#include <grpcpp/grpcpp.h>

#include <iostream>
#include <memory>
#include <string>

#include "greeter.grpc.fb.h"
#include "greeter_generated.h"

class GreeterServiceImpl final : public Greeter::Service {
  virtual grpc::Status SayHello(
      grpc::ServerContext* context,
      const flatbuffers::grpc::Message<HelloRequest>* request_msg,
      flatbuffers::grpc::Message<HelloReply>* response_msg) override {
    flatbuffers::grpc::MessageBuilder mb_;

    // We call GetRoot to "parse" the message. Verification is already
    // performed by default. See the notes below for more details.
    const HelloRequest* request = request_msg->GetRoot();

    // Fields are retrieved as usual with FlatBuffers
    const std::string& name = request->name()->str();

    // `flatbuffers::grpc::MessageBuilder` is a `FlatBufferBuilder` with a
    // special allocator for efficient gRPC buffer transfer, but otherwise
    // usage is the same as usual.
    auto msg_offset = mb_.CreateString("Hello, " + name);
    auto hello_offset = CreateHelloReply(mb_, msg_offset);
    mb_.Finish(hello_offset);

    // The `ReleaseMessage<T>()` function detaches the message from the
    // builder, so we can transfer the resopnse to gRPC while simultaneously
    // detaching that memory buffer from the builer.
    *response_msg = mb_.ReleaseMessage<HelloReply>();
    assert(response_msg->Verify());

    // Return an OK status.
    return grpc::Status::OK;
  }

  virtual grpc::Status SayManyHellos(
      grpc::ServerContext* context,
      const flatbuffers::grpc::Message<ManyHellosRequest>* request_msg,
      grpc::ServerWriter<flatbuffers::grpc::Message<HelloReply>>* writer)
      override {
    // The streaming usage below is simply a combination of standard gRPC
    // streaming with the FlatBuffers usage shown above.
    const ManyHellosRequest* request = request_msg->GetRoot();
    const std::string& name = request->name()->str();
    int num_greetings = request->num_greetings();

    for (int i = 0; i < num_greetings; i++) {
      auto msg_offset = mb_.CreateString("Many hellos, " + name);
      auto hello_offset = CreateHelloReply(mb_, msg_offset);
      mb_.Finish(hello_offset);
      writer->Write(mb_.ReleaseMessage<HelloReply>());
    }

    return grpc::Status::OK;
  }

  flatbuffers::grpc::MessageBuilder mb_;
};

void RunServer() {
  std::string server_address("0.0.0.0:50051");
  GreeterServiceImpl service;

  grpc::ServerBuilder builder;
  builder.AddListeningPort(server_address, grpc::InsecureServerCredentials());
  builder.RegisterService(&service);
  std::unique_ptr<grpc::Server> server(builder.BuildAndStart());
  std::cerr << "Server listening on " << server_address << std::endl;

  server->Wait();
}

int main(int argc, const char* argv[]) {
  RunServer();
  return 0;
}
