#ifndef POISSON_PROBLEM_H
#define POISSON_PROBLEM_H

#include <deal.II/base/function.h>

#include <deal.II/base/mpi_remote_point_evaluation.h>
#include <deal.II/base/point.h>
#include <deal.II/base/quadrature_lib.h>
#include <deal.II/base/logstream.h>
#include <deal.II/base/template_constraints.h>
#include <deal.II/base/tensor.h>
#include <deal.II/base/utilities.h>
#include <deal.II/base/index_set.h>

#include <deal.II/lac/vector.h>
#include <deal.II/lac/full_matrix.h>
#include <deal.II/lac/sparse_matrix.h>
#include <deal.II/lac/dynamic_sparsity_pattern.h>
#include <deal.II/lac/solver_cg.h>
#include <deal.II/lac/precondition.h>
#include <deal.II/lac/affine_constraints.h>

#include <deal.II/grid/tria.h>
#include <deal.II/grid/grid_generator.h>
#include <deal.II/grid/grid_tools.h>

#include <deal.II/dofs/dof_handler.h>
#include <deal.II/dofs/dof_tools.h>
#include <deal.II/dofs/dof_renumbering.h>

#include <deal.II/fe/fe_q.h>
#include <deal.II/fe/fe_values.h>

#include <deal.II/numerics/data_out.h>
#include <deal.II/numerics/vector_tools.h>
#include <deal.II/numerics/matrix_tools.h>
#include <deal.II/numerics/fe_field_function.h>

#include <deal.II/numerics/vector_tools_evaluate.h>
#include <deal.II/numerics/vector_tools_interpolate.h>
#include <memory>
#include <string>
#include <utility>
#include <vector>

#include "nufi/parameters.h"

using namespace dealii;

// =-=-=-=-= Poisson Solver =-=-=-=-=

template <int dim>
class PoissonProblem
{
public:
  PoissonProblem(unsigned int degree);

  void initialize();
  void solve_step();
  void run();

  void set_rhs_function(std::unique_ptr<Function<dim>> rhs_function);

  const Vector<double> &get_solution() const { return solution; }
  const DoFHandler<dim> &get_dof_handler() const { return dof_handler; }

  std::vector<double> sample_electric_field(double x_min, double x_max, unsigned int Nx);
  std::vector<double> sample_electric_potential(double x_min, double x_max, unsigned int Nx);

private:
  void create_mesh();
  void setup_system();
  void assemble_system();
  void solve();

  Triangulation<dim> triangulation;
  FE_Q<dim>          fe;
  DoFHandler<dim>    dof_handler;

  AffineConstraints<double> constraints;

  SparsityPattern      sparsity_pattern;
  SparseMatrix<double> system_matrix;

  Vector<double> solution;      // phi
  Vector<double> system_rhs;

  std::unique_ptr<const Function<dim>> rhs_function;

  MappingQ<dim> mapping;
};

// Utilities

template <int dim>
void PoissonProblem<dim>::set_rhs_function(std::unique_ptr<Function<dim>> rhs)
{
  rhs_function = std::move(rhs);
}

template <int dim>
PoissonProblem<dim>::PoissonProblem(unsigned int degree)
  : fe(degree)
  , dof_handler(triangulation)
  , mapping(degree)
{}

template <int dim>
std::vector<double> PoissonProblem<dim>::sample_electric_field(double x_min,double x_max,unsigned int Nx)
{
  std::vector<double> E_values(Nx);

  const double dx = (x_max - x_min) / (Nx - 1);

  for (unsigned int i = 0; i < Nx; ++i)
  {
      const double x = x_min + i * dx;
      const Point<dim> point(x);

      // 1. Find the active cell containing x
      const auto cell_point_pair =
          GridTools::find_active_cell_around_point(mapping,
                                                   dof_handler,
                                                   point);

      const auto cell = cell_point_pair.first;
      const Point<dim> &unit_point = cell_point_pair.second;

      // 2. FEPointEvaluation expects an ArrayView of points
      std::vector<Point<dim>> points(1, unit_point);
      ArrayView<const Point<dim>> point_view(points);

      FEPointEvaluation<1, dim> evaluator(mapping,
                                          dof_handler.get_fe(),
                                          update_gradients);

      // reinit with ArrayView of points
      evaluator.reinit(cell, point_view);

      Vector<double> local_dofs(dof_handler.get_fe().dofs_per_cell);
      cell->get_dof_values(solution, local_dofs);

      // 3. Evaluate gradient at this point
      evaluator.evaluate(local_dofs, EvaluationFlags::gradients);

      const Tensor<1, dim> grad_phi = evaluator.get_gradient(0);

      // 4. Compute E = -grad(phi)
      E_values[i] = -grad_phi[0];
  }

  return E_values;
}

template <int dim>
std::vector<double> PoissonProblem<dim>::sample_electric_potential(
    double x_min,
    double x_max,
    unsigned int Nx)
{
  std::vector<double> values(Nx);
  std::vector<Point<dim>> eval_points(Nx);

  double Lx = x_max - x_min;
  double dx = Lx / Nx;

  for(unsigned int i=0 ; i<Nx; ++i)
    eval_points[i] = Point<1, double>(x_min + i * dx);

  Utilities::MPI::RemotePointEvaluation<dim,dim> cache;
  cache.reinit(eval_points, triangulation, mapping);

  values = VectorTools::point_values<dim>(cache, dof_handler, solution);

  return values;
}

// dealii Poisson
 
template<int dim>
void PoissonProblem<dim>::create_mesh()
{

  GridGenerator::hyper_cube(triangulation,
                            Parameters::X_DOMAIN_LEFT,
                            Parameters::X_DOMAIN_RIGHT);


  std::vector<GridTools::PeriodicFacePair<
      typename Triangulation<dim>::cell_iterator>> periodic_faces;

  GridTools::collect_periodic_faces(triangulation,
                                    0, 1,   // boundary IDs
                                    0,      
                                    periodic_faces);

  triangulation.add_periodicity(periodic_faces);

  triangulation.refine_global(Parameters::GLOBAL_REFINEMENT);
}

template <int dim>
void PoissonProblem<dim>::setup_system()
{

  dof_handler.distribute_dofs(fe);

  constraints.clear();
  
  DoFTools::make_hanging_node_constraints(dof_handler, constraints);

  DoFTools::make_periodicity_constraints(dof_handler,
                                         0, 1,
                                         0,
                                         constraints);
  
  constraints.close();

  DynamicSparsityPattern dsp(dof_handler.n_dofs());
  DoFTools::make_sparsity_pattern(dof_handler, dsp, constraints);
  sparsity_pattern.copy_from(dsp);

  system_matrix.reinit(sparsity_pattern);

  solution.reinit(dof_handler.n_dofs());
  system_rhs.reinit(dof_handler.n_dofs());
}

template <int dim>
void PoissonProblem<dim>::assemble_system()
{
  QGauss<dim>  quadrature_formula(fe.degree + 1);
  FEValues<dim> fe_values(fe, quadrature_formula,
                          update_values |
                          update_gradients |
                          update_quadrature_points |
                          update_JxW_values);

  const unsigned int dofs_per_cell = fe.n_dofs_per_cell();

  FullMatrix<double> cell_matrix(dofs_per_cell, dofs_per_cell);
  Vector<double>     cell_rhs(dofs_per_cell);
  std::vector<types::global_dof_index> local_dof_indices(dofs_per_cell);

  Assert(rhs_function != nullptr, ExcMessage("RHS function not set"));

  for (const auto &cell : dof_handler.active_cell_iterators())
  {
    fe_values.reinit(cell);

    cell_matrix = 0;
    cell_rhs    = 0;

    for (const auto q : fe_values.quadrature_point_indices())
    {
      const double rho = rhs_function->value(fe_values.quadrature_point(q));

      for (const unsigned int i : fe_values.dof_indices())
        for (const unsigned int j : fe_values.dof_indices())
          cell_matrix(i, j) +=
            (fe_values.shape_grad(i, q) * // grad phi_i(x_q)
             fe_values.shape_grad(j, q) * // grad phi_j(x_q)
             fe_values.JxW(q));           // dx

      for (const unsigned int i : fe_values.dof_indices())
        cell_rhs(i) += (fe_values.shape_value(i, q) * // phi_i(x_q)
                        rho *                         // f(x_q)
                        fe_values.JxW(q));            // dx


    }

    cell->get_dof_indices(local_dof_indices);
    constraints.distribute_local_to_global(cell_matrix,
                                           cell_rhs,
                                           local_dof_indices,
                                           system_matrix,
                                           system_rhs);
    for (const unsigned int i : fe_values.dof_indices())
      for (const unsigned int j : fe_values.dof_indices())
        system_matrix.add(local_dof_indices[i],
                          local_dof_indices[j],
                          cell_matrix(i, j));

    for (const unsigned int i : fe_values.dof_indices())
      system_rhs(local_dof_indices[i]) += cell_rhs(i);

  }
  std::map<types::global_dof_index, double> boundary_values;
  // VectorTools::interpolate_boundary_values(dof_handler,
  //                                          types::boundary_id(0),
  //                                          Functions::ZeroFunction<1>(),
  //                                          boundary_values);
  MatrixTools::apply_boundary_values(boundary_values,
                                     system_matrix,
                                     solution,
                                     system_rhs);
}


template <int dim>
void PoissonProblem<dim>::solve()
{

  SolverControl            solver_control(Parameters::CONVERGENCE_ITERATIONS, Parameters::CONVERGENCE_LIMIT);
  SolverCG<Vector<double>> solver(solver_control);

  // PreconditionSSOR<SparseMatrix<double>> preconditioner;
  // preconditioner.initialize(system_matrix, 1.2);

  // solver.solve(system_matrix, solution, system_rhs, preconditioner);
  solver.solve(system_matrix, solution, system_rhs, PreconditionIdentity());
  // constraints.distribute(solution);
}

template <int dim>
void PoissonProblem<dim>::initialize()
{
  create_mesh();      // build grid
  setup_system();     // distribute DoFs and matrices
}

template <int dim>
void PoissonProblem<dim>::solve_step()
{
  assemble_system();
  solve();
}


// NuFI doesnt use this, kept only for testing PoissonProblem
template <int dim>
void PoissonProblem<dim>::run()
{
  create_mesh();
  setup_system();
  assemble_system();
  solve();
}

#endif