/*=========================================================================

   Library: iMSTK

   Copyright (c) Kitware, Inc. & Center for Modeling, Simulation,
   & Imaging in Medicine, Rensselaer Polytechnic Institute.

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

      http://www.apache.org/licenses/LICENSE-2.0.txt

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.

=========================================================================*/

#pragma once

#include "imstkMath.h"
#include <utility>

namespace imstk
{
///
/// \class NonLinearSystem
///
/// \brief Base class for a multi-variable nonlinear system
///
template<typename Matrix>
class NonLinearSystem
{
public:
    using VectorFunctionType = std::function<const Vectord& (const Vectord&, const bool)>;
    using MatrixFunctionType = std::function<const Matrix& (const Vectord&)>;
    // using VecMatPair = std::pair<const Vectord&, const Matrix&>;
    using VecMatPair = std::pair<const Vectord*, const Matrix*>;
    using VectorMatrixFunctionType    = std::function<VecMatPair(const Vectord&, const bool)>;
    using UpdateFunctionType          = std::function<void (const Vectord&, const bool)>;
    using UpdatePrevStateFunctionType = std::function<void ()>;

    NonLinearSystem() { }
    NonLinearSystem(const VectorFunctionType& F, const MatrixFunctionType& dF);
    NonLinearSystem(const VectorFunctionType& F, const MatrixFunctionType& dF, const VectorMatrixFunctionType& F_dF);

    virtual ~NonLinearSystem() { }

    ///
    /// \brief Set nonlinear method that evaluates the nonlinear function.
    ///
    virtual void setFunction(const VectorFunctionType& function);

    ///
    /// \brief Set the method that evaluates the gradient of the nonlinear function
    ///
    virtual void setJacobian(const MatrixFunctionType& function);

    ///
    /// \brief Evaluate function at a given state
    ///
    virtual const Vectord& evaluateF(const Vectord& x, const bool isSemiImplicit);

    ///
    /// \brief Evaluate gradient of the function at a given state
    ///
    virtual const Matrix& evaluateJacobian(const Vectord& x);

    ///
    /// \brief
    ///
    void setUnknownVector(Vectord& v)
    {
        m_unknown = &v;
    }

    ///
    /// \brief Get the vector used to populate the solution
    ///
    Vectord& getUnknownVector()
    {
        return *m_unknown;
    }

    /// \brief Get the vector denoting the filter
    ///
    /*void setLinearProjectors(std::vector<LinearProjectionConstraint>& f)
    {
        m_LinearProjConstraints = &f;
    }

    /// \brief Get the vector denoting the filter
    ///
    std::vector<LinearProjectionConstraint>& getLinearProjectors()
    {
        return *m_LinearProjConstraints;
    }*/

    ///
    /// \brief Set the update function
    ///
    void setUpdateFunction(const UpdateFunctionType& updateFunc)
    {
        m_FUpdate = updateFunc;
    }

    ///
    /// \brief Set the update function
    ///
    void setUpdatePreviousStatesFunction(const UpdatePrevStateFunctionType& updateFunc)
    {
        m_FUpdatePrevState = updateFunc;
    }

/// \brief Get the vector denoting the filter
///
/*void setDynamicLinearProjectors(std::vector<LinearProjectionConstraint>* f)
    {
        m_DynamicLinearProjConstraints = f;
    }

    /// \brief Get the vector denoting the filter
    ///
    std::vector<LinearProjectionConstraint>& getDynamicLinearProjectors()
    {
        return *m_DynamicLinearProjConstraints;
    }*/

    VectorFunctionType       m_F;  ///< Nonlinear function
    MatrixFunctionType       m_dF; ///< Gradient of the Nonlinear function with respect to the unknown vector
    VectorMatrixFunctionType m_F_dF;
    Vectord* m_unknown = nullptr;

    UpdateFunctionType m_FUpdate;
    UpdatePrevStateFunctionType m_FUpdatePrevState;
    /*std::vector<LinearProjectionConstraint>  *m_LinearProjConstraints;
    std::vector<LinearProjectionConstraint>  *m_DynamicLinearProjConstraints;*/
};
} // namespace imstk