/*
    * Copyright 2025 The Netty Project
    *
    * The Netty Project licenses this file to you 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:
    *
    * https://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.netty.handler.codec.http2;
  
  import io.netty.channel.ChannelFuture;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.channel.ChannelPromise;
  import io.netty.util.concurrent.Ticker;
  import io.netty.util.internal.logging.InternalLogger;
  import io.netty.util.internal.logging.InternalLoggerFactory;
  
  import java.util.concurrent.TimeUnit;
  
  /**
   * {@link DecoratingHttp2ConnectionEncoder} which guards against a remote peer that will trigger a massive amount
   * of RST frames on an existing connection.
   * This encoder will tear-down the connection once we reached the configured limit to reduce the risk of DDOS.
   */
  final class Http2MaxRstFrameLimitEncoder extends DecoratingHttp2ConnectionEncoder {
      private static final InternalLogger logger = InternalLoggerFactory.getInstance(Http2MaxRstFrameLimitEncoder.class);
  
      private final long nanosPerWindow;
      private final int maxRstFramesPerWindow;
      private final Ticker ticker;
      private long lastRstFrameNano;
      private int sendRstInWindow;
      private Http2LifecycleManager lifecycleManager;
  
      Http2MaxRstFrameLimitEncoder(Http2ConnectionEncoder delegate, int maxRstFramesPerWindow, int secondsPerWindow) {
          this(delegate, maxRstFramesPerWindow, secondsPerWindow, Ticker.systemTicker());
      }
  
      Http2MaxRstFrameLimitEncoder(Http2ConnectionEncoder delegate, int maxRstFramesPerWindow, int secondsPerWindow,
                                   Ticker ticker) {
          super(delegate);
          this.maxRstFramesPerWindow = maxRstFramesPerWindow;
          this.nanosPerWindow = TimeUnit.SECONDS.toNanos(secondsPerWindow);
          this.ticker = ticker;
          lastRstFrameNano = ticker.nanoTime();
      }
  
      @Override
      public void lifecycleManager(Http2LifecycleManager lifecycleManager) {
          this.lifecycleManager = lifecycleManager;
          super.lifecycleManager(lifecycleManager);
      }
  
      @Override
      public ChannelFuture writeRstStream(ChannelHandlerContext ctx, int streamId, long errorCode,
                                          ChannelPromise promise) {
          ChannelFuture future = super.writeRstStream(ctx, streamId, errorCode, promise);
          if (countRstFrameErrorCode(errorCode)) {
              long currentNano = ticker.nanoTime();
              if (currentNano - lastRstFrameNano >= nanosPerWindow) {
                  lastRstFrameNano = currentNano;
                  sendRstInWindow = 1;
              } else {
                  sendRstInWindow++;
                  if (sendRstInWindow > maxRstFramesPerWindow) {
                      Http2Exception exception = Http2Exception.connectionError(Http2Error.ENHANCE_YOUR_CALM,
                              "Maximum number %d of RST frames frames reached within %d seconds", maxRstFramesPerWindow,
                              TimeUnit.NANOSECONDS.toSeconds(nanosPerWindow));
  
                      logger.debug("{} Maximum number {} of RST frames reached within {} seconds, " +
                                      "closing connection with {} error", ctx.channel(), maxRstFramesPerWindow,
                              TimeUnit.NANOSECONDS.toSeconds(nanosPerWindow), exception.error(),
                              exception);
                      // First notify the Http2LifecycleManager and then close the connection.
                      lifecycleManager.onError(ctx, true, exception);
                      ctx.close();
                  }
              }
          }
  
          return future;
      }
  
      private boolean countRstFrameErrorCode(long errorCode) {
          // Don't count CANCEL and NO_ERROR as these might be ok.
          return errorCode != Http2Error.CANCEL.code() && errorCode != Http2Error.NO_ERROR.code();
      }
  }