#ifndef FESA_CONSTRAINTS_ESSENTIAL_CONSTRAINTS_H_
#define FESA_CONSTRAINTS_ESSENTIAL_CONSTRAINTS_H_

#include "fesa/core/status.h"
#include "fesa/math/sparse_matrix.h"
#include "fesa/math/vector.h"

namespace fesa {

class DofManager;

/// @brief Stores full-stiffness blocks in stable free/constrained order.
struct PartitionedStiffness {
  SparseMatrix kff;
  SparseMatrix kfc;
  SparseMatrix kcf;
  SparseMatrix kcc;
};

/// @brief Applies stable prescribed-displacement elimination.
class EssentialConstraints {
 public:
  /// @brief Partitions full stiffness into Kff, Kfc, Kcf, and Kcc.
  static Result<PartitionedStiffness> Partition(const SparseMatrix& full,
                                                const DofManager& dofs);

  /// @brief Gathers a full vector in stable free-equation order.
  static Vector GatherFree(const Vector& full, const DofManager& dofs);

  /// @brief Gathers a full vector in stable constrained-DOF order.
  static Vector GatherConstrained(const Vector& full, const DofManager& dofs);

  /// @brief Reconstructs full d from stable df and exact prescribed dc.
  static Vector ReconstructFull(const Vector& free_values,
                                const Vector& constrained_values,
                                const DofManager& dofs);
};

}  // namespace fesa

#endif  // FESA_CONSTRAINTS_ESSENTIAL_CONSTRAINTS_H_