// SPDX-FileCopyrightText: 2017 - 2024 The Ginkgo authors
//
// SPDX-License-Identifier: BSD-3-Clause

#ifndef GKO_PUBLIC_CORE_SOLVER_TRIANGULAR_HPP_
#define GKO_PUBLIC_CORE_SOLVER_TRIANGULAR_HPP_


#include <memory>
#include <utility>


#include <ginkgo/core/base/abstract_factory.hpp>
#include <ginkgo/core/base/array.hpp>
#include <ginkgo/core/base/dim.hpp>
#include <ginkgo/core/base/exception_helpers.hpp>
#include <ginkgo/core/base/lin_op.hpp>
#include <ginkgo/core/base/polymorphic_object.hpp>
#include <ginkgo/core/base/types.hpp>
#include <ginkgo/core/base/utils.hpp>
#include <ginkgo/core/config/config.hpp>
#include <ginkgo/core/config/registry.hpp>
#include <ginkgo/core/log/logger.hpp>
#include <ginkgo/core/matrix/csr.hpp>
#include <ginkgo/core/matrix/identity.hpp>
#include <ginkgo/core/solver/solver_base.hpp>


namespace gko {
namespace solver {


struct SolveStruct;


/**
 * A helper for algorithm selection in the triangular solvers.
 * It currently only matters for the Cuda executor as there,
 * we have a choice between the Ginkgo syncfree and cuSPARSE implementations.
 */
enum class trisolve_algorithm { sparselib, syncfree };


template <typename ValueType, typename IndexType>
class UpperTrs;


/**
 * LowerTrs is the triangular solver which solves the system L x = b, when L is
 * a lower triangular matrix. It works best when passing in a matrix in CSR
 * format. If the matrix is not in CSR, then the generate step converts it into
 * a CSR matrix. The generation fails if the matrix is not convertible to CSR.
 *
 * @note As the constructor uses the copy and convert functionality, it is not
 *       possible to create a empty solver or a solver with a matrix in any
 *       other format other than CSR, if none of the executor modules are being
 *       compiled with.
 *
 * @tparam ValueType  precision of matrix elements
 * @tparam IndexType  precision of matrix indices
 *
 * @ingroup solvers
 * @ingroup LinOp
 */
template <typename ValueType = default_precision, typename IndexType = int32>
class LowerTrs : public EnableLinOp<LowerTrs<ValueType, IndexType>>,
                 public EnableSolverBase<LowerTrs<ValueType, IndexType>,
                                         matrix::Csr<ValueType, IndexType>>,
                 public Transposable {
    friend class EnableLinOp<LowerTrs>;
    friend class EnablePolymorphicObject<LowerTrs, LinOp>;
    friend class UpperTrs<ValueType, IndexType>;

public:
    using value_type = ValueType;
    using index_type = IndexType;
    using transposed_type = UpperTrs<ValueType, IndexType>;

    std::unique_ptr<LinOp> transpose() const override;

    std::unique_ptr<LinOp> conj_transpose() const override;

    GKO_CREATE_FACTORY_PARAMETERS(parameters, Factory)
    {
        /**
         * Number of right hand sides.
         *
         * @note This value is currently only required for the CUDA
         *       trisolve_algorithm::sparselib algorithm.
         */
        gko::size_type GKO_FACTORY_PARAMETER_SCALAR(num_rhs, 1u);

        /**
         * Should the solver use the values on the diagonal of the system matrix
         * (false) or should it assume they are 1.0 (true)?
         */
        bool GKO_FACTORY_PARAMETER_SCALAR(unit_diagonal, false);

        /**
         * Select the implementation which is supposed to be used for
         * the triangular solver. This only matters for the Cuda
         * executor where the choice is between the Ginkgo (syncfree) and the
         * cuSPARSE (sparselib) implementation. Default is sparselib.
         */
        trisolve_algorithm GKO_FACTORY_PARAMETER_SCALAR(
            algorithm, trisolve_algorithm::sparselib);
    };
    GKO_ENABLE_LIN_OP_FACTORY(LowerTrs, parameters, Factory);
    GKO_ENABLE_BUILD_METHOD(Factory);

    /**
     * Create the parameters from the property_tree.
     * Because this is directly tied to the specific type, the value/index type
     * settings within config are ignored and type_descriptor is only used
     * for children configs.
     *
     * @param config  the property tree for setting
     * @param context  the registry
     * @param td_for_child  the type descriptor for children configs. The
     *                      default uses the value/index type of this class.
     *
     * @return parameters
     */
    static parameters_type parse(
        const config::pnode& config, const config::registry& context,
        const config::type_descriptor& td_for_child =
            config::make_type_descriptor<ValueType, IndexType>());

    /**
     * Copy-assigns a triangular solver. Preserves the executor, shallow-copies
     * the system matrix. If the executors mismatch, clones system matrix onto
     * this executor. Solver analysis information will be regenerated.
     */
    LowerTrs(const LowerTrs&);

    /**
     * Move-assigns a triangular solver. Preserves the executor, moves
     * the system matrix. If the executors mismatch, clones system matrix onto
     * this executor and regenerates solver analysis information. Moved-from
     * object is empty (0x0 and nullptr system matrix)
     */
    LowerTrs(LowerTrs&&);

    /**
     * Copy-constructs a triangular solver. Preserves the executor,
     * shallow-copies the system matrix. Solver analysis information will be
     * regenerated.
     */
    LowerTrs& operator=(const LowerTrs&);

    /**
     * Move-constructs a triangular solver. Preserves the executor, moves
     * the system matrix and solver analysis information. Moved-from
     * object is empty (0x0 and nullptr system matrix)
     */
    LowerTrs& operator=(LowerTrs&&);

protected:
    using CsrMatrix = matrix::Csr<ValueType, IndexType>;

    void apply_impl(const LinOp* b, LinOp* x) const override;

    void apply_impl(const LinOp* alpha, const LinOp* b, const LinOp* beta,
                    LinOp* x) const override;

    /**
     * Generates the analysis structure from the system matrix and the right
     * hand side needed for the level solver.
     */
    void generate();

    explicit LowerTrs(std::shared_ptr<const Executor> exec)
        : EnableLinOp<LowerTrs>(std::move(exec))
    {}

    explicit LowerTrs(const Factory* factory,
                      std::shared_ptr<const LinOp> system_matrix)
        : EnableLinOp<LowerTrs>(factory->get_executor(),
                                gko::transpose(system_matrix->get_size())),
          EnableSolverBase<LowerTrs<ValueType, IndexType>, CsrMatrix>{
              copy_and_convert_to<CsrMatrix>(factory->get_executor(),
                                             system_matrix)},
          parameters_{factory->get_parameters()}
    {
        this->generate();
    }

private:
    std::shared_ptr<solver::SolveStruct> solve_struct_;
};


template <typename ValueType, typename IndexType>
struct workspace_traits<LowerTrs<ValueType, IndexType>> {
    using Solver = LowerTrs<ValueType, IndexType>;
    // number of vectors used by this workspace
    static int num_vectors(const Solver&);
    // number of arrays used by this workspace
    static int num_arrays(const Solver&);
    // array containing the num_vectors names for the workspace vectors
    static std::vector<std::string> op_names(const Solver&);
    // array containing the num_arrays names for the workspace vectors
    static std::vector<std::string> array_names(const Solver&);
    // array containing all varying scalar vectors (independent of problem size)
    static std::vector<int> scalars(const Solver&);
    // array containing all varying vectors (dependent on problem size)
    static std::vector<int> vectors(const Solver&);

    // transposed input vector
    constexpr static int transposed_b = 0;
    // transposed output vector
    constexpr static int transposed_x = 1;
};


/**
 * UpperTrs is the triangular solver which solves the system U x = b, when U is
 * an upper triangular matrix. It works best when passing in a matrix in CSR
 * format. If the matrix is not in CSR, then the generate step converts it into
 * a CSR matrix. The generation fails if the matrix is not convertible to CSR.
 *
 * @note As the constructor uses the copy and convert functionality, it is not
 *       possible to create a empty solver or a solver with a matrix in any
 *       other format other than CSR, if none of the executor modules are being
 *       compiled with.
 *
 * @tparam ValueType  precision of matrix elements
 * @tparam IndexType  precision of matrix indices
 *
 * @ingroup solvers
 * @ingroup LinOp
 */
template <typename ValueType = default_precision, typename IndexType = int32>
class UpperTrs : public EnableLinOp<UpperTrs<ValueType, IndexType>>,
                 public EnableSolverBase<UpperTrs<ValueType, IndexType>,
                                         matrix::Csr<ValueType, IndexType>>,
                 public Transposable {
    friend class EnableLinOp<UpperTrs>;
    friend class EnablePolymorphicObject<UpperTrs, LinOp>;
    friend class LowerTrs<ValueType, IndexType>;

public:
    using value_type = ValueType;
    using index_type = IndexType;
    using transposed_type = LowerTrs<ValueType, IndexType>;

    std::unique_ptr<LinOp> transpose() const override;

    std::unique_ptr<LinOp> conj_transpose() const override;

    GKO_CREATE_FACTORY_PARAMETERS(parameters, Factory)
    {
        /**
         * Number of right hand sides.
         *
         * @note This value is currently only required for the CUDA
         *       trisolve_algorithm::sparselib algorithm.
         */
        gko::size_type GKO_FACTORY_PARAMETER_SCALAR(num_rhs, 1u);

        /**
         * Should the solver use the values on the diagonal of the system matrix
         * (false) or should it assume they are 1.0 (true)?
         */
        bool GKO_FACTORY_PARAMETER_SCALAR(unit_diagonal, false);

        /**
         * Select the implementation which is supposed to be used for
         * the triangular solver. This only matters for the Cuda
         * executor where the choice is between the Ginkgo (syncfree) and the
         * cuSPARSE (sparselib) implementation. Default is sparselib.
         */
        trisolve_algorithm GKO_FACTORY_PARAMETER_SCALAR(
            algorithm, trisolve_algorithm::sparselib);
    };
    GKO_ENABLE_LIN_OP_FACTORY(UpperTrs, parameters, Factory);
    GKO_ENABLE_BUILD_METHOD(Factory);

    /**
     * Create the parameters from the property_tree.
     * Because this is directly tied to the specific type, the value/index type
     * settings within config are ignored and type_descriptor is only used
     * for children configs.
     *
     * @param config  the property tree for setting
     * @param context  the registry
     * @param td_for_child  the type descriptor for children configs. The
     *                      default uses the value/index type of this class.
     *
     * @return parameters
     */
    static parameters_type parse(
        const config::pnode& config, const config::registry& context,
        const config::type_descriptor& td_for_child =
            config::make_type_descriptor<ValueType, IndexType>());

    /**
     * Copy-assigns a triangular solver. Preserves the executor, shallow-copies
     * the system matrix. If the executors mismatch, clones system matrix onto
     * this executor. Solver analysis information will be regenerated.
     */
    UpperTrs(const UpperTrs&);

    /**
     * Move-assigns a triangular solver. Preserves the executor, moves
     * the system matrix. If the executors mismatch, clones system matrix onto
     * this executor and regenerates solver analysis information. Moved-from
     * object is empty (0x0 and nullptr system matrix)
     */
    UpperTrs(UpperTrs&&);

    /**
     * Copy-constructs a triangular solver. Preserves the executor,
     * shallow-copies the system matrix. Solver analysis information will be
     * regenerated.
     */
    UpperTrs& operator=(const UpperTrs&);

    /**
     * Move-constructs a triangular solver. Preserves the executor, moves
     * the system matrix and solver analysis information. Moved-from
     * object is empty (0x0 and nullptr system matrix)
     */
    UpperTrs& operator=(UpperTrs&&);

protected:
    using CsrMatrix = matrix::Csr<ValueType, IndexType>;

    void apply_impl(const LinOp* b, LinOp* x) const override;

    void apply_impl(const LinOp* alpha, const LinOp* b, const LinOp* beta,
                    LinOp* x) const override;

    /**
     * Generates the analysis structure from the system matrix and the right
     * hand side(only dimensional info needed) needed for the level solver.
     */
    void generate();

    explicit UpperTrs(std::shared_ptr<const Executor> exec)
        : EnableLinOp<UpperTrs>(std::move(exec))
    {}

    explicit UpperTrs(const Factory* factory,
                      std::shared_ptr<const LinOp> system_matrix)
        : EnableLinOp<UpperTrs>(factory->get_executor(),
                                gko::transpose(system_matrix->get_size())),
          EnableSolverBase<UpperTrs<ValueType, IndexType>, CsrMatrix>{
              copy_and_convert_to<CsrMatrix>(factory->get_executor(),
                                             system_matrix)},
          parameters_{factory->get_parameters()}
    {
        this->generate();
    }

private:
    std::shared_ptr<solver::SolveStruct> solve_struct_;
};


template <typename ValueType, typename IndexType>
struct workspace_traits<UpperTrs<ValueType, IndexType>> {
    using Solver = UpperTrs<ValueType, IndexType>;
    // number of vectors used by this workspace
    static int num_vectors(const Solver&);
    // number of arrays used by this workspace
    static int num_arrays(const Solver&);
    // array containing the num_vectors names for the workspace vectors
    static std::vector<std::string> op_names(const Solver&);
    // array containing the num_arrays names for the workspace vectors
    static std::vector<std::string> array_names(const Solver&);
    // array containing all varying scalar vectors (independent of problem size)
    static std::vector<int> scalars(const Solver&);
    // array containing all varying vectors (dependent on problem size)
    static std::vector<int> vectors(const Solver&);

    // transposed input vector
    constexpr static int transposed_b = 0;
    // transposed output vector
    constexpr static int transposed_x = 1;
};


}  // namespace solver
}  // namespace gko


#endif  // GKO_PUBLIC_CORE_SOLVER_TRIANGULAR_HPP_
