// 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_SOLVEWITHGUESS_H
#define EIGEN_SOLVEWITHGUESS_H

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

namespace Eigen {

template <typename Decomposition, typename RhsType, typename GuessType>
class SolveWithGuess;

/** \class SolveWithGuess
 * \ingroup IterativeLinearSolvers_Module
 *
 * \brief Pseudo expression representing a solving operation
 *
 * \tparam Decomposition the type of the matrix or decomposition object
 * \tparam RhsType the type of the right-hand side
 * \tparam GuessType the type of the initial guess
 *
 * This class represents an expression of A.solve(B)
 * and most of the time this is the only way it is used.
 *
 */
namespace internal {

template <typename Decomposition, typename RhsType, typename GuessType>
struct traits<SolveWithGuess<Decomposition, RhsType, GuessType> > : traits<Solve<Decomposition, RhsType> > {};

}  // namespace internal

template <typename Decomposition, typename RhsType, typename GuessType>
class SolveWithGuess : public internal::generic_xpr_base<SolveWithGuess<Decomposition, RhsType, GuessType>, MatrixXpr,
                                                         typename internal::traits<RhsType>::StorageKind>::type {
 public:
  using Scalar = typename internal::traits<SolveWithGuess>::Scalar;
  using PlainObject = typename internal::traits<SolveWithGuess>::PlainObject;
  using Base = typename internal::generic_xpr_base<SolveWithGuess<Decomposition, RhsType, GuessType>, MatrixXpr,
                                                   typename internal::traits<RhsType>::StorageKind>::type;
  using Nested = typename internal::ref_selector<SolveWithGuess>::type;

  SolveWithGuess(const Decomposition &dec, const RhsType &rhs, const GuessType &guess)
      : m_dec(dec), m_rhs(rhs), m_guess(guess) {}

  EIGEN_DEVICE_FUNC constexpr Index rows() const noexcept { return m_dec.cols(); }
  EIGEN_DEVICE_FUNC constexpr Index cols() const noexcept { return m_rhs.cols(); }

  EIGEN_DEVICE_FUNC const Decomposition &dec() const { return m_dec; }
  EIGEN_DEVICE_FUNC const RhsType &rhs() const { return m_rhs; }
  EIGEN_DEVICE_FUNC const GuessType &guess() const { return m_guess; }

 protected:
  const Decomposition &m_dec;
  const RhsType &m_rhs;
  const GuessType &m_guess;

 private:
  Scalar coeff(Index row, Index col) const;
  Scalar coeff(Index i) const;
};

namespace internal {

// Evaluator of SolveWithGuess -> eval into a temporary
template <typename Decomposition, typename RhsType, typename GuessType>
struct evaluator<SolveWithGuess<Decomposition, RhsType, GuessType> >
    : public evaluator<typename SolveWithGuess<Decomposition, RhsType, GuessType>::PlainObject> {
  using SolveType = SolveWithGuess<Decomposition, RhsType, GuessType>;
  using PlainObject = typename SolveType::PlainObject;
  using Base = evaluator<PlainObject>;

  evaluator(const SolveType &solve) : m_result(solve.rows(), solve.cols()) {
    internal::construct_at<Base>(this, m_result);
    m_result = solve.guess();
    solve.dec()._solve_with_guess_impl(solve.rhs(), m_result);
  }

 protected:
  PlainObject m_result;
};

// Specialization for "dst = dec.solveWithGuess(rhs)"
// NOTE we need to specialize it for Dense2Dense to avoid ambiguous specialization error and a Sparse2Sparse
// specialization must exist somewhere
template <typename DstXprType, typename DecType, typename RhsType, typename GuessType, typename Scalar>
struct Assignment<DstXprType, SolveWithGuess<DecType, RhsType, GuessType>, internal::assign_op<Scalar, Scalar>,
                  Dense2Dense> {
  using SrcXprType = SolveWithGuess<DecType, RhsType, GuessType>;
  static void run(DstXprType &dst, const SrcXprType &src, const internal::assign_op<Scalar, Scalar> &) {
    Index dstRows = src.rows();
    Index dstCols = src.cols();
    if ((dst.rows() != dstRows) || (dst.cols() != dstCols)) dst.resize(dstRows, dstCols);

    dst = src.guess();
    src.dec()._solve_with_guess_impl(src.rhs(), dst);
  }
};

}  // end namespace internal

}  // end namespace Eigen

#endif  // EIGEN_SOLVEWITHGUESS_H