/*
 * 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.nettyutil.handler.ssh.client;

import com.google.common.base.Preconditions;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelOutboundHandlerAdapter;
import io.netty.channel.ChannelPromise;
import io.netty.util.concurrent.Future;
import io.netty.util.concurrent.GenericFutureListener;
import java.io.IOException;
import java.net.SocketAddress;
import org.apache.sshd.client.SshClient;
import org.apache.sshd.client.channel.ClientChannel;
import org.apache.sshd.client.future.AuthFuture;
import org.apache.sshd.client.future.ConnectFuture;
import org.apache.sshd.client.session.ClientSession;
import org.opendaylight.netconf.nettyutil.handler.ssh.authentication.AuthenticationHandler;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Netty SSH handler class. Acts as interface between Netty and SSH library.
 */
public class AsyncSshHandler extends ChannelOutboundHandlerAdapter {
    private static final Logger LOG = LoggerFactory.getLogger(AsyncSshHandler.class);

    public static final String SUBSYSTEM = "netconf";

    public static final int SSH_DEFAULT_NIO_WORKERS = 8;
    // Disable default timeouts from mina sshd
    private static final long DEFAULT_TIMEOUT = -1L;

    public static final SshClient DEFAULT_CLIENT;

    static {
        final SshClient c = SshClient.setUpDefaultClient();
        c.getProperties().put(SshClient.AUTH_TIMEOUT, Long.toString(DEFAULT_TIMEOUT));
        c.getProperties().put(SshClient.IDLE_TIMEOUT, Long.toString(DEFAULT_TIMEOUT));

        // TODO make configurable, or somehow reuse netty threadpool
        c.setNioWorkers(SSH_DEFAULT_NIO_WORKERS);
        c.start();
        DEFAULT_CLIENT = c;
    }

    private final AuthenticationHandler authenticationHandler;
    private final SshClient sshClient;
    private Future<?> negotiationFuture;

    private AsyncSshHandlerReader sshReadAsyncListener;
    private AsyncSshHandlerWriter sshWriteAsyncHandler;

    private ClientChannel channel;
    private ClientSession session;
    private ChannelPromise connectPromise;
    private GenericFutureListener negotiationFutureListener;

    public AsyncSshHandler(final AuthenticationHandler authenticationHandler, final SshClient sshClient,
            final Future<?> negotiationFuture) {
        this(authenticationHandler, sshClient);
        this.negotiationFuture = negotiationFuture;
    }

    /**
     * Constructor of {@code AsyncSshHandler}.
     *
     * @param authenticationHandler authentication handler
     * @param sshClient             started SshClient
     */
    public AsyncSshHandler(final AuthenticationHandler authenticationHandler,
                           final SshClient sshClient) {
        this.authenticationHandler = Preconditions.checkNotNull(authenticationHandler);
        this.sshClient = Preconditions.checkNotNull(sshClient);
    }

    public static AsyncSshHandler createForNetconfSubsystem(final AuthenticationHandler authenticationHandler) {
        return new AsyncSshHandler(authenticationHandler, DEFAULT_CLIENT);
    }

    /**
     * Create AsyncSshHandler for netconf subsystem. Negotiation future has to be set to success after successful
     * netconf negotiation.
     *
     * @param authenticationHandler authentication handler
     * @param negotiationFuture     negotiation future
     * @return                      {@code AsyncSshHandler}
     */
    public static AsyncSshHandler createForNetconfSubsystem(final AuthenticationHandler authenticationHandler,
            final Future<?> negotiationFuture) {
        return new AsyncSshHandler(authenticationHandler, DEFAULT_CLIENT, negotiationFuture);
    }

    private void startSsh(final ChannelHandlerContext ctx, final SocketAddress address) throws IOException {
        LOG.debug("Starting SSH to {} on channel: {}", address, ctx.channel());

        final ConnectFuture sshConnectionFuture = sshClient.connect(authenticationHandler.getUsername(), address);
        sshConnectionFuture.addListener(future -> {
            if (future.isConnected()) {
                handleSshSessionCreated(future, ctx);
            } else {
                handleSshSetupFailure(ctx, future.getException());
            }
        });
    }

    private synchronized void handleSshSessionCreated(final ConnectFuture future, final ChannelHandlerContext ctx) {
        try {
            LOG.trace("SSH session created on channel: {}", ctx.channel());

            session = future.getSession();
            final AuthFuture authenticateFuture = authenticationHandler.authenticate(session);
            final ClientSession localSession = session;
            authenticateFuture.addListener(future1 -> {
                if (future1.isSuccess()) {
                    handleSshAuthenticated(localSession, ctx);
                } else {
                    // Exception does not have to be set in the future, add simple exception in such case
                    final Throwable exception = future1.getException() == null
                            ? new IllegalStateException("Authentication failed") : future1.getException();
                    handleSshSetupFailure(ctx, exception);
                }
            });
        } catch (final IOException e) {
            handleSshSetupFailure(ctx, e);
        }
    }

    private synchronized void handleSshAuthenticated(final ClientSession newSession, final ChannelHandlerContext ctx) {
        try {
            LOG.debug("SSH session authenticated on channel: {}, server version: {}", ctx.channel(),
                    newSession.getServerVersion());

            channel = newSession.createSubsystemChannel(SUBSYSTEM);
            channel.setStreaming(ClientChannel.Streaming.Async);
            channel.open().addListener(future -> {
                if (future.isOpened()) {
                    handleSshChanelOpened(ctx);
                } else {
                    handleSshSetupFailure(ctx, future.getException());
                }
            });


        } catch (final IOException e) {
            handleSshSetupFailure(ctx, e);
        }
    }

    private synchronized void handleSshChanelOpened(final ChannelHandlerContext ctx) {
        LOG.trace("SSH subsystem channel opened successfully on channel: {}", ctx.channel());

        if (negotiationFuture == null) {
            connectPromise.setSuccess();
        }

        // TODO we should also read from error stream and at least log from that

        ClientChannel localChannel = channel;
        sshReadAsyncListener = new AsyncSshHandlerReader(() -> AsyncSshHandler.this.disconnect(ctx, ctx.newPromise()),
            ctx::fireChannelRead, localChannel.toString(), localChannel.getAsyncOut());

        // if readAsyncListener receives immediate close,
        // it will close this handler and closing this handler sets channel variable to null
        if (channel != null) {
            sshWriteAsyncHandler = new AsyncSshHandlerWriter(channel.getAsyncIn());
            ctx.fireChannelActive();
        }
    }

    private synchronized void handleSshSetupFailure(final ChannelHandlerContext ctx, final Throwable error) {
        LOG.warn("Unable to setup SSH connection on channel: {}", ctx.channel(), error);

        // If the promise is not yet done, we have failed with initial connect and set connectPromise to failure
        if (!connectPromise.isDone()) {
            connectPromise.setFailure(error);
        }

        disconnect(ctx, ctx.newPromise());
    }

    @Override
    public synchronized void write(final ChannelHandlerContext ctx, final Object msg, final ChannelPromise promise) {
        sshWriteAsyncHandler.write(ctx, msg, promise);
    }

    @Override
    public synchronized void connect(final ChannelHandlerContext ctx, final SocketAddress remoteAddress,
                                     final SocketAddress localAddress, final ChannelPromise promise) throws Exception {
        LOG.debug("SSH session connecting on channel {}. promise: {} ", ctx.channel(), connectPromise);
        this.connectPromise = promise;

        if (negotiationFuture != null) {
            negotiationFutureListener = future -> {
                if (future.isSuccess()) {
                    promise.setSuccess();
                }
            };
            //complete connection promise with netconf negotiation future
            negotiationFuture.addListener(negotiationFutureListener);
        }
        startSsh(ctx, remoteAddress);
    }

    @Override
    public void close(final ChannelHandlerContext ctx, final ChannelPromise promise) {
        disconnect(ctx, promise);
    }

    @SuppressWarnings("checkstyle:IllegalCatch")
    @Override
    public synchronized void disconnect(final ChannelHandlerContext ctx, final ChannelPromise promise) {
        LOG.trace("Closing SSH session on channel: {} with connect promise in state: {}",
                ctx.channel(),connectPromise);

        // If we have already succeeded and the session was dropped after,
        // we need to fire inactive to notify reconnect logic
        if (connectPromise.isSuccess()) {
            ctx.fireChannelInactive();
        }

        if (sshWriteAsyncHandler != null) {
            sshWriteAsyncHandler.close();
        }

        if (sshReadAsyncListener != null) {
            sshReadAsyncListener.close();
        }

        //If connection promise is not already set, it means negotiation failed
        //we must set connection promise to failure
        if (!connectPromise.isDone()) {
            connectPromise.setFailure(new IllegalStateException("Negotiation failed"));
        }

        //Remove listener from negotiation future, we don't want notifications
        //from negotiation anymore
        if (negotiationFuture != null) {
            negotiationFuture.removeListener(negotiationFutureListener);
        }

        if (session != null && !session.isClosed() && !session.isClosing()) {
            session.close(false).addListener(future -> {
                synchronized (this) {
                    if (!future.isClosed()) {
                        session.close(true);
                    }
                    session = null;
                }
            });
        }

        // Super disconnect is necessary in this case since we are using NioSocketChannel and it needs
        // to cleanup its resources e.g. Socket that it tries to open in its constructor
        // (https://bugs.opendaylight.org/show_bug.cgi?id=2430)
        // TODO better solution would be to implement custom ChannelFactory + Channel
        // that will use mina SSH lib internally: port this to custom channel implementation
        try {
            // Disconnect has to be closed after inactive channel event was fired, because it interferes with it
            super.disconnect(ctx, ctx.newPromise());
        } catch (final Exception e) {
            LOG.warn("Unable to cleanup all resources for channel: {}. Ignoring.", ctx.channel(), e);
        }

        channel = null;
        promise.setSuccess();
        LOG.debug("SSH session closed on channel: {}", ctx.channel());
    }

}