/*
 * Copyright (c) 2013 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.bgpcep.pcep.topology.provider;

import static java.util.Objects.requireNonNull;

import com.google.common.collect.Iterables;
import com.google.common.collect.Maps;
import com.google.common.util.concurrent.FluentFuture;
import com.google.common.util.concurrent.FutureCallback;
import com.google.common.util.concurrent.ListenableFuture;
import com.google.common.util.concurrent.MoreExecutors;
import io.netty.util.Timeout;
import io.netty.util.concurrent.Future;
import java.net.InetAddress;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Objects;
import java.util.Optional;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;
import org.checkerframework.checker.lock.qual.GuardedBy;
import org.checkerframework.checker.lock.qual.Holding;
import org.eclipse.jdt.annotation.NonNull;
import org.eclipse.jdt.annotation.Nullable;
import org.opendaylight.bgpcep.pcep.topology.provider.session.stats.SessionStateImpl;
import org.opendaylight.bgpcep.pcep.topology.provider.session.stats.TopologySessionStats;
import org.opendaylight.mdsal.binding.api.WriteTransaction;
import org.opendaylight.mdsal.common.api.CommitInfo;
import org.opendaylight.mdsal.common.api.LogicalDatastoreType;
import org.opendaylight.protocol.pcep.PCEPCloseTermination;
import org.opendaylight.protocol.pcep.PCEPSession;
import org.opendaylight.protocol.pcep.PCEPTerminationReason;
import org.opendaylight.protocol.pcep.TerminationReason;
import org.opendaylight.yang.gen.v1.urn.ietf.params.xml.ns.yang.ietf.inet.types.rev130715.IetfInetUtil;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.pcep.ietf.initiated.rev200720.Stateful1;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.pcep.ietf.stateful.rev200720.LspObject;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.pcep.ietf.stateful.rev200720.Path1;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.pcep.ietf.stateful.rev200720.PlspId;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.pcep.ietf.stateful.rev200720.SrpIdNumber;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.pcep.ietf.stateful.rev200720.StatefulTlv1Builder;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.pcep.ietf.stateful.rev200720.Tlvs1;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.pcep.ietf.stateful.rev200720.lsp.object.Lsp;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.pcep.ietf.stateful.rev200720.stateful.capability.tlv.Stateful;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.pcep.types.rev181109.Message;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.pcep.types.rev181109.Object;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.pcep.types.rev181109.open.object.open.Tlvs;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.topology.pcep.rev220730.LspId;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.topology.pcep.rev220730.Node1;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.topology.pcep.rev220730.Node1Builder;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.topology.pcep.rev220730.OperationResult;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.topology.pcep.rev220730.PccSyncState;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.topology.pcep.rev220730.TearDownSessionInput;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.topology.pcep.rev220730.lsp.metadata.Metadata;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.topology.pcep.rev220730.pcep.client.attributes.PathComputationClient;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.topology.pcep.rev220730.pcep.client.attributes.PathComputationClientBuilder;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.topology.pcep.rev220730.pcep.client.attributes.path.computation.client.ReportedLsp;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.topology.pcep.rev220730.pcep.client.attributes.path.computation.client.ReportedLspBuilder;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.topology.pcep.rev220730.pcep.client.attributes.path.computation.client.ReportedLspKey;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.topology.pcep.rev220730.pcep.client.attributes.path.computation.client.StatefulTlvBuilder;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.topology.pcep.rev220730.pcep.client.attributes.path.computation.client.reported.lsp.Path;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.topology.pcep.rev220730.pcep.client.attributes.path.computation.client.reported.lsp.PathKey;
import org.opendaylight.yang.gen.v1.urn.tbd.params.xml.ns.yang.network.topology.rev131021.network.topology.topology.Node;
import org.opendaylight.yangtools.yang.binding.DataObject;
import org.opendaylight.yangtools.yang.binding.InstanceIdentifier;
import org.opendaylight.yangtools.yang.common.RpcResult;
import org.opendaylight.yangtools.yang.common.RpcResultBuilder;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Base class for PCEP topology providers. It handles the common tasks involved in managing a PCEP server (PCE)
 * endpoint, and exposing a network topology based on it. It needs to be subclassed to form a fully functional block,
 * where the subclass provides handling of incoming messages.
 */
public abstract class AbstractTopologySessionListener implements TopologySessionListener, TopologySessionStats {
    private static final Logger LOG = LoggerFactory.getLogger(AbstractTopologySessionListener.class);

    private final AtomicBoolean statefulCapability = new AtomicBoolean(false);
    private final AtomicBoolean lspUpdateCapability = new AtomicBoolean(false);
    private final AtomicBoolean initiationCapability = new AtomicBoolean(false);

    @GuardedBy("this")
    final Map<PlspId, String> lsps = new HashMap<>();
    @GuardedBy("this")
    SessionStateImpl listenerState;

    // FIXME: clarify lifecycle rules of this map, most notably the interaction of multiple SrpIdNumbers
    @GuardedBy("this")
    private final Map<SrpIdNumber, PCEPRequest> requests = new HashMap<>();
    @GuardedBy("this")
    private final Map<String, ReportedLsp> lspData = new ConcurrentHashMap<>();
    private final ServerSessionManager serverSessionManager;
    private InstanceIdentifier<PathComputationClient> pccIdentifier;
    @GuardedBy("this")
    private TopologyNodeState nodeState;
    private final AtomicBoolean synced = new AtomicBoolean(false);
    @GuardedBy("this")
    private PCEPSession session;
    @GuardedBy("this")
    private SyncOptimization syncOptimization;
    @GuardedBy("this")
    private boolean triggeredResyncInProcess;

    AbstractTopologySessionListener(final ServerSessionManager serverSessionManager) {
        this.serverSessionManager = requireNonNull(serverSessionManager);
    }

    @Override
    public final void onSessionUp(final PCEPSession psession) {
        synchronized (serverSessionManager) {
            synchronized (this) {
                /*
                 * The session went up. Look up the router in Inventory model, create it if it
                 * is not there (marking that fact for later deletion), and mark it as
                 * synchronizing. Also create it in the topology model, with empty LSP list.
                 */
                final InetAddress peerAddress = psession.getRemoteAddress();

                syncOptimization = new SyncOptimization(psession);
                final boolean haveLspDbVersion = syncOptimization.isDbVersionPresent();

                final TopologyNodeState state =
                        serverSessionManager.takeNodeState(peerAddress, this, haveLspDbVersion);

                // takeNodeState(..) may fail when the server session manager is being restarted
                // due to configuration change
                if (state == null) {
                    LOG.error("Unable to fetch topology node state for PCEP session. Closing session {}", psession);
                    psession.close(TerminationReason.UNKNOWN);
                    onSessionTerminated(psession, new PCEPCloseTermination(TerminationReason.UNKNOWN));
                    return;
                }

                if (session != null || nodeState != null) {
                    LOG.error("PCEP session is already up with {}. Closing session {}", peerAddress, psession);
                    psession.close(TerminationReason.UNKNOWN);
                    onSessionTerminated(psession, new PCEPCloseTermination(TerminationReason.UNKNOWN));
                    return;
                }
                session = psession;
                nodeState = state;

                LOG.trace("Peer {} resolved to topology node {}", peerAddress, state.getNodeId());

                // Our augmentation in the topology node
                final PathComputationClientBuilder pccBuilder = new PathComputationClientBuilder()
                    .setIpAddress(IetfInetUtil.INSTANCE.ipAddressNoZoneFor(peerAddress));

                // Let subclass fill the details
                updateStatefulCapabilities(pccBuilder, peerAddress, psession.getRemoteTlvs());

                synced.set(isSynchronized());

                final InstanceIdentifier<Node1> topologyAugment = state.getNodeId().augmentation(Node1.class);
                pccIdentifier = topologyAugment.child(PathComputationClient.class);

                if (haveLspDbVersion) {
                    final Node initialNodeState = state.getInitialNodeState();
                    if (initialNodeState != null) {
                        loadLspData(initialNodeState, lspData, lsps, isIncrementalSynchro());
                        pccBuilder.setReportedLsp(
                            initialNodeState.augmentation(Node1.class).getPathComputationClient().getReportedLsp());
                    }
                }
                state.storeNode(topologyAugment,
                        new Node1Builder().setPathComputationClient(pccBuilder.build()).build(), psession);

                listenerState = new SessionStateImpl(this, psession);
                serverSessionManager.bind(state.getNodeId(), listenerState);
                LOG.info("Session with {} attached to topology node {}", peerAddress, state.getNodeId());
            }
        }
    }

    @Holding("this")
    private void updateStatefulCapabilities(final PathComputationClientBuilder pccBuilder,
            final InetAddress peerAddress, final @Nullable Tlvs remoteTlvs) {
        if (remoteTlvs != null) {
            final Tlvs1 statefulTlvs = remoteTlvs.augmentation(Tlvs1.class);
            if (statefulTlvs != null) {
                final Stateful stateful = statefulTlvs.getStateful();
                if (stateful != null) {
                    statefulCapability.set(true);
                    final var updateCap = stateful.getLspUpdateCapability();
                    if (updateCap != null) {
                        lspUpdateCapability.set(updateCap);
                    }
                    final Stateful1 stateful1 = stateful.augmentation(Stateful1.class);
                    if (stateful1 != null) {
                        final var initiation = stateful1.getInitiation();
                        if (initiation != null) {
                            initiationCapability.set(initiation);
                        }
                    }

                    pccBuilder.setReportedLsp(Map.of());
                    if (isSynchronized()) {
                        pccBuilder.setStateSync(PccSyncState.Synchronized);
                    } else if (isTriggeredInitialSynchro()) {
                        pccBuilder.setStateSync(PccSyncState.TriggeredInitialSync);
                    } else if (isIncrementalSynchro()) {
                        pccBuilder.setStateSync(PccSyncState.IncrementalSync);
                    } else {
                        pccBuilder.setStateSync(PccSyncState.InitialResync);
                    }
                    pccBuilder.setStatefulTlv(new StatefulTlvBuilder()
                        .addAugmentation(new StatefulTlv1Builder(statefulTlvs).build())
                        .build());
                    return;
                }
            }
        }
        LOG.debug("Peer {} does not advertise stateful TLV", peerAddress);
    }

    synchronized void updatePccState(final PccSyncState pccSyncState) {
        if (nodeState == null) {
            LOG.info("Server Session Manager is closed.");
            session.close(TerminationReason.UNKNOWN);
            return;
        }
        final MessageContext ctx = new MessageContext(nodeState.getChain().newWriteOnlyTransaction());
        updatePccNode(ctx, new PathComputationClientBuilder().setStateSync(pccSyncState).build());
        if (pccSyncState != PccSyncState.Synchronized) {
            synced.set(false);
            triggeredResyncInProcess = true;
        }
        // All set, commit the modifications
        ctx.trans.commit().addCallback(new FutureCallback<CommitInfo>() {
            @Override
            public void onSuccess(final CommitInfo result) {
                LOG.trace("Pcc Internal state for session {} updated successfully", session);
            }

            @Override
            public void onFailure(final Throwable cause) {
                LOG.error("Failed to update Pcc internal state for session {}", session, cause);
                session.close(TerminationReason.UNKNOWN);
            }
        }, MoreExecutors.directExecutor());
    }

    synchronized boolean isTriggeredSyncInProcess() {
        return triggeredResyncInProcess;
    }

    /**
     * Tear down the given PCEP session. It's OK to call this method even after the session
     * is already down. It always clear up the current session status.
     */
    @SuppressWarnings("checkstyle:IllegalCatch")
    private void tearDown(final PCEPSession psession) {
        requireNonNull(psession);
        synchronized (serverSessionManager) {
            synchronized (this) {
                serverSessionManager.releaseNodeState(nodeState, psession.getRemoteAddress(), isLspDbPersisted());
                clearNodeState();

                try {
                    if (session != null) {
                        session.close();
                    }
                    psession.close();
                } catch (final Exception e) {
                    LOG.error("Session {} cannot be closed.", psession, e);
                }
                session = null;
                listenerState = null;
                syncOptimization = null;
                clearRequests();
            }
        }
    }

    @Override
    public final void onSessionDown(final PCEPSession psession, final Exception exception) {
        LOG.warn("Session {} went down unexpectedly", psession, exception);
        tearDown(psession);
    }

    @Override
    public final void onSessionTerminated(final PCEPSession psession, final PCEPTerminationReason reason) {
        LOG.info("Session {} terminated by peer with reason {}", psession, reason);
        tearDown(psession);
    }

    @Override
    public final synchronized void onMessage(final PCEPSession psession, final Message message) {
        if (nodeState == null) {
            LOG.warn("Topology node state is null. Unhandled message {} on session {}", message, psession);
            psession.close(TerminationReason.UNKNOWN);
            return;
        }
        final MessageContext ctx = new MessageContext(nodeState.getChain().newWriteOnlyTransaction());

        if (onMessage(ctx, message)) {
            LOG.warn("Unhandled message {} on session {}", message, psession);
            //cancel not supported, submit empty transaction
            ctx.trans.commit().addCallback(new FutureCallback<CommitInfo>() {
                @Override
                public void onSuccess(final CommitInfo result) {
                    LOG.trace("Successful commit");
                }

                @Override
                public void onFailure(final Throwable trw) {
                    LOG.error("Failed commit", trw);
                }
            }, MoreExecutors.directExecutor());
            return;
        }

        ctx.trans.commit().addCallback(new FutureCallback<CommitInfo>() {
            @Override
            public void onSuccess(final CommitInfo result) {
                LOG.trace("Internal state for session {} updated successfully", psession);
                ctx.notifyRequests();

            }

            @Override
            public void onFailure(final Throwable throwable) {
                LOG.error("Failed to update internal state for session {}, closing it", psession, throwable);
                ctx.notifyRequests();
                psession.close(TerminationReason.UNKNOWN);
            }
        }, MoreExecutors.directExecutor());
    }

    /**
     * Perform revision-specific message processing when a message arrives.
     *
     * @param ctx     Message processing context
     * @param message Protocol message
     * @return True if the message type is not handle.
     */
    protected abstract boolean onMessage(MessageContext ctx, Message message);

    // Non-final for mocking
    @Override
    public void close() {
        synchronized (serverSessionManager) {
            synchronized (this) {
                clearNodeState();
                if (session != null) {
                    LOG.info("Closing session {}", session);
                    session.close(TerminationReason.UNKNOWN);
                    session = null;
                }
                listenerState = null;
                syncOptimization = null;
                clearRequests();
            }
        }
    }

    @Holding({"this.serverSessionManager", "this"})
    private void clearNodeState() {
        if (nodeState != null) {
            serverSessionManager.unbind(nodeState.getNodeId());
            LOG.debug("Clear Node state: {}", nodeState.getNodeId());
            nodeState = null;
        }
    }

    @Holding({"this.serverSessionManager", "this"})
    private void clearRequests() {
        // Clear all requests we know about
        for (final Entry<SrpIdNumber, PCEPRequest> e : requests.entrySet()) {
            // FIXME: exhaustive when we have JDK17+
            switch (e.getValue().cancel()) {
                case DONE:
                    // Done is done, nothing to do
                    LOG.trace("Request {} was done when session went down.", e.getKey());
                    break;
                case UNACKED:
                    // Peer has not acked: results in failure
                    LOG.info("Request {} was incomplete when session went down, failing the instruction",
                            e.getKey());
                    break;
                case UNSENT:
                    // Peer has not been sent to the peer: results in cancellation
                    LOG.debug("Request {} was not sent when session went down, cancelling the instruction",
                            e.getKey());
                    break;
                default:
                    break;
            }
        }
        requests.clear();
    }

    final synchronized PCEPRequest removeRequest(final SrpIdNumber id) {
        final PCEPRequest ret = requests.remove(id);
        if (ret != null && listenerState != null) {
            listenerState.processRequestStats(ret.getElapsedMillis());
        }
        LOG.trace("Removed request {} object {}", id, ret);
        return ret;
    }

    final synchronized ListenableFuture<OperationResult> sendMessage(final Message message, final SrpIdNumber requestId,
            final Metadata metadata) {
        final var sendFuture = session.sendMessage(message);
        listenerState.updateStatefulSentMsg(message);

        final short rpcTimeout = serverSessionManager.getRpcTimeout();
        LOG.trace("RPC response timeout value is {} seconds", rpcTimeout);

        final Timeout timeout;
        if (rpcTimeout > 0) {
            // Note: the timeout is held back by us holding the 'this' monitor, which timeoutExpired re-acquires
            timeout = serverSessionManager.timer().newTimeout(ignored -> timeoutExpired(requestId),
                rpcTimeout, TimeUnit.SECONDS);
            LOG.trace("Set up response timeout handler for request {}", requestId);
        } else {
            timeout = null;
        }

        final PCEPRequest req = new PCEPRequest(metadata, timeout);
        requests.put(requestId, req);

        sendFuture.addListener(future -> sendCompleted(future, requestId, req));
        return req.getFuture();
    }

    private void sendCompleted(final Future<?> future, final SrpIdNumber requestId, final PCEPRequest req) {
        if (!future.isSuccess()) {
            // FIXME: use concurrent operations and re-validate request vs. id
            synchronized (AbstractTopologySessionListener.this) {
                requests.remove(requestId);
            }
            req.cancel();
            LOG.info("Failed to send request {}, instruction cancelled", requestId, future.cause());
        } else {
            req.markUnacked();
            LOG.trace("Request {} sent to peer (object {})", requestId, req);
        }
    }

    private void timeoutExpired(final SrpIdNumber requestId) {
        final PCEPRequest req;
        synchronized (this) {
            req = requests.remove(requestId);
        }

        if (req != null) {
            LOG.info("Request {} timed-out waiting for response", requestId);
            req.cancel();
        }
    }

    /**
     * Update an LSP in the data store.
     *
     * @param ctx       Message context
     * @param id        Revision-specific LSP identifier
     * @param lspName   LSP name
     * @param rlb       Reported LSP builder
     * @param solicited True if the update was solicited
     * @param remove    True if this is an LSP path removal
     */
    protected final synchronized void updateLsp(final MessageContext ctx, final PlspId id, final String lspName,
            final ReportedLspBuilder rlb, final boolean solicited, final boolean remove) {

        final String name;
        if (lspName == null) {
            name = lsps.get(id);
            if (name == null) {
                LOG.error("PLSPID {} seen for the first time, not reporting the LSP", id);
                return;
            }
        } else {
            name = lspName;
        }

        LOG.debug("Saved LSP {} with name {}", id, name);
        lsps.put(id, name);

        final ReportedLsp previous = lspData.get(name);
        // if no previous report about the lsp exist, just proceed
        if (previous != null) {
            final Map<PathKey, Path> updatedPaths = makeBeforeBreak(rlb, previous, name, remove);
            // if all paths or the last path were deleted, delete whole tunnel
            if (updatedPaths.isEmpty()) {
                LOG.debug("All paths were removed, removing LSP with {}.", id);
                removeLsp(ctx, id);
                return;
            }
            rlb.setPath(updatedPaths);
        }
        rlb.withKey(new ReportedLspKey(name));
        rlb.setName(name);

        // If this is an unsolicited update. We need to make sure we retain the metadata already present
        if (solicited) {
            nodeState.setLspMetadata(name, rlb.getMetadata());
        } else {
            rlb.setMetadata(nodeState.getLspMetadata(name));
        }

        final ReportedLsp rl = rlb.build();
        ctx.trans.put(LogicalDatastoreType.OPERATIONAL, pccIdentifier.child(ReportedLsp.class, rlb.key()), rl);
        LOG.debug("LSP {} updated to MD-SAL", name);

        lspData.put(name, rl);
    }

    private static Map<PathKey, Path> makeBeforeBreak(final ReportedLspBuilder rlb, final ReportedLsp previous,
            final String name, final boolean remove) {
        // just one path should be reported
        final Path path = Iterables.getOnlyElement(rlb.getPath().values());
        final var reportedLspId = path.getLspId();
        final List<Path> updatedPaths;
        //lspId = 0 and remove = false -> tunnel is down, still exists but no path is signaled
        //remove existing tunnel's paths now, as explicit path remove will not come
        if (!remove && reportedLspId.getValue().toJava() == 0) {
            updatedPaths = new ArrayList<>();
            LOG.debug("Remove previous paths {} to this lsp name {}", previous.getPath(), name);
        } else {
            // check previous report for existing paths
            final Collection<Path> prev = previous.nonnullPath().values();
            updatedPaths = new ArrayList<>(prev);
            LOG.debug("Found previous paths {} to this lsp name {}", updatedPaths, name);
            for (final Path prevPath : prev) {
                //we found reported path in previous reports
                if (prevPath.getLspId().getValue().toJava() == 0 || prevPath.getLspId().equals(reportedLspId)) {
                    LOG.debug("Match on lsp-id {}", prevPath.getLspId().getValue());
                    // path that was reported previously and does have the same lsp-id, path will be updated
                    final boolean r = updatedPaths.remove(prevPath);
                    LOG.trace("Request removed? {}", r);
                }
            }
        }
        // if the path does not exist in previous report, add it to path list, it's a new ERO
        // only one path will be added
        //lspId is 0 means confirmation message that shouldn't be added (because we have no means of deleting it later)
        LOG.trace("Adding new path {} to {}", path, updatedPaths);
        updatedPaths.add(path);
        if (remove) {
            if (reportedLspId.getValue().toJava() == 0) {
                // if lsp-id also 0, remove all paths
                LOG.debug("Removing all paths.");
                updatedPaths.clear();
            } else {
                // path is marked to be removed
                LOG.debug("Removing path {} from {}", path, updatedPaths);
                final boolean r = updatedPaths.remove(path);
                LOG.trace("Request removed? {}", r);
            }
        }
        LOG.debug("Setting new paths {} to lsp {}", updatedPaths, name);
        return Maps.uniqueIndex(updatedPaths, Path::key);
    }

    /**
     * Indicate that the peer has completed state synchronization.
     *
     * @param ctx Message context
     */
    protected final synchronized void stateSynchronizationAchieved(final MessageContext ctx) {
        if (synced.getAndSet(true)) {
            LOG.debug("State synchronization achieved while synchronizing, not updating state");
            return;
        }

        triggeredResyncInProcess = false;
        updatePccNode(ctx, new PathComputationClientBuilder().setStateSync(PccSyncState.Synchronized).build());

        // The node has completed synchronization, cleanup metadata no longer reported back
        nodeState.cleanupExcept(lsps.values());
        LOG.debug("Session {} achieved synchronized state", session);
    }

    protected final synchronized void updatePccNode(final MessageContext ctx, final PathComputationClient pcc) {
        ctx.trans.merge(LogicalDatastoreType.OPERATIONAL, pccIdentifier, pcc);
    }

    protected final @NonNull InstanceIdentifier<ReportedLsp> lspIdentifier(final String name) {
        return pccIdentifier.child(ReportedLsp.class, new ReportedLspKey(name));
    }

    /**
     * Remove LSP from the database.
     *
     * @param ctx Message Context
     * @param id  Revision-specific LSP identifier
     */
    protected final synchronized void removeLsp(final MessageContext ctx, final PlspId id) {
        final String name = lsps.remove(id);
        LOG.debug("LSP {} removed", name);
        ctx.trans.delete(LogicalDatastoreType.OPERATIONAL, lspIdentifier(name));
        lspData.remove(name);
    }

    @Holding("this")
    final String lookupLspName(final PlspId id) {
        return lsps.get(requireNonNull(id, "ID parameter null."));
    }

    /**
     * Reads operational data on this node. Doesn't attempt to read the data,
     * if the node does not exist. In this case returns null.
     *
     * @param id InstanceIdentifier of the node
     * @return null if the node does not exists, or operational data
     */
    final synchronized <T extends DataObject> FluentFuture<Optional<T>> readOperationalData(
            final InstanceIdentifier<T> id) {
        return nodeState == null ? null : nodeState.readOperationalData(id);
    }

    protected abstract Object validateReportedLsp(Optional<ReportedLsp> rep, LspId input);

    protected abstract void loadLspData(Node node, Map<String, ReportedLsp> lspData, Map<PlspId, String> lsps,
            boolean incrementalSynchro);

    final boolean isLspDbPersisted() {
        return syncOptimization != null && syncOptimization.isSyncAvoidanceEnabled();
    }

    /**
     * Is Incremental synchronization if LSP-DB-VERSION are included,
     * LSP-DB-VERSION TLV values doesnt match, and  LSP-SYNC-CAPABILITY is enabled.
     */
    final synchronized boolean isIncrementalSynchro() {
        return syncOptimization != null && syncOptimization.isSyncAvoidanceEnabled()
                && syncOptimization.isDeltaSyncEnabled();
    }

    final synchronized boolean isTriggeredInitialSynchro() {
        return syncOptimization != null && syncOptimization.isTriggeredInitSyncEnabled();
    }

    final synchronized boolean isTriggeredReSyncEnabled() {
        return syncOptimization != null && syncOptimization.isTriggeredReSyncEnabled();
    }

    protected final synchronized boolean isSynchronized() {
        return syncOptimization != null && syncOptimization.doesLspDbMatch();
    }

    @Override
    public final int getDelegatedLspsCount() {
        return Math.toIntExact(lspData.values().stream()
            .map(ReportedLsp::getPath).filter(pathList -> pathList != null && !pathList.isEmpty())
            // pick the first path, as delegate status should be same in each path
            .map(pathList -> pathList.values().iterator().next())
            .map(path -> path.augmentation(Path1.class)).filter(Objects::nonNull)
            .map(LspObject::getLsp).filter(Objects::nonNull)
            .filter(Lsp::getDelegate)
            .count());
    }

    @Override
    public final boolean isSessionSynchronized() {
        return synced.get();
    }

    @Override
    public final boolean isInitiationCapability() {
        return initiationCapability.get();
    }

    @Override
    public final boolean isStatefulCapability() {
        return statefulCapability.get();
    }

    @Override
    public final boolean isLspUpdateCapability() {
        return lspUpdateCapability.get();
    }


    @Override
    public synchronized ListenableFuture<RpcResult<Void>> tearDownSession(final TearDownSessionInput input) {
        close();
        return RpcResultBuilder.<Void>success().buildFuture();
    }

    static final class MessageContext {
        private final Collection<PCEPRequest> requests = new ArrayList<>();
        private final WriteTransaction trans;

        private MessageContext(final WriteTransaction trans) {
            this.trans = requireNonNull(trans);
        }

        void resolveRequest(final PCEPRequest req) {
            requests.add(req);
        }

        private void notifyRequests() {
            for (final PCEPRequest r : requests) {
                r.finish(OperationResults.SUCCESS);
            }
        }
    }
}