/*
 * ============LICENSE_START=======================================================
 * ONAP
 * ================================================================================
 * Copyright (C) 2017-2019 AT&T Intellectual Property. All rights reserved.
 * ================================================================================
 * Licensed 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
 * 
 *      http://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.
 * ============LICENSE_END=========================================================
 */

package org.onap.policy.common.endpoints.event.comm.bus.internal;

import java.util.ArrayList;
import java.util.List;

import org.apache.commons.collections4.queue.CircularFifoQueue;
import org.onap.policy.common.endpoints.event.comm.Topic;
import org.onap.policy.common.endpoints.event.comm.TopicListener;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public abstract class TopicBase implements Topic {

    /**
     * Logger.
     */
    private static Logger logger = LoggerFactory.getLogger(TopicBase.class);

    /**
     * List of servers.
     */
    protected List<String> servers;

    /**
     * Topic.
     */
    protected final String topic;

    /**
     * Topic Alias.
     */
    protected final String effectiveTopic;

    /**
     * Event cache.
     */
    protected CircularFifoQueue<String> recentEvents = new CircularFifoQueue<>(10);

    /**
     * Am I running? reflects invocation of start()/stop() !locked & start() => alive stop() =>
     * !alive.
     */
    protected volatile boolean alive = false;

    /**
     * Am I locked? reflects invocation of lock()/unlock() operations locked => !alive (but not in
     * the other direction necessarily) locked => !offer, !run, !start, !stop (but this last one is
     * obvious since locked => !alive).
     */
    protected volatile boolean locked = false;

    /**
     * All my subscribers for new message notifications.
     */
    protected final ArrayList<TopicListener> topicListeners = new ArrayList<>();

    /**
     * Instantiates a new Topic Base.
     * 
     * @param servers list of servers
     * @param topic topic name
     * 
     * @throws IllegalArgumentException if invalid parameters are present
     */
    public TopicBase(List<String> servers, String topic) {
        this(servers, topic, topic);
    }

    /**
     * Instantiates a new Topic Base.
     *
     * @param servers list of servers
     * @param topic topic name
     *
     * @throws IllegalArgumentException if invalid parameters are present
     */
    public TopicBase(List<String> servers, String topic, String effectiveTopic) {

        if (servers == null || servers.isEmpty()) {
            throw new IllegalArgumentException("Server(s) must be provided");
        }

        if (topic == null || topic.isEmpty()) {
            throw new IllegalArgumentException("A Topic must be provided");
        }

        String effectiveTopicCopy;
        if (effectiveTopic == null || effectiveTopic.isEmpty()) {
            effectiveTopicCopy = topic;
        } else {
            effectiveTopicCopy = effectiveTopic;
        }

        this.servers = servers;
        this.topic = topic;
        this.effectiveTopic = effectiveTopicCopy;
    }

    @Override
    public void register(TopicListener topicListener) {

        logger.info("{}: registering {}", this, topicListener);

        synchronized (this) {
            if (topicListener == null) {
                throw new IllegalArgumentException("TopicListener must be provided");
            }

            for (TopicListener listener : this.topicListeners) {
                if (listener == topicListener) {
                    return;
                }
            }

            this.topicListeners.add(topicListener);
        }
    }

    @Override
    public void unregister(TopicListener topicListener) {

        logger.info("{}: unregistering {}", this, topicListener);

        synchronized (this) {
            if (topicListener == null) {
                throw new IllegalArgumentException("TopicListener must be provided");
            }

            this.topicListeners.remove(topicListener);
        }
    }

    /**
     * Broadcast event to all listeners.
     * 
     * @param message the event
     * @return true if all notifications are performed with no error, false otherwise
     */
    protected boolean broadcast(String message) {
        List<TopicListener> snapshotListeners = this.snapshotTopicListeners();

        boolean success = true;
        for (TopicListener topicListener : snapshotListeners) {
            try {
                topicListener.onTopicEvent(this.getTopicCommInfrastructure(), this.topic, message);
            } catch (Exception e) {
                logger.warn("{}: notification error @ {} because of {}", this, topicListener, e.getMessage(), e);
                success = false;
            }
        }
        return success;
    }

    /**
     * Take a snapshot of current topic listeners.
     * 
     * @return the topic listeners
     */
    protected synchronized List<TopicListener> snapshotTopicListeners() {
        @SuppressWarnings("unchecked")
        List<TopicListener> listeners = (List<TopicListener>) topicListeners.clone();
        return listeners;
    }

    @Override
    public boolean lock() {

        logger.info("{}: locking", this);

        synchronized (this) {
            if (this.locked) {
                return true;
            }

            this.locked = true;
        }

        return this.stop();
    }

    @Override
    public boolean unlock() {
        logger.info("{}: unlocking", this);

        synchronized (this) {
            if (!this.locked) {
                return true;
            }

            this.locked = false;
        }

        try {
            return this.start();
        } catch (Exception e) {
            logger.warn("{}: cannot after unlocking because of {}", this, e.getMessage(), e);
            return false;
        }
    }

    @Override
    public boolean isLocked() {
        return this.locked;
    }

    @Override
    public String getTopic() {
        return topic;
    }

    @Override
    public String getEffectiveTopic() {
        return effectiveTopic;
    }

    @Override
    public boolean isAlive() {
        return this.alive;
    }

    @Override
    public List<String> getServers() {
        return servers;
    }

    @Override
    public synchronized String[] getRecentEvents() {
        String[] events = new String[recentEvents.size()];
        return recentEvents.toArray(events);
    }


    @Override
    public String toString() {
        return "TopicBase [servers=" + servers
            + ", topic=" + topic
            + ", effectiveTopic=" + effectiveTopic
            + ", #recentEvents=" + recentEvents.size()
            + ", locked=" + locked
            + ", #topicListeners=" + topicListeners.size()
            + "]";
    }
}