this is a .sz stream, false otherwise
       */
      public static boolean matches(final byte[] signature, final int length) {
  
          if (length < SZ_SIGNATURE.length) {
              return false;
          }
  
          byte[] shortenedSig = signature;
          if (signature.length > SZ_SIGNATURE.length) {
              shortenedSig = Arrays.copyOf(signature, SZ_SIGNATURE.length);
          }
  
          return Arrays.equals(shortenedSig, SZ_SIGNATURE);
      }
  
      static long unmask(long x) {
          // ugly, maybe we should just have used ints and deal with the
          // overflow
          x -= MASK_OFFSET;
          x &= 0xffffFFFFL;
          return (x >> 17 | x << 15) & 0xffffFFFFL;
      }
  
      private long unreadBytes;
  
     private final CountingInputStream countingStream;
 
     /** The underlying stream to read compressed data from */
     private final PushbackInputStream inputStream;
 
     /** The dialect to expect */
     private final FramedSnappyDialect dialect;
 
     private SnappyCompressorInputStream currentCompressedChunk;
 
     // used in no-arg read method
     private final byte[] oneByte = new byte[1];
     private boolean endReached, inUncompressedChunk;
     private int uncompressedBytesRemaining;
     private long expectedChecksum = -1;
 
     private final int blockSize;
 
     private final PureJavaCrc32C checksum = new PureJavaCrc32C();
 
     private final ByteUtils.ByteSupplier supplier = this::readOneByte;
 
     /**
      * Constructs a new input stream that decompresses snappy-framed-compressed data from the specified input stream using the
      * {@link FramedSnappyDialect#STANDARD} dialect.
      *
      * @param in the InputStream from which to read the compressed data
      * @throws IOException if reading fails
      */
     public FramedSnappyCompressorInputStream(final InputStream in) throws IOException {
         this(in, FramedSnappyDialect.STANDARD);
     }
 
     /**
      * Constructs a new input stream that decompresses snappy-framed-compressed data from the specified input stream.
      *
      * @param in      the InputStream from which to read the compressed data
      * @param dialect the dialect used by the compressed stream
      * @throws IOException if reading fails
      */
     public FramedSnappyCompressorInputStream(final InputStream in, final FramedSnappyDialect dialect) throws IOException {
         this(in, SnappyCompressorInputStream.DEFAULT_BLOCK_SIZE, dialect);
     }
 
     /**
      * Constructs a new input stream that decompresses snappy-framed-compressed data from the specified input stream.
      *
      * @param in        the InputStream from which to read the compressed data
      * @param blockSize the block size to use for the compressed stream
      * @param dialect   the dialect used by the compressed stream
      * @throws IOException              if reading fails
      * @throws IllegalArgumentException if blockSize is not bigger than 0
      * @since 1.14
      */
     public FramedSnappyCompressorInputStream(final InputStream in, final int blockSize, final FramedSnappyDialect dialect) throws IOException {
         if (blockSize <= 0) {
             throw new IllegalArgumentException("blockSize must be bigger than 0");
         }
         countingStream = new CountingInputStream(in);
         this.inputStream = new PushbackInputStream(countingStream, 1);
         this.blockSize = blockSize;
         this.dialect = dialect;
         if (dialect.hasStreamIdentifier()) {
             readStreamIdentifier();
         }
     }
 
     /** {@inheritDoc} */
     @Override
     public int available() throws IOException {
         if (inUncompressedChunk) {
             return Math.min(uncompressedBytesRemaining, inputStream.available());
         }
         if (currentCompressedChunk != null) {
             return currentCompressedChunk.available();
         }
         return 0;
     }
 
     /** {@inheritDoc} */
     @Override
     public void close() throws IOException {
         try {
             if (currentCompressedChunk != null) {
                 currentCompressedChunk.close();
                 currentCompressedChunk = null;
             }
         } finally {
             inputStream.close();
         }
     }
 
     /**
      * @since 1.17
      */
     @Override
     public long getCompressedCount() {
         return countingStream.getByteCount() - unreadBytes;
     }
 
     /** {@inheritDoc} */
     @Override
     public int read() throws IOException {
         return read(oneByte, 0, 1) == -1 ? -1 : oneByte[0] & 0xFF;
     }
 
     /** {@inheritDoc} */
     @Override
     public int read(final byte[] b, final int off, final int len) throws IOException {
         if (len == 0) {
             return 0;
         }
         int read = readOnce(b, off, len);
         if (read == -1) {
             readNextBlock();
             if (endReached) {
                 return -1;
             }
             read = readOnce(b, off, len);
         }
         return read;
     }
 
     private long readCrc() throws IOException {
         final byte[] b = new byte[4];
         final int read = IOUtils.readFully(inputStream, b);
         count(read);
         if (read != 4) {
             throw new IOException("Premature end of stream");
         }
         return ByteUtils.fromLittleEndian(b);
     }
 
     private void readNextBlock() throws IOException {
         verifyLastChecksumAndReset();
         inUncompressedChunk = false;
         final int type = readOneByte();
         if (type == -1) {
             endReached = true;
         } else if (type == STREAM_IDENTIFIER_TYPE) {
             inputStream.unread(type);
             unreadBytes++;
             pushedBackBytes(1);
             readStreamIdentifier();
             readNextBlock();
         } else if (type == PADDING_CHUNK_TYPE || type > MAX_UNSKIPPABLE_TYPE && type <= MAX_SKIPPABLE_TYPE) {
             skipBlock();
             readNextBlock();
         } else if (type >= MIN_UNSKIPPABLE_TYPE && type <= MAX_UNSKIPPABLE_TYPE) {
             throw new IOException("Unskippable chunk with type " + type + " (hex " + Integer.toHexString(type) + ")" + " detected.");
         } else if (type == UNCOMPRESSED_CHUNK_TYPE) {
             inUncompressedChunk = true;
             uncompressedBytesRemaining = readSize() - 4 /* CRC */;
             if (uncompressedBytesRemaining < 0) {
                 throw new IOException("Found illegal chunk with negative size");
             }
             expectedChecksum = unmask(readCrc());
         } else if (type == COMPRESSED_CHUNK_TYPE) {
             final boolean expectChecksum = dialect.usesChecksumWithCompressedChunks();
             final long size = readSize() - (expectChecksum ? 4L : 0L);
             if (size < 0) {
                 throw new IOException("Found illegal chunk with negative size");
             }
             if (expectChecksum) {
                 expectedChecksum = unmask(readCrc());
             } else {
                 expectedChecksum = -1;
             }
             currentCompressedChunk = new SnappyCompressorInputStream(new BoundedInputStream(inputStream, size), blockSize);
             // constructor reads uncompressed size
             count(currentCompressedChunk.getBytesRead());
         } else {
             // impossible as all potential byte values have been covered
             throw new IOException("Unknown chunk type " + type + " detected.");
         }
     }
 
     /**
      * Read from the current chunk into the given array.
      *
      * @return -1 if there is no current chunk or the number of bytes read from the current chunk (which may be -1 if the end of the chunk is reached).
      */
     private int readOnce(final byte[] b, final int off, final int len) throws IOException {
         int read = -1;
         if (inUncompressedChunk) {
             final int amount = Math.min(uncompressedBytesRemaining, len);
             if (amount == 0) {
                 return -1;
             }
             read = inputStream.read(b, off, amount);
             if (read != -1) {
                 uncompressedBytesRemaining -= read;
                 count(read);
             }
         } else if (currentCompressedChunk != null) {
             final long before = currentCompressedChunk.getBytesRead();
             read = currentCompressedChunk.read(b, off, len);
             if (read == -1) {
                 currentCompressedChunk.close();
                 currentCompressedChunk = null;
             } else {
                 count(currentCompressedChunk.getBytesRead() - before);
             }
         }
         if (read > 0) {
             checksum.update(b, off, read);
         }
         return read;
     }
 
     private int readOneByte() throws IOException {
         final int b = inputStream.read();
         if (b != -1) {
             count(1);
             return b & 0xFF;
         }
         return -1;
     }
 
     private int readSize() throws IOException {
         return (int) ByteUtils.fromLittleEndian(supplier, 3);
     }
 
     private void readStreamIdentifier() throws IOException {
         final byte[] b = new byte[10];
         final int read = IOUtils.readFully(inputStream, b);
         count(read);
         if (10 != read || !matches(b, 10)) {
             throw new IOException("Not a framed Snappy stream");
         }
     }
 
     private void skipBlock() throws IOException {
         final int size = readSize();
         if (size < 0) {
             throw new IOException("Found illegal chunk with negative size");
         }
         final long read = org.apache.commons.io.IOUtils.skip(inputStream, size);
         count(read);
         if (read != size) {
             throw new IOException("Premature end of stream");
         }
     }
 
     private void verifyLastChecksumAndReset() throws IOException {
         if (expectedChecksum >= 0 && expectedChecksum != checksum.getValue()) {
             throw new IOException("Checksum verification failed");
         }
         expectedChecksum = -1;
         checksum.reset();
     }
 
 }