/*
 * Copyright (c) 1996, 2018, 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
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package java.io;


import java.nio.CharBuffer;
import java.util.Objects;

/**
 * Abstract class for reading character streams. The only methods that a
 * subclass must implement are read(char[], int, int) and close(). Most
 * subclasses, however, will override some of the methods defined here in order
 * to provide higher efficiency, additional functionality, or both.
 *
 *
 * @see BufferedReader
 * @see LineNumberReader
 * @see CharArrayReader
 * @see InputStreamReader
 * @see FileReader
 * @see FilterReader
 * @see PushbackReader
 * @see PipedReader
 * @see StringReader
 * @see Writer
 *
 * @author Mark Reinhold
 * @since 1.1
 */

public abstract class Reader implements Readable, Closeable {

 private static final int TRANSFER_BUFFER_SIZE = 8192;

 /**
 * Returns a new {@code Reader} that reads no characters. The returned
 * stream is initially open. The stream is closed by calling the
 * {@code close()} method. Subsequent calls to {@code close()} have no
 * effect.
 *
 * <p> While the stream is open, the {@code read()}, {@code read(char[])},
 * {@code read(char[], int, int)}, {@code read(Charbuffer)}, {@code
 * ready()}, {@code skip(long)}, and {@code transferTo()} methods all
 * behave as if end of stream has been reached. After the stream has been
 * closed, these methods all throw {@code IOException}.
 *
 * <p> The {@code markSupported()} method returns {@code false}. The
 * {@code mark()} and {@code reset()} methods throw an {@code IOException}.
 *
 * <p> The {@link #lock object} used to synchronize operations on the
 * returned {@code Reader} is not specified.
 *
 * @return a {@code Reader} which reads no characters
 *
 * @since 11
 */
 public static Reader nullReader() {
 return new Reader() {
 private volatile boolean closed;

 private void ensureOpen() throws IOException {
 if (closed) {
 throw new IOException("Stream closed");
 }
 }

 @Override
 public int read() throws IOException {
 ensureOpen();
 return -1;
 }

 @Override
 public int read(char[] cbuf, int off, int len) throws IOException {
 Objects.checkFromIndexSize(off, len, cbuf.length);
 ensureOpen();
 if (len == 0) {
 return 0;
 }
 return -1;
 }

 @Override
 public int read(CharBuffer target) throws IOException {
 Objects.requireNonNull(target);
 ensureOpen();
 if (target.hasRemaining()) {
 return -1;
 }
 return 0;
 }

 @Override
 public boolean ready() throws IOException {
 ensureOpen();
 return false;
 }

 @Override
 public long skip(long n) throws IOException {
 ensureOpen();
 return 0L;
 }

 @Override
 public long transferTo(Writer out) throws IOException {
 Objects.requireNonNull(out);
 ensureOpen();
 return 0L;
 }

 @Override
 public void close() {
 closed = true;
 }
 };
 }

 /**
 * The object used to synchronize operations on this stream. For
 * efficiency, a character-stream object may use an object other than
 * itself to protect critical sections. A subclass should therefore use
 * the object in this field rather than {@code this} or a synchronized
 * method.
 */
 protected Object lock;

 /**
 * Creates a new character-stream reader whose critical sections will
 * synchronize on the reader itself.
 */
 protected Reader() {
 this.lock = this;
 }

 /**
 * Creates a new character-stream reader whose critical sections will
 * synchronize on the given object.
 *
 * @param lock The Object to synchronize on.
 */
 protected Reader(Object lock) {
 if (lock == null) {
 throw new NullPointerException();
 }
 this.lock = lock;
 }

 /**
 * Attempts to read characters into the specified character buffer.
 * The buffer is used as a repository of characters as-is: the only
 * changes made are the results of a put operation. No flipping or
 * rewinding of the buffer is performed.
 *
 * @param target the buffer to read characters into
 * @return The number of characters added to the buffer, or
 * -1 if this source of characters is at its end
 * @throws IOException if an I/O error occurs
 * @throws NullPointerException if target is null
 * @throws java.nio.ReadOnlyBufferException if target is a read only buffer
 * @since 1.5
 */
 public int read(java.nio.CharBuffer target) throws IOException {
 int len = target.remaining();
 char[] cbuf = new char[len];
 int n = read(cbuf, 0, len);
 if (n > 0)
 target.put(cbuf, 0, n);
 return n;
 }

 /**
 * Reads a single character. This method will block until a character is
 * available, an I/O error occurs, or the end of the stream is reached.
 *
 * <p> Subclasses that intend to support efficient single-character input
 * should override this method.
 *
 * @return The character read, as an integer in the range 0 to 65535
 * ({@code 0x00-0xffff}), or -1 if the end of the stream has
 * been reached
 *
 * @exception IOException If an I/O error occurs
 */
 public int read() throws IOException {
 char cb[] = new char[1];
 if (read(cb, 0, 1) == -1)
 return -1;
 else
 return cb[0];
 }

 /**
 * Reads characters into an array. This method will block until some input
 * is available, an I/O error occurs, or the end of the stream is reached.
 *
 * @param cbuf Destination buffer
 *
 * @return The number of characters read, or -1
 * if the end of the stream
 * has been reached
 *
 * @exception IOException If an I/O error occurs
 */
 public int read(char cbuf[]) throws IOException {
 return read(cbuf, 0, cbuf.length);
 }

 /**
 * Reads characters into a portion of an array. This method will block
 * until some input is available, an I/O error occurs, or the end of the
 * stream is reached.
 *
 * @param cbuf Destination buffer
 * @param off Offset at which to start storing characters
 * @param len Maximum number of characters to read
 *
 * @return The number of characters read, or -1 if the end of the
 * stream has been reached
 *
 * @exception IOException If an I/O error occurs
 * @exception IndexOutOfBoundsException
 * If {@code off} is negative, or {@code len} is negative,
 * or {@code len} is greater than {@code cbuf.length - off}
 */
 public abstract int read(char cbuf[], int off, int len) throws IOException;

 /** Maximum skip-buffer size */
 private static final int maxSkipBufferSize = 8192;

 /** Skip buffer, null until allocated */
 private char skipBuffer[] = null;

 /**
 * Skips characters. This method will block until some characters are
 * available, an I/O error occurs, or the end of the stream is reached.
 *
 * @param n The number of characters to skip
 *
 * @return The number of characters actually skipped
 *
 * @exception IllegalArgumentException If <code>n</code> is negative.
 * @exception IOException If an I/O error occurs
 */
 public long skip(long n) throws IOException {
 if (n < 0L)
 throw new IllegalArgumentException("skip value is negative");
 int nn = (int) Math.min(n, maxSkipBufferSize);
 synchronized (lock) {
 if ((skipBuffer == null) || (skipBuffer.length < nn))
 skipBuffer = new char[nn];
 long r = n;
 while (r > 0) {
 int nc = read(skipBuffer, 0, (int)Math.min(r, nn));
 if (nc == -1)
 break;
 r -= nc;
 }
 return n - r;
 }
 }

 /**
 * Tells whether this stream is ready to be read.
 *
 * @return True if the next read() is guaranteed not to block for input,
 * false otherwise. Note that returning false does not guarantee that the
 * next read will block.
 *
 * @exception IOException If an I/O error occurs
 */
 public boolean ready() throws IOException {
 return false;
 }

 /**
 * Tells whether this stream supports the mark() operation. The default
 * implementation always returns false. Subclasses should override this
 * method.
 *
 * @return true if and only if this stream supports the mark operation.
 */
 public boolean markSupported() {
 return false;
 }

 /**
 * Marks the present position in the stream. Subsequent calls to reset()
 * will attempt to reposition the stream to this point. Not all
 * character-input streams support the mark() operation.
 *
 * @param readAheadLimit Limit on the number of characters that may be
 * read while still preserving the mark. After
 * reading this many characters, attempting to
 * reset the stream may fail.
 *
 * @exception IOException If the stream does not support mark(),
 * or if some other I/O error occurs
 */
 public void mark(int readAheadLimit) throws IOException {
 throw new IOException("mark() not supported");
 }

 /**
 * Resets the stream. If the stream has been marked, then attempt to
 * reposition it at the mark. If the stream has not been marked, then
 * attempt to reset it in some way appropriate to the particular stream,
 * for example by repositioning it to its starting point. Not all
 * character-input streams support the reset() operation, and some support
 * reset() without supporting mark().
 *
 * @exception IOException If the stream has not been marked,
 * or if the mark has been invalidated,
 * or if the stream does not support reset(),
 * or if some other I/O error occurs
 */
 public void reset() throws IOException {
 throw new IOException("reset() not supported");
 }

 /**
 * Closes the stream and releases any system resources associated with
 * it. Once the stream has been closed, further read(), ready(),
 * mark(), reset(), or skip() invocations will throw an IOException.
 * Closing a previously closed stream has no effect.
 *
 * @exception IOException If an I/O error occurs
 */
 public abstract void close() throws IOException;

 /**
 * Reads all characters from this reader and writes the characters to the
 * given writer in the order that they are read. On return, this reader
 * will be at end of the stream. This method does not close either reader
 * or writer.
 * <p>
 * This method may block indefinitely reading from the reader, or
 * writing to the writer. The behavior for the case where the reader
 * and/or writer is <i>asynchronously closed</i>, or the thread
 * interrupted during the transfer, is highly reader and writer
 * specific, and therefore not specified.
 * <p>
 * If an I/O error occurs reading from the reader or writing to the
 * writer, then it may do so after some characters have been read or
 * written. Consequently the reader may not be at end of the stream and
 * one, or both, streams may be in an inconsistent state. It is strongly
 * recommended that both streams be promptly closed if an I/O error occurs.
 *
 * @param out the writer, non-null
 * @return the number of characters transferred
 * @throws IOException if an I/O error occurs when reading or writing
 * @throws NullPointerException if {@code out} is {@code null}
 *
 * @since 10
 */
 public long transferTo(Writer out) throws IOException {
 Objects.requireNonNull(out, "out");
 long transferred = 0;
 char[] buffer = new char[TRANSFER_BUFFER_SIZE];
 int nRead;
 while ((nRead = read(buffer, 0, TRANSFER_BUFFER_SIZE)) >= 0) {
 out.write(buffer, 0, nRead);
 transferred += nRead;
 }
 return transferred;
 }

}