/*
 * Copyright (c) 2014 Cisco Systems, Inc. and others.  All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v1.0 which accompanies this distribution,
 * and is available at http://www.eclipse.org/legal/epl-v10.html
 */
package org.opendaylight.netconf.sal.connect.netconf;

import com.google.common.base.Optional;
import com.google.common.base.Preconditions;
import com.google.common.base.Predicates;
import com.google.common.collect.Collections2;
import com.google.common.collect.Lists;
import com.google.common.collect.Sets;
import com.google.common.util.concurrent.CheckedFuture;
import com.google.common.util.concurrent.FutureCallback;
import com.google.common.util.concurrent.Futures;
import com.google.common.util.concurrent.ListenableFuture;
import com.google.common.util.concurrent.ListeningExecutorService;
import com.google.common.util.concurrent.MoreExecutors;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.LinkedList;
import java.util.List;
import java.util.Set;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.stream.Collectors;
import javax.annotation.concurrent.GuardedBy;
import org.opendaylight.controller.md.sal.dom.api.DOMNotification;
import org.opendaylight.controller.md.sal.dom.api.DOMRpcException;
import org.opendaylight.controller.md.sal.dom.api.DOMRpcResult;
import org.opendaylight.controller.md.sal.dom.api.DOMRpcService;
import org.opendaylight.netconf.api.NetconfMessage;
import org.opendaylight.netconf.sal.connect.api.MessageTransformer;
import org.opendaylight.netconf.sal.connect.api.NetconfDeviceSchemas;
import org.opendaylight.netconf.sal.connect.api.NetconfDeviceSchemasResolver;
import org.opendaylight.netconf.sal.connect.api.RemoteDevice;
import org.opendaylight.netconf.sal.connect.api.RemoteDeviceCommunicator;
import org.opendaylight.netconf.sal.connect.api.RemoteDeviceHandler;
import org.opendaylight.netconf.sal.connect.netconf.listener.NetconfDeviceCapabilities;
import org.opendaylight.netconf.sal.connect.netconf.listener.NetconfDeviceCommunicator;
import org.opendaylight.netconf.sal.connect.netconf.listener.NetconfSessionPreferences;
import org.opendaylight.netconf.sal.connect.netconf.sal.NetconfDeviceRpc;
import org.opendaylight.netconf.sal.connect.netconf.schema.NetconfRemoteSchemaYangSourceProvider;
import org.opendaylight.netconf.sal.connect.netconf.schema.YangLibrarySchemaYangSourceProvider;
import org.opendaylight.netconf.sal.connect.netconf.schema.mapping.BaseSchema;
import org.opendaylight.netconf.sal.connect.netconf.schema.mapping.NetconfMessageTransformer;
import org.opendaylight.netconf.sal.connect.netconf.util.NetconfMessageTransformUtil;
import org.opendaylight.netconf.sal.connect.util.RemoteDeviceId;
import org.opendaylight.yang.gen.v1.urn.ietf.params.xml.ns.yang.ietf.netconf.notifications.rev120206.NetconfCapabilityChange;
import org.opendaylight.yang.gen.v1.urn.opendaylight.netconf.node.topology.rev150114.netconf.node.connection.status.available.capabilities.AvailableCapabilityBuilder;
import org.opendaylight.yang.gen.v1.urn.opendaylight.netconf.node.topology.rev150114.netconf.node.connection.status.unavailable.capabilities.UnavailableCapability;
import org.opendaylight.yangtools.yang.common.QName;
import org.opendaylight.yangtools.yang.model.api.SchemaContext;
import org.opendaylight.yangtools.yang.model.repo.api.MissingSchemaSourceException;
import org.opendaylight.yangtools.yang.model.repo.api.RevisionSourceIdentifier;
import org.opendaylight.yangtools.yang.model.repo.api.SchemaContextFactory;
import org.opendaylight.yangtools.yang.model.repo.api.SchemaRepository;
import org.opendaylight.yangtools.yang.model.repo.api.SchemaResolutionException;
import org.opendaylight.yangtools.yang.model.repo.api.SchemaSourceException;
import org.opendaylight.yangtools.yang.model.repo.api.SchemaSourceRepresentation;
import org.opendaylight.yangtools.yang.model.repo.api.SourceIdentifier;
import org.opendaylight.yangtools.yang.model.repo.api.YangTextSchemaSource;
import org.opendaylight.yangtools.yang.model.repo.spi.PotentialSchemaSource;
import org.opendaylight.yangtools.yang.model.repo.spi.SchemaSourceProvider;
import org.opendaylight.yangtools.yang.model.repo.spi.SchemaSourceRegistration;
import org.opendaylight.yangtools.yang.model.repo.spi.SchemaSourceRegistry;
import org.opendaylight.yangtools.yang.parser.util.ASTSchemaSource;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 *  This is a mediator between NetconfDeviceCommunicator and NetconfDeviceSalFacade.
 */
public class NetconfDevice
        implements RemoteDevice<NetconfSessionPreferences, NetconfMessage, NetconfDeviceCommunicator> {

    private static final Logger LOG = LoggerFactory.getLogger(NetconfDevice.class);

    protected final RemoteDeviceId id;
    private final boolean reconnectOnSchemasChange;

    protected final SchemaContextFactory schemaContextFactory;
    private final RemoteDeviceHandler<NetconfSessionPreferences> salFacade;
    private final ListeningExecutorService processingExecutor;
    protected final SchemaSourceRegistry schemaRegistry;
    protected final SchemaRepository schemaRepository;
    private final NetconfDeviceSchemasResolver stateSchemasResolver;
    private final NotificationHandler notificationHandler;
    protected final List<SchemaSourceRegistration<? extends SchemaSourceRepresentation>> sourceRegistrations =
            new ArrayList<>();
    @GuardedBy("this")
    private boolean connected = false;

    // Message transformer is constructed once the schemas are available
    private MessageTransformer<NetconfMessage> messageTransformer;

    /**
     * Create rpc implementation capable of handling RPC for monitoring and notifications
     * even before the schemas of remote device are downloaded.
     */
    static NetconfDeviceRpc getRpcForInitialization(final NetconfDeviceCommunicator listener,
                                                    final boolean notificationSupport) {
        final BaseSchema baseSchema = notificationSupport
                ? BaseSchema.BASE_NETCONF_CTX_WITH_NOTIFICATIONS
                : BaseSchema.BASE_NETCONF_CTX;

        return new NetconfDeviceRpc(baseSchema.getSchemaContext(), listener,
                new NetconfMessageTransformer(baseSchema.getSchemaContext(), false, baseSchema));
    }

    public NetconfDevice(final SchemaResourcesDTO schemaResourcesDTO, final RemoteDeviceId id,
                         final RemoteDeviceHandler<NetconfSessionPreferences> salFacade,
                         final ExecutorService globalProcessingExecutor, final boolean reconnectOnSchemasChange) {
        this.id = id;
        this.reconnectOnSchemasChange = reconnectOnSchemasChange;
        this.schemaRegistry = schemaResourcesDTO.getSchemaRegistry();
        this.schemaRepository = schemaResourcesDTO.getSchemaRepository();
        this.schemaContextFactory = schemaResourcesDTO.getSchemaContextFactory();
        this.salFacade = salFacade;
        this.stateSchemasResolver = schemaResourcesDTO.getStateSchemasResolver();
        this.processingExecutor = MoreExecutors.listeningDecorator(globalProcessingExecutor);
        this.notificationHandler = new NotificationHandler(salFacade, id);
    }

    @Override
    public void onRemoteSessionUp(final NetconfSessionPreferences remoteSessionCapabilities,
                                  final NetconfDeviceCommunicator listener) {
        // SchemaContext setup has to be performed in a dedicated thread since
        // we are in a netty thread in this method
        // Yang models are being downloaded in this method and it would cause a
        // deadlock if we used the netty thread
        // http://netty.io/wiki/thread-model.html
        setConnected(true);
        LOG.debug("{}: Session to remote device established with {}", id, remoteSessionCapabilities);

        final NetconfDeviceRpc initRpc =
                getRpcForInitialization(listener, remoteSessionCapabilities.isNotificationsSupported());
        final DeviceSourcesResolver task =
                new DeviceSourcesResolver(remoteSessionCapabilities, id, stateSchemasResolver, initRpc);
        final ListenableFuture<DeviceSources> sourceResolverFuture = processingExecutor.submit(task);

        if (shouldListenOnSchemaChange(remoteSessionCapabilities)) {
            registerToBaseNetconfStream(initRpc, listener);
        }

        final FutureCallback<DeviceSources> resolvedSourceCallback = new FutureCallback<DeviceSources>() {
            @Override
            public void onSuccess(final DeviceSources result) {
                addProvidedSourcesToSchemaRegistry(result);
                setUpSchema(result);
            }

            private void setUpSchema(final DeviceSources result) {
                processingExecutor.submit(new SchemaSetup(result, remoteSessionCapabilities, listener));
            }

            @Override
            public void onFailure(final Throwable throwable) {
                LOG.warn("{}: Unexpected error resolving device sources: {}", id, throwable);
                handleSalInitializationFailure(throwable, listener);
            }
        };

        Futures.addCallback(sourceResolverFuture, resolvedSourceCallback, MoreExecutors.directExecutor());
    }

    private void registerToBaseNetconfStream(final NetconfDeviceRpc deviceRpc,
                                             final NetconfDeviceCommunicator listener) {
        // TODO check whether the model describing create subscription is present in schema
        // Perhaps add a default schema context to support create-subscription if the model was not provided
        // (same as what we do for base netconf operations in transformer)
        final CheckedFuture<DOMRpcResult, DOMRpcException> rpcResultListenableFuture = deviceRpc.invokeRpc(
                NetconfMessageTransformUtil.toPath(NetconfMessageTransformUtil.CREATE_SUBSCRIPTION_RPC_QNAME),
                NetconfMessageTransformUtil.CREATE_SUBSCRIPTION_RPC_CONTENT);

        final NotificationHandler.NotificationFilter filter = new NotificationHandler.NotificationFilter() {
            @Override
            public Optional<DOMNotification> filterNotification(final DOMNotification notification) {
                if (isCapabilityChanged(notification)) {
                    LOG.info("{}: Schemas change detected, reconnecting", id);
                    // Only disconnect is enough,
                    // the reconnecting nature of the connector will take care of reconnecting
                    listener.disconnect();
                    return Optional.absent();
                }
                return Optional.of(notification);
            }

            private boolean isCapabilityChanged(final DOMNotification notification) {
                return notification.getBody().getNodeType().equals(NetconfCapabilityChange.QNAME);
            }
        };

        Futures.addCallback(rpcResultListenableFuture, new FutureCallback<DOMRpcResult>() {
            @Override
            public void onSuccess(final DOMRpcResult domRpcResult) {
                notificationHandler.addNotificationFilter(filter);
            }

            @Override
            public void onFailure(final Throwable throwable) {
                LOG.warn("Unable to subscribe to base notification stream. Schemas will not be reloaded on the fly",
                        throwable);
            }
        }, MoreExecutors.directExecutor());
    }

    private boolean shouldListenOnSchemaChange(final NetconfSessionPreferences remoteSessionCapabilities) {
        return remoteSessionCapabilities.isNotificationsSupported() && reconnectOnSchemasChange;
    }

    private synchronized void handleSalInitializationSuccess(final SchemaContext result,
                                        final NetconfSessionPreferences remoteSessionCapabilities,
                                        final DOMRpcService deviceRpc) {
        //NetconfDevice.SchemaSetup can complete after NetconfDeviceCommunicator was closed. In that case do nothing,
        //since salFacade.onDeviceDisconnected was already called.
        if (connected) {
            final BaseSchema baseSchema =
                remoteSessionCapabilities.isNotificationsSupported()
                        ? BaseSchema.BASE_NETCONF_CTX_WITH_NOTIFICATIONS : BaseSchema.BASE_NETCONF_CTX;
            messageTransformer = new NetconfMessageTransformer(result, true, baseSchema);

            updateTransformer(messageTransformer);
            // salFacade.onDeviceConnected has to be called before the notification handler is initialized
            salFacade.onDeviceConnected(result, remoteSessionCapabilities, deviceRpc);
            notificationHandler.onRemoteSchemaUp(messageTransformer);

            LOG.info("{}: Netconf connector initialized successfully", id);
        } else {
            LOG.warn("{}: Device communicator was closed before schema setup finished.", id);
        }
    }

    private void handleSalInitializationFailure(final Throwable throwable,
                                                final RemoteDeviceCommunicator<NetconfMessage> listener) {
        LOG.error("{}: Initialization in sal failed, disconnecting from device", id, throwable);
        listener.close();
        onRemoteSessionDown();
        resetMessageTransformer();
    }

    /**
     * Set the transformer to null as is in initial state.
     */
    private void resetMessageTransformer() {
        updateTransformer(null);
    }

    private void updateTransformer(final MessageTransformer<NetconfMessage> transformer) {
        messageTransformer = transformer;
    }

    private synchronized void setConnected(final boolean connected) {
        this.connected = connected;
    }

    private void addProvidedSourcesToSchemaRegistry(final DeviceSources deviceSources) {
        final SchemaSourceProvider<YangTextSchemaSource> yangProvider = deviceSources.getSourceProvider();
        for (final SourceIdentifier sourceId : deviceSources.getProvidedSources()) {
            sourceRegistrations.add(schemaRegistry.registerSchemaSource(yangProvider,
                    PotentialSchemaSource.create(
                            sourceId, YangTextSchemaSource.class, PotentialSchemaSource.Costs.REMOTE_IO.getValue())));
        }
    }

    @Override
    public void onRemoteSessionDown() {
        setConnected(false);
        notificationHandler.onRemoteSchemaDown();

        salFacade.onDeviceDisconnected();
        for (final SchemaSourceRegistration<? extends SchemaSourceRepresentation> sourceRegistration
                : sourceRegistrations) {
            sourceRegistration.close();
        }
        resetMessageTransformer();
    }

    @Override
    public void onRemoteSessionFailed(final Throwable throwable) {
        setConnected(false);
        salFacade.onDeviceFailed(throwable);
    }

    @Override
    public void onNotification(final NetconfMessage notification) {
        notificationHandler.handleNotification(notification);
    }

    /**
     * Just a transfer object containing schema related dependencies. Injected in constructor.
     */
    public static class SchemaResourcesDTO {
        private final SchemaSourceRegistry schemaRegistry;
        private final SchemaRepository schemaRepository;
        private final SchemaContextFactory schemaContextFactory;
        private final NetconfDeviceSchemasResolver stateSchemasResolver;

        public SchemaResourcesDTO(final SchemaSourceRegistry schemaRegistry,
                                  final SchemaRepository schemaRepository,
                                  final SchemaContextFactory schemaContextFactory,
                                  final NetconfDeviceSchemasResolver deviceSchemasResolver) {
            this.schemaRegistry = Preconditions.checkNotNull(schemaRegistry);
            this.schemaRepository = Preconditions.checkNotNull(schemaRepository);
            this.schemaContextFactory = Preconditions.checkNotNull(schemaContextFactory);
            this.stateSchemasResolver = Preconditions.checkNotNull(deviceSchemasResolver);
        }

        public SchemaSourceRegistry getSchemaRegistry() {
            return schemaRegistry;
        }

        public SchemaRepository getSchemaRepository() {
            return schemaRepository;
        }

        public SchemaContextFactory getSchemaContextFactory() {
            return schemaContextFactory;
        }

        public NetconfDeviceSchemasResolver getStateSchemasResolver() {
            return stateSchemasResolver;
        }
    }

    /**
     * Schema building callable.
     */
    private static class DeviceSourcesResolver implements Callable<DeviceSources> {

        private final NetconfDeviceRpc deviceRpc;
        private final NetconfSessionPreferences remoteSessionCapabilities;
        private final RemoteDeviceId id;
        private final NetconfDeviceSchemasResolver stateSchemasResolver;

        DeviceSourcesResolver(final NetconfDeviceRpc deviceRpc,
                              final NetconfSessionPreferences remoteSessionCapabilities,
                              final RemoteDeviceId id, final NetconfDeviceSchemasResolver stateSchemasResolver) {
            this.deviceRpc = deviceRpc;
            this.remoteSessionCapabilities = remoteSessionCapabilities;
            this.id = id;
            this.stateSchemasResolver = stateSchemasResolver;
        }

        DeviceSourcesResolver(final NetconfSessionPreferences remoteSessionCapabilities, final RemoteDeviceId id,
                                     final NetconfDeviceSchemasResolver stateSchemasResolver,
                                     final NetconfDeviceRpc rpcForMonitoring) {
            this(rpcForMonitoring, remoteSessionCapabilities, id, stateSchemasResolver);
        }

        @Override
        public DeviceSources call() throws Exception {
            final NetconfDeviceSchemas availableSchemas =
                    stateSchemasResolver.resolve(deviceRpc, remoteSessionCapabilities, id);
            LOG.debug("{}: Schemas exposed by ietf-netconf-monitoring: {}", id,
                    availableSchemas.getAvailableYangSchemasQNames());

            final Set<QName> requiredSources = Sets.newHashSet(remoteSessionCapabilities.getModuleBasedCaps());
            final Set<QName> providedSources = availableSchemas.getAvailableYangSchemasQNames();

            final Set<QName> requiredSourcesNotProvided = Sets.difference(requiredSources, providedSources);
            if (!requiredSourcesNotProvided.isEmpty()) {
                LOG.warn("{}: Netconf device does not provide all yang models reported in hello message capabilities,"
                        + " required but not provided: {}", id, requiredSourcesNotProvided);
                LOG.warn("{}: Attempting to build schema context from required sources", id);
            }

            // Here all the sources reported in netconf monitoring are merged with those reported in hello.
            // It is necessary to perform this since submodules are not mentioned in hello but still required.
            // This clashes with the option of a user to specify supported yang models manually in configuration
            // for netconf-connector and as a result one is not able to fully override yang models of a device.
            // It is only possible to add additional models.
            final Set<QName> providedSourcesNotRequired = Sets.difference(providedSources, requiredSources);
            if (!providedSourcesNotRequired.isEmpty()) {
                LOG.warn("{}: Netconf device provides additional yang models not reported in "
                        + "hello message capabilities: {}", id, providedSourcesNotRequired);
                LOG.warn("{}: Adding provided but not required sources as required to prevent failures", id);
                LOG.debug("{}: Netconf device reported in hello: {}", id, requiredSources);
                requiredSources.addAll(providedSourcesNotRequired);
            }

            final SchemaSourceProvider<YangTextSchemaSource> sourceProvider;
            if (availableSchemas instanceof LibraryModulesSchemas) {
                sourceProvider = new YangLibrarySchemaYangSourceProvider(id,
                        ((LibraryModulesSchemas) availableSchemas).getAvailableModels());
            } else {
                sourceProvider = new NetconfRemoteSchemaYangSourceProvider(id, deviceRpc);
            }

            return new DeviceSources(requiredSources, providedSources, sourceProvider);
        }
    }

    /**
     * Contains RequiredSources - sources from capabilities.
     */
    private static final class DeviceSources {
        private final Set<QName> requiredSources;
        private final Set<QName> providedSources;
        private final SchemaSourceProvider<YangTextSchemaSource> sourceProvider;

        DeviceSources(final Set<QName> requiredSources, final Set<QName> providedSources,
                             final SchemaSourceProvider<YangTextSchemaSource> sourceProvider) {
            this.requiredSources = requiredSources;
            this.providedSources = providedSources;
            this.sourceProvider = sourceProvider;
        }

        public Set<QName> getRequiredSourcesQName() {
            return requiredSources;
        }

        public Set<QName> getProvidedSourcesQName() {
            return providedSources;
        }

        public Collection<SourceIdentifier> getRequiredSources() {
            return Collections2.transform(requiredSources, DeviceSources::toSourceId);
        }

        public Collection<SourceIdentifier> getProvidedSources() {
            return Collections2.transform(providedSources, DeviceSources::toSourceId);
        }

        public SchemaSourceProvider<YangTextSchemaSource> getSourceProvider() {
            return sourceProvider;
        }

        private static SourceIdentifier toSourceId(final QName input) {
            return RevisionSourceIdentifier.create(input.getLocalName(),
                Optional.fromNullable(input.getFormattedRevision()));
        }
    }

    /**
     * Schema builder that tries to build schema context from provided sources or biggest subset of it.
     */
    private final class SchemaSetup implements Runnable {
        private final DeviceSources deviceSources;
        private final NetconfSessionPreferences remoteSessionCapabilities;
        private final RemoteDeviceCommunicator<NetconfMessage> listener;
        private final NetconfDeviceCapabilities capabilities;

        SchemaSetup(final DeviceSources deviceSources, final NetconfSessionPreferences remoteSessionCapabilities,
                           final RemoteDeviceCommunicator<NetconfMessage> listener) {
            this.deviceSources = deviceSources;
            this.remoteSessionCapabilities = remoteSessionCapabilities;
            this.listener = listener;
            this.capabilities = remoteSessionCapabilities.getNetconfDeviceCapabilities();
        }

        @Override
        public void run() {

            final Collection<SourceIdentifier> requiredSources = deviceSources.getRequiredSources();
            final Collection<SourceIdentifier> missingSources = filterMissingSources(requiredSources);

            capabilities.addUnresolvedCapabilities(getQNameFromSourceIdentifiers(missingSources),
                    UnavailableCapability.FailureReason.MissingSource);

            requiredSources.removeAll(missingSources);
            setUpSchema(requiredSources);
        }

        private Collection<SourceIdentifier> filterMissingSources(final Collection<SourceIdentifier> requiredSources) {

            return requiredSources.parallelStream().filter(sourceIdentifier -> {
                boolean remove = false;
                try {
                    schemaRepository.getSchemaSource(sourceIdentifier, ASTSchemaSource.class).checkedGet();
                } catch (SchemaSourceException e) {
                    remove = true;
                }
                return remove;
            }).collect(Collectors.toList());
        }

        /**
         * Build schema context, in case of success or final failure notify device.
         */
        @SuppressWarnings("checkstyle:IllegalCatch")
        private void setUpSchema(Collection<SourceIdentifier> requiredSources) {
            while (!requiredSources.isEmpty()) {
                LOG.trace("{}: Trying to build schema context from {}", id, requiredSources);
                try {
                    final CheckedFuture<SchemaContext, SchemaResolutionException> schemaBuilderFuture =
                            schemaContextFactory.createSchemaContext(requiredSources);
                    final SchemaContext result = schemaBuilderFuture.checkedGet();
                    LOG.debug("{}: Schema context built successfully from {}", id, requiredSources);
                    final Collection<QName> filteredQNames = Sets.difference(deviceSources.getRequiredSourcesQName(),
                            capabilities.getUnresolvedCapabilites().keySet());
                    capabilities.addCapabilities(filteredQNames.stream().map(entry -> new AvailableCapabilityBuilder()
                            .setCapability(entry.toString()).setCapabilityOrigin(
                                    remoteSessionCapabilities.getModuleBasedCapsOrigin().get(entry)).build())
                            .collect(Collectors.toList()));

                    capabilities.addNonModuleBasedCapabilities(remoteSessionCapabilities
                            .getNonModuleCaps().stream().map(entry -> new AvailableCapabilityBuilder()
                                    .setCapability(entry).setCapabilityOrigin(
                                            remoteSessionCapabilities.getNonModuleBasedCapsOrigin().get(entry)).build())
                            .collect(Collectors.toList()));

                    handleSalInitializationSuccess(result, remoteSessionCapabilities, getDeviceSpecificRpc(result));
                    return;
                } catch (final SchemaResolutionException e) {
                    // schemaBuilderFuture.checkedGet() throws only SchemaResolutionException
                    // that might be wrapping a MissingSchemaSourceException so we need to look
                    // at the cause of the exception to make sure we don't misinterpret it.
                    if (e.getCause() instanceof MissingSchemaSourceException) {
                        requiredSources = handleMissingSchemaSourceException(
                                requiredSources, (MissingSchemaSourceException) e.getCause());
                        continue;
                    }
                    requiredSources = handleSchemaResolutionException(requiredSources, e);
                } catch (final Exception e) {
                    // unknown error, fail
                    handleSalInitializationFailure(e, listener);
                    return;
                }
            }
            // No more sources, fail
            final IllegalStateException cause = new IllegalStateException(id + ": No more sources for schema context");
            handleSalInitializationFailure(cause, listener);
            salFacade.onDeviceFailed(cause);
        }

        private Collection<SourceIdentifier> handleMissingSchemaSourceException(
                final Collection<SourceIdentifier> requiredSources, final MissingSchemaSourceException exception) {
            // In case source missing, try without it
            final SourceIdentifier missingSource = exception.getSourceId();
            LOG.warn("{}: Unable to build schema context, missing source {}, will reattempt without it", id,
                    missingSource);
            LOG.debug("{}: Unable to build schema context, missing source {}, will reattempt without it",
                    exception);
            final Collection<QName> qNameOfMissingSource =
                    getQNameFromSourceIdentifiers(Sets.newHashSet(missingSource));
            if (!qNameOfMissingSource.isEmpty()) {
                capabilities.addUnresolvedCapabilities(
                        qNameOfMissingSource, UnavailableCapability.FailureReason.MissingSource);
            }
            return stripUnavailableSource(requiredSources, missingSource);
        }

        private Collection<SourceIdentifier> handleSchemaResolutionException(
            final Collection<SourceIdentifier> requiredSources, final SchemaResolutionException resolutionException) {
            // In case resolution error, try only with resolved sources
            // There are two options why schema resolution exception occurred : unsatisfied imports or flawed model
            // FIXME Do we really have assurance that these two cases cannot happen at once?
            if (resolutionException.getFailedSource() != null) {
                // flawed model - exclude it
                final SourceIdentifier failedSourceId = resolutionException.getFailedSource();
                LOG.warn("{}: Unable to build schema context, failed to resolve source {}, will reattempt without it",
                        id, failedSourceId);
                LOG.warn("{}: Unable to build schema context, failed to resolve source {}, will reattempt without it",
                        id, resolutionException);
                capabilities.addUnresolvedCapabilities(getQNameFromSourceIdentifiers(
                        Collections.singleton(failedSourceId)), UnavailableCapability.FailureReason.UnableToResolve);
                return stripUnavailableSource(requiredSources, resolutionException.getFailedSource());
            }
            // unsatisfied imports
            final Set<SourceIdentifier> unresolvedSources = resolutionException.getUnsatisfiedImports().keySet();
            capabilities.addUnresolvedCapabilities(
                getQNameFromSourceIdentifiers(unresolvedSources), UnavailableCapability.FailureReason.UnableToResolve);
            LOG.warn("{}: Unable to build schema context, unsatisfied imports {}, will reattempt with resolved only",
                    id, resolutionException.getUnsatisfiedImports());
            LOG.debug("{}: Unable to build schema context, unsatisfied imports {}, will reattempt with resolved only",
                    resolutionException);
            return resolutionException.getResolvedSources();
        }

        protected NetconfDeviceRpc getDeviceSpecificRpc(final SchemaContext result) {
            return new NetconfDeviceRpc(result, listener, new NetconfMessageTransformer(result, true));
        }

        private Collection<SourceIdentifier> stripUnavailableSource(final Collection<SourceIdentifier> requiredSources,
                                                                    final SourceIdentifier sourceIdToRemove) {
            final LinkedList<SourceIdentifier> sourceIdentifiers = Lists.newLinkedList(requiredSources);
            final boolean removed = sourceIdentifiers.remove(sourceIdToRemove);
            Preconditions.checkState(
                    removed, "{}: Trying to remove {} from {} failed", id, sourceIdToRemove, requiredSources);
            return sourceIdentifiers;
        }

        private Collection<QName> getQNameFromSourceIdentifiers(final Collection<SourceIdentifier> identifiers) {
            final Collection<QName> qNames = Collections2.transform(identifiers, this::getQNameFromSourceIdentifier);

            if (qNames.isEmpty()) {
                LOG.debug("{}: Unable to map any source identifiers to a capability reported by device : {}", id,
                        identifiers);
            }
            return Collections2.filter(qNames, Predicates.notNull());
        }

        private QName getQNameFromSourceIdentifier(final SourceIdentifier identifier) {
            // Required sources are all required and provided merged in DeviceSourcesResolver
            for (final QName qname : deviceSources.getRequiredSourcesQName()) {
                if (!qname.getLocalName().equals(identifier.getName())) {
                    continue;
                }

                final String rev = getNullableRev(identifier);
                if (rev == null) {
                    if (qname.getRevision() == null) {
                        return qname;
                    }
                } else if (qname.getFormattedRevision().equals(rev)) {
                    return qname;
                }
            }
            LOG.warn("Unable to map identifier to a devices reported capability: {} Available: {}",identifier,
                    deviceSources.getRequiredSourcesQName());
            // return null since we cannot find the QName,
            // this capability will be removed from required sources and not reported as unresolved-capability
            return null;
        }

        private String getNullableRev(final SourceIdentifier identifier) {
            final String rev = identifier.getRevision();
            return rev == null || SourceIdentifier.NOT_PRESENT_FORMATTED_REVISION.equals(rev) ? null : rev;
        }
    }
}