/*
 * @(#)CharArrayReader.java	1.25 05/11/17
 *
 * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package java.io;

/**
 * This class implements a character buffer that can be used as a
 * character-input stream.
 *
 * @author	Herb Jellinek
 * @version 	1.25, 11/17/05
 * @since       JDK1.1
 */
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
     * <tt>offset</tt>.  The total number of <tt>char</tt> values that can be
     * read from this reader will be either <tt>length</tt> or
     * <tt>buf.length-offset</tt>, whichever is smaller.
     *
     * @throws IllegalArgumentException
     *         If <tt>offset</tt> is negative or greater than
     *         <tt>buf.length</tt>, or if <tt>length</tt> 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.
     * 
     * @exception   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
     * 
     * @exception   IOException  If an I/O error occurs
     */
    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;
	    }
	    if (pos + len > count) {
		len = count - pos;
	    }
	    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</code> parameter may be negative, even though the
     * <code>skip</code> method of the {@link Reader} superclass throws
     * an exception in this case. If <code>n</code> is negative, then
     * this method does nothing and returns <code>0</code>.
     *
     * @param n The number of characters to skip
     * @return       The number of characters actually skipped
     * @exception  IOException If the stream is closed, or an I/O error occurs
     */
    public long skip(long n) throws IOException {
	synchronized (lock) {
	    ensureOpen();
	    if (pos + n > count) {
		n = count - pos;
	    }
	    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.
     *
     * @exception  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.
     *
     * @exception  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.
     *
     * @exception  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.
     */
    public void close() {
	buf = null;
    }
}