/*
 * Copyright 2019 The gRPC Authors
 *
 * 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.examples.hedging;

import io.grpc.Grpc;
import io.grpc.InsecureServerCredentials;
import io.grpc.Metadata;
import io.grpc.Server;
import io.grpc.ServerCall;
import io.grpc.ServerCall.Listener;
import io.grpc.ServerCallHandler;
import io.grpc.ServerInterceptor;
import io.grpc.examples.helloworld.GreeterGrpc;
import io.grpc.examples.helloworld.HelloReply;
import io.grpc.examples.helloworld.HelloRequest;
import io.grpc.stub.StreamObserver;
import java.io.IOException;
import java.util.Random;
import java.util.concurrent.TimeUnit;
import java.util.logging.Logger;

/**
 * A HelloWorld server that responds to requests with a long latency tail.
 */
public class HedgingHelloWorldServer {
  private static final Logger logger = Logger.getLogger(HedgingHelloWorldServer.class.getName());

  private Server server;

  private void start() throws IOException {
    /* The port on which the server should run */
    int port = 50051;
    server = Grpc.newServerBuilderForPort(port, InsecureServerCredentials.create())
        .addService(new GreeterImpl())
        .intercept(new LatencyInjectionInterceptor())
        .build()
        .start();
    logger.info("Server started, listening on " + port);
    Runtime.getRuntime().addShutdownHook(new Thread() {
      @Override
      public void run() {
        // Use stderr here since the logger may have been reset by its JVM shutdown hook.
        System.err.println("*** shutting down gRPC server since JVM is shutting down");
        try {
          HedgingHelloWorldServer.this.stop();
        } catch (InterruptedException e) {
          e.printStackTrace(System.err);
        }
        System.err.println("*** server shut down");
      }
    });
  }

  private void stop() throws InterruptedException {
    if (server != null) {
      server.shutdown().awaitTermination(30, TimeUnit.SECONDS);
    }
  }

  /**
   * Await termination on the main thread since the grpc library uses daemon threads.
   */
  private void blockUntilShutdown() throws InterruptedException {
    if (server != null) {
      server.awaitTermination();
    }
  }

  /**
   * Main launches the server from the command line.
   */
  public static void main(String[] args) throws IOException, InterruptedException {
    final HedgingHelloWorldServer server = new HedgingHelloWorldServer();
    server.start();
    server.blockUntilShutdown();
  }

  static class GreeterImpl extends GreeterGrpc.GreeterImplBase {

    @Override
    public void sayHello(HelloRequest req, StreamObserver<HelloReply> responseObserver) {
      HelloReply reply = HelloReply.newBuilder().setMessage("Hello " + req.getName()).build();
      responseObserver.onNext(reply);
      responseObserver.onCompleted();
    }
  }

  static class LatencyInjectionInterceptor implements ServerInterceptor {

    @Override
    public <HelloRequestT, HelloReplyT> Listener<HelloRequestT> interceptCall(
        ServerCall<HelloRequestT, HelloReplyT> call,
        Metadata headers, ServerCallHandler<HelloRequestT, HelloReplyT> next) {
      int random = new Random().nextInt(100);
      long delay = 0;
      if (random < 1) {
        delay = 10_000;
      } else if (random < 5) {
        delay = 5_000;
      } else if (random < 10) {
        delay = 2_000;
      }

      if (delay > 0) {
        try {
          Thread.sleep(delay);
        } catch (InterruptedException e) {
          Thread.currentThread().interrupt();
        }
      }
      return next.startCall(call, headers);
    }
  }
}
