/*
 * 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
 *
 *   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.
 */
package org.apache.felix.eventadmin.impl.handler;

import java.util.Collection;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.CopyOnWriteArrayList;

import org.apache.felix.eventadmin.impl.util.Matchers;
import org.osgi.framework.BundleContext;
import org.osgi.framework.ServiceReference;
import org.osgi.service.event.Event;
import org.osgi.service.event.EventHandler;
import org.osgi.util.tracker.ServiceTracker;

/**
 * The event handler tracker keeps track of all event handler services.
 *
 * @author <a href="mailto:dev@felix.apache.org">Felix Project Team</a>
 */
public class EventHandlerTracker extends ServiceTracker<EventHandler, EventHandlerProxy> {

    /** The proxies in this list match all events. */
	private final List<EventHandlerProxy> matchingAllEvents;

    /** This is a map for exact topic matches. The key is the topic,
     * the value is a list of proxies.
     */
    private final Map<String, List<EventHandlerProxy>> matchingTopic;

	/** This is a map for wildcard topics. The key is the prefix of the topic,
	 * the value is a list of proxies
	 */
	private final Map<String, List<EventHandlerProxy>> matchingPrefixTopic;


	/** The context for the proxies. */
	private HandlerContext handlerContext;

    public EventHandlerTracker(final BundleContext context) {
		super(context, EventHandler.class.getName(), null);

		// we start with empty collections
		this.matchingAllEvents = new CopyOnWriteArrayList<>();
		this.matchingTopic = new ConcurrentHashMap<>();
		this.matchingPrefixTopic = new ConcurrentHashMap<>();
	}

    /**
     * Update the timeout configuration.
     * @param ignoreTimeout
     */
    public void update(final String[] ignoreTimeout, final boolean requireTopic) {
        final Matchers.Matcher[] ignoreTimeoutMatcher = Matchers.createPackageMatchers(ignoreTimeout);
        this.handlerContext = new HandlerContext(this.context, ignoreTimeoutMatcher, requireTopic);
    }

    /**
	 * @see org.osgi.util.tracker.ServiceTracker#addingService(org.osgi.framework.ServiceReference)
	 */
	@Override
    public EventHandlerProxy addingService(final ServiceReference<EventHandler> reference) {
		final EventHandlerProxy proxy = new EventHandlerProxy(this.handlerContext, reference);
		if ( proxy.update() ) {
			this.put(proxy);
		}
		return proxy;
	}

	/**
	 * @see org.osgi.util.tracker.ServiceTracker#modifiedService(org.osgi.framework.ServiceReference, java.lang.Object)
	 */
	@Override
    public void modifiedService(final ServiceReference<EventHandler> reference, final EventHandlerProxy proxy) {
	    this.remove(proxy);
	    if ( proxy.update() ) {
            this.put(proxy);
	    }
	}

	/**
	 * @see org.osgi.util.tracker.ServiceTracker#removedService(org.osgi.framework.ServiceReference, java.lang.Object)
	 */
	@Override
    public void removedService(final ServiceReference<EventHandler> reference, final EventHandlerProxy proxy) {
        this.remove(proxy);
        proxy.dispose();
	}

	private void updateMap(final Map<String, List<EventHandlerProxy>> proxyListMap, final String key, final EventHandlerProxy proxy, final boolean add) {
        List<EventHandlerProxy> proxies = proxyListMap.get(key);
        if (proxies == null)
        {
            if ( !add )
            {
                return;
            }
            proxies = new CopyOnWriteArrayList<>();
            proxyListMap.put(key, proxies);
        }

        if ( add )
        {
            proxies.add(proxy);
        }
        else
        {
            proxies.remove(proxy);
            if ( proxies.size() == 0 )
            {
                proxyListMap.remove(key);
            }
        }
	}

	/**
	 * Check the topics of the event handler and put it into the
	 * corresponding collections.
	 */
	private synchronized void put(final EventHandlerProxy proxy) {
		final String[] topics = proxy.getTopics();
		if ( topics == null )
		{
		    this.matchingAllEvents.add(proxy);
		}
		else
		{
    		for(int i = 0; i < topics.length; i++) {
    			final String topic = topics[i];

    			if ( topic.endsWith("/*") )
    			{
                    // prefix topic: we remove the /*
    				final String prefix = topic.substring(0, topic.length() - 2);
                    this.updateMap(this.matchingPrefixTopic, prefix, proxy, true);
    			}
    			else
    			{
    			    // exact match
                    this.updateMap(this.matchingTopic, topic, proxy, true);
    			}
    		}
		}
	}

    /**
     * Check the topics of the event handler and remove it from the
     * corresponding collections.
     */
	private synchronized void remove(final EventHandlerProxy proxy) {
        final String[] topics = proxy.getTopics();
        if ( topics == null )
        {
            this.matchingAllEvents.remove(proxy);
        } else {
            for(int i = 0; i < topics.length; i++) {
                final String topic = topics[i];

                if ( topic.endsWith("/*") )
                {
                    // prefix topic: we remove the /*
                    final String prefix = topic.substring(0, topic.length() - 2);
                    this.updateMap(this.matchingPrefixTopic, prefix, proxy, false);
                }
                else
                {
                    // exact match
                    this.updateMap(this.matchingTopic, topic, proxy, false);
                }
            }
        }
	}

	/**
	 * Get all handlers for this event
	 *
	 * @param event The event topic
	 * @return All handlers for the event
	 */
	public Collection<EventHandlerProxy> getHandlers(final Event event) {
	    final String topic = event.getTopic();

		final Set<EventHandlerProxy> handlers = new HashSet<>();

		// Add all handlers matching everything
        this.checkHandlerAndAdd(handlers, this.matchingAllEvents, event);

		// Now check for prefix matches
		if ( !this.matchingPrefixTopic.isEmpty() )
		{
		    int pos = topic.lastIndexOf('/');
			while (pos != -1)
			{
			    final String prefix = topic.substring(0, pos);
		        this.checkHandlerAndAdd(handlers, this.matchingPrefixTopic.get(prefix), event);

				pos = prefix.lastIndexOf('/');
			}
		}

		// Add the handlers for matching topic names
		this.checkHandlerAndAdd(handlers, this.matchingTopic.get(topic), event);

		return handlers;
	}

	   /**
     * Get all handlers for this event
     *
     * @param event The event topic
     * @return All handlers for the event
     */
    public Collection<EventHandlerProxy> getDeniedHandlers() {
        final Set<EventHandlerProxy> handlers = new HashSet<>();

        for(final EventHandlerProxy p : this.matchingAllEvents) {
            if ( p.isDenied() ) {
                handlers.add(p);
            }
        }

        for(final List<EventHandlerProxy> l : this.matchingPrefixTopic.values()) {
            for(final EventHandlerProxy p :l) {
                if ( p.isDenied() ) {
                    handlers.add(p);
                }
            }
        }
        for(final List<EventHandlerProxy> l : this.matchingTopic.values()) {
            for(final EventHandlerProxy p :l) {
                if ( p.isDenied() ) {
                    handlers.add(p);
                }
            }
        }

        return handlers;
    }

	/**
	 * Checks each handler from the proxy list if it can deliver the event
	 * If the event can be delivered, the proxy is added to the handlers.
	 */
	private void checkHandlerAndAdd( final Set<EventHandlerProxy> handlers,
	        final List<EventHandlerProxy> proxies,
	        final Event event)
	{
	    if ( proxies != null )
	    {
            for(final EventHandlerProxy p : proxies)
            {
                if ( p.canDeliver(event) )
                {
                    handlers.add(p);
                }
            }
	    }
	}

    /**
     * The context object passed to the proxies.
     */
    static final class HandlerContext
    {
        /** The bundle context. */
        public final BundleContext bundleContext;

        /** The matchers for ignore timeout handling. */
        public final Matchers.Matcher[] ignoreTimeoutMatcher;

        /** Is a topic required. */
        public final boolean requireTopic;

        public HandlerContext(final BundleContext bundleContext,
                final Matchers.Matcher[] ignoreTimeoutMatcher,
                final boolean   requireTopic)
        {
            this.bundleContext = bundleContext;
            this.ignoreTimeoutMatcher = ignoreTimeoutMatcher;
            this.requireTopic = requireTopic;
        }
    }
}