/*
 * Copyright (c) 1996, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 */

package java.io;


/**
 * A character stream whose source is a string.
 *
 * @author Mark Reinhold
 * @since JDK1.1
 */

public class StringReader extends Reader {

 private String str;
 private int length;
 private int next = 0;
 private int mark = 0;

 /**
 * Creates a new string reader.
 *
 * @param s String providing the character stream.
 */
 public StringReader(String s) {
 this.str = s;
 this.length = s.length();
 }

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

 /**
 * Reads a single character.
 *
 * @return The character read, or -1 if the end of the stream has been
 * reached
 *
 * @exception IOException If an I/O error occurs
 */
 public int read() throws IOException {
 synchronized (lock) {
 ensureOpen();
 if (next >= length)
 return -1;
 return str.charAt(next++);
 }
 }

 /**
 * Reads characters into a portion of an array.
 *
 * @param cbuf Destination buffer
 * @param off Offset at which to start writing 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
 */
 public int read(char cbuf[], int off, int len) throws IOException {
 synchronized (lock) {
 ensureOpen();
 if ((off < 0) || (off > cbuf.length) || (len < 0) ||
 ((off + len) > cbuf.length) || ((off + len) < 0)) {
 throw new IndexOutOfBoundsException();
 } else if (len == 0) {
 return 0;
 }
 if (next >= length)
 return -1;
 int n = Math.min(length - next, len);
 str.getChars(next, next + n, cbuf, off);
 next += n;
 return n;
 }
 }

 /**
 * Skips the specified number of characters in the stream. Returns
 * the number of characters that were skipped.
 *
 * <p>The <code>ns</code> parameter may be negative, even though the
 * <code>skip</code> method of the {@link Reader} superclass throws
 * an exception in this case. Negative values of <code>ns</code> cause the
 * stream to skip backwards. Negative return values indicate a skip
 * backwards. It is not possible to skip backwards past the beginning of
 * the string.
 *
 * <p>If the entire string has been read or skipped, then this method has
 * no effect and always returns 0.
 *
 * @exception IOException If an I/O error occurs
 */
 public long skip(long ns) throws IOException {
 synchronized (lock) {
 ensureOpen();
 if (next >= length)
 return 0;
 // Bound skip by beginning and end of the source
 long n = Math.min(length - next, ns);
 n = Math.max(-next, n);
 next += n;
 return n;
 }
 }

 /**
 * Tells whether this stream is ready to be read.
 *
 * @return True if the next read() is guaranteed not to block for input
 *
 * @exception IOException If the stream is closed
 */
 public boolean ready() throws IOException {
 synchronized (lock) {
 ensureOpen();
 return true;
 }
 }

 /**
 * Tells whether this stream supports the mark() operation, which it does.
 */
 public boolean markSupported() {
 return true;
 }

 /**
 * Marks the present position in the stream. Subsequent calls to reset()
 * will reposition the stream to this point.
 *
 * @param readAheadLimit Limit on the number of characters that may be
 * read while still preserving the mark. Because
 * the stream's input comes from a string, there
 * is no actual limit, so this argument must not
 * be negative, but is otherwise ignored.
 *
 * @exception IllegalArgumentException If {@code readAheadLimit < 0}
 * @exception IOException If an I/O error occurs
 */
 public void mark(int readAheadLimit) throws IOException {
 if (readAheadLimit < 0){
 throw new IllegalArgumentException("Read-ahead limit < 0");
 }
 synchronized (lock) {
 ensureOpen();
 mark = next;
 }
 }

 /**
 * Resets the stream to the most recent mark, or to the beginning of the
 * string if it has never been marked.
 *
 * @exception IOException If an I/O error occurs
 */
 public void reset() throws IOException {
 synchronized (lock) {
 ensureOpen();
 next = mark;
 }
 }

 /**
 * Closes the stream and releases any system resources associated with
 * it. Once the stream has been closed, further read(),
 * ready(), mark(), or reset() invocations will throw an IOException.
 * Closing a previously closed stream has no effect.
 */
 public void close() {
 str = null;
 }
}