/*
 * @(#)Guard.java	1.7 03/12/19
 *
 * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package com.sun.corba.se.spi.orbutil.fsm;

/**
 *
 * @author Ken Cavanaugh
 */
public interface Guard
{
    public static final class Complement extends GuardBase {
	private Guard guard ;

	public Complement( GuardBase guard ) 
	{
	    super( "not(" + guard.getName() + ")" ) ;
	    this.guard = guard ;
	}

	public Result evaluate( FSM fsm, Input in )
	{
	    return guard.evaluate( fsm, in ).complement() ;
	}
    }

    public static final class Result {
	private String name ;

	private Result( String name ) 
	{
	    this.name = name ;
	}

	public static Result convert( boolean res ) 
	{
	    return res ? ENABLED : DISABLED ;
	}

	public Result complement() 
	{
	    if (this == ENABLED)
		return DISABLED ;
	    else if (this == DISABLED)
		return ENABLED ;
	    else 
		return DEFERED ;
	}
	
	public String toString()
	{
	    return "Guard.Result[" + name + "]" ;
	}

	public static final Result ENABLED = new Result( "ENABLED" ) ;
	public static final Result DISABLED = new Result( "DISABLED" ) ;
	public static final Result DEFERED = new Result( "DEFERED" ) ;
    }

    /** Called by the state engine to determine whether a
    * transition is enabled, defered, or disabled.
    * The result is interpreted as follows:
    * <ul>
    * <li>ENABLED if the transition is ready to proceed
    * <li>DISABLED if the transition is not ready to proceed
    * <li>DEFERED if the action associated with the transition
    * is to be deferred.  This means that the input will not be 
    * acted upon, but rather it will be saved for later execution.
    * Typically this is implemented using a CondVar wait, and the
    * blocked thread represents the defered input.  The defered
    * input is retried when the thread runs again.
    * </ul>
    *
    * @param FSM fsm is the state machine causing this action.
    * @param Input in is the input that caused the transition.
    */
    public Result evaluate( FSM fsm, Input in ) ;
}

// end of Action.java