/*
    *  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.io.input;
  
  import java.io.BufferedInputStream;
  import java.io.IOException;
  import java.io.InputStream;
  
  import org.apache.commons.io.IOUtils;
  import org.apache.commons.io.build.AbstractStreamBuilder;
  
  /**
   * An unsynchronized version of {@link BufferedInputStream}, not thread-safe.
   * <p>
   * Wraps an existing {@link InputStream} and <em>buffers</em> the input. Expensive interaction with the underlying input stream is minimized, since most
   * (smaller) requests can be satisfied by accessing the buffer alone. The drawback is that some extra space is required to hold the buffer and that copying
   * takes place when filling that buffer, but this is usually outweighed by the performance benefits.
   * </p>
   * <p>
   * To build an instance, use {@link Builder}.
   * </p>
   * <p>
   * A typical application pattern for the class looks like this:
   * </p>
   *
   * <pre>
   * UnsynchronizedBufferedInputStream s = new UnsynchronizedBufferedInputStream.Builder().
   *   .setInputStream(new FileInputStream(&quot;file.java&quot;))
   *   .setBufferSize(8192)
   *   .get();
   * </pre>
   * <p>
   * Provenance: Apache Harmony and modified.
   * </p>
   *
   * @see Builder
   * @see BufferedInputStream
   * @since 2.12.0
   */
  //@NotThreadSafe
  public final class UnsynchronizedBufferedInputStream extends UnsynchronizedFilterInputStream {
  
      // @formatter:off
      /**
       * Builds a new {@link UnsynchronizedBufferedInputStream}.
       *
       * <p>
       * Using File IO:
       * </p>
       * <pre>{@code
       * UnsynchronizedBufferedInputStream s = UnsynchronizedBufferedInputStream.builder()
       *   .setFile(file)
       *   .setBufferSize(8192)
       *   .get();}
       * </pre>
       * <p>
       * Using NIO Path:
       * </p>
       * <pre>{@code
       * UnsynchronizedBufferedInputStream s = UnsynchronizedBufferedInputStream.builder()
       *   .setPath(path)
       *   .setBufferSize(8192)
       *   .get();}
       * </pre>
       *
       * @see #get()
       */
      // @formatter:on
      public static class Builder extends AbstractStreamBuilder<UnsynchronizedBufferedInputStream, Builder> {
  
          /**
           * Constructs a builder of {@link UnsynchronizedBufferedInputStream}.
           */
          public Builder() {
              // empty
          }
  
          /**
           * Builds a new {@link UnsynchronizedBufferedInputStream}.
           * <p>
           * You must set an aspect that supports {@link #getInputStream()} on this builder, otherwise, this method throws an exception.
           * </p>
           * <p>
           * This builder uses the following aspects:
          * </p>
          * <ul>
          * <li>{@link #getInputStream()}</li>
          * <li>{@link #getBufferSize()}</li>
          * </ul>
          *
          * @return a new instance.
          * @throws IllegalStateException         if the {@code origin} is {@code null}.
          * @throws UnsupportedOperationException if the origin cannot be converted to an {@link InputStream}.
          * @throws IOException                   if an I/O error occurs converting to an {@link InputStream} using {@link #getInputStream()}.
          * @see #getInputStream()
          * @see #getBufferSize()
          * @see #getUnchecked()
          */
         @Override
         public UnsynchronizedBufferedInputStream get() throws IOException {
             return new UnsynchronizedBufferedInputStream(this);
         }
 
     }
 
     /**
      * The buffer containing the current bytes read from the target InputStream.
      */
     protected volatile byte[] buffer;
 
     /**
      * The total number of bytes inside the byte array {@code buffer}.
      */
     protected int count;
 
     /**
      * The current limit, which when passed, invalidates the current mark.
      */
     protected int markLimit;
 
     /**
      * The currently marked position. -1 indicates no mark has been set or the mark has been invalidated.
      */
     protected int markPos = IOUtils.EOF;
 
     /**
      * The current position within the byte array {@code buffer}.
      */
     protected int pos;
 
     /**
      * Constructs a new {@code BufferedInputStream} on the {@link InputStream} {@code in}. The buffer size is specified by the parameter {@code size} and all
      * reads are now filtered through this stream.
      *
      * @param builder   A builder providing the input stream and buffer size.
      * @throws IOException if an I/O error occurs.
      * @throws IllegalArgumentException if {@code size < 0}.
      */
     @SuppressWarnings("resource")
     private UnsynchronizedBufferedInputStream(final Builder builder) throws IOException {
         super(builder.getInputStream());
         final int bufferSize = builder.getBufferSize();
         if (bufferSize <= 0) {
             throw new IllegalArgumentException("Size must be > 0");
         }
         buffer = new byte[bufferSize];
     }
 
     /**
      * Returns the number of bytes that are available before this stream will block. This method returns the number of bytes available in the buffer plus those
      * available in the source stream.
      *
      * @return the number of bytes available before blocking.
      * @throws IOException if this stream is closed.
      */
     @Override
     public int available() throws IOException {
         final InputStream localIn = inputStream; // 'in' could be invalidated by close()
         if (buffer == null || localIn == null) {
             throw new IOException("Stream is closed");
         }
         return count - pos + localIn.available();
     }
 
     /**
      * Closes this stream. The source stream is closed and any resources associated with it are released.
      *
      * @throws IOException if an error occurs while closing this stream.
      */
     @Override
     public void close() throws IOException {
         buffer = null;
         final InputStream localIn = inputStream;
         inputStream = null;
         if (localIn != null) {
             localIn.close();
         }
     }
 
     private int fillBuffer(final InputStream localIn, byte[] localBuf) throws IOException {
         if (markPos == IOUtils.EOF || pos - markPos >= markLimit) {
             /* Mark position not set or exceeded readLimit */
             final int result = localIn.read(localBuf);
             if (result > 0) {
                 markPos = IOUtils.EOF;
                 pos = 0;
                 count = result;
             }
             return result;
         }
         if (markPos == 0 && markLimit > localBuf.length) {
             /* Increase buffer size to accommodate the readLimit */
             int newLength = localBuf.length * 2;
             if (newLength > markLimit) {
                 newLength = markLimit;
             }
             final byte[] newbuf = new byte[newLength];
             System.arraycopy(localBuf, 0, newbuf, 0, localBuf.length);
             // Reassign buffer, which will invalidate any local references
             // FIXME: what if buffer was null?
             localBuf = buffer = newbuf;
         } else if (markPos > 0) {
             System.arraycopy(localBuf, markPos, localBuf, 0, localBuf.length - markPos);
         }
         // Set the new position and mark position
         pos -= markPos;
         count = markPos = 0;
         final int bytesread = localIn.read(localBuf, pos, localBuf.length - pos);
         count = bytesread <= 0 ? pos : pos + bytesread;
         return bytesread;
     }
 
     byte[] getBuffer() {
         return buffer;
     }
 
     /**
      * Sets a mark position in this stream. The parameter {@code readLimit} indicates how many bytes can be read before a mark is invalidated. Calling
      * {@code reset()} will reposition the stream back to the marked position if {@code readLimit} has not been surpassed. The underlying buffer may be
      * increased in size to allow {@code readLimit} number of bytes to be supported.
      *
      * @param readLimit the number of bytes that can be read before the mark is invalidated.
      * @see #reset()
      */
     @Override
     public void mark(final int readLimit) {
         markLimit = readLimit;
         markPos = pos;
     }
 
     /**
      * Indicates whether {@code BufferedInputStream} supports the {@code mark()} and {@code reset()} methods.
      *
      * @return {@code true} for BufferedInputStreams.
      * @see #mark(int)
      * @see #reset()
      */
     @Override
     public boolean markSupported() {
         return true;
     }
 
     /**
      * Reads a single byte from this stream and returns it as an integer in the range from 0 to 255. Returns -1 if the end of the source string has been
      * reached. If the internal buffer does not contain any available bytes then it is filled from the source stream and the first byte is returned.
      *
      * @return the byte read or -1 if the end of the source stream has been reached.
      * @throws IOException if this stream is closed or another IOException occurs.
      */
     @Override
     public int read() throws IOException {
         // Use local refs since buf and in may be invalidated by an
         // unsynchronized close()
         byte[] localBuf = buffer;
         final InputStream localIn = inputStream;
         if (localBuf == null || localIn == null) {
             throw new IOException("Stream is closed");
         }
 
         /* Are there buffered bytes available? */
         if (pos >= count && fillBuffer(localIn, localBuf) == IOUtils.EOF) {
             return IOUtils.EOF; /* no, fill buffer */
         }
         // localBuf may have been invalidated by fillbuf
         if (localBuf != buffer) {
             localBuf = buffer;
             if (localBuf == null) {
                 throw new IOException("Stream is closed");
             }
         }
 
         /* Did filling the buffer fail with -1 (EOF)? */
         if (count - pos > 0) {
             return localBuf[pos++] & 0xFF;
         }
         return IOUtils.EOF;
     }
 
     /**
      * Reads at most {@code length} bytes from this stream and stores them in byte array {@code buffer} starting at offset {@code offset}. Returns the number of
      * bytes actually read or -1 if no bytes were read and the end of the stream was encountered. If all the buffered bytes have been used, a mark has not been
      * set and the requested number of bytes is larger than the receiver's buffer size, this implementation bypasses the buffer and simply places the results
      * directly into {@code buffer}.
      *
      * @param dest the byte array in which to store the bytes read.
      * @param offset the initial position in {@code buffer} to store the bytes read from this stream.
      * @param length the maximum number of bytes to store in {@code buffer}.
      * @return the number of bytes actually read or -1 if end of stream.
      * @throws IndexOutOfBoundsException if {@code offset < 0} or {@code length < 0}, or if {@code offset + length} is greater than the size of {@code buffer}.
      * @throws IOException               if the stream is already closed or another IOException occurs.
      */
     @Override
     public int read(final byte[] dest, int offset, final int length) throws IOException {
         // Use local ref since buf may be invalidated by an unsynchronized
         // close()
         byte[] localBuf = buffer;
         if (localBuf == null) {
             throw new IOException("Stream is closed");
         }
         // avoid int overflow
         if (offset > dest.length - length || offset < 0 || length < 0) {
             throw new IndexOutOfBoundsException();
         }
         if (length == 0) {
             return 0;
         }
         final InputStream localIn = inputStream;
         if (localIn == null) {
             throw new IOException("Stream is closed");
         }
 
         int required;
         if (pos < count) {
             /* There are bytes available in the buffer. */
             final int copylength = count - pos >= length ? length : count - pos;
             System.arraycopy(localBuf, pos, dest, offset, copylength);
             pos += copylength;
             if (copylength == length || localIn.available() == 0) {
                 return copylength;
             }
             offset += copylength;
             required = length - copylength;
         } else {
             required = length;
         }
 
         while (true) {
             final int read;
             /*
              * If we're not marked and the required size is greater than the buffer, simply read the bytes directly bypassing the buffer.
              */
             if (markPos == IOUtils.EOF && required >= localBuf.length) {
                 read = localIn.read(dest, offset, required);
                 if (read == IOUtils.EOF) {
                     return required == length ? IOUtils.EOF : length - required;
                 }
             } else {
                 if (fillBuffer(localIn, localBuf) == IOUtils.EOF) {
                     return required == length ? IOUtils.EOF : length - required;
                 }
                 // localBuf may have been invalidated by fillBuffer()
                 if (localBuf != buffer) {
                     localBuf = buffer;
                     if (localBuf == null) {
                         throw new IOException("Stream is closed");
                     }
                 }
 
                 read = count - pos >= required ? required : count - pos;
                 System.arraycopy(localBuf, pos, dest, offset, read);
                 pos += read;
             }
             required -= read;
             if (required == 0) {
                 return length;
             }
             if (localIn.available() == 0) {
                 return length - required;
             }
             offset += read;
         }
     }
 
     /**
      * Resets this stream to the last marked location.
      *
      * @throws IOException if this stream is closed, no mark has been set or the mark is no longer valid because more than {@code readLimit} bytes have been
      *                     read since setting the mark.
      * @see #mark(int)
      */
     @Override
     public void reset() throws IOException {
         if (buffer == null) {
             throw new IOException("Stream is closed");
         }
         if (IOUtils.EOF == markPos) {
             throw new IOException("Mark has been invalidated");
         }
         pos = markPos;
     }
 
     /**
      * Skips {@code amount} number of bytes in this stream. Subsequent {@code read()}'s will not return these bytes unless {@code reset()} is used.
      *
      * @param amount the number of bytes to skip. {@code skip} does nothing and returns 0 if {@code amount} is less than zero.
      * @return the number of bytes actually skipped.
      * @throws IOException if this stream is closed or another IOException occurs.
      */
     @Override
     public long skip(final long amount) throws IOException {
         // Use local refs since buf and in may be invalidated by an
         // unsynchronized close()
         final byte[] localBuf = buffer;
         final InputStream localIn = inputStream;
         if (localBuf == null) {
             throw new IOException("Stream is closed");
         }
         if (amount < 1) {
             return 0;
         }
         if (localIn == null) {
             throw new IOException("Stream is closed");
         }
 
         if (count - pos >= amount) {
             // (int count - int pos) here is always an int so amount is also in the int range if the above test is true.
             // We can safely cast to int and avoid static analysis warnings.
             pos += (int) amount;
             return amount;
         }
         int read = count - pos;
         pos = count;
 
         if (markPos != IOUtils.EOF && amount <= markLimit) {
             if (fillBuffer(localIn, localBuf) == IOUtils.EOF) {
                 return read;
             }
             if (count - pos >= amount - read) {
                 // (int count - int pos) here is always an int so (amount - read) is also in the int range if the above test is true.
                 // We can safely cast to int and avoid static analysis warnings.
                 pos += (int) amount - read;
                 return amount;
             }
             // Couldn't get all the bytes, skip what we read
             read += count - pos;
             pos = count;
             return read;
         }
         return read + localIn.skip(amount - read);
     }
 }