/*
  Copyright 2014 SINTEF ICT, Applied Mathematics.

  This file is part of the Open Porous Media project (OPM).

  OPM is free software: you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation, either version 3 of the License, or
  (at your option) any later version.

  OPM is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with OPM.  If not, see <http://www.gnu.org/licenses/>.
*/

#ifndef OPM_ANISOTROPICEIKONAL_HEADER_INCLUDED
#define OPM_ANISOTROPICEIKONAL_HEADER_INCLUDED

#include <opm/core/utility/SparseTable.hpp>
#include <vector>
#include <set>
#include <map>

#include <boost/version.hpp>

#define BOOST_HEAP_AVAILABLE ((BOOST_VERSION / 100 % 1000) >= 49)

#if BOOST_HEAP_AVAILABLE
#include <boost/heap/fibonacci_heap.hpp>
#endif

struct UnstructuredGrid;

namespace Opm
{
    /// A solver for the anisotropic eikonal equation:
    ///    \f[ || \nabla u^T M^{-1}(x) \nabla u || = 1 \qquad x \in \Omega \f]
    /// where M(x) is a symmetric positive definite matrix.
    /// The boundary conditions are assumed to be
    ///    \f[ u(x) = 0 \qquad x \in \partial\Omega \f].
    class AnisotropicEikonal2d
    {
    public:
        /// Construct solver.
        /// \param[in] grid      A 2d grid.
        explicit AnisotropicEikonal2d(const UnstructuredGrid& grid);

        /// Solve the eikonal equation.
        /// \param[in]  metric            Array of metric tensors, M, for each cell.
        /// \param[in]  startcells        Array of cells where u = 0 at the centroid.
        /// \param[out] solution          Array of solution to the eikonal equation.
        void solve(const double* metric,
                   const std::vector<int>& startcells,
                   std::vector<double>& solution);
    private:
#if BOOST_HEAP_AVAILABLE
        // Grid and topology.
        const UnstructuredGrid& grid_;
        SparseTable<int> cell_neighbours_;

        // Keep track of accepted cells.
        std::vector<char> is_accepted_;
        std::set<int> accepted_front_;

        // Quantities relating to anisotropy.
        std::vector<double> grid_radius_;
        std::vector<double> aniso_ratio_;
        const double safety_factor_;

        // Keep track of considered cells.
        typedef std::pair<double, int> ValueAndCell;
        typedef boost::heap::compare<std::greater<ValueAndCell>> Comparator;
        typedef boost::heap::fibonacci_heap<ValueAndCell, Comparator> Heap;
        Heap considered_;
        typedef Heap::handle_type HeapHandle;
        std::map<int, HeapHandle> considered_handles_;
        std::vector<char> is_considered_;

        bool isClose(const int c1, const int c2) const;
        double computeValue(const int cell, const double* metric, const double* solution) const;
        double computeValueUpdate(const int cell, const double* metric, const double* solution, const int new_cell) const;
        double computeFromLine(const int cell, const int from, const double* metric, const double* solution) const;
        double computeFromTri(const int cell, const int n0, const int n1, const double* metric, const double* solution) const;

        const ValueAndCell& topConsidered() const;
        void pushConsidered(const ValueAndCell& vc);
        void popConsidered();

        void computeGridRadius();
        void computeAnisoRatio(const double* metric);
#endif // BOOST_HEAP_AVAILABLE
    };

} // namespace Opm


#endif // OPM_ANISOTROPICEIKONAL_HEADER_INCLUDED