DMDirc-Util/src/main/java/com/dmdirc/util/collections/ListenerList.java

/*
 * Copyright (c) 2006-2017 DMDirc Developers
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated
 * documentation files (the "Software"), to deal in the Software without restriction, including without limitation the
 * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all copies or substantial portions of the
 * Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
 * WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS
 * OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
 * OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

package com.dmdirc.util.collections;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.Collection;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.CopyOnWriteArrayList;

/**
 * Represents a list of event listeners, similar to EventListenerList, but
 * not swing specific.
 */
public class ListenerList {

    /** The map of class->listener or string->listener that we're using. */
    private final Map<Object, Collection<Object>> listeners = new HashMap<>();

    /**
     * Adds a new listener of the specified type to this listener list.
     *
     * @param <T> The type of listener to be added
     * @param listenerType The type of listener to be added
     * @param listener The listener to be added
     */
    public <T> void add(final Class<T> listenerType, final T listener) {
        if (listener == null) {
            throw new IllegalArgumentException("Listener cannot be null");
        }
        if (!listeners.containsKey(listenerType)) {
            listeners.put(listenerType, new CopyOnWriteArrayList<>());
        }

        listeners.get(listenerType).add(listener);
    }

    /**
     * Adds a new listener of the specified type to this listener list.
     *
     * @param listenerType The name of the type of listener that's being added
     * @param listener The listener to be added
     */
    public void add(final String listenerType, final Object listener) {
        if (listener == null) {
            throw new IllegalArgumentException("Listener cannot be null");
        }
        if (!listeners.containsKey(listenerType)) {
            listeners.put(listenerType, new CopyOnWriteArrayList<>());
        }

        listeners.get(listenerType).add(listener);
    }

    /**
     * Removes the specified listener from the list of listeners for the
     * specified type.
     *
     * @param <T> The type of listener to be removed
     * @param listenerType The type that the listener should be removed from
     * @param listener The listener to be removed
     */
    public <T> void remove(final Class<T> listenerType, final T listener) {
        get(listenerType).remove(listener);
    }

    /**
     * Removes the specified listener from the list of listeners for the
     * specified type.
     *
     * @param listenerType The name of the type that the listener should be
     * removed from
     * @param listener The listener to be removed
     */
    public void remove(final String listenerType, final Object listener) {
        get(listenerType).remove(listener);
    }

    /**
     * Retrieves the list of listeners for the specified type.
     *
     * @param <T> The type of listener to be retrieved
     * @param listenerType The type of listener that's being retrieved
     * @return A list of listeners for the specified type
     */
    @SuppressWarnings("unchecked")
    public <T> Collection<T> get(final Class<T> listenerType) {
        if (listeners.containsKey(listenerType)) {
            return (Collection<T>) listeners.get(listenerType);
        } else {
            return new CopyOnWriteArrayList<>();
        }
    }

    /**
     * Retrieves the list of listeners for the specified type.
     *
     * @param listenerType The type of listener to be retrieved
     * @return A list of listeners for the specified type
     */
    public Collection<Object> get(final String listenerType) {
        if (listeners.containsKey(listenerType)) {
            return listeners.get(listenerType);
        } else {
            return new CopyOnWriteArrayList<>();
        }
    }

    /**
     * Returns a callable proxy of the specified type. Methods called on the
     * returned proxy will be proxied to all of the registered listeners.
     *
     * @param <T> The type of listener to be called
     * @param listenerType The type of listener to be called
     * @return A proxy instance that can be used to call methods
     */
    @SuppressWarnings("unchecked")
    public <T> T getCallable(final Class<T> listenerType) {
        return (T) Proxy.newProxyInstance(listenerType.getClassLoader(),
                new Class<?>[] { listenerType }, new CallHandler<>(listenerType));
    }

    /**
     * Utility class to handle calls to a "callable" interface as returned by
     * {@link #getCallable(Class)}.
     *
     * @param <T> The type of listener being called
     */
    private class CallHandler<T> implements InvocationHandler {

        /** The type of listener this handler is handling. */
        private final Class<T> listenerType;

        /**
         * Creates a new call handler for the specified type of listener.
         *
         * @param listenerType The type of listener to handle
         */
        CallHandler(final Class<T> listenerType) {
            this.listenerType = listenerType;
        }

        @Override
        public Object invoke(final Object proxy, final Method method,
                final Object[] args) throws Throwable {
            for (T target : get(listenerType)) {
                try {
                    method.invoke(target, args);
                } catch (IllegalAccessException | IllegalArgumentException ex) {
                    // Ignore, not possible
                } catch (InvocationTargetException ex) {
                    throw ex.getCause();
                }
            }

            return null;
        }

    }

}