// This file is part of Eigen, a lightweight C++ template library
// for linear algebra.
//
// Copyright (C) 2014 Gael Guennebaud <gael.guennebaud@inria.fr>
//
// This Source Code Form is subject to the terms of the Mozilla
// Public License v. 2.0. If a copy of the MPL was not distributed
// with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
// SPDX-License-Identifier: MPL-2.0

#ifndef EIGEN_SPARSESOLVERBASE_H
#define EIGEN_SPARSESOLVERBASE_H

// IWYU pragma: private
#include "./InternalHeaderCheck.h"

namespace Eigen {

namespace internal {

/** \internal
 * Helper functions to solve with a sparse right-hand-side and result.
 * The rhs is decomposed into small vertical panels which are solved through dense temporaries.
 */
template <typename Decomposition, typename Rhs, typename Dest>
std::enable_if_t<Rhs::ColsAtCompileTime != 1 && Dest::ColsAtCompileTime != 1> solve_sparse_through_dense_panels(
    const Decomposition& dec, const Rhs& rhs, Dest& dest) {
  EIGEN_STATIC_ASSERT((Dest::Flags & RowMajorBit) == 0, THIS_METHOD_IS_ONLY_FOR_COLUMN_MAJOR_MATRICES);
  typedef typename Dest::Scalar DestScalar;
  // we process the sparse rhs per block of NbColsAtOnce columns temporarily stored into a dense matrix.
  static const Index NbColsAtOnce = 4;
  Index rhsCols = rhs.cols();
  Index size = rhs.rows();
  // the temporary matrices do not need more columns than NbColsAtOnce:
  Index tmpCols = (std::min)(rhsCols, NbColsAtOnce);
  Eigen::Matrix<DestScalar, Dynamic, Dynamic> tmp(size, tmpCols);
  Eigen::Matrix<DestScalar, Dynamic, Dynamic> tmpX(size, tmpCols);
  for (Index k = 0; k < rhsCols; k += NbColsAtOnce) {
    Index actualCols = std::min<Index>(rhsCols - k, NbColsAtOnce);
    tmp.leftCols(actualCols) = rhs.middleCols(k, actualCols);
    tmpX.leftCols(actualCols) = dec.solve(tmp.leftCols(actualCols));
    dest.middleCols(k, actualCols) = tmpX.leftCols(actualCols).sparseView();
  }
}

// Overload for vector as rhs
template <typename Decomposition, typename Rhs, typename Dest>
std::enable_if_t<Rhs::ColsAtCompileTime == 1 || Dest::ColsAtCompileTime == 1> solve_sparse_through_dense_panels(
    const Decomposition& dec, const Rhs& rhs, Dest& dest) {
  typedef typename Dest::Scalar DestScalar;
  Index size = rhs.rows();
  Eigen::Matrix<DestScalar, Dynamic, 1> rhs_dense(rhs);
  Eigen::Matrix<DestScalar, Dynamic, 1> dest_dense(size);
  dest_dense = dec.solve(rhs_dense);
  dest = dest_dense.sparseView();
}

}  // end namespace internal

/** \class SparseSolverBase
 * \ingroup SparseCore_Module
 * \brief A base class for sparse solvers
 *
 * \tparam Derived the actual type of the solver.
 *
 */
template <typename Derived>
class SparseSolverBase {
 public:
  /** Default constructor */
  SparseSolverBase() = default;

  SparseSolverBase(const SparseSolverBase&) = delete;
  SparseSolverBase& operator=(const SparseSolverBase&) = delete;

  SparseSolverBase(SparseSolverBase&& other) : m_isInitialized{other.m_isInitialized} {}

  ~SparseSolverBase() = default;

  Derived& derived() { return *static_cast<Derived*>(this); }
  const Derived& derived() const { return *static_cast<const Derived*>(this); }

  /** \returns an expression of the solution x of \f$ A x = b \f$ using the current decomposition of A.
   *
   * \sa compute()
   */
  template <typename Rhs>
  inline Solve<Derived, Rhs> solve(const MatrixBase<Rhs>& b) const {
    eigen_assert(m_isInitialized && "Solver is not initialized.");
    eigen_assert(derived().rows() == b.rows() && "solve(): invalid number of rows of the right hand side matrix b");
    return Solve<Derived, Rhs>(derived(), b.derived());
  }

  /** \returns an expression of the solution x of \f$ A x = b \f$ using the current decomposition of A.
   *
   * \sa compute()
   */
  template <typename Rhs>
  inline Solve<Derived, Rhs> solve(const SparseMatrixBase<Rhs>& b) const {
    eigen_assert(m_isInitialized && "Solver is not initialized.");
    eigen_assert(derived().rows() == b.rows() && "solve(): invalid number of rows of the right hand side matrix b");
    return Solve<Derived, Rhs>(derived(), b.derived());
  }

#ifndef EIGEN_PARSED_BY_DOXYGEN
  /** \internal default implementation of solving with a sparse rhs */
  template <typename Rhs, typename Dest>
  void _solve_impl(const SparseMatrixBase<Rhs>& b, SparseMatrixBase<Dest>& dest) const {
    internal::solve_sparse_through_dense_panels(derived(), b.derived(), dest.derived());
  }
#endif  // EIGEN_PARSED_BY_DOXYGEN

 protected:
  mutable bool m_isInitialized = false;
};

}  // end namespace Eigen

#endif  // EIGEN_SPARSESOLVERBASE_H