/*
 * 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 io.netty.channel.Channel;
import io.netty.util.Timeout;
import io.netty.util.Timer;
import io.netty.util.TimerTask;
import io.netty.util.concurrent.Promise;

import java.util.List;
import java.util.concurrent.TimeUnit;

import javax.annotation.concurrent.GuardedBy;

import org.opendaylight.protocol.bgp.parser.AsNumberUtil;
import org.opendaylight.protocol.bgp.parser.BGPDocumentedException;
import org.opendaylight.protocol.bgp.parser.BGPError;
import org.opendaylight.protocol.bgp.parser.BGPSessionListener;
import org.opendaylight.protocol.bgp.rib.impl.spi.BGPSessionPreferences;
import org.opendaylight.protocol.framework.AbstractSessionNegotiator;
import org.opendaylight.protocol.util.Values;
import org.opendaylight.yang.gen.v1.urn.ietf.params.xml.ns.yang.ietf.inet.types.rev100924.AsNumber;
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.OpenBuilder;
import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.message.rev130919.open.BgpParameters;
import org.opendaylight.yangtools.yang.binding.Notification;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Preconditions;

public final class BGPSessionNegotiator extends AbstractSessionNegotiator<Notification, BGPSessionImpl> {
	// 4 minutes recommended in http://tools.ietf.org/html/rfc4271#section-8.2.2
	protected static final int INITIAL_HOLDTIMER = 4;

	/**
	 * @see <a href="http://tools.ietf.org/html/rfc6793">BGP Support for 4-Octet AS Number Space</a>
	 */
	private static final int AS_TRANS = 23456;

	@VisibleForTesting
	public enum State {
		/**
		 * Negotiation has not started yet.
		 */
		Idle,
		/**
		 * We have sent our Open message, and are waiting for the peer's Open message.
		 */
		OpenSent,
		/**
		 * We have received the peer's Open message, which is acceptable, and we're waiting the acknowledgement of our
		 * Open message.
		 */
		OpenConfirm,
		/**
		 * The negotiation finished.
		 */
		Finished,
	}

	private static final Logger LOG = LoggerFactory.getLogger(BGPSessionNegotiator.class);
	private final BGPSessionPreferences localPref;
	private final BGPSessionListener listener;
	private final AsNumber remoteAs;
	private final Timer timer;

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

	@GuardedBy("this")
	private BGPSessionImpl session;

	public BGPSessionNegotiator(final Timer timer, final Promise<BGPSessionImpl> promise, final Channel channel,
			final BGPSessionPreferences initialPrefs, final AsNumber remoteAs, final BGPSessionListener listener) {
		super(promise, channel);
		this.listener = Preconditions.checkNotNull(listener);
		this.localPref = Preconditions.checkNotNull(initialPrefs);
		this.remoteAs = Preconditions.checkNotNull(remoteAs);
		this.timer = Preconditions.checkNotNull(timer);
	}

	@Override
	protected void startNegotiation() {
		Preconditions.checkState(this.state == State.Idle);
		int as = this.localPref.getMyAs().getValue().intValue();
		// Set as AS_TRANS if the value is bigger than 2B
		if (as > Values.UNSIGNED_SHORT_MAX_VALUE) {
			as = AS_TRANS;
		}
		this.sendMessage(new OpenBuilder().setMyAsNumber(as).setHoldTimer(
				this.localPref.getHoldTime()).setBgpIdentifier(this.localPref.getBgpId()).setBgpParameters(this.localPref.getParams()).build());
		this.state = State.OpenSent;

		final Object lock = this;
		this.timer.newTimeout(new TimerTask() {
			@Override
			public void run(final Timeout timeout) {
				synchronized (lock) {
					if (BGPSessionNegotiator.this.state != State.Finished) {
						BGPSessionNegotiator.this.sendMessage(buildErrorNotify(BGPError.HOLD_TIMER_EXPIRED));
						negotiationFailed(new BGPDocumentedException("HoldTimer expired", BGPError.FSM_ERROR));
						BGPSessionNegotiator.this.state = State.Finished;
					}
				}
			}
		}, INITIAL_HOLDTIMER, TimeUnit.MINUTES);
	}

	@Override
	protected synchronized void handleMessage(final Notification msg) {
		LOG.debug("Channel {} handling message in state {}", this.channel, this.state);

		switch (this.state) {
		case Finished:
		case Idle:
			this.sendMessage(buildErrorNotify(BGPError.FSM_ERROR));
			return;
		case OpenConfirm:
			if (msg instanceof Keepalive) {
				negotiationSuccessful(this.session);
				LOG.info("BGP Session with peer {} established successfully.", this.channel);
			} else if (msg instanceof Notify) {
				final Notify ntf = (Notify) msg;
				negotiationFailed(new BGPDocumentedException("Peer refusal", BGPError.forValue(ntf.getErrorCode(), ntf.getErrorSubcode())));
			}
			this.state = State.Finished;
			return;
		case OpenSent:
			if (msg instanceof Open) {
				final Open openObj = (Open) msg;
				handleOpen(openObj);
				return;
			}
			break;
		}

		// Catch-all for unexpected message
		LOG.warn("Channel {} state {} unexpected message {}", this.channel, this.state, msg);
		this.sendMessage(buildErrorNotify(BGPError.FSM_ERROR));
		negotiationFailed(new BGPDocumentedException("Unexpected message", BGPError.FSM_ERROR));
		this.state = State.Finished;
	}

	private static Notify buildErrorNotify(final BGPError err) {
		return new NotifyBuilder().setErrorCode(err.getCode()).setErrorSubcode(err.getSubcode()).build();
	}

	private void handleOpen(final Open openObj) {
		final AsNumber as = AsNumberUtil.advertizedAsNumber(openObj);
		if (!this.remoteAs.equals(as)) {
			LOG.warn("Unexpected remote AS number. Expecting {}, got {}", this.remoteAs, as);
			this.sendMessage(buildErrorNotify(BGPError.BAD_PEER_AS));
			negotiationFailed(new BGPDocumentedException("Peer AS number mismatch", BGPError.BAD_PEER_AS));
			this.state = State.Finished;
			return;
		}

		final List<BgpParameters> prefs = openObj.getBgpParameters();
		if (prefs != null && !prefs.isEmpty()) {
			if (!prefs.containsAll(this.localPref.getParams())) {
				LOG.info("BGP Open message session parameters differ, session still accepted.");
			}
			this.sendMessage(new KeepaliveBuilder().build());
			this.session = new BGPSessionImpl(this.timer, this.listener, this.channel, openObj, this.localPref.getHoldTime());
			this.state = State.OpenConfirm;
			LOG.debug("Channel {} moved to OpenConfirm state with remote proposal {}", this.channel, openObj);
			return;
		}

		this.sendMessage(buildErrorNotify(BGPError.UNSPECIFIC_OPEN_ERROR));
		negotiationFailed(new BGPDocumentedException("Open message unacceptable. Check the configuration of BGP speaker.", BGPError.UNSPECIFIC_OPEN_ERROR));
		this.state = State.Finished;
	}

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