/*
 * 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.protocol.bgp.rib.impl;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Objects;
import com.google.common.base.Objects.ToStringHelper;
import com.google.common.base.Preconditions;
import com.google.common.collect.Sets;
import io.netty.channel.Channel;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelFutureListener;
import java.io.IOException;
import java.util.Date;
import java.util.Set;
import java.util.concurrent.TimeUnit;
import javax.annotation.concurrent.GuardedBy;
import org.opendaylight.protocol.bgp.parser.AsNumberUtil;
import org.opendaylight.protocol.bgp.parser.BGPError;
import org.opendaylight.protocol.bgp.parser.BgpTableTypeImpl;
import org.opendaylight.protocol.bgp.rib.spi.BGPSession;
import org.opendaylight.protocol.bgp.rib.spi.BGPSessionListener;
import org.opendaylight.protocol.bgp.rib.spi.BGPTerminationReason;
import org.opendaylight.protocol.framework.AbstractProtocolSession;
import org.opendaylight.yang.gen.v1.urn.ietf.params.xml.ns.yang.ietf.inet.types.rev100924.AsNumber;
import org.opendaylight.yang.gen.v1.urn.ietf.params.xml.ns.yang.ietf.inet.types.rev100924.Ipv4Address;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.message.rev130919.Keepalive;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.message.rev130919.KeepaliveBuilder;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.message.rev130919.Notify;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.message.rev130919.NotifyBuilder;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.message.rev130919.Open;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.message.rev130919.Update;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.message.rev130919.open.BgpParameters;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.message.rev130919.open.bgp.parameters.CParameters;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.multiprotocol.rev130919.BgpTableType;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.multiprotocol.rev130919.open.bgp.parameters.c.parameters.MultiprotocolCase;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.rib.rev130925.rib.TablesKey;
import org.opendaylight.yangtools.yang.binding.Notification;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

@VisibleForTesting
public class BGPSessionImpl extends AbstractProtocolSession<Notification> implements BGPSession {

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

    private static final Notification KEEP_ALIVE = new KeepaliveBuilder().build();

    /**
     * Internal session state.
     */
    public enum State {
        /**
         * The session object is created by the negotiator in OpenConfirm state. While in this state, the session object
         * is half-alive, e.g. the timers are running, but the session is not completely up, e.g. it has not been
         * announced to the listener. If the session is torn down in this state, we do not inform the listener.
         */
        OpenConfirm,
        /**
         * The session has been completely established.
         */
        Up,
        /**
         * The session has been closed. It will not be resurrected.
         */
        Idle,
    }

    /**
     * System.nanoTime value about when was sent the last message.
     */
    @VisibleForTesting
    private long lastMessageSentAt;

    /**
     * System.nanoTime value about when was received the last message
     */
    private long lastMessageReceivedAt;

    private final BGPSessionListener listener;

    private final BGPSynchronization sync;

    private int kaCounter = 0;

    private final Channel channel;

    @GuardedBy("this")
    private State state = State.OpenConfirm;

    private final Set<BgpTableType> tableTypes;
    private final int holdTimerValue;
    private final int keepAlive;
    private final AsNumber asNumber;
    private final Ipv4Address bgpId;

    public BGPSessionImpl(final BGPSessionListener listener, final Channel channel, final Open remoteOpen, final int localHoldTimer) {
        this.listener = Preconditions.checkNotNull(listener);
        this.channel = Preconditions.checkNotNull(channel);
        this.holdTimerValue = (remoteOpen.getHoldTimer() < localHoldTimer) ? remoteOpen.getHoldTimer() : localHoldTimer;
        LOG.info("BGP HoldTimer new value: {}", this.holdTimerValue);
        this.keepAlive = this.holdTimerValue / 3;
        this.asNumber = AsNumberUtil.advertizedAsNumber(remoteOpen);

        final Set<TablesKey> tts = Sets.newHashSet();
        final Set<BgpTableType> tats = Sets.newHashSet();
        if (remoteOpen.getBgpParameters() != null) {
            for (final BgpParameters param : remoteOpen.getBgpParameters()) {
                final CParameters cp = param.getCParameters();
                if (cp instanceof MultiprotocolCase) {
                    final TablesKey tt = new TablesKey(((MultiprotocolCase) cp).getMultiprotocolCapability().getAfi(), ((MultiprotocolCase) cp).getMultiprotocolCapability().getSafi());
                    LOG.trace("Added table type to sync {}", tt);
                    tts.add(tt);
                    tats.add(new BgpTableTypeImpl(tt.getAfi(), tt.getSafi()));
                }
            }
        }

        this.sync = new BGPSynchronization(this, this.listener, tts);
        this.tableTypes = tats;

        if (this.holdTimerValue != 0) {
            channel.eventLoop().schedule(new Runnable() {
                @Override
                public void run() {
                    handleHoldTimer();
                }
            }, this.holdTimerValue, TimeUnit.SECONDS);

            channel.eventLoop().schedule(new Runnable() {
                @Override
                public void run() {
                    handleKeepaliveTimer();
                }
            }, this.keepAlive, TimeUnit.SECONDS);
        }
        this.bgpId = remoteOpen.getBgpIdentifier();
    }

    @Override
    public synchronized void close() {
        LOG.info("Closing session: {}", this);
        if (this.state != State.Idle) {
            this.sendMessage(new NotifyBuilder().setErrorCode(BGPError.CEASE.getCode()).setErrorSubcode((short)0).build());
            this.channel.close();
            this.state = State.Idle;
        }
    }

    /**
     * Handles incoming message based on their type.
     *
     * @param msg incoming message
     */
    @Override
    public synchronized void handleMessage(final Notification msg) {
        // Update last reception time
        this.lastMessageReceivedAt = System.nanoTime();

        if (msg instanceof Open) {
            // Open messages should not be present here
            this.terminate(BGPError.FSM_ERROR);
        } else if (msg instanceof Notify) {
            // Notifications are handled internally
            LOG.info("Session closed because Notification message received: {} / {}", ((Notify) msg).getErrorCode(),
                ((Notify) msg).getErrorSubcode());
            this.closeWithoutMessage();
            this.listener.onSessionTerminated(this, new BGPTerminationReason(BGPError.forValue(((Notify) msg).getErrorCode(),
                ((Notify) msg).getErrorSubcode())));
        } else if (msg instanceof Keepalive) {
            // Keepalives are handled internally
            LOG.trace("Received KeepAlive messsage.");
            this.kaCounter++;
            if (this.kaCounter >= 2) {
                this.sync.kaReceived();
            }
        } else {
            // All others are passed up
            this.listener.onMessage(this, msg);
            this.sync.updReceived((Update) msg);
        }
    }

    @Override
    public synchronized void endOfInput() {
        if (this.state == State.Up) {
            this.listener.onSessionDown(this, new IOException("End of input detected. Close the session."));
        }
    }

    synchronized void sendMessage(final Notification msg) {
        try {
            this.channel.writeAndFlush(msg).addListener(
                new ChannelFutureListener() {
                    @Override
                    public void operationComplete(final ChannelFuture f) {
                        if (!f.isSuccess()) {
                            LOG.info("Failed to send message {} to socket {}", msg, f.cause(), BGPSessionImpl.this.channel);
                        } else {
                            LOG.trace("Message {} sent to socket {}", msg, BGPSessionImpl.this.channel);
                        }
                    }
                });
            this.lastMessageSentAt = System.nanoTime();
        } catch (final Exception e) {
            LOG.warn("Message {} was not sent.", msg, e);
        }
    }

    private synchronized void closeWithoutMessage() {
        LOG.debug("Closing session: {}", this);
        this.channel.close();
        this.state = State.Idle;
    }

    /**
     * Closes PCEP session from the parent with given reason. A message needs to be sent, but parent doesn't have to be
     * modified, because he initiated the closing. (To prevent concurrent modification exception).
     *
     * @param closeObject
     */
    private void terminate(final BGPError error) {
        this.sendMessage(new NotifyBuilder().setErrorCode(error.getCode()).setErrorSubcode(error.getSubcode()).build());
        this.closeWithoutMessage();

        this.listener.onSessionTerminated(this, new BGPTerminationReason(error));
    }

    /**
     * If HoldTimer expires, the session ends. If a message (whichever) was received during this period, the HoldTimer
     * will be rescheduled by HOLD_TIMER_VALUE + the time that has passed from the start of the HoldTimer to the time at
     * which the message was received. If the session was closed by the time this method starts to execute (the session
     * state will become IDLE), then rescheduling won't occur.
     */
    private synchronized void handleHoldTimer() {
        if (this.state == State.Idle) {
            return;
        }

        final long ct = System.nanoTime();
        final long nextHold = this.lastMessageReceivedAt + TimeUnit.SECONDS.toNanos(this.holdTimerValue);

        if (ct >= nextHold) {
            LOG.debug("HoldTimer expired. {}", new Date());
            this.terminate(BGPError.HOLD_TIMER_EXPIRED);
        } else {
            this.channel.eventLoop().schedule(new Runnable() {
                @Override
                public void run() {
                    handleHoldTimer();
                }
            }, nextHold - ct, TimeUnit.NANOSECONDS);
        }
    }

    /**
     * If KeepAlive Timer expires, sends KeepAlive message. If a message (whichever) was send during this period, the
     * KeepAlive Timer will be rescheduled by KEEP_ALIVE_TIMER_VALUE + the time that has passed from the start of the
     * KeepAlive timer to the time at which the message was sent. If the session was closed by the time this method
     * starts to execute (the session state will become IDLE), that rescheduling won't occur.
     */
    private synchronized void handleKeepaliveTimer() {
        if (this.state == State.Idle) {
            return;
        }

        final long ct = System.nanoTime();
        long nextKeepalive = this.lastMessageSentAt + TimeUnit.SECONDS.toNanos(this.keepAlive);

        if (ct >= nextKeepalive) {
            this.sendMessage(KEEP_ALIVE);
            nextKeepalive = this.lastMessageSentAt + TimeUnit.SECONDS.toNanos(this.keepAlive);
        }
        this.channel.eventLoop().schedule(new Runnable() {
            @Override
            public void run() {
                handleKeepaliveTimer();
            }
        }, nextKeepalive - ct, TimeUnit.NANOSECONDS);
    }

    @Override
    public final String toString() {
        return addToStringAttributes(Objects.toStringHelper(this)).toString();
    }

    protected ToStringHelper addToStringAttributes(final ToStringHelper toStringHelper) {
        toStringHelper.add("channel", this.channel);
        toStringHelper.add("state", this.getState());
        return toStringHelper;
    }

    @Override
    public Set<BgpTableType> getAdvertisedTableTypes() {
        return this.tableTypes;
    }

    @Override
    protected synchronized void sessionUp() {
        this.state = State.Up;
        this.listener.onSessionUp(this);
    }

    public synchronized State getState() {
        return this.state;
    }

    @Override
    public final Ipv4Address getBgpId() {
        return this.bgpId;
    }

    @Override
    public final AsNumber getAsNumber() {
        return this.asNumber;
    }

    synchronized boolean isWritable() {
        return this.channel != null && this.channel.isWritable();
    }

    synchronized void schedule(final Runnable task) {
        Preconditions.checkState(this.channel != null);
        this.channel.eventLoop().submit(task);

    }

    @VisibleForTesting
    protected synchronized void setLastMessageSentAt(final long lastMessageSentAt) {
        this.lastMessageSentAt = lastMessageSentAt;
    }
}