/* A register with one trigger port that accepts read requests.

 Copyright (c) 2004-2014 The Regents of the University of California.
 All rights reserved.
 Permission is hereby granted, without written agreement and without
 license or royalty fees, to use, copy, modify, and distribute this
 software and its documentation for any purpose, provided that the above
 copyright notice and the following two paragraphs appear in all copies
 of this software.

 IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO ANY PARTY
 FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
 ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN IF
 THE UNIVERSITY OF CALIFORNIA HAS BEEN ADVISED OF THE POSSIBILITY OF
 SUCH DAMAGE.

 THE UNIVERSITY OF CALIFORNIA SPECIFICALLY DISCLAIMS ANY WARRANTIES,
 INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE
 PROVIDED HEREUNDER IS ON AN "AS IS" BASIS, AND THE UNIVERSITY OF
 CALIFORNIA HAS NO OBLIGATION TO PROVIDE MAINTENANCE, SUPPORT, UPDATES,
 ENHANCEMENTS, OR MODIFICATIONS.

 PT_COPYRIGHT_VERSION_2
 COPYRIGHTENDKEY

 */
package ptolemy.domains.de.lib;

import ptolemy.data.Token;
import ptolemy.kernel.CompositeEntity;
import ptolemy.kernel.util.IllegalActionException;
import ptolemy.kernel.util.NameDuplicationException;

///////////////////////////////////////////////////////////////////
//// Register

/**
 A register is a stateful actor with a trigger port that accepts
 read requests.
 <p>
 In the fire() method, if there is an event on the <i>trigger</i>
 input port, this actor will produce an output event. The value
 of the output event will be the previously recorded event
 from the <i>input</i> port, or the value of the <i>initialValue</i>
 parameter if there has been no previous input event. If, however,
 <i>initialValue</i> contains no value, then no output will be
 produced. In the postfire() method, if there is an input event on
 the <i>input</i> port, then its value is recorded to be used
 in future firings as the value of the output.
 <p>
 The inputs can be of any token type, but the <i>output</i> port
 is constrained to be of a type at least that of the <i>input</i>
 port and the <i>initialValue</i> parameter.
 <p>
 This class extends MostRecent. Unlike its base class, this actor
 can be used to break dependencies in a feedback loop in that
 the input tokens are consumed from the input ports after the outputs
 are generated. Another difference is that the Register actor can be
 fired when either the trigger port or the input port has a token, while
 the Sampler can only be fired when the trigger port receives a token.
 <p>
 Both the <i>input</i> port and the <i>output</i> port are multiports.
 Generally, their widths should match. Otherwise, if the width of the
 <i>input</i> is greater than the width of the <i>output</i>, the extra
 input tokens will not appear on any output, although they will be
 consumed from the input port. If the width of the <i>output</i> is
 greater than that of the <i>input</i>, then the last few channels of
 the <i>output</i> will never emit tokens.
 <p>
 Note: If the width of the input changes during execution, then the
 most recent inputs are forgotten, as if the execution of the model
 were starting over.

 @author Edward A. Lee, Haiyang Zheng
 @version $Id: Register.java 69607 2014-07-30 17:07:26Z cxh $
 @since Ptolemy II 4.1
 @Pt.ProposedRating Yellow (eal)
 @Pt.AcceptedRating Red (eal)
 @see ptolemy.domains.de.lib.MostRecent
 */
public class Register extends MostRecent {
    /** Construct an actor with the given container and name.
     *  @param container The container.
     *  @param name The name of this actor.
     *  @exception IllegalActionException If the actor cannot be contained
     *   by the proposed container.
     *  @exception NameDuplicationException If the container already has an
     *   actor with this name.
     */
    public Register(CompositeEntity container, String name)
            throws NameDuplicationException, IllegalActionException {
        super(container, name);

        _attachText("_iconDescription", "<svg>\n"
                + "<rect x=\"-10\" y=\"-20\" " + "width=\"20\" height=\"40\" "
                + "style=\"fill:white\"/>\n" + "</svg>\n");
    }

    ///////////////////////////////////////////////////////////////////
    ////                         public methods                    ////

    /** Declare that the <i>output</i>
     *  does not depend on the <i>input</i> in a firing.
     *  @exception IllegalActionException If the causality interface
     *  cannot be computed.
     *  @see #getCausalityInterface()
     */
    @Override
    public void declareDelayDependency() throws IllegalActionException {
        // Declare that output does not immediately depend on the input.
        _declareDelayDependency(input, output, 0.0);
        // Note the dependency between trigger and output port is not
        // declared. This is because declaring a dependency
        // of 0.0 really means (0.0, 1) (i.e., the output does not
        // immediately depend on the trigger). However, in this case the
        // output could immediately depend on the trigger port.
    }

    /** If there is a token in the <i>trigger</i> port, emit the previously
     *  seen inputs from the <i>input</i> port. If there has been no
     *  previous input tokens, but the <i>initialValue</i> parameter
     *  has been set, emit the value of the <i>initialValue</i> parameter.
     *  Otherwise, emit nothing.
     *  @exception IllegalActionException If there is no director.
     */
    @Override
    public void fire() throws IllegalActionException {
        // Don't call "super.fire();", this actor extends another actor.
        int inputWidth = input.getWidth();
        int outputWidth = output.getWidth();
        int commonWidth = Math.min(inputWidth, outputWidth);

        // If the <i>initialValue</i> parameter was not set, or if the
        // width of the input has changed.
        if (_lastInputs == null || _lastInputs.length != inputWidth) {
            _lastInputs = new Token[inputWidth];
        }

        sendOutputIfTriggered(commonWidth);
    }

    /** Indicate that this actor can fire even if the inputs are not
     *  known. This enables the actor to be used in SR and Continuous.
     *  @return False.
     */
    @Override
    public boolean isStrict() {
        return false;
    }

    /** Read and record the inputs.
     *  @return What the superclass returns.
     *  @exception IllegalActionException If the superclass throws it.
     */
    @Override
    public boolean postfire() throws IllegalActionException {
        int inputWidth = input.getWidth();
        int outputWidth = output.getWidth();
        int commonWidth = Math.min(inputWidth, outputWidth);
        readInputs(commonWidth, inputWidth);
        return super.postfire();
    }

    /** Return true if there is any token in the input or the trigger
     *  port. This ensures that if an input is provided without a
     *  trigger, it will get recorded.
     *  @exception IllegalActionException If the base class throws it.
     */
    @Override
    public boolean prefire() throws IllegalActionException {
        boolean inputPresent = false;

        if (input.isOutsideConnected()) {
            for (int i = 0; i < input.getWidth(); i++) {
                if (input.hasToken(0)) {
                    inputPresent = true;
                    break;
                }
            }
        }
        return inputPresent || super.prefire();
    }
}