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

#include <memory>


#include <ginkgo/core/base/composition.hpp>
#include <ginkgo/core/base/lin_op.hpp>
#include <ginkgo/core/base/polymorphic_object.hpp>
#include <ginkgo/core/config/config.hpp>
#include <ginkgo/core/config/registry.hpp>
#include <ginkgo/core/factorization/factorization.hpp>
#include <ginkgo/core/matrix/csr.hpp>
#include <ginkgo/core/matrix/sparsity_csr.hpp>


namespace gko {
namespace experimental {
namespace factorization {


/**
 * Computes a Cholesky factorization of a symmetric, positive-definite sparse
 * matrix. This LinOpFactory returns a Factorization storing the L and L^H
 * factors for the provided system matrix in matrix::Csr format. If no symbolic
 * factorization is provided, it will be computed first.
 *
 * @tparam ValueType  the type used to store values of the system matrix
 * @tparam IndexType  the type used to store sparsity pattern indices of the
 *                    system matrix
 */
template <typename ValueType, typename IndexType>
class Cholesky
    : public EnablePolymorphicObject<Cholesky<ValueType, IndexType>,
                                     LinOpFactory>,
      public EnablePolymorphicAssignment<Cholesky<ValueType, IndexType>> {
public:
    struct parameters_type;
    friend class EnablePolymorphicObject<Cholesky, LinOpFactory>;
    friend class enable_parameters_type<parameters_type, Cholesky>;

    using value_type = ValueType;
    using index_type = IndexType;
    using matrix_type = matrix::Csr<value_type, index_type>;
    using sparsity_pattern_type = matrix::SparsityCsr<value_type, index_type>;
    using factorization_type = Factorization<value_type, index_type>;

    struct parameters_type
        : public enable_parameters_type<parameters_type, Cholesky> {
        /**
         * The combined sparsity pattern L + L^H of the factors L and L^H. It
         * can be used to avoid the potentially costly symbolic factorization of
         * the system matrix if its symbolic factorization is already known. If
         * it is set to nullptr, the symbolic factorization will be computed.
         */
        std::shared_ptr<const sparsity_pattern_type>
            GKO_FACTORY_PARAMETER_SCALAR(symbolic_factorization, nullptr);

        /**
         * The `system_matrix`, which will be given to this factory, must be
         * sorted (first by row, then by column) in order for the algorithm
         * to work. If it is known that the matrix will be sorted, this
         * parameter can be set to `true` to skip the sorting (therefore,
         * shortening the runtime).
         * However, if it is unknown or if the matrix is known to be not sorted,
         * it must remain `false`, otherwise, the algorithm may produce
         * incorrect results or crash.
         */
        bool GKO_FACTORY_PARAMETER_SCALAR(skip_sorting, false);
    };

    /**
     * Returns the parameters used to construct the factory.
     *
     * @return the parameters used to construct the factory.
     */
    const parameters_type& get_parameters() { return parameters_; }

    /**
     * @copydoc get_parameters
     */
    const parameters_type& get_parameters() const { return parameters_; }

    /**
     * @copydoc LinOpFactory::generate
     * @note This function overrides the default LinOpFactory::generate to
     *       return a Factorization instead of a generic LinOp, which would need
     *       to be cast to Factorization again to access its factors.
     *       It is only necessary because smart pointers aren't covariant.
     */
    std::unique_ptr<factorization_type> generate(
        std::shared_ptr<const LinOp> system_matrix) const;

    /** Creates a new parameter_type to set up the factory. */
    static parameters_type build() { return {}; }

    /**
     * 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>());

protected:
    explicit Cholesky(std::shared_ptr<const Executor> exec,
                      const parameters_type& params = {});

    std::unique_ptr<LinOp> generate_impl(
        std::shared_ptr<const LinOp> system_matrix) const override;

private:
    parameters_type parameters_;
};


}  // namespace factorization
}  // namespace experimental
}  // namespace gko
