/*
 * Copyright DataStax, Inc.
 *
 * 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 com.datastax.oss.driver.internal.core.channel;

import io.netty.channel.ChannelDuplexHandler;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelPromise;
import io.netty.util.concurrent.Future;
import io.netty.util.concurrent.ImmediateEventExecutor;
import io.netty.util.concurrent.PromiseCombiner;
import java.net.SocketAddress;
import net.jcip.annotations.NotThreadSafe;

A handler that delays the promise returned by bootstrap.connect(), in order to run a custom initialization process before making the channel available to clients. 
This handler is not shareable. It must be installed by the channel initializer, as the last
channel in the pipeline.
It will be notified via onRealConnect(ChannelHandlerContext) when the real underlying connection is established. It can then start sending messages on the connection, while external clients are still waiting on their promise. Once the custom initialization is finished, the clients' promise can be completed with setConnectSuccess() or setConnectFailure(Throwable). /**
 * A handler that delays the promise returned by {@code bootstrap.connect()}, in order to run a
 * custom initialization process before making the channel available to clients.
 *
 * <p>This handler is not shareable. It must be installed by the channel initializer, as the last
 * channel in the pipeline.
 *
 * <p>It will be notified via {@link #onRealConnect(ChannelHandlerContext)} when the real underlying
 * connection is established. It can then start sending messages on the connection, while external
 * clients are still waiting on their promise. Once the custom initialization is finished, the
 * clients' promise can be completed with {@link #setConnectSuccess()} or {@link
 * #setConnectFailure(Throwable)}.
 */
@NotThreadSafe
public abstract class ConnectInitHandler extends ChannelDuplexHandler {
  // the completion of the custom initialization process
  private ChannelPromise initPromise;
  private ChannelHandlerContext ctx;

  @Override
  public void connect(
      ChannelHandlerContext ctx,
      SocketAddress remoteAddress,
      SocketAddress localAddress,
      ChannelPromise callerPromise)
      throws Exception {
    this.ctx = ctx;
    initPromise = ctx.channel().newPromise();

    // the completion of the real underlying connection:
    ChannelPromise realConnectPromise = ctx.channel().newPromise();
    super.connect(ctx, remoteAddress, localAddress, realConnectPromise);
    realConnectPromise.addListener(future -> onRealConnect(ctx));

    // Make the caller's promise wait on the other two:
    PromiseCombiner combiner = new PromiseCombiner(ImmediateEventExecutor.INSTANCE);
    combiner.addAll(new Future[] {realConnectPromise, initPromise});
    combiner.finish(callerPromise);
  }

  protected abstract void onRealConnect(ChannelHandlerContext ctx);

  protected boolean setConnectSuccess() {
    boolean result = initPromise.trySuccess();
    if (result) {
      ctx.pipeline().remove(this);
    }
    return result;
  }

  protected void setConnectFailure(Throwable cause) {
    if (initPromise.tryFailure(cause)) {
      ctx.channel().close();
    }
  }
}