/*
 * 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.client.mdsal;

import com.google.common.base.Strings;
import com.google.common.collect.ImmutableMap;
import com.google.common.util.concurrent.Futures;
import com.google.common.util.concurrent.ListenableFuture;
import java.io.EOFException;
import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.Queue;
import java.util.concurrent.Semaphore;
import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
import org.eclipse.jdt.annotation.Nullable;
import org.opendaylight.netconf.api.DocumentedException;
import org.opendaylight.netconf.api.NetconfMessage;
import org.opendaylight.netconf.api.NetconfTerminationReason;
import org.opendaylight.netconf.api.xml.XmlElement;
import org.opendaylight.netconf.api.xml.XmlNetconfConstants;
import org.opendaylight.netconf.api.xml.XmlUtil;
import org.opendaylight.netconf.client.NetconfClientSession;
import org.opendaylight.netconf.client.NetconfClientSessionListener;
import org.opendaylight.netconf.client.NetconfMessageUtil;
import org.opendaylight.netconf.client.mdsal.api.NetconfSessionPreferences;
import org.opendaylight.netconf.client.mdsal.api.RemoteDevice;
import org.opendaylight.netconf.client.mdsal.api.RemoteDeviceCommunicator;
import org.opendaylight.netconf.client.mdsal.api.RemoteDeviceId;
import org.opendaylight.yangtools.yang.common.ErrorSeverity;
import org.opendaylight.yangtools.yang.common.ErrorTag;
import org.opendaylight.yangtools.yang.common.ErrorType;
import org.opendaylight.yangtools.yang.common.QName;
import org.opendaylight.yangtools.yang.common.RpcError;
import org.opendaylight.yangtools.yang.common.RpcResult;
import org.opendaylight.yangtools.yang.common.RpcResultBuilder;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class NetconfDeviceCommunicator implements NetconfClientSessionListener, RemoteDeviceCommunicator {
    private static final Logger LOG = LoggerFactory.getLogger(NetconfDeviceCommunicator.class);

    protected final RemoteDevice<NetconfDeviceCommunicator> remoteDevice;
    private final @Nullable UserPreferences overrideNetconfCapabilities;
    protected final RemoteDeviceId id;
    private final Lock sessionLock = new ReentrantLock();

    private final Semaphore semaphore;
    private final int concurentRpcMsgs;

    private final Queue<Request> requests = new ArrayDeque<>();
    private NetconfClientSession currentSession;

    // isSessionClosing indicates a close operation on the session is issued and
    // tearDown will surely be called later to finish the close.
    // Used to allow only one thread to enter tearDown and other threads should
    // NOT enter it simultaneously and should end its close operation without
    // calling tearDown to release the locks they hold to avoid deadlock.
    private static final AtomicIntegerFieldUpdater<NetconfDeviceCommunicator> CLOSING_UPDATER =
            AtomicIntegerFieldUpdater.newUpdater(NetconfDeviceCommunicator.class, "closing");
    private volatile int closing;

    public boolean isSessionClosing() {
        return closing != 0;
    }

    public NetconfDeviceCommunicator(final RemoteDeviceId id,
            final RemoteDevice<NetconfDeviceCommunicator> remoteDevice, final int rpcMessageLimit) {
        this(id, remoteDevice, rpcMessageLimit, null);
    }

    public NetconfDeviceCommunicator(final RemoteDeviceId id,
            final RemoteDevice<NetconfDeviceCommunicator> remoteDevice, final int rpcMessageLimit,
            final @Nullable UserPreferences overrideNetconfCapabilities) {
        concurentRpcMsgs = rpcMessageLimit;
        this.id = id;
        this.remoteDevice = remoteDevice;
        this.overrideNetconfCapabilities = overrideNetconfCapabilities;
        semaphore = rpcMessageLimit > 0 ? new Semaphore(rpcMessageLimit) : null;
    }

    @Override
    public void onSessionUp(final NetconfClientSession session) {
        sessionLock.lock();
        try {
            LOG.debug("{}: Session established", id);
            currentSession = session;

            var netconfSessionPreferences = NetconfSessionPreferences.fromNetconfSession(session);
            LOG.trace("{}: Session advertised capabilities: {}", id, netconfSessionPreferences);

            final var localOverride = overrideNetconfCapabilities;
            if (localOverride != null) {
                final var sessionPreferences = localOverride.sessionPreferences();
                netconfSessionPreferences = localOverride.overrideModuleCapabilities()
                        ? netconfSessionPreferences.replaceModuleCaps(sessionPreferences)
                        : netconfSessionPreferences.addModuleCaps(sessionPreferences);

                netconfSessionPreferences = localOverride.overrideNonModuleCapabilities()
                        ? netconfSessionPreferences.replaceNonModuleCaps(sessionPreferences)
                        : netconfSessionPreferences.addNonModuleCaps(sessionPreferences);
                LOG.debug("{}: Session capabilities overridden, capabilities that will be used: {}", id,
                        netconfSessionPreferences);
            }

            remoteDevice.onRemoteSessionUp(netconfSessionPreferences, this);
        } finally {
            sessionLock.unlock();
        }
    }

    public void disconnect() {
        // If session is already in closing, no need to close it again
        if (currentSession != null && startClosing() && currentSession.isUp()) {
            currentSession.close();
        }
    }

    private void tearDown(final String reason) {
        if (!isSessionClosing()) {
            LOG.warn("It's curious that no one to close the session but tearDown is called!");
        }
        LOG.debug("Tearing down {}", reason);
        final List<UncancellableFuture<RpcResult<NetconfMessage>>> futuresToCancel = new ArrayList<>();
        sessionLock.lock();
        try {
            if (currentSession != null) {
                currentSession = null;
                /*
                 * Walk all requests, check if they have been executing
                 * or cancelled and remove them from the queue.
                 */
                final Iterator<Request> it = requests.iterator();
                while (it.hasNext()) {
                    final Request r = it.next();
                    if (r.future.isUncancellable()) {
                        futuresToCancel.add(r.future);
                        it.remove();
                    } else if (r.future.isCancelled()) {
                        // This just does some house-cleaning
                        it.remove();
                    }
                }

                remoteDevice.onRemoteSessionDown();
            }
        } finally {
            sessionLock.unlock();
        }

        // Notify pending request futures outside of the sessionLock to avoid unnecessarily
        // blocking the caller.
        for (final UncancellableFuture<RpcResult<NetconfMessage>> future : futuresToCancel) {
            if (Strings.isNullOrEmpty(reason)) {
                future.set(createSessionDownRpcResult());
            } else {
                future.set(createErrorRpcResult(ErrorType.TRANSPORT, reason));
            }
        }

        closing = 0;
    }

    private RpcResult<NetconfMessage> createSessionDownRpcResult() {
        return createErrorRpcResult(ErrorType.TRANSPORT,
                String.format("The netconf session to %1$s is disconnected", id.name()));
    }

    private static RpcResult<NetconfMessage> createErrorRpcResult(final ErrorType errorType, final String message) {
        return RpcResultBuilder.<NetconfMessage>failed()
            .withError(errorType, ErrorTag.OPERATION_FAILED, message).build();
    }

    @Override
    public void onSessionDown(final NetconfClientSession session, final Exception exception) {
        // If session is already in closing, no need to call tearDown again.
        if (startClosing()) {
            if (exception instanceof EOFException) {
                LOG.info("{}: Session went down: {}", id, exception.getMessage());
            } else {
                LOG.warn("{}: Session went down", id, exception);
            }
            tearDown(null);
        }
    }

    @Override
    public void onSessionTerminated(final NetconfClientSession session, final NetconfTerminationReason reason) {
        // onSessionTerminated is called directly by disconnect, no need to compare and set isSessionClosing.
        LOG.warn("{}: Session terminated {}", id, reason);
        tearDown(reason.getErrorMessage());
    }

    @Override
    public void close() {
        // Disconnect from device
        // tear down not necessary, called indirectly by the close in disconnect()
        disconnect();
    }

    @Override
    public void onMessage(final NetconfClientSession session, final NetconfMessage message) {
        /*
         * Dispatch between notifications and messages. Messages need to be processed
         * with lock held, notifications do not.
         */
        if (isNotification(message)) {
            processNotification(message);
        } else {
            processMessage(message);
        }
    }

    @Override
    public void onError(final NetconfClientSession session, final Exception failure) {
        final Request request = pollRequest();
        if (request != null) {
            request.future.set(RpcResultBuilder.<NetconfMessage>failed()
                .withRpcError(toRpcError(new DocumentedException(failure.getMessage(),
                    ErrorType.APPLICATION, ErrorTag.MALFORMED_MESSAGE, ErrorSeverity.ERROR)))
                .build());
        } else {
            LOG.warn("{}: Ignoring unsolicited failure {}", id, failure.toString());
        }
    }

    private @Nullable Request pollRequest() {
        Request request;
        sessionLock.lock();

        try {
            request = requests.peek();
            if (request != null && request.future.isUncancellable()) {
                request = requests.poll();
                // we have just removed one request from the queue
                // we can also release one permit
                if (semaphore != null) {
                    semaphore.release();
                }
            } else {
                request = null;
            }
        } finally {
            sessionLock.unlock();
        }
        return request;
    }

    private void processMessage(final NetconfMessage message) {
        final Request request = pollRequest();
        if (request == null) {
            // No matching request, bail out
            LOG.warn("{}: Ignoring unsolicited message {}", id, msgToS(message));
            return;
        }

        LOG.debug("{}: Message received {}", id, message);

        if (LOG.isTraceEnabled()) {
            LOG.trace("{}: Matched request: {} to response: {}", id, msgToS(request.request), msgToS(message));
        }

        final String inputMsgId = request.request.getDocument().getDocumentElement()
            .getAttribute(XmlNetconfConstants.MESSAGE_ID);
        final String outputMsgId = message.getDocument().getDocumentElement()
            .getAttribute(XmlNetconfConstants.MESSAGE_ID);
        if (!inputMsgId.equals(outputMsgId)) {
            // FIXME: we should be able to transform directly to RpcError without an intermediate exception
            final var ex = new DocumentedException("Response message contained unknown \"message-id\"", null,
                ErrorType.PROTOCOL, ErrorTag.BAD_ATTRIBUTE, ErrorSeverity.ERROR,
                ImmutableMap.of("actual-message-id", outputMsgId, "expected-message-id", inputMsgId));
            LOG.warn("{}: Invalid request-reply match, reply message contains different message-id, "
                + "request: {}, response: {}", id, msgToS(request.request), msgToS(message));

            request.future.set(RpcResultBuilder.<NetconfMessage>failed().withRpcError(toRpcError(ex)).build());

            // recursively processing message to eventually find matching request
            processMessage(message);
            return;
        }

        if (NetconfMessageUtil.isErrorMessage(message)) {
            // FIXME: we should be able to transform directly to RpcError without an intermediate exception
            final var ex = DocumentedException.fromXMLDocument(message.getDocument());
            LOG.warn("{}: Error reply from remote device, request: {}, response: {}",
                id, msgToS(request.request), msgToS(message));
            request.future.set(RpcResultBuilder.<NetconfMessage>failed().withRpcError(toRpcError(ex)).build());
            return;
        }

        request.future.set(RpcResultBuilder.success(message).build());
    }

    private static String msgToS(final NetconfMessage msg) {
        return XmlUtil.toString(msg.getDocument());
    }

    private static RpcError toRpcError(final DocumentedException ex) {
        final var errorInfo = ex.getErrorInfo();
        final String infoString;
        if (errorInfo != null) {
            final var sb = new StringBuilder();
            for (var e : errorInfo.entrySet()) {
                final var tag = e.getKey();
                sb.append('<').append(tag).append('>').append(e.getValue()).append("</").append(tag).append('>');
            }
            infoString = sb.toString();
        } else {
            infoString = "";
        }

        return ex.getErrorSeverity() == ErrorSeverity.ERROR
            ? RpcResultBuilder.newError(ex.getErrorType(), ex.getErrorTag(), ex.getLocalizedMessage(), null,
                infoString, ex.getCause())
            : RpcResultBuilder.newWarning(ex.getErrorType(), ex.getErrorTag(), ex.getLocalizedMessage(), null,
                infoString, ex.getCause());
    }

    @Override
    public ListenableFuture<RpcResult<NetconfMessage>> sendRequest(final NetconfMessage message, final QName rpc) {
        sessionLock.lock();
        try {
            if (semaphore != null && !semaphore.tryAcquire()) {
                LOG.warn("Limit of concurrent rpc messages was reached (limit: {}). Rpc reply message is needed. "
                    + "Discarding request of Netconf device with id: {}", concurentRpcMsgs, id.name());
                return Futures.immediateFailedFuture(new DocumentedException(
                        "Limit of rpc messages was reached (Limit :" + concurentRpcMsgs
                        + ") waiting for emptying the queue of Netconf device with id: " + id.name()));
            }

            return sendRequestWithLock(message, rpc);
        } finally {
            sessionLock.unlock();
        }
    }

    private ListenableFuture<RpcResult<NetconfMessage>> sendRequestWithLock(final NetconfMessage message,
                                                                            final QName rpc) {
        if (LOG.isTraceEnabled()) {
            LOG.trace("{}: Sending message {}", id, msgToS(message));
        }

        if (currentSession == null) {
            LOG.warn("{}: Session is disconnected, failing RPC request {}",
                    id, message);
            return Futures.immediateFuture(createSessionDownRpcResult());
        }

        final Request req = new Request(new UncancellableFuture<>(true), message);
        requests.add(req);

        currentSession.sendMessage(req.request).addListener(future -> {
            if (!future.isSuccess()) {
                // We expect that a session down will occur at this point
                LOG.debug("{}: Failed to send request {}", id,
                        XmlUtil.toString(req.request.getDocument()),
                        future.cause());

                if (future.cause() != null) {
                    req.future.set(createErrorRpcResult(ErrorType.TRANSPORT, future.cause().getLocalizedMessage()));
                } else {
                    req.future.set(createSessionDownRpcResult()); // assume session is down
                }
                req.future.setException(future.cause());
            } else {
                LOG.trace("Finished sending request {}", req.request);
            }
        });

        return req.future;
    }

    private void processNotification(final NetconfMessage notification) {
        if (LOG.isTraceEnabled()) {
            LOG.trace("{}: Notification received: {}", id, notification);
        }

        remoteDevice.onNotification(notification);
    }

    private static boolean isNotification(final NetconfMessage message) {
        if (message.getDocument() == null) {
            // We have no message, which mean we have a FailedNetconfMessage
            return false;
        }
        final XmlElement xmle = XmlElement.fromDomDocument(message.getDocument());
        return XmlNetconfConstants.NOTIFICATION_ELEMENT_NAME.equals(xmle.getName()) ;
    }

    private static final class Request {
        final UncancellableFuture<RpcResult<NetconfMessage>> future;
        final NetconfMessage request;

        private Request(final UncancellableFuture<RpcResult<NetconfMessage>> future,
                        final NetconfMessage request) {
            this.future = future;
            this.request = request;
        }
    }

    private boolean startClosing() {
        return CLOSING_UPDATER.compareAndSet(this, 0, 1);
    }
}