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	/*
	* Copyright (c) 1994, 2019, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/

	package java.io;

	/**
	* A {@code PushbackInputStream} adds
	* functionality to another input stream, namely
	* the ability to "push back" or "unread" bytes,
	* by storing pushed-back bytes in an internal buffer.
	* This is useful in situations where
	* it is convenient for a fragment of code
	* to read an indefinite number of data bytes
	* that are delimited by a particular byte
	* value; after reading the terminating byte,
	* the code fragment can "unread" it, so that
	* the next read operation on the input stream
	* will reread the byte that was pushed back.
	* For example, bytes representing the characters
	* constituting an identifier might be terminated
	* by a byte representing an operator character;
	* a method whose job is to read just an identifier
	* can read until it sees the operator and
	* then push the operator back to be re-read.
	*
	* @author David Connelly
	* @author Jonathan Payne
	* @since 1.0
	*/
	public class PushbackInputStream extends FilterInputStream {
	/**
	* The pushback buffer.
	* @since 1.1
	*/
	protected byte[] buf;

	/**
	* The position within the pushback buffer from which the next byte will
	* be read. When the buffer is empty, {@code pos} is equal to
	* {@code buf.length}; when the buffer is full, {@code pos} is
	* equal to zero.
	*
	* @since 1.1
	*/
	protected int pos;

	/**
	* Check to make sure that this stream has not been closed
	*/
	private void ensureOpen() throws IOException {
	if (in == null)
	throw new IOException("Stream closed");
	}

	/**
	* Creates a {@code PushbackInputStream}
	* with a pushback buffer of the specified {@code size},
	* and saves its argument, the input stream
	* {@code in}, for later use. Initially,
	* the pushback buffer is empty.
	*
	* @param in the input stream from which bytes will be read.
	* @param size the size of the pushback buffer.
	* @throws IllegalArgumentException if {@code size <= 0}
	* @since 1.1
	*/
	public PushbackInputStream(InputStream in, int size) {
	super(in);
	if (size <= 0) {
	throw new IllegalArgumentException("size <= 0");
	}
	this.buf = new byte[size];
	this.pos = size;
	}

	/**
	* Creates a {@code PushbackInputStream}
	* with a 1-byte pushback buffer, and saves its argument, the input stream
	* {@code in}, for later use. Initially,
	* the pushback buffer is empty.
	*
	* @param in the input stream from which bytes will be read.
	*/
	public PushbackInputStream(InputStream in) {
	this(in, 1);
	}

	/**
	* Reads the next byte of data from this input stream. The value
	* byte is returned as an {@code int} in the range
	* {@code 0} to {@code 255}. If no byte is available
	* because the end of the stream has been reached, the value
	* {@code -1} is returned. This method blocks until input data
	* is available, the end of the stream is detected, or an exception
	* is thrown.
	*
	* <p> This method returns the most recently pushed-back byte, if there is
	* one, and otherwise calls the {@code read} method of its underlying
	* input stream and returns whatever value that method returns.
	*
	* @return the next byte of data, or {@code -1} if the end of the
	* stream has been reached.
	* @throws IOException if this input stream has been closed by
	* invoking its {@link #close()} method,
	* or an I/O error occurs.
	* @see java.io.InputStream#read()
	*/
	public int read() throws IOException {
	ensureOpen();
	if (pos < buf.length) {
	return buf[pos++] & 0xff;
	}
	return super.read();
	}

	/**
	* Reads up to {@code len} bytes of data from this input stream into
	* an array of bytes. This method first reads any pushed-back bytes; after
	* that, if fewer than {@code len} bytes have been read then it
	* reads from the underlying input stream. If {@code len} is not zero, the method
	* blocks until at least 1 byte of input is available; otherwise, no
	* bytes are read and {@code 0} is returned.
	*
	* @param b the buffer into which the data is read.
	* @param off the start offset in the destination array {@code b}
	* @param len the maximum number of bytes read.
	* @return the total number of bytes read into the buffer, or
	* {@code -1} if there is no more data because the end of
	* the stream has been reached.
	* @throws NullPointerException If {@code b} is {@code null}.
	* @throws IndexOutOfBoundsException If {@code off} is negative,
	* {@code len} is negative, or {@code len} is greater than
	* {@code b.length - off}
	* @throws IOException if this input stream has been closed by
	* invoking its {@link #close()} method,
	* or an I/O error occurs.
	* @see java.io.InputStream#read(byte[], int, int)
	*/
	public int read(byte[] b, int off, int len) throws IOException {
	ensureOpen();
	if (b == null) {
	throw new NullPointerException();
	} else if (off < 0 \|\| len < 0 \|\| len > b.length - off) {
	throw new IndexOutOfBoundsException();
	} else if (len == 0) {
	return 0;
	}

	int avail = buf.length - pos;
	if (avail > 0) {
	if (len < avail) {
	avail = len;
	}
	System.arraycopy(buf, pos, b, off, avail);
	pos += avail;
	off += avail;
	len -= avail;
	}
	if (len > 0) {
	len = super.read(b, off, len);
	if (len == -1) {
	return avail == 0 ? -1 : avail;
	}
	return avail + len;
	}
	return avail;
	}

	/**
	* Pushes back a byte by copying it to the front of the pushback buffer.
	* After this method returns, the next byte to be read will have the value
	* {@code (byte)b}.
	*
	* @param b the {@code int} value whose low-order
	* byte is to be pushed back.
	* @throws IOException If there is not enough room in the pushback
	* buffer for the byte, or this input stream has been closed by
	* invoking its {@link #close()} method.
	*/
	public void unread(int b) throws IOException {
	ensureOpen();
	if (pos == 0) {
	throw new IOException("Push back buffer is full");
	}
	buf[--pos] = (byte)b;
	}

	/**
	* Pushes back a portion of an array of bytes by copying it to the front
	* of the pushback buffer. After this method returns, the next byte to be
	* read will have the value {@code b[off]}, the byte after that will
	* have the value {@code b[off+1]}, and so forth.
	*
	* @param b the byte array to push back.
	* @param off the start offset of the data.
	* @param len the number of bytes to push back.
	* @throws NullPointerException If {@code b} is {@code null}.
	* @throws IOException If there is not enough room in the pushback
	* buffer for the specified number of bytes,
	* or this input stream has been closed by
	* invoking its {@link #close()} method.
	* @since 1.1
	*/
	public void unread(byte[] b, int off, int len) throws IOException {
	ensureOpen();
	if (len > pos) {
	throw new IOException("Push back buffer is full");
	}
	pos -= len;
	System.arraycopy(b, off, buf, pos, len);
	}

	/**
	* Pushes back an array of bytes by copying it to the front of the
	* pushback buffer. After this method returns, the next byte to be read
	* will have the value {@code b[0]}, the byte after that will have the
	* value {@code b[1]}, and so forth.
	*
	* @param b the byte array to push back
	* @throws NullPointerException If {@code b} is {@code null}.
	* @throws IOException If there is not enough room in the pushback
	* buffer for the specified number of bytes,
	* or this input stream has been closed by
	* invoking its {@link #close()} method.
	* @since 1.1
	*/
	public void unread(byte[] b) throws IOException {
	unread(b, 0, b.length);
	}

	/**
	* Returns an estimate of the number of bytes that can be read (or
	* skipped over) from this input stream without blocking by the next
	* invocation of a method for this input stream. The next invocation might be
	* the same thread or another thread. A single read or skip of this
	* many bytes will not block, but may read or skip fewer bytes.
	*
	* <p> The method returns the sum of the number of bytes that have been
	* pushed back and the value returned by {@link
	* java.io.FilterInputStream#available available}.
	*
	* @return the number of bytes that can be read (or skipped over) from
	* the input stream without blocking.
	* @throws IOException if this input stream has been closed by
	* invoking its {@link #close()} method,
	* or an I/O error occurs.
	* @see java.io.FilterInputStream#in
	* @see java.io.InputStream#available()
	*/
	public int available() throws IOException {
	ensureOpen();
	int n = buf.length - pos;
	int avail = super.available();
	return n > (Integer.MAX_VALUE - avail)
	? Integer.MAX_VALUE
	: n + avail;
	}

	/**
	* Skips over and discards {@code n} bytes of data from this
	* input stream. The {@code skip} method may, for a variety of
	* reasons, end up skipping over some smaller number of bytes,
	* possibly zero. If {@code n} is negative, no bytes are skipped.
	*
	* <p> The {@code skip} method of {@code PushbackInputStream}
	* first skips over the bytes in the pushback buffer, if any. It then
	* calls the {@code skip} method of the underlying input stream if
	* more bytes need to be skipped. The actual number of bytes skipped
	* is returned.
	*
	* @param n {@inheritDoc}
	* @return {@inheritDoc}
	* @throws IOException if the stream has been closed by
	* invoking its {@link #close()} method,
	* {@code in.skip(n)} throws an IOException,
	* or an I/O error occurs.
	* @see java.io.FilterInputStream#in
	* @see java.io.InputStream#skip(long n)
	* @since 1.2
	*/
	public long skip(long n) throws IOException {
	ensureOpen();
	if (n <= 0) {
	return 0;
	}

	long pskip = buf.length - pos;
	if (pskip > 0) {
	if (n < pskip) {
	pskip = n;
	}
	pos += pskip;
	n -= pskip;
	}
	if (n > 0) {
	pskip += super.skip(n);
	}
	return pskip;
	}

	/**
	* Tests if this input stream supports the {@code mark} and
	* {@code reset} methods, which it does not.
	*
	* @return {@code false}, since this class does not support the
	* {@code mark} and {@code reset} methods.
	* @see java.io.InputStream#mark(int)
	* @see java.io.InputStream#reset()
	*/
	public boolean markSupported() {
	return false;
	}

	/**
	* Marks the current position in this input stream.
	*
	* <p> The {@code mark} method of {@code PushbackInputStream}
	* does nothing.
	*
	* @param readlimit the maximum limit of bytes that can be read before
	* the mark position becomes invalid.
	* @see java.io.InputStream#reset()
	*/
	public synchronized void mark(int readlimit) {
	}

	/**
	* Repositions this stream to the position at the time the
	* {@code mark} method was last called on this input stream.
	*
	* <p> The method {@code reset} for class
	* {@code PushbackInputStream} does nothing except throw an
	* {@code IOException}.
	*
	* @throws IOException if this method is invoked.
	* @see java.io.InputStream#mark(int)
	* @see java.io.IOException
	*/
	public synchronized void reset() throws IOException {
	throw new IOException("mark/reset not supported");
	}

	/**
	* Closes this input stream and releases any system resources
	* associated with the stream.
	* Once the stream has been closed, further read(), unread(),
	* available(), reset(), or skip() invocations will throw an IOException.
	* Closing a previously closed stream has no effect.
	*
	* @throws IOException if an I/O error occurs.
	*/
	public synchronized void close() throws IOException {
	if (in == null)
	return;
	in.close();
	in = null;
	buf = null;
	}
	}

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