/*
 * Copyright 2016 Open Networking Laboratory
 *
 * 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.
 */

package org.onosproject.incubator.net.routing.impl;

import org.apache.felix.scr.annotations.Activate;
import org.apache.felix.scr.annotations.Component;
import org.apache.felix.scr.annotations.Deactivate;
import org.apache.felix.scr.annotations.Reference;
import org.apache.felix.scr.annotations.ReferenceCardinality;
import org.apache.felix.scr.annotations.Service;
import org.onlab.packet.IpAddress;
import org.onlab.packet.MacAddress;
import org.onosproject.event.ListenerService;
import org.onosproject.incubator.net.routing.ResolvedRoute;
import org.onosproject.incubator.net.routing.Route;
import org.onosproject.incubator.net.routing.RouteAdminService;
import org.onosproject.incubator.net.routing.RouteEvent;
import org.onosproject.incubator.net.routing.RouteListener;
import org.onosproject.incubator.net.routing.RouteService;
import org.onosproject.incubator.net.routing.RouteStore;
import org.onosproject.incubator.net.routing.RouteStoreDelegate;
import org.onosproject.incubator.net.routing.RouteTableId;
import org.onosproject.net.Host;
import org.onosproject.net.host.HostEvent;
import org.onosproject.net.host.HostListener;
import org.onosproject.net.host.HostService;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import javax.annotation.concurrent.GuardedBy;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.Optional;
import java.util.Set;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadFactory;
import java.util.function.Function;
import java.util.stream.Collectors;

import static java.util.concurrent.Executors.newSingleThreadExecutor;
import static org.onlab.util.Tools.groupedThreads;

/**
 * Implementation of the unicast route service.
 */
@Service
@Component
public class RouteManager implements ListenerService<RouteEvent, RouteListener>,
        RouteService, RouteAdminService {

    private final Logger log = LoggerFactory.getLogger(getClass());

    private RouteStoreDelegate delegate = new InternalRouteStoreDelegate();
    private InternalHostListener hostListener = new InternalHostListener();

    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
    protected RouteStore routeStore;

    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
    protected HostService hostService;

    @GuardedBy(value = "this")
    private Map<RouteListener, ListenerQueue> listeners = new HashMap<>();

    private ThreadFactory threadFactory;

    @Activate
    protected void activate() {
        threadFactory = groupedThreads("onos/route", "listener-%d");

        routeStore.setDelegate(delegate);
        hostService.addListener(hostListener);

    }

    @Deactivate
    protected void deactivate() {
        listeners.values().forEach(l -> l.stop());

        routeStore.unsetDelegate(delegate);
        hostService.removeListener(hostListener);
    }

    /**
     * {@inheritDoc}
     *
     * In a departure from other services in ONOS, calling addListener will
     * cause all current routes to be pushed to the listener before any new
     * events are sent. This allows a listener to easily get the exact set of
     * routes without worrying about missing any.
     *
     * @param listener listener to be added
     */
    @Override
    public void addListener(RouteListener listener) {
        synchronized (this) {
            log.debug("Synchronizing current routes to new listener");
            ListenerQueue l = new ListenerQueue(listener);
            routeStore.getRouteTables().forEach(table -> {
                Collection<Route> routes = routeStore.getRoutes(table);
                if (routes != null) {
                    routes.forEach(route ->
                        l.post(new RouteEvent(RouteEvent.Type.ROUTE_UPDATED,
                                        new ResolvedRoute(route, routeStore.getNextHop(route.nextHop())))));
                }
            });

            listeners.put(listener, l);

            l.start();
            log.debug("Route synchronization complete");
        }
    }

    @Override
    public void removeListener(RouteListener listener) {
        synchronized (this) {
            ListenerQueue l = listeners.remove(listener);
            if (l != null) {
                l.stop();
            }
        }
    }

    /**
     * Posts an event to all listeners.
     *
     * @param event event
     */
    private void post(RouteEvent event) {
        synchronized (this) {
            listeners.values().forEach(l -> l.post(event));
        }
    }

    @Override
    public Map<RouteTableId, Collection<Route>> getAllRoutes() {
        return routeStore.getRouteTables().stream()
                .collect(Collectors.toMap(Function.identity(),
                        table -> (table == null) ?
                                 Collections.emptySet() : routeStore.getRoutes(table)));
    }

    @Override
    public Route longestPrefixMatch(IpAddress ip) {
        return routeStore.longestPrefixMatch(ip);
    }

    @Override
    public void update(Collection<Route> routes) {
        synchronized (this) {
            routes.forEach(route -> {
                routeStore.updateRoute(route);
                resolve(route);
            });
        }
    }

    @Override
    public void withdraw(Collection<Route> routes) {
        synchronized (this) {
            routes.forEach(route -> routeStore.removeRoute(route));
        }
    }

    private void resolve(Route route) {
        // Monitor the IP address for updates of the MAC address
        hostService.startMonitoringIp(route.nextHop());

        MacAddress nextHopMac = routeStore.getNextHop(route.nextHop());
        if (nextHopMac == null) {
            Set<Host> hosts = hostService.getHostsByIp(route.nextHop());
            Optional<Host> host = hosts.stream().findFirst();
            if (host.isPresent()) {
                nextHopMac = host.get().mac();
            }
        }

        if (nextHopMac != null) {
            routeStore.updateNextHop(route.nextHop(), nextHopMac);
        }
    }

    private void hostUpdated(Host host) {
        synchronized (this) {
            for (IpAddress ip : host.ipAddresses()) {
                routeStore.updateNextHop(ip, host.mac());
            }
        }
    }

    private void hostRemoved(Host host) {
        synchronized (this) {
            for (IpAddress ip : host.ipAddresses()) {
                routeStore.removeNextHop(ip, host.mac());
            }
        }
    }

    /**
     * Queues updates for a route listener to ensure they are received in the
     * correct order.
     */
    private class ListenerQueue {

        private final ExecutorService executorService;
        private final BlockingQueue<RouteEvent> queue;
        private final RouteListener listener;

        /**
         * Creates a new listener queue.
         *
         * @param listener route listener to queue updates for
         */
        public ListenerQueue(RouteListener listener) {
            this.listener = listener;
            queue = new LinkedBlockingQueue<>();
            executorService = newSingleThreadExecutor(threadFactory);
        }

        /**
         * Posts and event to the listener.
         *
         * @param event event
         */
        public void post(RouteEvent event) {
            queue.add(event);
        }

        /**
         * Initiates event delivery to the listener.
         */
        public void start() {
            executorService.execute(this::poll);
        }

        /**
         * Halts event delivery to the listener.
         */
        public void stop() {
            executorService.shutdown();
        }

        private void poll() {
            try {
                while (true) {
                    listener.event(queue.take());
                }
            } catch (InterruptedException e) {
                log.info("Route listener event thread shutting down: {}", e.getMessage());
            }
        }

    }

    /**
     * Delegate to receive events from the route store.
     */
    private class InternalRouteStoreDelegate implements RouteStoreDelegate {
        @Override
        public void notify(RouteEvent event) {
            post(event);
        }
    }

    /**
     * Internal listener for host events.
     */
    private class InternalHostListener implements HostListener {
        @Override
        public void event(HostEvent event) {
            switch (event.type()) {
            case HOST_ADDED:
            case HOST_UPDATED:
                hostUpdated(event.subject());
                break;
            case HOST_REMOVED:
                hostRemoved(event.subject());
                break;
            case HOST_MOVED:
                break;
            default:
                break;
            }
        }
    }

}