/*
 * Copyright 2015, gRPC 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 io.grpc.netty;

import static io.netty.buffer.Unpooled.directBuffer;
import static io.netty.buffer.Unpooled.unreleasableBuffer;
import static io.netty.handler.codec.http2.Http2CodecUtil.getEmbeddedHttp2Exception;

import com.google.common.annotations.VisibleForTesting;
import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.http2.Http2ConnectionDecoder;
import io.netty.handler.codec.http2.Http2ConnectionEncoder;
import io.netty.handler.codec.http2.Http2Exception;
import io.netty.handler.codec.http2.Http2LocalFlowController;
import io.netty.handler.codec.http2.Http2Settings;
import io.netty.handler.codec.http2.Http2Stream;
import java.util.concurrent.TimeUnit;

/**
 * Base class for all Netty gRPC handlers. This class standardizes exception handling (always
 * shutdown the connection) as well as sending the initial connection window at startup.
 */
abstract class AbstractNettyHandler extends GrpcHttp2ConnectionHandler {
  private static final long GRACEFUL_SHUTDOWN_NO_TIMEOUT = -1;
  private boolean autoTuneFlowControlOn = false;
  private int initialConnectionWindow;
  private ChannelHandlerContext ctx;
  private final FlowControlPinger flowControlPing = new FlowControlPinger();

  private static final int BDP_MEASUREMENT_PING = 1234;
  private static final ByteBuf payloadBuf =
      unreleasableBuffer(directBuffer(8).writeLong(BDP_MEASUREMENT_PING));

  AbstractNettyHandler(Http2ConnectionDecoder decoder,
                       Http2ConnectionEncoder encoder,
                       Http2Settings initialSettings) {
    super(decoder, encoder, initialSettings);

    // During a graceful shutdown, wait until all streams are closed.
    gracefulShutdownTimeoutMillis(GRACEFUL_SHUTDOWN_NO_TIMEOUT);

    // Extract the connection window from the settings if it was set.
    this.initialConnectionWindow = initialSettings.initialWindowSize() == null ? -1 :
            initialSettings.initialWindowSize();
  }

  @Override
  public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
    this.ctx = ctx;
    // Sends the connection preface if we haven't already.
    super.handlerAdded(ctx);
    sendInitialConnectionWindow();
  }

  @Override
  public void channelActive(ChannelHandlerContext ctx) throws Exception {
    // Sends connection preface if we haven't already.
    super.channelActive(ctx);
    sendInitialConnectionWindow();
  }

  @Override
  public final void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
    Http2Exception embedded = getEmbeddedHttp2Exception(cause);
    if (embedded == null) {
      // There was no embedded Http2Exception, assume it's a connection error. Subclasses are
      // responsible for storing the appropriate status and shutting down the connection.
      onError(ctx, cause);
    } else {
      super.exceptionCaught(ctx, cause);
    }
  }

  protected final ChannelHandlerContext ctx() {
    return ctx;
  }

  /**
   * Sends initial connection window to the remote endpoint if necessary.
   */
  private void sendInitialConnectionWindow() throws Http2Exception {
    if (ctx.channel().isActive() && initialConnectionWindow > 0) {
      Http2Stream connectionStream = connection().connectionStream();
      int currentSize = connection().local().flowController().windowSize(connectionStream);
      int delta = initialConnectionWindow - currentSize;
      decoder().flowController().incrementWindowSize(connectionStream, delta);
      initialConnectionWindow = -1;
      ctx.flush();
    }
  }

  @VisibleForTesting
  FlowControlPinger flowControlPing() {
    return flowControlPing;
  }

  @VisibleForTesting
  void setAutoTuneFlowControl(boolean isOn) {
    autoTuneFlowControlOn = isOn;
  }

  /**
   * Class for handling flow control pinging and flow control window updates as necessary.
   */
  final class FlowControlPinger {

    private static final int MAX_WINDOW_SIZE = 8 * 1024 * 1024;
    private int pingCount;
    private int pingReturn;
    private boolean pinging;
    private int dataSizeSincePing;
    private float lastBandwidth; // bytes per second
    private long lastPingTime;

    public int payload() {
      return BDP_MEASUREMENT_PING;
    }

    public int maxWindow() {
      return MAX_WINDOW_SIZE;
    }

    public void onDataRead(int dataLength, int paddingLength) {
      if (!autoTuneFlowControlOn) {
        return;
      }
      if (!isPinging()) {
        setPinging(true);
        sendPing(ctx());
      }
      incrementDataSincePing(dataLength + paddingLength);
    }

    public void updateWindow() throws Http2Exception {
      if (!autoTuneFlowControlOn) {
        return;
      }
      pingReturn++;
      long elapsedTime = (System.nanoTime() - lastPingTime);
      if (elapsedTime == 0) {
        elapsedTime = 1;
      }
      long bandwidth = (getDataSincePing() * TimeUnit.SECONDS.toNanos(1)) / elapsedTime;
      Http2LocalFlowController fc = decoder().flowController();
      // Calculate new window size by doubling the observed BDP, but cap at max window
      int targetWindow = Math.min(getDataSincePing() * 2, MAX_WINDOW_SIZE);
      setPinging(false);
      int currentWindow = fc.initialWindowSize(connection().connectionStream());
      if (targetWindow > currentWindow && bandwidth > lastBandwidth) {
        lastBandwidth = bandwidth;
        int increase = targetWindow - currentWindow;
        fc.incrementWindowSize(connection().connectionStream(), increase);
        fc.initialWindowSize(targetWindow);
        Http2Settings settings = new Http2Settings();
        settings.initialWindowSize(targetWindow);
        frameWriter().writeSettings(ctx(), settings, ctx().newPromise());
      }

    }

    private boolean isPinging() {
      return pinging;
    }

    private void setPinging(boolean pingOut) {
      pinging = pingOut;
    }

    private void sendPing(ChannelHandlerContext ctx) {
      setDataSizeSincePing(0);
      lastPingTime = System.nanoTime();
      encoder().writePing(ctx, false, payloadBuf.slice(), ctx.newPromise());
      pingCount++;
    }

    private void incrementDataSincePing(int increase) {
      int currentSize = getDataSincePing();
      setDataSizeSincePing(currentSize + increase);
    }

    @VisibleForTesting
    int getPingCount() {
      return pingCount;
    }

    @VisibleForTesting
    int getPingReturn() {
      return pingReturn;
    }

    @VisibleForTesting
    int getDataSincePing() {
      return dataSizeSincePing;
    }

    @VisibleForTesting
    void setDataSizeSincePing(int dataSize) {
      dataSizeSincePing = dataSize;
    }
  }
}
