/*
 * Copyright (c) 2014 Red Hat, Inc. and others
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License 2.0 which is available at
 * http://www.eclipse.org/legal/epl-2.0, or the Apache License, Version 2.0
 * which is available at https://www.apache.org/licenses/LICENSE-2.0.
 *
 * SPDX-License-Identifier: EPL-2.0 OR Apache-2.0
 */

package io.vertx.core.streams.impl;

import io.vertx.core.Handler;
import io.vertx.core.streams.Pump;
import io.vertx.core.streams.ReadStream;
import io.vertx.core.streams.WriteStream;

Pumps data from a ReadStream to a WriteStream and performs flow control where necessary to prevent the write stream buffer from getting overfull.
 Instances of this class read bytes from a ReadStream and write them to a WriteStream. If data can be read faster than it can be written this could result in the write queue of the WriteStream growing without bound, eventually causing it to exhaust all available RAM.
 To prevent this, after each write, instances of this class check whether the write queue of the WriteStream is full, and if so, the ReadStream is paused, and a drainHandler is set on the WriteStream. When the WriteStream has processed half of its backlog, the drainHandler will be called, which results in the pump resuming the ReadStream.
 This class can be used to pump from any ReadStream to any WriteStream, e.g. from an HttpServerRequest to an AsyncFile, or from NetSocket to a WebSocket.

Instances of this class are not thread-safe.

Author:
Tim Fox/**
 * Pumps data from a {@link io.vertx.core.streams.ReadStream} to a {@link io.vertx.core.streams.WriteStream} and performs flow control where necessary to
 * prevent the write stream buffer from getting overfull.<p>
 * Instances of this class read bytes from a {@link io.vertx.core.streams.ReadStream} and write them to a {@link io.vertx.core.streams.WriteStream}. If data
 * can be read faster than it can be written this could result in the write queue of the {@link io.vertx.core.streams.WriteStream} growing
 * without bound, eventually causing it to exhaust all available RAM.<p>
 * To prevent this, after each write, instances of this class check whether the write queue of the {@link
 * io.vertx.core.streams.WriteStream} is full, and if so, the {@link io.vertx.core.streams.ReadStream} is paused, and a {@code drainHandler} is set on the
 * {@link io.vertx.core.streams.WriteStream}. When the {@link io.vertx.core.streams.WriteStream} has processed half of its backlog, the {@code drainHandler} will be
 * called, which results in the pump resuming the {@link io.vertx.core.streams.ReadStream}.<p>
 * This class can be used to pump from any {@link io.vertx.core.streams.ReadStream} to any {@link io.vertx.core.streams.WriteStream},
 * e.g. from an {@link io.vertx.core.http.HttpServerRequest} to an {@link io.vertx.core.file.AsyncFile},
 * or from {@link io.vertx.core.net.NetSocket} to a {@link io.vertx.core.http.WebSocket}.<p>
 *
 * Instances of this class are not thread-safe.<p>
 *
 * @author <a href="http://tfox.org">Tim Fox</a>
 */
public class PumpImpl<T> implements Pump {

  private final ReadStream<T> readStream;
  private final WriteStream<T> writeStream;
  private final Handler<T> dataHandler;
  private final Handler<Void> drainHandler;
  private int pumped;

  
Create a new Pump with the given ReadStream and WriteStream. Set the write queue max size of the write stream to maxWriteQueueSize /**
   * Create a new {@code Pump} with the given {@code ReadStream} and {@code WriteStream}. Set the write queue max size
   * of the write stream to {@code maxWriteQueueSize}
   */
  PumpImpl(ReadStream<T> rs, WriteStream<T> ws, int maxWriteQueueSize) {
    this(rs, ws);
    this.writeStream.setWriteQueueMaxSize(maxWriteQueueSize);
  }

  PumpImpl(ReadStream<T> rs, WriteStream<T> ws) {
    this.readStream = rs;
    this.writeStream = ws;
    drainHandler = v-> readStream.resume();
    dataHandler = data -> {
      writeStream.write(data);
      incPumped();
      if (writeStream.writeQueueFull()) {
        readStream.pause();
        writeStream.drainHandler(drainHandler);
      }
    };
  }

  
Set the write queue max size to maxSize /**
   * Set the write queue max size to {@code maxSize}
   */
  @Override
  public PumpImpl setWriteQueueMaxSize(int maxSize) {
    writeStream.setWriteQueueMaxSize(maxSize);
    return this;
  }

  
Start the Pump. The Pump can be started and stopped multiple times.
/**
   * Start the Pump. The Pump can be started and stopped multiple times.
   */
  @Override
  public PumpImpl start() {
    readStream.handler(dataHandler);
    return this;
  }

  
Stop the Pump. The Pump can be started and stopped multiple times.
/**
   * Stop the Pump. The Pump can be started and stopped multiple times.
   */
  @Override
  public PumpImpl stop() {
    writeStream.drainHandler(null);
    readStream.handler(null);
    return this;
  }

  
Return the total number of elements pumped by this pump.
/**
   * Return the total number of elements pumped by this pump.
   */
  @Override
  public synchronized int numberPumped() {
    return pumped;
  }

  // Note we synchronize as numberPumped can be called from a different thread however incPumped will always
  // be called from the same thread so we benefit from bias locked optimisation which should give a very low
  // overhead
  private synchronized void incPumped() {
    pumped++;
  }


}