/*
 * Copyright (c) 1996, 2013, Oracle and/or its affiliates. All rights reserved.
 * Copyright (C) 2014-2020 MicroEJ Corp. - EDC compliance and optimizations.
 * 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;

import ej.annotation.Nullable;

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

public class StringReader extends Reader {

	@Nullable
	private String str;

	private final 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 (this.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
	 */
	@Override
	public int read() throws IOException {
		synchronized (this.lock) {
			ensureOpen();
			if (this.next >= this.length) {
				return -1;
			}
			String str = this.str;
			assert str != null;
			return str.charAt(this.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
	 */
	@Override
	public int read(char cbuf[], int off, int len) throws IOException {
		synchronized (this.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 (this.next >= this.length) {
				return -1;
			}
			int n = Math.min(this.length - this.next, len);
			String str = this.str;
			assert str != null;
			str.getChars(this.next, this.next + n, cbuf, off);
			this.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
	 */
	@Override
	public long skip(long ns) throws IOException {
		synchronized (this.lock) {
			ensureOpen();
			if (this.next >= this.length) {
				return 0;
			}
			// Bound skip by beginning and end of the source
			long n = Math.min(this.length - this.next, ns);
			n = Math.max(-this.next, n);
			this.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
	 */
	@Override
	public boolean ready() throws IOException {
		synchronized (this.lock) {
			ensureOpen();
			return true;
		}
	}

	/**
	 * Tells whether this stream supports the mark() operation, which it does.
	 */
	@Override
	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
	 */
	@Override
	public void mark(int readAheadLimit) throws IOException {
		if (readAheadLimit < 0) {
			throw new IllegalArgumentException("Read-ahead limit < 0");
		}
		synchronized (this.lock) {
			ensureOpen();
			this.mark = this.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
	 */
	@Override
	public void reset() throws IOException {
		synchronized (this.lock) {
			ensureOpen();
			this.next = this.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.
	 */
	@Override
	public void close() {
		this.str = null;
	}
}