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

import com.google.common.base.Preconditions;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelOutboundHandler;
import io.netty.channel.ChannelOutboundHandlerAdapter;
import io.netty.channel.ChannelPromise;
import java.io.IOException;
import java.net.SocketAddress;
import org.apache.sshd.ClientChannel;
import org.apache.sshd.ClientSession;
import org.apache.sshd.SshClient;
import org.apache.sshd.client.future.AuthFuture;
import org.apache.sshd.client.future.ConnectFuture;
import org.apache.sshd.client.future.OpenFuture;
import org.apache.sshd.common.future.CloseFuture;
import org.apache.sshd.common.future.SshFutureListener;
import org.apache.sshd.common.io.IoInputStream;
import org.apache.sshd.common.io.IoOutputStream;
import org.apache.sshd.common.io.IoReadFuture;
import org.apache.sshd.common.io.IoWriteFuture;
import org.apache.sshd.common.io.WritePendingException;
import org.apache.sshd.common.util.Buffer;
import org.opendaylight.controller.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 logger = LoggerFactory.getLogger(AsyncSshHandler.class);
    public static final String SUBSYSTEM = "netconf";

    public static final SshClient DEFAULT_CLIENT = SshClient.setUpDefaultClient();

    public static final int SSH_DEFAULT_NIO_WORKERS = 8;

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

    private final AuthenticationHandler authenticationHandler;
    private final SshClient sshClient;

    private SshReadAsyncListener sshReadAsyncListener;
    private SshWriteAsyncHandler sshWriteAsyncHandler;

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


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

    /**
     *
     * @param authenticationHandler
     * @param sshClient started SshClient
     * @throws IOException
     */
    public AsyncSshHandler(final AuthenticationHandler authenticationHandler, final SshClient sshClient) throws IOException {
        this.authenticationHandler = Preconditions.checkNotNull(authenticationHandler);
        this.sshClient = Preconditions.checkNotNull(sshClient);
        // Start just in case
        sshClient.start();
    }

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

        final ConnectFuture sshConnectionFuture = sshClient.connect(authenticationHandler.getUsername(), address);
        sshConnectionFuture.addListener(new SshFutureListener<ConnectFuture>() {
            @Override
            public void operationComplete(final ConnectFuture future) {
                if (future.isConnected()) {
                    handleSshSessionCreated(future, ctx);
                } else {
                    handleSshSetupFailure(ctx, future.getException());
                }
            }
        });
    }

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

            session = future.getSession();
            final AuthFuture authenticateFuture = authenticationHandler.authenticate(session);
            authenticateFuture.addListener(new SshFutureListener<AuthFuture>() {
                @Override
                public void operationComplete(final AuthFuture future) {
                    if (future.isSuccess()) {
                        handleSshAuthenticated(session, ctx);
                    } else {
                        handleSshSetupFailure(ctx, future.getException());
                    }
                }
            });
        } catch (final IOException e) {
            handleSshSetupFailure(ctx, e);
        }
    }

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

            channel = session.createSubsystemChannel(SUBSYSTEM);
            channel.setStreaming(ClientChannel.Streaming.Async);
            channel.open().addListener(new SshFutureListener<OpenFuture>() {
                @Override
                public void operationComplete(final OpenFuture 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) {
        logger.trace("SSH subsystem channel opened successfully on channel: {}", ctx.channel());

        connectPromise.setSuccess();
        connectPromise = null;

        sshReadAsyncListener = new SshReadAsyncListener(ctx, channel.getAsyncOut());
        sshWriteAsyncHandler = new SshWriteAsyncHandler(this, channel.getAsyncIn());

        ctx.fireChannelActive();
    }

    private synchronized void handleSshSetupFailure(final ChannelHandlerContext ctx, final Throwable e) {
        logger.warn("Unable to setup SSH connection on channel: {}", ctx.channel(), e);
        connectPromise.setFailure(e);
        connectPromise = null;
        throw new IllegalStateException("Unable to setup SSH connection on channel: " + ctx.channel(), e);
    }

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

    private static void handleSshSessionClosed(final ChannelHandlerContext ctx) {
        logger.debug("SSH session closed on channel: {}", ctx.channel());
        ctx.fireChannelInactive();
    }

    @Override
    public synchronized void connect(final ChannelHandlerContext ctx, final SocketAddress remoteAddress, final SocketAddress localAddress, final ChannelPromise promise) throws Exception {
        this.connectPromise = promise;
        startSsh(ctx, remoteAddress);
    }

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

    @Override
    public synchronized void disconnect(final ChannelHandlerContext ctx, final ChannelPromise promise) {
        if(sshReadAsyncListener != null) {
            sshReadAsyncListener.close();
        }

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

        if(session!= null && !session.isClosed() && !session.isClosing()) {
            session.close(false).addListener(new SshFutureListener<CloseFuture>() {
                @Override
                public void operationComplete(final CloseFuture future) {
                    if (future.isClosed() == false) {
                        session.close(true);
                    }
                    session = null;
                }
            });
        }

        channel = null;
        promise.setSuccess();

        handleSshSessionClosed(ctx);
    }

    /**
     * Listener over async input stream from SSH session.
     * This listeners schedules reads in a loop until the session is closed or read fails.
     */
    private static class SshReadAsyncListener implements SshFutureListener<IoReadFuture>, AutoCloseable {
        private static final int BUFFER_SIZE = 8192;

        private final ChannelHandlerContext ctx;

        private IoInputStream asyncOut;
        private Buffer buf;
        private IoReadFuture currentReadFuture;

        public SshReadAsyncListener(final ChannelHandlerContext ctx, final IoInputStream asyncOut) {
            this.ctx = ctx;
            this.asyncOut = asyncOut;
            buf = new Buffer(BUFFER_SIZE);
            asyncOut.read(buf).addListener(this);
        }

        @Override
        public synchronized void operationComplete(final IoReadFuture future) {
            if(future.getException() != null) {

                if(asyncOut.isClosed() || asyncOut.isClosing()) {
                    // We are closing
                    handleSshSessionClosed(ctx);
                } else {
                    logger.warn("Exception while reading from SSH remote on channel {}", ctx.channel(), future.getException());
                    throw new IllegalStateException("Exception while reading from SSH remote on channel " + ctx.channel(), future.getException());
                }
            }

            if (future.getRead() > 0) {
                ctx.fireChannelRead(Unpooled.wrappedBuffer(buf.array(), 0, future.getRead()));

                // Schedule next read
                buf = new Buffer(BUFFER_SIZE);
                currentReadFuture = asyncOut.read(buf);
                currentReadFuture.addListener(this);
            }
        }

        @Override
        public synchronized void close() {
            // Remove self as listener on close to prevent reading from closed input
            if(currentReadFuture != null) {
                currentReadFuture.removeListener(this);
            }

            asyncOut = null;
        }
    }

    private static final class SshWriteAsyncHandler implements AutoCloseable {
        public static final int MAX_PENDING_WRITES = 100;

        private final ChannelOutboundHandler channelHandler;
        private IoOutputStream asyncIn;

        // Counter that holds the amount of pending write messages
        // Pending write can occur in case remote window is full
        // In such case, we need to wait for the pending write to finish
        private int pendingWriteCounter;
        // Last write future, that can be pending
        private IoWriteFuture lastWriteFuture;

        public SshWriteAsyncHandler(final ChannelOutboundHandler channelHandler, final IoOutputStream asyncIn) {
            this.channelHandler = channelHandler;
            this.asyncIn = asyncIn;
        }

        public synchronized void write(final ChannelHandlerContext ctx, final Object msg, final ChannelPromise promise) {
            try {
                if(asyncIn.isClosed() || asyncIn.isClosing()) {
                    handleSshSessionClosed(ctx);
                } else {
                    lastWriteFuture = asyncIn.write(toBuffer(msg));
                    lastWriteFuture.addListener(new SshFutureListener<IoWriteFuture>() {

                        @Override
                        public void operationComplete(final IoWriteFuture future) {
                            ((ByteBuf) msg).release();

                            // Notify success or failure
                            if (future.isWritten()) {
                                promise.setSuccess();
                            }
                            promise.setFailure(future.getException());

                            // Reset last pending future
                            synchronized (SshWriteAsyncHandler.this) {
                                lastWriteFuture = null;
                            }
                        }
                    });
                }
            } catch (final WritePendingException e) {
                // Check limit for pending writes
                pendingWriteCounter++;
                if(pendingWriteCounter > MAX_PENDING_WRITES) {
                    handlePendingFailed(ctx, new IllegalStateException("Too much pending writes(" + MAX_PENDING_WRITES + ") on channel: " + ctx.channel() +
                            ", remote window is not getting read or is too small"));
                }

                logger.debug("Write pending to SSH remote on channel: {}, current pending count: {}", ctx.channel(), pendingWriteCounter);

                // In case of pending, re-invoke write after pending is finished
                lastWriteFuture.addListener(new SshFutureListener<IoWriteFuture>() {
                    @Override
                    public void operationComplete(final IoWriteFuture future) {
                        if(future.isWritten()) {
                            synchronized (SshWriteAsyncHandler.this) {
                                // Pending done, decrease counter
                                pendingWriteCounter--;
                            }
                            write(ctx, msg, promise);
                        } else {
                            // Cannot reschedule pending, fail
                            handlePendingFailed(ctx, e);
                        }
                    }

                });
            }
        }

        private void handlePendingFailed(final ChannelHandlerContext ctx, final Exception e) {
            logger.warn("Exception while writing to SSH remote on channel {}", ctx.channel(), e);
            try {
                channelHandler.disconnect(ctx, ctx.newPromise());
            } catch (final Exception ex) {
                // This should not happen
                throw new IllegalStateException(ex);
            }
        }

        @Override
        public void close() {
            asyncIn = null;
        }

        private Buffer toBuffer(final Object msg) {
            // TODO Buffer vs ByteBuf translate, Can we handle that better ?
            Preconditions.checkState(msg instanceof ByteBuf);
            final ByteBuf byteBuf = (ByteBuf) msg;
            final byte[] temp = new byte[byteBuf.readableBytes()];
            byteBuf.readBytes(temp, 0, byteBuf.readableBytes());
            return new Buffer(temp);
        }

    }
}