/*
 * @(#)PipedReader.java	1.12 00/02/02
 *
 * Copyright 1996-2000 Sun Microsystems, Inc. All Rights Reserved.
 * 
 * This software is the proprietary information of Sun Microsystems, Inc.  
 * Use is subject to license terms.
 * 
 */

package java.io;


/**
 * Piped character-input streams.
 *
 * @version 	1.12, 00/02/02
 * @author	Mark Reinhold
 * @since	JDK1.1
 */

public class PipedReader extends Reader {
    boolean closedByWriter = false;
    boolean closedByReader = false;
    boolean connected = false;

    /* REMIND: identification of the read and write sides needs to be
       more sophisticated.  Either using thread groups (but what about
       pipes within a thread?) or using finalization (but it may be a
       long time until the next GC). */
    Thread readSide;
    Thread writeSide;

    /**
     * The size of the pipe's circular input buffer.
     */
    static final int PIPE_SIZE = 1024;

    /**
     * The circular buffer into which incoming data is placed.
     */
    char buffer[] = new char[PIPE_SIZE];

    /**
     * The index of the position in the circular buffer at which the 
     * next character of data will be stored when received from the connected 
     * piped writer. <code>in<0</code> implies the buffer is empty, 
     * <code>in==out</code> implies the buffer is full
     */
    int in = -1;

    /**
     * The index of the position in the circular buffer at which the next 
     * character of data will be read by this piped reader.
     */
    int out = 0;

    /**
     * Creates a <code>PipedReader</code> so
     * that it is connected to the piped writer
     * <code>src</code>. Data written to <code>src</code> 
     * will then be  available as input from this stream.
     *
     * @param      src   the stream to connect to.
     * @exception  IOException  if an I/O error occurs.
     */
    public PipedReader(PipedWriter src) throws IOException {
	connect(src);
    }

    /**
     * Creates a <code>PipedReader</code> so
     * that it is not  yet connected. It must be
     * connected to a <code>PipedWriter</code>
     * before being used.
     *
     * @see     java.io.PipedReader#connect(java.io.PipedWriter)
     * @see     java.io.PipedWriter#connect(java.io.PipedReader)
     */
    public PipedReader() {
    }

    /**
     * Causes this piped reader to be connected
     * to the piped  writer <code>src</code>.
     * If this object is already connected to some
     * other piped writer, an <code>IOException</code>
     * is thrown.
     * <p>
     * If <code>src</code> is an
     * unconnected piped writer and <code>snk</code>
     * is an unconnected piped reader, they
     * may be connected by either the call:
     * <p>
     * <pre><code>snk.connect(src)</code> </pre> 
     * <p>
     * or the call:
     * <p>
     * <pre><code>src.connect(snk)</code> </pre> 
     * <p>
     * The two
     * calls have the same effect.
     *
     * @param      src   The piped writer to connect to.
     * @exception  IOException  if an I/O error occurs.
     */
    public void connect(PipedWriter src) throws IOException {
	src.connect(this);
    }
    
    /**
     * Receives a char of data.  This method will block if no input is
     * available.
     */
    synchronized void receive(int c) throws IOException {
        if (!connected) {
            throw new IOException("Pipe not connected");
        } else if (closedByWriter || closedByReader) {
	    throw new IOException("Pipe closed");
	} else if (readSide != null && !readSide.isAlive()) {
            throw new IOException("Read end dead");
        }

	writeSide = Thread.currentThread();
	while (in == out) {
	    if ((readSide != null) && !readSide.isAlive()) {
		throw new IOException("Pipe broken");
	    }
	    /* full: kick any waiting readers */
	    notifyAll();	
	    try {
	        wait(1000);
	    } catch (InterruptedException ex) {
		throw new java.io.InterruptedIOException();
	    }
	}
	if (in < 0) {
	    in = 0;
	    out = 0;
	}
	buffer[in++] = (char) c;
	if (in >= buffer.length) {
	    in = 0;
	}
    }

    /**
     * Receives data into an array of characters.  This method will
     * block until some input is available. 
     */
    synchronized void receive(char c[], int off, int len)  throws IOException {
	while (--len >= 0) {
	    receive(c[off++]);
	}
    }

    /**
     * Notifies all waiting threads that the last character of data has been
     * received.
     */
    synchronized void receivedLast() {
	closedByWriter = true;
	notifyAll();
    }

    /**
     * Reads the next character of data from this piped stream.
     * If no character is available because the end of the stream 
     * has been reached, the value <code>-1</code> is returned. 
     * This method blocks until input data is available, the end of
     * the stream is detected, or an exception is thrown. 
     *
     * If a thread was providing data characters
     * to the connected piped writer, but
     * the  thread is no longer alive, then an
     * <code>IOException</code> is thrown.
     *
     * @return     the next character of data, or <code>-1</code> if the end of the
     *             stream is reached.
     * @exception  IOException  if the pipe is broken.
     */
    public synchronized int read()  throws IOException {
        if (!connected) {
            throw new IOException("Pipe not connected");
        } else if (closedByReader) {
	    throw new IOException("Pipe closed");
	} else if (writeSide != null && !writeSide.isAlive()
                   && !closedByWriter && (in < 0)) {
            throw new IOException("Write end dead");
        }

        readSide = Thread.currentThread();
	int trials = 2;
	while (in < 0) {
	    if (closedByWriter) { 
		/* closed by writer, return EOF */
		return -1;
	    }
	    if ((writeSide != null) && (!writeSide.isAlive()) && (--trials < 0)) {
		throw new IOException("Pipe broken");
	    }
            /* might be a writer waiting */
	    notifyAll();
	    try {
	        wait(1000);
	    } catch (InterruptedException ex) {
		throw new java.io.InterruptedIOException();
	    }
 	}
	int ret = buffer[out++];
	if (out >= buffer.length) {
	    out = 0;
	}
	if (in == out) {
            /* now empty */
	    in = -1;		
	}
	return ret;
    }

    /**
     * Reads up to <code>len</code> characters of data from this piped
     * stream into an array of characters. Less than <code>len</code> characters
     * will be read if the end of the data stream is reached. This method 
     * blocks until at least one character of input is available. 
     * If a thread was providing data characters to the connected piped output, 
     * but the thread is no longer alive, then an <code>IOException</code> 
     * is thrown.
     *
     * @param      cbuf     the buffer into which the data is read.
     * @param      off   the start offset of the data.
     * @param      len   the maximum number of characters read.
     * @return     the total number of characters read into the buffer, or
     *             <code>-1</code> if there is no more data because the end of
     *             the stream has been reached.
     * @exception  IOException  if an I/O error occurs.
     */
    public synchronized int read(char cbuf[], int off, int len)  throws IOException {
        if (!connected) {
            throw new IOException("Pipe not connected");
        } else if (closedByReader) {
	    throw new IOException("Pipe closed");
	} else if (writeSide != null && !writeSide.isAlive()
                   && !closedByWriter && (in < 0)) {
            throw new IOException("Write end dead");
        }

        if ((off < 0) || (off > cbuf.length) || (len < 0) ||
            ((off + len) > cbuf.length) || ((off + len) < 0)) {
	    throw new IndexOutOfBoundsException();
	} else if (len == 0) {
	    return 0;
	}

        /* possibly wait on the first character */
	int c = read();		
	if (c < 0) {
	    return -1;
	}
	cbuf[off] =  (char)c;
	int rlen = 1;
	while ((in >= 0) && (--len > 0)) {
	    cbuf[off + rlen] = buffer[out++];
	    rlen++;
	    if (out >= buffer.length) {
		out = 0;
	    }
	    if (in == out) {
                /* now empty */
		in = -1;	
	    }
	}
	return rlen;
    }

    /**
     * Tell whether this stream is ready to be read.  A piped character
     * stream is ready if the circular buffer is not empty.
     *
     * @exception  IOException  If an I/O error occurs
     */
    public synchronized boolean ready() throws IOException {
        if (!connected) {
            throw new IOException("Pipe not connected");
        } else if (closedByReader) {
	    throw new IOException("Pipe closed");
	} else if (writeSide != null && !writeSide.isAlive()
                   && !closedByWriter && (in < 0)) {
            throw new IOException("Write end dead");
        }
        if (in < 0) {
            return false;
        } else {
            return true;
        }
    }
 
    /**
     * Closes this piped stream and releases any system resources 
     * associated with the stream. 
     *
     * @exception  IOException  if an I/O error occurs.
     */
    public void close()  throws IOException {
	in = -1;
	closedByReader = true;
    }
}