/*

 * 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 character stream whose source is a string.

 *

 * @author      Mark Reinhold

 * @since       1.1

 */

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

     *

     */

    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

     *

     */

    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.

     *

     */

    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

     *

     */

    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.

     *

     */

    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.

     *

     */

    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. This method will block

     * while there is another thread blocking on the reader.

     */

    public void close() {

        synchronized (lock) {

            str = null;

        }

    }

}