/*
 * Copyright (C) 2009-2018 Lightbend Inc. <https://www.lightbend.com>
 */

package jdocs.io.japi;

import java.net.InetSocketAddress;
import java.util.LinkedList;
import java.util.Queue;

import akka.actor.ActorRef;
import akka.actor.AbstractActor;
import akka.event.Logging;
import akka.event.LoggingAdapter;
import akka.io.Tcp.CommandFailed;
import akka.io.Tcp.ConnectionClosed;
import akka.io.Tcp.Event;
import akka.io.Tcp.Received;
import akka.io.Tcp.Write;
import akka.io.Tcp.WritingResumed;
import akka.io.TcpMessage;
import akka.util.ByteString;

//#echo-handler
public class EchoHandler extends AbstractActor {

  final LoggingAdapter log = Logging
      .getLogger(getContext().getSystem(), getSelf());

  final ActorRef connection;
  final InetSocketAddress remote;

  public static final long MAX_STORED = 100000000;
  public static final long HIGH_WATERMARK = MAX_STORED * 5 / 10;
  public static final long LOW_WATERMARK = MAX_STORED * 2 / 10;
  
  private long transferred;
  private int storageOffset = 0;
  private long stored = 0;
  private Queue<ByteString> storage = new LinkedList<ByteString>();

  private boolean suspended = false;
  
  private static class Ack implements Event {
    public final int ack;
    public Ack(int ack) {
      this.ack = ack;
    }
  }

  public EchoHandler(ActorRef connection, InetSocketAddress remote) {
    this.connection = connection;
    this.remote = remote;
    
    writing = writing();

    // sign death pact: this actor stops when the connection is closed
    getContext().watch(connection);

    // start out in optimistic write-through mode
    getContext().become(writing);
  }
  
  @Override
    public Receive createReceive() {
      return writing;
    }

  private final Receive writing;
  
  private Receive writing() { 
    return receiveBuilder()
      .match(Received.class, msg -> {
        final ByteString data = msg.data();
        connection.tell(TcpMessage.write(data, new Ack(currentOffset())), getSelf());
        buffer(data);

      })
      .match(Integer.class,  msg -> {
        acknowledge(msg);
      })
      .match(CommandFailed.class, msg -> {
        final Write w = (Write) msg.cmd();
        connection.tell(TcpMessage.resumeWriting(), getSelf());
        getContext().become(buffering((Ack) w.ack()));
      })
      .match(ConnectionClosed.class, msg -> {
        if (msg.isPeerClosed()) {
          if (storage.isEmpty()) {
            getContext().stop(getSelf());
          } else {
            getContext().become(closing());
          }
        }
      })
      .build();
  }

  //#buffering
  
  final static class BufferingState {
    int toAck = 10;
    boolean peerClosed = false;
  }
  
  protected Receive buffering(final Ack nack) {
    final BufferingState state = new BufferingState();
    
    return receiveBuilder()
      .match(Received.class, msg -> {
        buffer(msg.data());

      })
      .match(WritingResumed.class, msg -> {
        writeFirst();

      })
      .match(ConnectionClosed.class, msg -> {
        if (msg.isPeerClosed())
          state.peerClosed = true;
        else
          getContext().stop(getSelf());

      })
      .match(Integer.class, ack -> {
        acknowledge(ack);

        if (ack >= nack.ack) {
          // otherwise it was the ack of the last successful write

          if (storage.isEmpty()) {
            if (state.peerClosed)
              getContext().stop(getSelf());
            else
              getContext().become(writing);

          } else {
            if (state.toAck > 0) {
              // stay in ACK-based mode for a short while
              writeFirst();
              --state.toAck;
            } else {
              // then return to NACK-based again
              writeAll();
              if (state.peerClosed)
                getContext().become(closing());
              else
                getContext().become(writing);
            }
          }
        }
      })
      .build();
  }
  //#buffering

  //#closing
  protected Receive closing() {
    return receiveBuilder()
      .match(CommandFailed.class, msg -> {
        // the command can only have been a Write
        connection.tell(TcpMessage.resumeWriting(), getSelf());
        getContext().become(closeResend(), false);
      })
      .match(Integer.class, msg -> {  
        acknowledge(msg);
        if (storage.isEmpty())
          getContext().stop(getSelf());
      })
      .build();
  }

  protected Receive closeResend() {
    return receiveBuilder()
      .match(WritingResumed.class, msg -> {
        writeAll();
        getContext().unbecome();
      })
      .match(Integer.class, msg -> {
        acknowledge(msg);
      })
      .build();
  }
  //#closing

  //#storage-omitted

  @Override
  public void postStop() {
    log.info("transferred {} bytes from/to [{}]", transferred, remote);
  }

  //#helpers
  protected void buffer(ByteString data) {
    storage.add(data);
    stored += data.size();

    if (stored > MAX_STORED) {
      log.warning("drop connection to [{}] (buffer overrun)", remote);
      getContext().stop(getSelf());

    } else if (stored > HIGH_WATERMARK) {
      log.debug("suspending reading at {}", currentOffset());
      connection.tell(TcpMessage.suspendReading(), getSelf());
      suspended = true;
    }
  }

  protected void acknowledge(int ack) {
    assert ack == storageOffset;
    assert !storage.isEmpty();

    final ByteString acked = storage.remove();
    stored -= acked.size();
    transferred += acked.size();
    storageOffset += 1;

    if (suspended && stored < LOW_WATERMARK) {
      log.debug("resuming reading");
      connection.tell(TcpMessage.resumeReading(), getSelf());
      suspended = false;
    }
  }
  //#helpers

  protected int currentOffset() {
    return storageOffset + storage.size();
  }

  protected void writeAll() {
    int i = 0;
    for (ByteString data : storage) {
      connection.tell(TcpMessage.write(data, new Ack(storageOffset + i++)), getSelf());
    }
  }

  protected void writeFirst() {
    connection.tell(TcpMessage.write(storage.peek(), new Ack(storageOffset)), getSelf());
  }

  //#storage-omitted
}
//#echo-handler
