/* A polymorphic select, which routes specified input channels to the output.

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 COPYRIGHTENDKEY

 Code review issue: This actor reads data in prefire.
 */
package ptolemy.actor.lib;

import ptolemy.actor.TypedIOPort;
import ptolemy.data.IntToken;
import ptolemy.data.type.BaseType;
import ptolemy.kernel.CompositeEntity;
import ptolemy.kernel.util.IllegalActionException;
import ptolemy.kernel.util.NameDuplicationException;
import ptolemy.kernel.util.StringAttribute;

///////////////////////////////////////////////////////////////////
//// Select

/**
 <p>A polymorphic select, which routes specified input channels to the
 output.  This actor has two input ports, the <i>input</i> port for
 data, and the <i>control</i> port to select which input channel to
 read.  In an iteration, if an input token is available at the
 <i>control</i> input, that token is read, and its value is noted.  Its
 value specifies the input channel that should be read next. If an
 input token is available on the specified channel of the <i>input</i>
 port, then that token is read and sent to the output.

 </p><p> The actor indicates a willingness to fire in its prefire() method
 if there is an input available on the channel specified by the most
 recently seen token on the <i>control</i> port.  If no token has ever
 been received on the <i>control</i> port, then channel zero is assumed
 to be the one to read.  If the value of the most recently received
 token on the <i>control</i> port is out of range (less than zero, or
 greater than or equal to the width of the input), then the actor will
 not fire() (although it will continue to consume tokens on the
 <i>control</i> port in its prefire() method).

 </p><p> This actor is similar to the {@link ptolemy.actor.lib.Multiplexor}
 actor, except that it never discards input tokens.  Tokens on
 channels that are not selected are not consumed.

 </p><p> Note that in the DE domain, where this actor is commonly used, if
 a new value is given to the <i>control</i> port, then all previously
 unread input tokens on the specified input channel will be read at the
 same firing time, in the order in which they arrived.</p>

 <p>Note further that this actor is subtly different from the
 {@link BooleanSelect} actor. In addition to the obvious difference
 that the latter accepts only two input streams, the latter also
 requires two firings to produce an output. The BooleanSelect actor
 is designed to work with DDF, but because of the multiple firings,
 will not work with DE or SR. This actor will, because it consumes
 the control input and the data input in the same firing.

 @author Edward A. Lee
 @version $Id$
 @since Ptolemy II 1.0
 @Pt.ProposedRating Green (neuendor)
 @Pt.AcceptedRating Yellow (liuj)
 */
public class Select extends Transformer {
    /** Construct an actor in the specified container with the specified
     *  name.
     *  @param container The container.
     *  @param name The name of this actor within the container.
     *  @exception IllegalActionException If the actor cannot be contained
     *   by the proposed container.
     *  @exception NameDuplicationException If the name coincides with
     *   an actor already in the container.
     */
    public Select(CompositeEntity container, String name)
            throws IllegalActionException, NameDuplicationException {
        super(container, name);

        input.setMultiport(true);

        control = new TypedIOPort(this, "control", true, false);
        control.setTypeEquals(BaseType.INT);

        // Put the control input on the bottom of the actor.
        StringAttribute controlCardinal = new StringAttribute(control,
                "_cardinal");
        controlCardinal.setExpression("SOUTH");
    }

    ///////////////////////////////////////////////////////////////////
    ////                     ports and parameters                  ////

    /** Input port for control tokens, which specify the output channel
     *  to produce data on.  The type is int. */
    public TypedIOPort control;

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

    /** Read an input token from the specified input channel and produce
     *  it on the output.
     *  @exception IllegalActionException If there is no director.
     */
    @Override
    public void fire() throws IllegalActionException {
        super.fire();
        // Redo this check in case the control has changed since prefire().
        if (input.hasToken(_control)) {
            output.send(0, input.get(_control));
        }
    }

    /** Initialize this actor so that channel zero of <i>input</i> is read
     *  from until a token arrives on the <i>control</i> input.
     *  @exception IllegalActionException If the parent class throws it.
     */
    @Override
    public void initialize() throws IllegalActionException {
        super.initialize();
        _control = 0;
    }

    /** Read a control token, if there is one, and check to see
     *  whether an input is available on the input channel specified by
     *  the most recent control token, if it is in range.
     *  Return false if there is no input token to read.
     *  Otherwise, return whatever the superclass returns.
     *  @return True if the actor is ready to fire.
     *  @exception IllegalActionException If there is no director.
     */
    @Override
    public boolean prefire() throws IllegalActionException {
        if (control.hasToken(0)) {
            _control = ((IntToken) control.get(0)).intValue();
        }

        if (_control < 0 || _control > input.getWidth()
                || !input.hasToken(_control)) {
            return false;
        }

        return super.prefire();
    }

    ///////////////////////////////////////////////////////////////////
    ////                         private variables                 ////
    // The most recently read control token.
    private int _control = 0;
}