// Copyright 2017 The Nomulus Authors. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package google.registry.proxy;

import static google.registry.proxy.Protocol.PROTOCOL_KEY;
import static google.registry.proxy.handler.RelayHandler.RELAY_CHANNEL_KEY;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.monitoring.metrics.MetricReporter;
import google.registry.proxy.Protocol.BackendProtocol;
import google.registry.proxy.Protocol.FrontendProtocol;
import google.registry.proxy.ProxyModule.ProxyComponent;
import google.registry.util.FormattingLogger;
import io.netty.bootstrap.Bootstrap;
import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.Channel;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelHandler;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelOption;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.util.concurrent.Future;
import io.netty.util.internal.logging.InternalLoggerFactory;
import io.netty.util.internal.logging.JdkLoggerFactory;
import java.util.HashMap;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import javax.inject.Provider;

/**
 * A multi-protocol proxy server that listens on port(s) specified in {@link
 * ProxyModule.ProxyComponent#portToProtocolMap()} }.
 */
public class ProxyServer implements Runnable {

  private static final FormattingLogger logger = FormattingLogger.getLoggerForCallerClass();

  /** Maximum length of the queue of incoming connections. */
  private static final int MAX_SOCKET_BACKLOG = 128;

  private final ImmutableMap<Integer, FrontendProtocol> portToProtocolMap;
  private final HashMap<Integer, Channel> portToChannelMap = new HashMap<>();
  private final EventLoopGroup eventGroup = new NioEventLoopGroup();

  ProxyServer(ProxyComponent proxyComponent) {
    this.portToProtocolMap = proxyComponent.portToProtocolMap();
  }

  /**
   * A {@link ChannelInitializer} for connections from a client of a certain protocol.
   *
   * <p>The {@link #initChannel} method does the following:
   *
   * <ol>
   *   <li>Determine the {@link FrontendProtocol} of the inbound {@link Channel} from its parent
   *       {@link Channel}, i. e. the {@link Channel} that binds to local port and listens.
   *   <li>Add handlers for the {@link FrontendProtocol} to the inbound {@link Channel}.
   *   <li>Establish an outbound {@link Channel} that serves as the relay channel of the inbound
   *       {@link Channel}, as specified by {@link FrontendProtocol#relayProtocol}.
   *   <li>After the outbound {@link Channel} connects successfully, enable {@link
   *       ChannelOption#AUTO_READ} on the inbound {@link Channel} to start reading.
   * </ol>
   */
  private static class ServerChannelInitializer extends ChannelInitializer<NioSocketChannel> {
    @Override
    protected void initChannel(NioSocketChannel inboundChannel) throws Exception {
      // Add inbound channel handlers.
      FrontendProtocol inboundProtocol =
          (FrontendProtocol) inboundChannel.parent().attr(PROTOCOL_KEY).get();
      inboundChannel.attr(PROTOCOL_KEY).set(inboundProtocol);
      addHandlers(inboundChannel.pipeline(), inboundProtocol.handlerProviders());

      if (inboundProtocol.isHealthCheck()) {
        // A health check server protocol has no relay channel. It simply replies to incoming
        // request with a preset response.
        inboundChannel.config().setAutoRead(true);
      } else {
        // Connect to the relay (outbound) channel specified by the BackendProtocol.
        BackendProtocol outboundProtocol = inboundProtocol.relayProtocol();
        Bootstrap bootstrap =
            new Bootstrap()
                // Use the same thread to connect to the relay channel, therefore avoiding
                // synchronization handling due to interactions between the two channels
                .group(inboundChannel.eventLoop())
                .channel(NioSocketChannel.class)
                .handler(
                    new ChannelInitializer<NioSocketChannel>() {
                      @Override
                      protected void initChannel(NioSocketChannel outboundChannel)
                          throws Exception {
                        addHandlers(
                            outboundChannel.pipeline(), outboundProtocol.handlerProviders());
                      }
                    })
                .option(ChannelOption.SO_KEEPALIVE, true)
                // Outbound channel relays to inbound channel.
                .attr(RELAY_CHANNEL_KEY, inboundChannel)
                .attr(PROTOCOL_KEY, outboundProtocol);
        ChannelFuture outboundChannelFuture =
            bootstrap.connect(outboundProtocol.host(), outboundProtocol.port());
        outboundChannelFuture.addListener(
            (ChannelFuture future) -> {
              if (future.isSuccess()) {
                Channel outboundChannel = future.channel();
                // Inbound channel relays to outbound channel.
                inboundChannel.attr(RELAY_CHANNEL_KEY).set(outboundChannel);
                // Outbound channel established successfully, inbound channel can start reading.
                // This setter also calls channel.read() to request read operation.
                inboundChannel.config().setAutoRead(true);
                logger.infofmt(
                    "Relay established: %s <-> %s\nSERVER: %s\nCLIENT: %s",
                    inboundProtocol.name(),
                    outboundProtocol.name(),
                    inboundChannel,
                    outboundChannel);
              } else {
                logger.severefmt(
                    future.cause(),
                    "Cannot connect to relay channel for %s protocol connection from %s.",
                    inboundProtocol.name(),
                    inboundChannel.remoteAddress().getHostName());
              }
            });
      }
    }

    private static void addHandlers(
        ChannelPipeline channelPipeline,
        ImmutableList<Provider<? extends ChannelHandler>> handlerProviders) {
      for (Provider<? extends ChannelHandler> handlerProvider : handlerProviders) {
        channelPipeline.addLast(handlerProvider.get());
      }
    }
  }

  @Override
  public void run() {
    try {
      ServerBootstrap serverBootstrap =
          new ServerBootstrap()
              .group(eventGroup)
              .channel(NioServerSocketChannel.class)
              .childHandler(new ServerChannelInitializer())
              .option(ChannelOption.SO_BACKLOG, MAX_SOCKET_BACKLOG)
              .childOption(ChannelOption.SO_KEEPALIVE, true)
              // Do not read before relay channel is established.
              .childOption(ChannelOption.AUTO_READ, false);

      // Bind to each port specified in portToHandlersMap.
      portToProtocolMap.forEach(
          (port, protocol) -> {
            try {
              // Wait for binding to be established for each listening port.
              ChannelFuture serverChannelFuture = serverBootstrap.bind(port).sync();
              if (serverChannelFuture.isSuccess()) {
                logger.infofmt(
                    "Start listening on port %s for %s protocol.", port, protocol.name());
                Channel serverChannel = serverChannelFuture.channel();
                serverChannel.attr(PROTOCOL_KEY).set(protocol);
                portToChannelMap.put(port, serverChannel);
              }
            } catch (InterruptedException e) {
              logger.severefmt(
                  e, "Cannot listen on port %s for %s protocol.", port, protocol.name());
            }
          });

      // Wait for all listening ports to close.
      portToChannelMap.forEach(
          (port, channel) -> {
            try {
              // Block until all server channels are closed.
              ChannelFuture unusedFuture = channel.closeFuture().sync();
              logger.infofmt(
                  "Stop listening on port %s for %s protocol.",
                  port, channel.attr(PROTOCOL_KEY).get().name());
            } catch (InterruptedException e) {
              logger.severefmt(
                  e,
                  "Listening on port %s for %s protocol interrupted.",
                  port,
                  channel.attr(PROTOCOL_KEY).get().name());
            }
          });
    } finally {
      logger.info("Shutting down server...");
      Future<?> unusedFuture = eventGroup.shutdownGracefully();
    }
  }

  public static void main(String[] args) throws Exception {
    // Use JDK logger for Netty's LoggingHandler,
    // which is what google.registry.util.FormattingLog uses under the hood.
    InternalLoggerFactory.setDefaultFactory(JdkLoggerFactory.INSTANCE);

    // Configure the components, this needs to run first so that the logging format is properly
    // configured for each environment.
    ProxyComponent proxyComponent =
        DaggerProxyModule_ProxyComponent.builder()
            .proxyModule(new ProxyModule().parse(args))
            .build();

    MetricReporter metricReporter = proxyComponent.metricReporter();
    try {
      metricReporter.startAsync().awaitRunning(10, TimeUnit.SECONDS);
      logger.info("Started up MetricReporter");
    } catch (TimeoutException timeoutException) {
      logger.severefmt("Failed to initialize MetricReporter: %s", timeoutException);
    }

    Runtime.getRuntime()
        .addShutdownHook(
            new Thread(
                () -> {
                  try {
                    metricReporter.stopAsync().awaitTerminated(10, TimeUnit.SECONDS);
                    logger.info("Shut down MetricReporter");
                  } catch (TimeoutException timeoutException) {
                    logger.warningfmt("Failed to stop MetricReporter: %s", timeoutException);
                  }
                }));

    new ProxyServer(proxyComponent).run();
  }
}