src/main/java/org/apache/commons/scxml2/NotificationRegistry.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.scxml2;

import java.util.HashMap;
import java.util.LinkedHashSet;
import java.util.Map;
import java.util.Set;

import org.apache.commons.scxml2.model.EnterableState;
import org.apache.commons.scxml2.model.Observable;
import org.apache.commons.scxml2.model.Transition;
import org.apache.commons.scxml2.model.TransitionTarget;

/**
 * The registry where SCXML listeners are recorded for nodes of
 * interest such as the {@code SCXML} root,
 * {@code EnterableState}s and {@code Transition}s.
 * The notification registry keeps track of all
 * {@code SCXMLListener}s attached and notifies relevant
 * listeners of the events that interest them.
 */
public final class NotificationRegistry {

    /**
     * The Map of all listeners keyed by {@link Observable#getObservableId()}.
     */
    private final Map<Integer, Set<SCXMLListener>> regs;

    /**
     * Constructs a new instance.
     */
    public NotificationRegistry() {
        this.regs = new HashMap<>();
    }

    /**
     * Register this SCXMLListener for this Observable.
     *
     * @param source The observable this listener wants to listen to
     * @param lst The listener
     */
    synchronized void addListener(final Observable source, final SCXMLListener lst) {
        if (source != null && source.getObservableId() != null) {
            final Set<SCXMLListener> entries = regs.computeIfAbsent(source.getObservableId(), k -> new LinkedHashSet<>());
            entries.add(lst);
        }
    }

    /**
     * Inform all relevant listeners that a EnterableState has been
     * entered.
     *
     * @param source The Observable
     * @param state The EnterableState that was entered
     */
    public synchronized void fireOnEntry(final Observable source,
            final EnterableState state) {
        if (source != null && source.getObservableId() != null) {
            final Set<SCXMLListener> entries = regs.get(source.getObservableId());
            if (entries != null) {
                for (final SCXMLListener lst : entries) {
                    lst.onEntry(state);
                }
            }
        }
    }

    /**
     * Inform all relevant listeners that a EnterableState has been
     * exited.
     *
     * @param source The Observable
     * @param state The EnterableState that was exited
     */
    public synchronized void fireOnExit(final Observable source,
            final EnterableState state) {
        if (source != null && source.getObservableId() != null) {
            final Set<SCXMLListener> entries = regs.get(source.getObservableId());
            if (entries != null) {
                for (final SCXMLListener lst : entries) {
                    lst.onExit(state);
                }
            }
        }
    }

    /**
     * Inform all relevant listeners of a transition that has occurred.
     *
     * @param source The Observable
     * @param from The source EnterableState
     * @param to The destination EnterableState
     * @param transition The Transition that was taken
     * @param event The event name triggering the transition
     */
    public synchronized void fireOnTransition(final Observable source,
            final TransitionTarget from, final TransitionTarget to,
            final Transition transition, final String event) {
        if (source != null && source.getObservableId() != null) {
            final Set<SCXMLListener> entries = regs.get(source.getObservableId());
            if (entries != null) {
                for (final SCXMLListener lst : entries) {
                    lst.onTransition(from, to, transition, event);
                }
            }
        }
    }

    /**
     * Deregister this SCXMLListener for this Observable.
     *
     * @param source The observable this listener wants to stop listening to
     * @param lst The listener
     */
    synchronized void removeListener(final Observable source, final SCXMLListener lst) {
        if (source != null && source.getObservableId() != null) {
            final Set<SCXMLListener> entries = regs.get(source.getObservableId());
            if (entries != null) {
                entries.remove(lst);
                if (entries.isEmpty()) {
                    regs.remove(source.getObservableId());
                }
            }
        }
    }
}