/*
 This file is part of GNUnet.
 (C) 2011, 2012 Christian Grothoff (and other contributing authors)

 GNUnet is free software; you can redistribute it and/or modify
 it under the terms of the GNU General Public License as published
 by the Free Software Foundation; either version 3, or (at your
 option) any later version.

 GNUnet is distributed in the hope that it will be useful, but
 WITHOUT ANY WARRANTY; without even the implied warranty of
 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 General Public License for more details.

 You should have received a copy of the GNU General Public License
 along with GNUnet; see the file COPYING.  If not, write to the
 Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 Boston, MA 02111-1307, USA.
 */

package org.gnunet.util;

import org.gnunet.construct.Construct;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.IOError;
import java.io.IOException;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.SocketChannel;
import java.nio.channels.spi.SelectorProvider;
import java.util.LinkedList;
import java.util.List;

/**
 * Integrates sockets with the gnunet-java message loop / the scheduler.
 */
public class Connection {
    private static final Logger logger = LoggerFactory
            .getLogger(Connection.class);

    /**
     * The underlying socket the client is using to talk with the service.
     */
    private SocketChannel connectionChannel = null;

    /**
     * The list of all address probes.
     * Each address probe tries to connect via a different address.
     */
    private List<AddressProbe> addressProbes = null;

    /**
     * The task that is currently used by the resolve mechanism.
     */
    private Cancelable resolveHandle = null;

    /**
     * The task that is responsible for establishing the connection to the server.
     */
    private Cancelable connectHandle = null;

    /**
     * The ReceiveTask responsible for receiving a whole message from the service
     * and calling the respective MessageReceiver.
     */
    private Scheduler.TaskIdentifier receiveTaskId;

    private MessageReceiver currentReceiver;

    private AbsoluteTime receiveDeadline;

    /**
     * The handle for the current transmission. Writes data to the socket.
     */
    private TransmitHelper currentTransmitHelper = null;

    /**
     * The handle for the next transmission. The next transmission will become the current
     * transmission once the current transmission has completed.
     * While nextTransmitHelper is not null, no new transmit requests may be scheduled.
     */
    private TransmitHelper nextTransmitHelper = null;

    /**
     * Has the last call to the mst produced a message?
     */
    private boolean processedMessage;

    /**
     * The transmitters passed to transmitReadyNotify(...) write to this buffer by calling
     * methods on the MessageSink passed to the Transmitter.transmit(MessageSink s) method.
     * Initially, this buffer has the size of the smallest possible messages, but grows when
     * transmitting larger messages.
     */
    private ByteBuffer transmitBuffer = ByteBuffer.allocate(GnunetMessage.Header.SIZE);

    /**
     * Has the connection been disconnected?
     */
    private boolean disconnected = false;

    /**
     * Timeout task for the connect notify.
     */
    private Scheduler.TaskIdentifier notifyConnectedTimeout;

    /**
     * Continuation to call when connected.
     */
    private Continuation notifyConnectedContinuation;

    /**
     * Message stream tokenizer for messages received from the connection.
     */
    private MessageStreamTokenizer mst;

    /**
     * An address probe is a connection to a socket that may succeed or not.
     * The first address probe that succeeded is used for this connection.
     */
    private static class AddressProbe {
        Cancelable connectTask;
        SocketChannel channel;

        public void cancel() {
            if (connectTask != null) {
                connectTask.cancel();
            }
            if (channel != null) {
                try {
                    channel.close();
                } catch (IOException e) {
                    // nothing we can do here
                }
            }
        }
    }

    /**
     * Represents a getRequestIdentifier for transmission.
     */
    public interface TransmitHandle extends Cancelable {
        /**
         * Cancel a getRequestIdentifier for the transmit ready notification.
         * This does *not* onCancel a transmission that already has been started.
         */
        public void cancel();
    }

    /**
     * An interface that allows the Transmitter.transmit method to deliver their messages
     * to the client, which sends them to the service.
     */
    public interface MessageSink {
        public void send(GnunetMessage.Body m);
    }

    /**
     * The ReceiveTask is responsible for receiving a whole
     * GnunetMessage and call the respective MessageReceiver with the message on success,
     * and null on failure or timeout.
     */
    private class ReceiveTask implements Scheduler.Task {
        /**
         * The task object's work is over, either because it succeeded at its job,
         * or it has been canceled.
         */
        public boolean done;

        private void error() {
            currentReceiver.handleError();
            done = true;
        }

        @Override
        public void run(Scheduler.RunContext ctx) {
            if (currentReceiver == null) {
                throw new AssertionError();
            }
            receiveTaskId = null;
            if (ctx.reasons.contains(Scheduler.Reason.TIMEOUT)) {
                error();
            } else if (ctx.reasons.contains(Scheduler.Reason.READ_READY)) {
                logger.debug("ready to receive");
                try {
                    processedMessage = false;
                    logger.debug("reading into mst ...");
                    int n = mst.readFrom(connectionChannel, true);
                    logger.debug("read {} bytes into mst", n);
                    if (processedMessage) {
                        done = true;
                        return;
                    }
                    if (-1 == n) {
                        error();
                        return;
                    }
                } catch (IOException e) {
                    logger.debug("got IOException ({}, {})", e.getClass().getName(), e.getMessage());
                    error();
                    return;
                }
                if (receiveDeadline.isDue()) {
                    error();
                    return;
                }
                receiveTaskId = Scheduler.addRead(receiveDeadline.getRemaining(), connectionChannel, this);
            } else if (ctx.reasons.contains(Scheduler.Reason.SHUTDOWN)) {
                done = true;
            } else {
                // XXX: what to do here?
                throw new RuntimeException("receive failed");
            }
        }
    }


    private class TransmitHelper implements Scheduler.Task, MessageSink {
        private final MessageTransmitter transmitter;

        private Cancelable notifyTimeoutTask;

        private Cancelable transmitTask = null;

        public TransmitHelper(final MessageTransmitter transmitter, RelativeTime notifyTimeout) {
            this.transmitter = transmitter;

            Scheduler.TaskConfiguration tc = new Scheduler.TaskConfiguration(notifyTimeout,
                    new Scheduler.Task() {
                        @Override
                        public void run(Scheduler.RunContext ctx) {
                            transmitter.handleError();
                        }
                    });

            notifyTimeoutTask = tc.schedule();
        }

        public void cancel() {
            if (transmitTask != null) {
                transmitTask.cancel();
                transmitTask = null;
            }
            if (notifyTimeoutTask != null) {
                notifyTimeoutTask.cancel();
                notifyTimeoutTask = null;
            }
        }

        @Override
        public void run(Scheduler.RunContext ctx) {
            this.transmitTask = null;
            if (connectionChannel == null) {
                logger.error("could not write to channel (null)");
                return;
            }
            try {
                int n = connectionChannel.write(transmitBuffer);
                // logger.debug("connectionChannel has written " + n + " bytes to " + connectionChannel.socket().toString());
            } catch (IOException e) {
                throw new IOError(e);
            }
            if (transmitBuffer.remaining() == 0) {
                logger.debug("transmit buffer fully sent");
                if (nextTransmitHelper == null) {
                    currentTransmitHelper = null;
                } else {
                    currentTransmitHelper = nextTransmitHelper;
                    // we need to to this so the transmit callback can do notifyTransmitReady
                    TransmitHelper tmpTransmitHelper = nextTransmitHelper;
                    nextTransmitHelper = null;
                    tmpTransmitHelper.start();

                }
            } else {
                schedule();
            }
        }

        /**
         * called to notify when we are ready to put new messages in the transmit buffer
         */
        public void start() {
            notifyTimeoutTask.cancel();
            notifyTimeoutTask = null;
            transmitBuffer.clear();
            transmitter.transmit(TransmitHelper.this);
            transmitBuffer.flip();
            schedule();
        }

        private void schedule() {
            if (disconnected) {
                return;
            }
            // timeout is forever, because there is no way to directly limit the transmission time
            // of a message, only the max. wait time before transmission.
            // onCancel must be called on the transmitTask if we disconnect
            Scheduler.TaskConfiguration tc = new Scheduler.TaskConfiguration(RelativeTime.FOREVER, this);
            tc.addSelectEvent(connectionChannel, SelectionKey.OP_WRITE);
            this.transmitTask = tc.schedule();
        }

        @Override
        public void send(final GnunetMessage.Body m) {
            final GnunetMessage gm = new GnunetMessage();
            gm.header = new GnunetMessage.Header();
            gm.body = m;
            Construct.patch(gm);
            gm.header.messageSize = Construct.getSize(gm);
            byte[] b = Construct.toBinary(gm);
            if (b.length != gm.header.messageSize) {
                throw new AssertionError(
                        String.format("tried to send message with binary size %s but size in header %s",
                                b.length, gm.header.messageSize));
            }
            logger.debug("sending message (size={},type={}) over {}",
                    new String[] {String.valueOf(b.length), String.valueOf(gm.header.messageType), connectionChannel.socket().toString()});
            if (transmitBuffer.remaining() < b.length) {
                ByteBuffer buf = ByteBuffer.allocate(b.length + transmitBuffer.capacity());
                transmitBuffer.flip();
                buf.put(transmitBuffer);
                transmitBuffer = buf;
            }
            transmitBuffer.put(b);
        }
    }

    private class ConnectionMstCallback implements MstCalllback {
        private void dispatch(GnunetMessage.Body mb) {
            if (processedMessage) {
                throw new AssertionError();
            }
            if (null == currentReceiver) {
                throw new AssertionError();
            }
            currentReceiver.process(mb);
            processedMessage = true;
        }
        @Override
        public void onUnknownMessage(UnknownMessageBody b) {
            dispatch(b);
        }

        @Override
        public void onKnownMessage(GnunetMessage msg) {
            dispatch(msg.body);
        }
    }

    /**
     * Create a connection to the given hostname/port.
     *
     * @param hostname name of the host to connect to
     * @param port     port of the host to connect to
     */
    public Connection(String hostname, int port) {
        mst = new MessageStreamTokenizer(new ConnectionMstCallback());
        addressProbes = new LinkedList<AddressProbe>();
        ConnectionResolveHandler addressHandler = new ConnectionResolveHandler(port);
        resolveHandle = Resolver.getInstance().resolveHostname(hostname, RelativeTime.FOREVER, addressHandler);
    }

    public Connection(SocketChannel sock) {
        mst = new MessageStreamTokenizer(new ConnectionMstCallback());
        assert sock != null;
        this.connectionChannel = sock;
    }


    class ConnectionResolveHandler implements Resolver.AddressCallback {
        private final int port;

        public ConnectionResolveHandler(int port) {
            this.port = port;
        }

        @Override
        public void onAddress(InetAddress addr) {
            final SocketChannel channel = createChannel();
            try {
                channel.connect(new InetSocketAddress(addr, port));
            } catch (IOException e) {
                logger.error("could not connect to host");
                return;
            }

            final AddressProbe addressProbe = new AddressProbe();
            addressProbe.channel = channel;
            Scheduler.TaskConfiguration tc = new Scheduler.TaskConfiguration(RelativeTime.FOREVER,
                    new Scheduler.Task() {
                        @Override
                        public void run(Scheduler.RunContext ctx) {
                            addressProbe.connectTask = null;
                            if (ctx.reasons.contains(Scheduler.Reason.SHUTDOWN)) {
                                return;
                            }
                            Connection.this.finishConnect(addressProbe);
                        }
                    });

            // our channel has already disconnected
            if (!channel.isOpen()) {
                return;
            }

            tc.addSelectEvent(channel, SelectionKey.OP_CONNECT);

            addressProbe.connectTask = tc.schedule();
        }

        @Override
        public void onFinished() {
            resolveHandle = null;
        }

        @Override
        public void onTimeout() {
            // do nothing
            // todo: is this correct?
        }
    }


    /**
     * Actually connect the socket that select reported as ready to connect.
     * Discards all remaining address probes.
     */
    private void finishConnect(AddressProbe probe) {
        // can happen if the addres probe task was already scheduled
        if (connectionChannel != null) {
            try {
                probe.channel.close();
            } catch (IOException e) {
                logger.error("could not close channel", e);
            }
            return;
        }

        SocketChannel channel = probe.channel;
        boolean connected;
        try {
            connected = channel.finishConnect();
        } catch (IOException e) {
            logger.debug("finishConnect() was not successful: {}", (Object) e);
            return;
        }

        if (!connected) {
            logger.error("socket reported OP_CONNECT but is not connected");
            return;
        }

        for (AddressProbe addressProbe : addressProbes) {
            if (addressProbe != probe && addressProbe.connectTask != null) {
                addressProbe.connectTask.cancel();
                try {
                    addressProbe.channel.close();
                } catch (IOException e) {
                    logger.error("could not close channel", e);
                }
            }
        }

        addressProbes.clear();

        connectionChannel = channel;

        if (currentTransmitHelper != null) {
            currentTransmitHelper.start();
        }
        Continuation c = notifyConnectedContinuation;
        notifyConnectedContinuation = null;
        if (notifyConnectedTimeout != null) {
            notifyConnectedTimeout.cancel();
            notifyConnectedTimeout = null;
        }
        if (c != null) {
            c.cont(true);
        }
    }

    /**
     * Open a channel for this connection in non-blocking mode
     */
    private SocketChannel createChannel() {
        try {
            SocketChannel channel = SelectorProvider.provider().openSocketChannel();
            channel.configureBlocking(false);
            return channel;
        } catch (IOException e) {
            // this is fatal, no retry necessary
            throw new IOError(e);
        }
    }

    public boolean isConnected() {
        return connectionChannel != null && connectionChannel.isConnected();
    }

    /**
     * Receive one message from the network.
     *
     * @param timeout  deadline after which receiver.onError() will be called
     * @param receiver MessageReceiver that is responsible for the received message
     */
    public void receive(final RelativeTime timeout, final MessageReceiver receiver) {
        if (receiveTaskId != null)
            throw new AssertionError("already receiving");
        if (!isConnected()) {
            throw new AssertionError("cannot receive if not connected");
        }

        currentReceiver = receiver;
        receiveDeadline = timeout.toAbsolute();

        // make sure that the receiver is never called directly
        Scheduler.add(new Scheduler.Task() {
            @Override
            public void run(Scheduler.RunContext ctx) {
                // full message still in buffer?
                processedMessage = false;
                if (mst.extractOne()) {
                    logger.debug("full message was in buffer, not reading from socket");
                    if (!processedMessage) {
                        throw new AssertionError();
                    }
                    return;
                }

                // did we get disconnected in the mean time?
                if (connectionChannel == null) {
                    return;
                }

                final ReceiveTask task = new ReceiveTask();
                receiveTaskId = Scheduler.addRead(timeout, connectionChannel, task);
            }
        });
    }

    /**
     * Call the transmitter once the we are ready to transmit data.
     *
     * @param size        number of bytes to send
     * @param timeout     after how long should we give up (and call transmitter.transmit(null))
     * @param transmitter the MessageTransmitter object to call once the client is ready to transmit or
     *                    when the timeout is over. Guaranteed to be called *after* notifyTransmitReady has returned.
     * @return a handle that can be used to onCancel the transmit getRequestIdentifier, null if getRequestIdentifier could be satisfied immediately
     */
    public TransmitHandle notifyTransmitReady(int size, RelativeTime timeout, final MessageTransmitter transmitter) {
        if (disconnected) {
            throw new AssertionError("notifyTransmitReady called on a closed connection");
        }
        if (nextTransmitHelper != null) {
            throw new AssertionError(
                    "previous transmit getRequestIdentifier must have completed before calling notifyTransmitReady again");
        }

        if (timeout.getMicroseconds() <= 0) {
            throw new AssertionError("notifyTransmitReady timeout must be positive");
        }

        if (!isConnected()) {
            throw new AssertionError("notifyTransmitHandle can only be called once connected");
        }

        final TransmitHelper transmit = new TransmitHelper(transmitter, timeout);

        if (currentTransmitHelper == null) {
            currentTransmitHelper = transmit;
            currentTransmitHelper.start();
            return null;
        }

        nextTransmitHelper = transmit;

        return new TransmitHandle() {
            @Override
            public void cancel() {
                transmit.cancel();
            }
        };
    }

    /**
     * Call cont after establishing the connection or when the timeout has occured.
     *
     * @param timeout timeout
     * @param cont    continuation to call
     * @return a handle to cancel the notification
     */
    Cancelable notifyConnected(RelativeTime timeout, final Continuation cont) {
        if (notifyConnectedTimeout != null) {
            throw new AssertionError();
        }
        this.notifyConnectedContinuation = cont;
        this.notifyConnectedTimeout = Scheduler.addDelayed(timeout, new Scheduler.Task() {
            @Override
            public void run(Scheduler.RunContext ctx) {
                Continuation c = notifyConnectedContinuation;
                notifyConnectedContinuation = null;
                Connection.this.notifyConnectedTimeout = null;
                if (c != null) {
                    c.cont(false);
                }
            }
        });
        return this.notifyConnectedTimeout;
    }

    /**
     * Disconnect. There must not be any pending transmit/receive requests.
     * Any buffered data scheduled for writing is discarded.
     */
    public void disconnect() {
        if (disconnected) {
            logger.error("disconnect called twice");
        }
        disconnected = true;
        if (notifyConnectedTimeout != null) {
            notifyConnectedTimeout.cancel();
            notifyConnectedTimeout = null;
        }
        if (receiveTaskId != null) {
            receiveTaskId.cancel();
            receiveTaskId = null;
        }
        if (currentTransmitHelper != null) {
            currentTransmitHelper.cancel();
            currentTransmitHelper = null;
        }
        if (nextTransmitHelper != null) {
            nextTransmitHelper.cancel();
            nextTransmitHelper = null;
        }
        if (resolveHandle != null) {
            resolveHandle.cancel();
            resolveHandle = null;
        }
        if (connectHandle != null) {
            connectHandle.cancel();
            connectHandle = null;
        }
        if (connectionChannel != null) {
            try {
                connectionChannel.close();
            } catch (IOException e) {
                throw new IOError(e);
            }
            connectionChannel = null;
        }

        if (addressProbes != null) {
            for (AddressProbe ap : addressProbes) {
                ap.cancel();
            }
        }
    }
}