/*

 * Copyright (c) 1996, 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;

/**

 * This class implements a character buffer that can be used as a

 * character-input stream.

 *

 * @author      Herb Jellinek

 * @since       1.1

 */

public class CharArrayReader extends Reader {

    /** The character buffer. */

    protected char buf[];

    /** The current buffer position. */

    protected int pos;

    /** The position of mark in buffer. */

    protected int markedPos = 0;

    /**

     *  The index of the end of this buffer.  There is not valid

     *  data at or beyond this index.

     */

    protected int count;

    /**

     * Creates a CharArrayReader from the specified array of chars.

     * @param buf       Input buffer (not copied)

     */

    public CharArrayReader(char buf[]) {

        this.buf = buf;

        this.pos = 0;

        this.count = buf.length;

    }

    /**

     * Creates a CharArrayReader from the specified array of chars.

     *

     * <p> The resulting reader will start reading at the given

     * {@code offset}.  The total number of {@code char} values that can be

     * read from this reader will be either {@code length} or

     * {@code buf.length-offset}, whichever is smaller.

     *

     * @throws IllegalArgumentException

     *         If {@code offset} is negative or greater than

     *         {@code buf.length}, or if {@code length} is negative, or if

     *         the sum of these two values is negative.

     *

     * @param buf       Input buffer (not copied)

     * @param offset    Offset of the first char to read

     * @param length    Number of chars to read

     */

    public CharArrayReader(char buf[], int offset, int length) {

        if ((offset < 0) || (offset > buf.length) || (length < 0) ||

            ((offset + length) < 0)) {

            throw new IllegalArgumentException();

        }

        this.buf = buf;

        this.pos = offset;

        this.count = Math.min(offset + length, buf.length);

        this.markedPos = offset;

    }

    /** Checks to make sure that the stream has not been closed */

    private void ensureOpen() throws IOException {

        if (buf == null)

            throw new IOException("Stream closed");

    }

    /**

     * Reads a single character.

     *

     * @throws      IOException  If an I/O error occurs

     */

    public int read() throws IOException {

        synchronized (lock) {

            ensureOpen();

            if (pos >= count)

                return -1;

            else

                return buf[pos++];

        }

    }

    /**

     * Reads characters into a portion of an array.

     * @param   b  Destination buffer

     * @param   off  Offset at which to start storing characters

     * @param   len   Maximum number of characters to read

     * @return  The actual number of characters read, or -1 if

     *          the end of the stream has been reached

     *

     * @throws  IOException  If an I/O error occurs

     * @throws  IndexOutOfBoundsException {@inheritDoc}

     */

    public int read(char b[], int off, int len) throws IOException {

        synchronized (lock) {

            ensureOpen();

            if ((off < 0) || (off > b.length) || (len < 0) ||

                ((off + len) > b.length) || ((off + len) < 0)) {

                throw new IndexOutOfBoundsException();

            } else if (len == 0) {

                return 0;

            }

            if (pos >= count) {

                return -1;

            }

            int avail = count - pos;

            if (len > avail) {

                len = avail;

            }

            if (len <= 0) {

                return 0;

            }

            System.arraycopy(buf, pos, b, off, len);

            pos += len;

            return len;

        }

    }

    /**

     * Skips characters.  Returns the number of characters that were skipped.

     *

     * <p>The {@code n} parameter may be negative, even though the

     * {@code skip} method of the {@link Reader} superclass throws

     * an exception in this case. If {@code n} is negative, then

     * this method does nothing and returns {@code 0}.

     *

     * @param      n The number of characters to skip

     * @return     The number of characters actually skipped

     * @throws     IOException If the stream is closed, or an I/O error occurs

     */

    public long skip(long n) throws IOException {

        synchronized (lock) {

            ensureOpen();

            long avail = count - pos;

            if (n > avail) {

                n = avail;

            }

            if (n < 0) {

                return 0;

            }

            pos += n;

            return n;

        }

    }

    /**

     * Tells whether this stream is ready to be read.  Character-array readers

     * are always ready to be read.

     *

     * @throws     IOException  If an I/O error occurs

     */

    public boolean ready() throws IOException {

        synchronized (lock) {

            ensureOpen();

            return (count - pos) > 0;

        }

    }

    /**

     * 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 character array,

     *                         there is no actual limit; hence this argument is

     *                         ignored.

     *

     * @throws     IOException  If an I/O error occurs

     */

    public void mark(int readAheadLimit) throws IOException {

        synchronized (lock) {

            ensureOpen();

            markedPos = pos;

        }

    }

    /**

     * Resets the stream to the most recent mark, or to the beginning if it has

     * never been marked.

     *

     * @throws     IOException  If an I/O error occurs

     */

    public void reset() throws IOException {

        synchronized (lock) {

            ensureOpen();

            pos = markedPos;

        }

    }

    /**

     * 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. This method will block

     * while there is another thread blocking on the reader.

     */

    public void close() {

        synchronized (lock) {

            buf = null;

        }

    }

}