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#ifndef FUSE_OPTIMIZERS__FIXED_LAG_SMOOTHER_HPP_
#define FUSE_OPTIMIZERS__FIXED_LAG_SMOOTHER_HPP_

#include <atomic>
#include <condition_variable>
#include <functional>
#include <memory>
#include <mutex>
#include <string>
#include <thread>
#include <vector>

#include <fuse_core/graph.hpp>
#include <fuse_core/transaction.hpp>
#include <fuse_optimizers/fixed_lag_smoother_params.hpp>
#include <fuse_optimizers/optimizer.hpp>
#include <fuse_optimizers/variable_stamp_index.hpp>
#include <fuse_graphs/hash_graph.hpp>
#include <fuse_constraints/marginalize_variables.hpp>

#include <rclcpp/rclcpp.hpp>
#include <std_srvs/srv/empty.hpp>


namespace fuse_optimizers
{

class FixedLagSmoother : public Optimizer
{
public:
  FUSE_SMART_PTR_DEFINITIONS(FixedLagSmoother)
  using ParameterType = FixedLagSmootherParams;

  FixedLagSmoother(
    fuse_core::node_interfaces::NodeInterfaces<ALL_FUSE_CORE_NODE_INTERFACES> interfaces,
    fuse_core::Graph::UniquePtr graph = nullptr
  );

  virtual ~FixedLagSmoother();

protected:
  struct TransactionQueueElement
  {
    std::string sensor_name;
    fuse_core::Transaction::SharedPtr transaction;

    const rclcpp::Time & stamp() const {return transaction->stamp();}
    const rclcpp::Time & minStamp() const {return transaction->minStamp();}
    const rclcpp::Time & maxStamp() const {return transaction->maxStamp();}
  };

  using TransactionQueue = std::vector<TransactionQueueElement>;

  // Read-only after construction
  std::thread optimization_thread_;
  ParameterType params_;

  // Inherently thread-safe
  std::atomic<bool> ignited_;
  std::atomic<bool> optimization_running_;
  std::atomic<bool> started_;

  // Guarded by pending_transactions_mutex_
  std::mutex pending_transactions_mutex_;
  TransactionQueue pending_transactions_;

  // Guarded by optimization_mutex_
  std::mutex optimization_mutex_;
  // fuse_core::Graph* graph_ member from the base class
  rclcpp::Time lag_expiration_;
  fuse_core::Transaction marginal_transaction_;
  VariableStampIndex timestamp_tracking_;
  ceres::Solver::Summary summary_;

  // Guarded by optimization_requested_mutex_
  std::mutex optimization_requested_mutex_;
  rclcpp::Time optimization_deadline_;
  bool optimization_request_;
  std::condition_variable optimization_requested_;

  // Guarded by start_time_mutex_
  mutable std::mutex start_time_mutex_;
  rclcpp::Time start_time_ {0, 0, RCL_ROS_TIME};

  // Ordering ROS objects with callbacks last
  rclcpp::TimerBase::SharedPtr optimize_timer_;
  rclcpp::Service<std_srvs::srv::Empty>::SharedPtr reset_service_server_;

  void autostart();

  void preprocessMarginalization(const fuse_core::Transaction & new_transaction);

  rclcpp::Time computeLagExpirationTime() const;

  std::vector<fuse_core::UUID> computeVariablesToMarginalize(const rclcpp::Time & lag_expiration);

  void postprocessMarginalization(const fuse_core::Transaction & marginal_transaction);

  void optimizationLoop();

  void optimizerTimerCallback();

  void processQueue(fuse_core::Transaction & transaction, const rclcpp::Time & lag_expiration);

  bool resetServiceCallback(
    const std::shared_ptr<std_srvs::srv::Empty::Request>,
    std::shared_ptr<std_srvs::srv::Empty::Response>
  );

  rclcpp::Time getStartTime() const
  {
    std::lock_guard<std::mutex> lock(start_time_mutex_);
    return start_time_;
  }

  void setStartTime(const rclcpp::Time & start_time)
  {
    std::lock_guard<std::mutex> lock(start_time_mutex_);
    start_time_ = start_time;
  }

  void transactionCallback(
    const std::string & sensor_name,
    fuse_core::Transaction::SharedPtr transaction) override;

  void setDiagnostics(diagnostic_updater::DiagnosticStatusWrapper & status) override;
};

}  // namespace fuse_optimizers

#endif  // FUSE_OPTIMIZERS__FIXED_LAG_SMOOTHER_HPP_