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package com.sun.grizzly;

import java.nio.ByteBuffer;

/**
 * An interface that knows how to parse bytes into a protocol data unit.
 *
 * @author Charlie Hunt
 */
public interface ProtocolParser {
    
    /**
     * Is this ProtocolParser expecting more data ?
     * 
     * This method is typically called after a call to 
     * {@link ProtocolParser#hasNextMessage()} to determine if the
     * {@link ByteBuffer} which has been parsed contains a partial message
     * 
     * @return - true if more bytes are needed to construct a
     *           message;  false, if no 
     *           additional bytes remain to be parsed into a protocol data unit.
     *	 	 Note that if no partial message exists, this method should
     *		 return false.
     */
    public boolean isExpectingMoreData();
    
    /**
     * Are there more bytes to be parsed in the {@link ByteBuffer} given
     * to this ProtocolParser's {@link ProtocolParser#startBuffer()} ?
     * 
     * This method is typically called after processing the protocol message,
     * to determine if the {@link ByteBuffer} has more bytes which
     * need to parsed into a next message.
     * 
     * @return true if there are more bytes to be parsed.
     *         Otherwise false.
     */
    public boolean hasMoreBytesToParse();

    
    /**
     * Get the next complete message from the buffer, which can then be
     * processed by the next filter in the protocol chain. Because not all
     * filters will understand protocol messages, this method should also
     * set the position and limit of the buffer at the start and end
     * boundaries of the message. Filters in the protocol chain can
     * retrieve this message via context.getAttribute(MESSAGE)
     *
     * @return The next message in the buffer. If there isn't such a message,
     *	return null.
     *
     */
    public T getNextMessage();

    /**
     * Indicates whether the buffer has a complete message that can be
     * returned from {@link ProtocolParser#getNextMessage()}. Smart 
     * implementations of this will set up all the information so that an
     * actual call to {@link ProtocolParser#getNextMessage()} doesn't need to
     * re-parse the data.
     */
    public boolean hasNextMessage();

    /**
     * Set the buffer to be parsed. This method should store the buffer and
     * its state so that subsequent calls to
     * {@link ProtocolParser#getNextMessage()} will return distinct messages,
     * and the buffer can be restored after parsing when the
     * {@link ProtocolParser#releaseBuffer()} method is called.
     */
    public void startBuffer(ByteBuffer bb);
    
    /**
     * No more parsing will be done on the buffer passed to
     * {@link ProtocolParser#startBuffer()}.
     * Set up the buffer so that its position is the first byte that was
     * not part of a full message, and its limit is the original limit of
     * the buffer.
     *
     * @return -- true if the parser has saved some state (e.g. information
     * data in the buffer that hasn't been returned in a full message);
     * otherwise false. If this method returns true, the framework will
     * make sure that the same parser is used to process the buffer after
     * more data has been read.
     */
    public boolean releaseBuffer();

    /**
     * Used to associate a particular parser with a connection
     */
    public static String PARSER = "ProtocolParser";

    /**
     * Holds the message returned from getNextMessage for
     * use by downstream filters
     */
    public static String MESSAGE = "ProtocolMessage";
}