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package com.digitalpetri.modbus.client;

import com.digitalpetri.fsm.FsmContext;
import com.digitalpetri.modbus.ModbusRtuFrame;
import com.digitalpetri.modbus.ModbusRtuResponseFrameParser;
import com.digitalpetri.modbus.ModbusRtuResponseFrameParser.Accumulated;
import com.digitalpetri.modbus.ModbusRtuResponseFrameParser.ParseError;
import com.digitalpetri.modbus.ModbusRtuResponseFrameParser.ParserState;
import com.digitalpetri.modbus.internal.util.ExecutionQueue;
import com.digitalpetri.netty.fsm.ChannelActions;
import com.digitalpetri.netty.fsm.ChannelFsm;
import com.digitalpetri.netty.fsm.ChannelFsmConfig;
import com.digitalpetri.netty.fsm.ChannelFsmFactory;
import com.digitalpetri.netty.fsm.Event;
import com.digitalpetri.netty.fsm.State;
import io.netty.bootstrap.Bootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.Channel;
import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelOption;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.CompletionStage;
import java.util.concurrent.atomic.AtomicReference;
import java.util.function.Consumer;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Modbus RTU/TCP client transport; a {@link ModbusRtuClientTransport} that sends and receives
 * {@link ModbusRtuFrame}s over TCP.
 */
public class NettyRtuClientTransport implements ModbusRtuClientTransport {

  private final Logger logger = LoggerFactory.getLogger(getClass());

  private final ModbusRtuResponseFrameParser frameParser = new ModbusRtuResponseFrameParser();
  private final AtomicReference> frameReceiver = new AtomicReference<>();

  private final ChannelFsm channelFsm;
  private final ExecutionQueue executionQueue;

  private final NettyClientTransportConfig config;

  public NettyRtuClientTransport(NettyClientTransportConfig config) {
    this.config = config;

    channelFsm = ChannelFsmFactory.newChannelFsm(
        ChannelFsmConfig.newBuilder()
            .setExecutor(config.executor())
            .setLazy(config.reconnectLazy())
            .setPersistent(config.connectPersistent())
            .setChannelActions(new ModbusRtuChannelActions())
            .build()
    );

    channelFsm.addTransitionListener(
        (from, to, via) ->
            logger.debug("onStateTransition: {} -> {} via {}", from, to, via)
    );

    executionQueue = new ExecutionQueue(config.executor());
  }

  @Override
  public CompletableFuture connect() {
    return channelFsm.connect().thenApply(c -> null);
  }

  @Override
  public CompletableFuture disconnect() {
    return channelFsm.disconnect();
  }

  @Override
  public boolean isConnected() {
    return channelFsm.getState() == State.Connected;
  }

  @Override
  public CompletionStage send(ModbusRtuFrame frame) {
    return channelFsm.getChannel().thenCompose(channel -> {
      ByteBuf buffer = Unpooled.buffer();
      buffer.writeByte(frame.unitId());
      buffer.writeBytes(frame.pdu());
      buffer.writeBytes(frame.crc());

      var future = new CompletableFuture();

      channel.writeAndFlush(buffer).addListener((ChannelFutureListener) channelFuture -> {
        if (channelFuture.isSuccess()) {
          future.complete(null);
        } else {
          future.completeExceptionally(channelFuture.cause());
        }
      });

      return future;
    });
  }

  @Override
  public void receive(Consumer frameReceiver) {
    this.frameReceiver.set(frameReceiver);
  }

  @Override
  public void resetFrameParser() {
    frameParser.reset();
  }

  private class ModbusRtuClientFrameReceiver extends SimpleChannelInboundHandler {

    @Override
    protected void channelRead0(ChannelHandlerContext ctx, ByteBuf buffer) {
      byte[] data = new byte[buffer.readableBytes()];
      buffer.readBytes(data);

      ParserState state = frameParser.parse(data);

      if (state instanceof Accumulated a) {
        try {
          onFrameReceived(a.frame());
        } finally {
          frameParser.reset();
        }
      } else if (state instanceof ParseError e) {
        logger.error("Error parsing frame: {}", e.error());

        frameParser.reset();
        ctx.close();
      }
    }

    private void onFrameReceived(ModbusRtuFrame frame) {
      Consumer frameReceiver = NettyRtuClientTransport.this.frameReceiver.get();
      if (frameReceiver != null) {
        executionQueue.submit(() -> frameReceiver.accept(frame));
      }
    }

  }

  private class ModbusRtuChannelActions implements ChannelActions {

    @Override
    public CompletableFuture connect(FsmContext fsmContext) {
      var bootstrap = new Bootstrap()
          .channel(NioSocketChannel.class)
          .group(config.eventLoopGroup())
          .option(ChannelOption.CONNECT_TIMEOUT_MILLIS, (int) config.connectTimeout().toMillis())
          .option(ChannelOption.TCP_NODELAY, Boolean.TRUE)
          .handler(new ChannelInitializer() {
            @Override
            protected void initChannel(SocketChannel channel) {
              channel.pipeline().addLast(new ModbusRtuClientFrameReceiver());

              config.pipelineCustomizer().accept(channel.pipeline());
            }
          });

      config.bootstrapCustomizer().accept(bootstrap);

      var future = new CompletableFuture();

      bootstrap.connect(config.hostname(), config.port()).addListener(
          (ChannelFutureListener) channelFuture -> {
            if (channelFuture.isSuccess()) {
              future.complete(channelFuture.channel());
            } else {
              future.completeExceptionally(channelFuture.cause());
            }
          }
      );

      return future;
    }

    @Override
    public CompletableFuture disconnect(
        FsmContext fsmContext,
        Channel channel
    ) {

      var future = new CompletableFuture();

      channel.close().addListener(
          (ChannelFutureListener) channelFuture ->
              future.complete(null)
      );

      return future;
    }

  }

  /**
   * Create a new {@link NettyRtuClientTransport} with a callback that allows customizing the
   * configuration.
   *
   * @param configure a {@link Consumer} that accepts a
   *     {@link NettyClientTransportConfig.Builder} instance to configure.
   * @return a new {@link NettyRtuClientTransport}.
   */
  public static NettyRtuClientTransport create(
      Consumer configure
  ) {

    var config = NettyClientTransportConfig.create(configure);

    return new NettyRtuClientTransport(config);
  }

}