#ifndef FESA_ANALYSIS_HHT_REDUCED_INTEGRATOR_H_
#define FESA_ANALYSIS_HHT_REDUCED_INTEGRATOR_H_
#include <utility>
#include "analysis/hht_reduced_internal.h"
namespace fesa::hht_reduced_internal {
struct ReducedHistory {
  Vector p{0U};
  Vector velocity{0U};
  Vector acceleration{0U};
  Vector algorithmic_acceleration{0U};
  Vector z{0U};
};

/// @brief Keeps every private predictor compensation channel before a trial.
struct ReducedShellPredictor {
  Vector pp{0U};
  Vector vpp{0U};
  Vector coordinate_low{0U};
  Vector increment_trace{0U};
  Vector increment_trace_compensation{0U};
  Vector increment_trace_absolute_sum{0U};
};

struct ReducedShellRateRequest {
  const FixedChart& chart;
  const ReducedHistory& history;
  const Vector& trial_algorithmic;
  const Vector& vpp;
  bool copy_translation_rates;
  const Vector& retained_velocity;
  const Vector& retained_acceleration;
  double h;
  const HhtParameters& parameters;
};

struct ReducedShellTrialRates {
  Vector velocity{0U};
  Vector acceleration{0U};
};

/// @brief Handles private shell predictors and exact sparse rate
/// reconstruction.
/// @note Chart/root/solver are non-owning call views; no history is committed.
class ShellHhtIntegrator {
public:
  virtual ~ShellHhtIntegrator() = default;
  virtual ReducedShellPredictor
  Predict(const ReducedHistory& history, double h,
          const HhtParameters& parameters) const = 0;
  /// @note Output buffers have history.p.Size() entries and do not alias any
  /// request input or each other. The caller owns their allocation/lifetime.
  virtual void EvaluateRates(const ReducedShellRateRequest& request,
                              Vector& velocity, Vector& acceleration) const = 0;
  virtual Result<ReconstructedRates>
  ReconstructPhysicalRates(const FixedChart& chart, const EmbeddingRoot& root,
                           const Vector& velocity, const Vector& acceleration,
                           TangentSolver& solver) const = 0;
};

/// @brief Sequences one private predictor, pending endpoint and commit.
/// @note Callables are synchronous borrowed views. They retain all original
/// evaluation/diagnostic/commit policy; no accepted history is owned here.
template <typename Evaluate, typename Commit>
Status RunReducedHhtStep(const ShellHhtIntegrator& integrator,
                         const ReducedHistory& history, double h,
                         const HhtParameters& parameters,
                         Evaluate&& evaluate, Commit&& commit) {
  auto predictor = integrator.Predict(history, h, parameters);
  auto pending = evaluate(integrator, std::move(predictor));
  if (!pending.HasValue()) return pending.GetStatus();
  return commit(std::move(pending.Value()));
}
}  // namespace fesa::hht_reduced_internal
#endif  // FESA_ANALYSIS_HHT_REDUCED_INTEGRATOR_H_