text: // Copyright 2021 DeepMind Technologies Limited
  //
  // 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.
  
  #ifndef OPEN_SPIEL_UTILS_DATA_LOGGER_H_
  #define OPEN_SPIEL_UTILS_DATA_LOGGER_H_
  
  #include <string>
  #include <utility>
  #include <vector>
  
  #include "open_spiel/abseil-cpp/absl/time/time.h"
  #include "open_spiel/utils/file.h"
  #include "open_spiel/utils/json.h"
  
  namespace open_spiel {
  
  class DataLogger {
   public:
    using Record = json::Object;
  
    virtual ~DataLogger() = default;
    virtual void Write(Record record) = 0;
    virtual void Flush() {}
  };
  
  // Writes to a file in http://jsonlines.org/ format.
  class DataLoggerJsonLines : public DataLogger {
   public:
    explicit DataLoggerJsonLines(const std::string& path, const std::string& name,
                                 bool flush = false,
                                 const std::string& mode = "w",
                                 absl::Time start_time = absl::Now());
    ~DataLoggerJsonLines() override;
  
    // The json lines logger is move only.
    DataLoggerJsonLines(DataLoggerJsonLines&& other) = default;
    DataLoggerJsonLines& operator=(DataLoggerJsonLines&& other) = default;
    DataLoggerJsonLines(const DataLoggerJsonLines&) = delete;
    DataLoggerJsonLines& operator=(const DataLoggerJsonLines&) = delete;
  
    void Write(Record record) override;
    void Flush() override;
  
   private:
    file::File fd_;
    bool flush_;
    absl::Time start_time_;
  };
  
  class DataLoggerNoop : public DataLogger {
   public:
    ~DataLoggerNoop() override = default;
    void Write(Record record) override {}
  };
  
  }  // namespace open_spiel
  
  #endif  // OPEN_SPIEL_UTILS_DATA_LOGGER_H_
  