/*
 * Copyright 2015 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.store.app;

import com.google.common.base.Charsets;
import com.google.common.collect.ImmutableSet;
import com.google.common.util.concurrent.ListenableFuture;

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.util.KryoNamespace;
import org.onosproject.app.ApplicationDescription;
import org.onosproject.app.ApplicationEvent;
import org.onosproject.app.ApplicationException;
import org.onosproject.app.ApplicationState;
import org.onosproject.app.ApplicationStore;
import org.onosproject.cluster.ClusterService;
import org.onosproject.cluster.ControllerNode;
import org.onosproject.common.app.ApplicationArchive;
import org.onosproject.core.Application;
import org.onosproject.core.ApplicationId;
import org.onosproject.core.ApplicationIdStore;
import org.onosproject.core.DefaultApplication;
import org.onosproject.core.Permission;
import org.onosproject.store.cluster.messaging.ClusterCommunicationService;
import org.onosproject.store.cluster.messaging.ClusterMessage;
import org.onosproject.store.cluster.messaging.ClusterMessageHandler;
import org.onosproject.store.cluster.messaging.MessageSubject;
import org.onosproject.store.impl.EventuallyConsistentMap;
import org.onosproject.store.impl.EventuallyConsistentMapEvent;
import org.onosproject.store.impl.EventuallyConsistentMapImpl;
import org.onosproject.store.impl.EventuallyConsistentMapListener;
import org.onosproject.store.impl.WallclockClockManager;
import org.onosproject.store.serializers.KryoNamespaces;
import org.slf4j.Logger;

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.Set;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;

import static com.google.common.io.ByteStreams.toByteArray;
import static java.util.concurrent.TimeUnit.MILLISECONDS;
import static org.onlab.util.Tools.namedThreads;
import static org.onosproject.app.ApplicationEvent.Type.*;
import static org.onosproject.store.app.GossipApplicationStore.InternalState.*;
import static org.onosproject.store.impl.EventuallyConsistentMapEvent.Type.PUT;
import static org.onosproject.store.impl.EventuallyConsistentMapEvent.Type.REMOVE;
import static org.slf4j.LoggerFactory.getLogger;

/**
 * Manages inventory of applications in a distributed data store that uses
 * optimistic replication and gossip based anti-entropy techniques.
 */
@Component(immediate = true)
@Service
public class GossipApplicationStore extends ApplicationArchive
        implements ApplicationStore {

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

    private static final MessageSubject APP_BITS_REQUEST = new MessageSubject("app-bits-request");

    private static final int FETCH_TIMEOUT_MS = 10_000;
    private static final int LOAD_TIMEOUT_MS = 5_000;

    public enum InternalState {
        INSTALLED, ACTIVATED, DEACTIVATED
    }

    private final ScheduledExecutorService executor =
            Executors.newSingleThreadScheduledExecutor(namedThreads("onos-app-store"));

    private EventuallyConsistentMap<ApplicationId, Application> apps;
    private EventuallyConsistentMap<Application, InternalState> states;
    private EventuallyConsistentMap<Application, Set<Permission>> permissions;

    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
    protected ClusterCommunicationService clusterCommunicator;

    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
    protected ClusterService clusterService;

    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
    protected ApplicationIdStore idStore;

    @Activate
    public void activate() {
        KryoNamespace.Builder intentSerializer = KryoNamespace.newBuilder()
                .register(KryoNamespaces.API)
                .register(InternalState.class);

        clusterCommunicator.addSubscriber(APP_BITS_REQUEST, new InternalBitServer());

        apps = new EventuallyConsistentMapImpl<>("apps", clusterService,
                                                 clusterCommunicator,
                                                 intentSerializer,
                                                 new WallclockClockManager<>());

        states = new EventuallyConsistentMapImpl<>("app-states",
                                                   clusterService,
                                                   clusterCommunicator,
                                                   intentSerializer,
                                                   new WallclockClockManager<>());
        states.addListener(new InternalAppStatesListener());

        permissions = new EventuallyConsistentMapImpl<>("app-permissions",
                                                        clusterService,
                                                        clusterCommunicator,
                                                        intentSerializer,
                                                        new WallclockClockManager<>());

        // FIXME: figure out load from disk; this will require resolving the dual authority problem

        executor.schedule(this::pruneUninstalledApps, LOAD_TIMEOUT_MS, MILLISECONDS);

        log.info("Started");
    }

    private void loadFromDisk() {
        for (String name : getApplicationNames()) {
            create(getApplicationDescription(name));
            // load app permissions
        }
    }

    @Deactivate
    public void deactivate() {
        apps.destroy();
        states.destroy();
        permissions.destroy();
        log.info("Stopped");
    }

    @Override
    public Set<Application> getApplications() {
        return ImmutableSet.copyOf(apps.values());
    }

    @Override
    public ApplicationId getId(String name) {
        return idStore.getAppId(name);
    }

    @Override
    public Application getApplication(ApplicationId appId) {
        return apps.get(appId);
    }

    @Override
    public ApplicationState getState(ApplicationId appId) {
        Application app = apps.get(appId);
        InternalState s = app == null ? null : states.get(app);
        return s == null ? null : s == ACTIVATED ?
                ApplicationState.ACTIVE : ApplicationState.INSTALLED;
    }

    @Override
    public Application create(InputStream appDescStream) {
        ApplicationDescription appDesc = saveApplication(appDescStream);
        return create(appDesc);
    }

    private Application create(ApplicationDescription appDesc) {
        Application app = registerApp(appDesc);
        apps.put(app.id(), app);
        states.put(app, INSTALLED);
        return app;
    }

    @Override
    public void remove(ApplicationId appId) {
        Application app = apps.get(appId);
        if (app != null) {
            apps.remove(appId);
            states.remove(app);
            permissions.remove(app);
        }
    }

    @Override
    public void activate(ApplicationId appId) {
        Application app = apps.get(appId);
        if (app != null) {
            states.put(app, ACTIVATED);
        }
    }

    @Override
    public void deactivate(ApplicationId appId) {
        Application app = apps.get(appId);
        if (app != null) {
            states.put(app, DEACTIVATED);
        }
    }

    @Override
    public Set<Permission> getPermissions(ApplicationId appId) {
        Application app = apps.get(appId);
        return app != null ? permissions.get(app) : null;
    }

    @Override
    public void setPermissions(ApplicationId appId, Set<Permission> permissions) {
        Application app = getApplication(appId);
        if (app != null) {
            this.permissions.put(app, permissions);
            delegate.notify(new ApplicationEvent(APP_PERMISSIONS_CHANGED, app));
        }
    }

    /**
     * Listener to application state distributed map changes.
     */
    private final class InternalAppStatesListener
            implements EventuallyConsistentMapListener<Application, InternalState> {
        @Override
        public void event(EventuallyConsistentMapEvent<Application, InternalState> event) {
            Application app = event.key();
            InternalState state = event.value();

            if (event.type() == PUT) {
                if (state == INSTALLED) {
                    fetchBitsIfNeeded(app);
                    delegate.notify(new ApplicationEvent(APP_INSTALLED, app));

                } else if (state == ACTIVATED) {
                    installAppIfNeeded(app);
                    setActive(app.id().name());
                    delegate.notify(new ApplicationEvent(APP_ACTIVATED, app));

                } else if (state == DEACTIVATED) {
                    clearActive(app.id().name());
                    delegate.notify(new ApplicationEvent(APP_DEACTIVATED, app));
                }
            } else if (event.type() == REMOVE) {
                delegate.notify(new ApplicationEvent(APP_UNINSTALLED, app));
                purgeApplication(app.id().name());
            }
        }
    }

    /**
     * Determines if the application bits are available locally.
     */
    private boolean appBitsAvailable(Application app) {
        try {
            ApplicationDescription appDesc = getApplicationDescription(app.id().name());
            return appDesc.version().equals(app.version());
        } catch (ApplicationException e) {
            return false;
        }
    }

    /**
     * Fetches the bits from the cluster peers if necessary.
     */
    private void fetchBitsIfNeeded(Application app) {
        if (!appBitsAvailable(app)) {
            fetchBits(app);
        }
    }

    /**
     * Installs the application if necessary from the application peers.
     */
    private void installAppIfNeeded(Application app) {
        if (!appBitsAvailable(app)) {
            fetchBits(app);
            delegate.notify(new ApplicationEvent(APP_INSTALLED, app));
        }
    }

    /**
     * Fetches the bits from the cluster peers.
     */
    private void fetchBits(Application app) {
        ControllerNode localNode = clusterService.getLocalNode();
        ClusterMessage message = new ClusterMessage(localNode.id(), APP_BITS_REQUEST,
                                                    app.id().name().getBytes(Charsets.UTF_8));
        //Map<ControllerNode, ListenableFuture<byte[]>> futures = new HashMap<>();
        CountDownLatch latch = new CountDownLatch(1);

        // FIXME: send message with name & version to make sure we don't get served old bits

        log.info("Downloading bits for application {}", app.id().name());
        for (ControllerNode node : clusterService.getNodes()) {
            try {
                ListenableFuture<byte[]> future = clusterCommunicator.sendAndReceive(message, node.id());
                future.addListener(new InternalBitListener(app, node, future, latch), executor);
            } catch (IOException e) {
                log.debug("Unable to request bits for application {} from node {}",
                          app.id().name(), node.id());
            }
        }

        try {
            if (!latch.await(FETCH_TIMEOUT_MS, MILLISECONDS)) {
                log.warn("Unable to fetch bits for application {}", app.id().name());
            }
        } catch (InterruptedException e) {
            log.warn("Interrupted while fetching bits for application {}", app.id().name());
        }
    }

    /**
     * Responder to requests for application bits.
     */
    private class InternalBitServer implements ClusterMessageHandler {
        @Override
        public void handle(ClusterMessage message) {
            String name = new String(message.payload(), Charsets.UTF_8);
            try {
                message.respond(toByteArray(getApplicationInputStream(name)));
            } catch (Exception e) {
                log.debug("Unable to read bits for application {}", name);
            }
        }
    }

    /**
     * Processes completed fetch requests.
     */
    private class InternalBitListener implements Runnable {
        private final Application app;
        private final ControllerNode node;
        private final ListenableFuture<byte[]> future;
        private final CountDownLatch latch;

        public InternalBitListener(Application app, ControllerNode node,
                                   ListenableFuture<byte[]> future, CountDownLatch latch) {
            this.app = app;
            this.node = node;
            this.future = future;
            this.latch = latch;
        }

        @Override
        public void run() {
            if (latch.getCount() > 0 && !future.isCancelled()) {
                try {
                    byte[] bits = future.get(1, MILLISECONDS);
                    saveApplication(new ByteArrayInputStream(bits));
                    log.info("Downloaded bits for application {} from node {}",
                             app.id().name(), node.id());
                    latch.countDown();
                } catch (Exception e) {
                    log.warn("Unable to fetch bits for application {} from node {}",
                             app.id().name(), node.id());
                }
            }
        }
    }

    /**
     * Prunes applications which are not in the map, but are on disk.
     */
    private void pruneUninstalledApps() {
        for (String name : getApplicationNames()) {
            if (getApplication(getId(name)) == null) {
                Application app = registerApp(getApplicationDescription(name));
                delegate.notify(new ApplicationEvent(APP_UNINSTALLED, app));
                purgeApplication(app.id().name());
            }
        }
    }

    /**
     * Produces a registered application from the supplied description.
     */
    private Application registerApp(ApplicationDescription appDesc) {
        ApplicationId appId = idStore.registerApplication(appDesc.name());
        return new DefaultApplication(appId, appDesc.version(), appDesc.description(),
                                      appDesc.origin(), appDesc.permissions(),
                                      appDesc.featuresRepo(), appDesc.features());
    }
}