/*
    * 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
    *
   *   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 org.apache.commons.compress.compressors.lz77support;
  
  import java.io.IOException;
  import java.io.InputStream;
  import java.util.Arrays;
  
  import org.apache.commons.compress.compressors.CompressorInputStream;
  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.BoundedInputStream;
  
  /**
   * Encapsulates code common to LZ77 decompressors.
   *
   * <p>
   * Assumes the stream consists of blocks of literal data and back-references (called copies) in any order. Of course the first block must be a literal block for
   * the scheme to work - unless the {@link #prefill prefill} method has been used to provide initial data that is never returned by {@link #read read} but only
   * used for back-references.
   * </p>
   *
   * <p>
   * Subclasses must override the three-arg {@link #read read} method as the no-arg version delegates to it and the default implementation delegates to the no-arg
   * version, leading to infinite mutual recursion and a {@code StackOverflowError} otherwise.
   * </p>
   *
   * <p>
   * The contract for subclasses' {@code read} implementation is:
   * </p>
   * <ul>
   *
   * <li>keep track of the current state of the stream. Is it inside a literal block or a back-reference or in-between blocks?</li>
   *
   * <li>Use {@link #readOneByte} to access the underlying stream directly.</li>
   *
   * <li>If a new literal block starts, use {@link #startLiteral} to tell this class about it and read the literal data using {@link #readLiteral} until it
   * returns {@code 0}. {@link #hasMoreDataInBlock} will return {@code false} before the next call to {@link #readLiteral} would return {@code 0}.</li>
   *
   * <li>If a new back-reference starts, use {@link #startBackReference} to tell this class about it and read the literal data using {@link #readBackReference}
   * until it returns {@code 0}. {@link #hasMoreDataInBlock} will return {@code false} before the next call to {@link #readBackReference} would return
   * {@code 0}.</li>
   *
   * <li>If the end of the stream has been reached, return {@code -1} as this class' methods will never do so themselves.</li>
   *
   * </ul>
   *
   * <p>
   * {@link #readOneByte} and {@link #readLiteral} update the counter for bytes read.
   * </p>
   *
   * @since 1.14
   */
  public abstract class AbstractLZ77CompressorInputStream extends CompressorInputStream implements InputStreamStatistics {
  
      /** Size of the window - must be bigger than the biggest offset expected. */
      private final int windowSize;
  
      /**
       * Buffer to write decompressed bytes to for back-references, will be three times windowSize big.
       *
       * <p>
       * Three times so we can slide the whole buffer a windowSize to the left once we've read twice windowSize and still have enough data inside of it to satisfy
       * back-references.
       * </p>
       */
      private final byte[] buf;
  
      /** One behind the index of the last byte in the buffer that was written, i.e. the next position to write to */
      private int writeIndex;
  
      /** Index of the next byte to be read. */
      private int readIndex;
  
      /** The underlying stream to read compressed data from */
      private final BoundedInputStream in;
  
      /** Number of bytes still to be read from the current literal or back-reference. */
      private long bytesRemaining;
  
      /** Offset of the current back-reference. */
      private int backReferenceOffset;
 
     /** Uncompressed size */
     private int size;
 
     // used in no-arg read method
     private final byte[] oneByte = new byte[1];
 
     /**
      * Supplier that delegates to {@link #readOneByte}.
      */
     protected final ByteUtils.ByteSupplier supplier = this::readOneByte;
 
     /**
      * Creates a new LZ77 input stream.
      *
      * @param is         An InputStream to read compressed data from
      * @param windowSize Size of the window kept for back-references, must be bigger than the biggest offset expected.
      * @throws IllegalArgumentException if windowSize is not bigger than 0
      */
     public AbstractLZ77CompressorInputStream(final InputStream is, final int windowSize) {
         this.in = BoundedInputStream.builder().setInputStream(is).asSupplier().get();
         if (windowSize <= 0) {
             throw new IllegalArgumentException("windowSize must be bigger than 0");
         }
         this.windowSize = windowSize;
         buf = new byte[3 * windowSize];
         writeIndex = readIndex = 0;
         bytesRemaining = 0;
     }
 
     /** {@inheritDoc} */
     @Override
     public int available() {
         return writeIndex - readIndex;
     }
 
     /** {@inheritDoc} */
     @Override
     public void close() throws IOException {
         in.close();
     }
 
     /**
      * @since 1.17
      */
     @Override
     public long getCompressedCount() {
         return in.getCount();
     }
 
     /**
      * Gets the uncompressed size of the stream
      *
      * @return the uncompressed size
      */
     public int getSize() {
         return size;
     }
 
     /**
      * Is there still data remaining inside the current block?
      *
      * @return true if there is still data remaining inside the current block.
      */
     protected final boolean hasMoreDataInBlock() {
         return bytesRemaining > 0;
     }
 
     /**
      * Adds some initial data to fill the window with.
      *
      * <p>
      * This is used if the stream has been cut into blocks and back-references of one block may refer to data of the previous block(s). One such example is the
      * LZ4 frame format using block dependency.
      * </p>
      *
      * @param data the data to fill the window with.
      * @throws IllegalStateException if the stream has already started to read data
      */
     public void prefill(final byte[] data) {
         if (writeIndex != 0) {
             throw new IllegalStateException("The stream has already been read from, can't prefill anymore");
         }
         // we don't need more data than the big offset could refer to, so cap it
         final int len = Math.min(windowSize, data.length);
         // we need the last data as we are dealing with *back*-references
         System.arraycopy(data, data.length - len, buf, 0, len);
         writeIndex += len;
         readIndex += len;
     }
 
     /** {@inheritDoc} */
     @Override
     public int read() throws IOException {
         return read(oneByte, 0, 1) == -1 ? -1 : oneByte[0] & 0xFF;
     }
 
     /**
      * Reads data from the current back-reference.
      *
      * @param b   buffer to write data to
      * @param off offset to start writing to
      * @param len maximum amount of data to read
      * @return number of bytes read, may be 0. Will never return -1 as EOF-detection is the responsibility of the subclass
      * @throws NullPointerException      if {@code b} is null
      * @throws IndexOutOfBoundsException if {@code off} is negative, {@code len} is negative, or {@code len} is greater than {@code b.length - off}
      */
     protected final int readBackReference(final byte[] b, final int off, final int len) {
         final int avail = available();
         if (len > avail) {
             tryToCopy(len - avail);
         }
         return readFromBuffer(b, off, len);
     }
 
     private int readFromBuffer(final byte[] b, final int off, final int len) {
         final int readable = Math.min(len, available());
         if (readable > 0) {
             System.arraycopy(buf, readIndex, b, off, readable);
             readIndex += readable;
             if (readIndex > 2 * windowSize) {
                 slideBuffer();
             }
         }
         size += readable;
         return readable;
     }
 
     /**
      * Reads data from the current literal block.
      *
      * @param b   buffer to write data to
      * @param off offset to start writing to
      * @param len maximum amount of data to read
      * @return number of bytes read, may be 0. Will never return -1 as EOF-detection is the responsibility of the subclass
      * @throws IOException               if the underlying stream throws or signals an EOF before the amount of data promised for the block have been read
      * @throws NullPointerException      if {@code b} is null
      * @throws IndexOutOfBoundsException if {@code off} is negative, {@code len} is negative, or {@code len} is greater than {@code b.length - off}
      */
     protected final int readLiteral(final byte[] b, final int off, final int len) throws IOException {
         final int avail = available();
         if (len > avail) {
             tryToReadLiteral(len - avail);
         }
         return readFromBuffer(b, off, len);
     }
 
     /**
      * Reads a single byte from the real input stream and ensures the data is accounted for.
      *
      * @return the byte read as value between 0 and 255 or -1 if EOF has been reached.
      * @throws IOException if the underlying stream throws
      */
     protected final int readOneByte() throws IOException {
         final int b = in.read();
         if (b != -1) {
             count(1);
             return b & 0xFF;
         }
         return -1;
     }
 
     private void slideBuffer() {
         System.arraycopy(buf, windowSize, buf, 0, windowSize * 2);
         writeIndex -= windowSize;
         readIndex -= windowSize;
     }
 
     /**
      * Used by subclasses to signal the next block contains a back-reference with the given coordinates.
      *
      * @param offset the offset of the back-reference
      * @param length the length of the back-reference
      * @throws IllegalArgumentException if offset not bigger than 0 or bigger than the number of bytes available for back-references or if length is negative
      */
     protected final void startBackReference(final int offset, final long length) {
         if (offset <= 0 || offset > writeIndex) {
             throw new IllegalArgumentException("offset must be bigger than 0 but not bigger than the number of bytes available for back-references");
         }
         if (length < 0) {
             throw new IllegalArgumentException("length must not be negative");
         }
         backReferenceOffset = offset;
         bytesRemaining = length;
     }
 
     /**
      * Used by subclasses to signal the next block contains the given amount of literal data.
      *
      * @param length the length of the block
      * @throws IllegalArgumentException if length is negative
      */
     protected final void startLiteral(final long length) {
         if (length < 0) {
             throw new IllegalArgumentException("length must not be negative");
         }
         bytesRemaining = length;
     }
 
     private void tryToCopy(final int bytesToCopy) {
         // this will fit into the buffer without sliding and not
         // require more than is available inside the back-reference
         final int copy = Math.min((int) Math.min(bytesToCopy, bytesRemaining), buf.length - writeIndex);
         if (copy == 0) {
             // NOP
         } else if (backReferenceOffset == 1) { // pretty common special case
             final byte last = buf[writeIndex - 1];
             Arrays.fill(buf, writeIndex, writeIndex + copy, last);
             writeIndex += copy;
         } else if (copy < backReferenceOffset) {
             System.arraycopy(buf, writeIndex - backReferenceOffset, buf, writeIndex, copy);
             writeIndex += copy;
         } else {
             // back-reference overlaps with the bytes created from it
             // like go back two bytes and then copy six (by copying
             // the last two bytes three time).
             final int fullRots = copy / backReferenceOffset;
             for (int i = 0; i < fullRots; i++) {
                 System.arraycopy(buf, writeIndex - backReferenceOffset, buf, writeIndex, backReferenceOffset);
                 writeIndex += backReferenceOffset;
             }
 
             final int pad = copy - backReferenceOffset * fullRots;
             if (pad > 0) {
                 System.arraycopy(buf, writeIndex - backReferenceOffset, buf, writeIndex, pad);
                 writeIndex += pad;
             }
         }
         bytesRemaining -= copy;
     }
 
     private void tryToReadLiteral(final int bytesToRead) throws IOException {
         // min of "what is still inside the literal", "what does the user want" and "how much can fit into the buffer"
         final int reallyTryToRead = Math.min((int) Math.min(bytesToRead, bytesRemaining), buf.length - writeIndex);
         final int bytesRead = reallyTryToRead > 0 ? IOUtils.readFully(in, buf, writeIndex, reallyTryToRead) : 0 /* happens for bytesRemaining == 0 */;
         count(bytesRead);
         if (reallyTryToRead != bytesRead) {
             throw new IOException("Premature end of stream reading literal");
         }
         writeIndex += reallyTryToRead;
         bytesRemaining -= reallyTryToRead;
     }
 }