text: /*
   * Copyright 2019 Google LLC.
   * 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
   *
   *     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.
   */
  
  #ifndef PRIVATE_JOIN_AND_COMPUTE_MESSAGE_SINK_H_
  #define PRIVATE_JOIN_AND_COMPUTE_MESSAGE_SINK_H_
  
  #include "absl/memory/memory.h"
  #include "private_join_and_compute/private_join_and_compute.pb.h"
  #include "private_join_and_compute/util/status.inc"
  
  namespace private_join_and_compute {
  
  // An interface for message sinks.
  template <typename T>
  class MessageSink {
   public:
    virtual ~MessageSink() = default;
  
    // Subclasses should accept a message and process it appropriately.
    virtual Status Send(const T& message) = 0;
  
   protected:
    MessageSink() = default;
  };
  
  // A dummy message sink, that simply stores the last message received, and
  // allows retrieval. Intended for testing.
  template <typename T>
  class DummyMessageSink : public MessageSink<T> {
   public:
    ~DummyMessageSink() override = default;
  
    // Simply copies the message.
    Status Send(const T& message) override {
      last_message_ = absl::make_unique<T>(message);
      return OkStatus();
    }
  
    // Will fail if no message was received.
    const T& last_message() { return *last_message_; }
  
   private:
    std::unique_ptr<T> last_message_;
  };
  
  }  // namespace private_join_and_compute
  
  #endif  // PRIVATE_JOIN_AND_COMPUTE_MESSAGE_SINK_H_
  