/*
  Copyright 2012 SINTEF ICT, Applied Mathematics.
  Copyright 2012 Statoil ASA.

  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/>.
*/

#if HAVE_CONFIG_H
#include "config.h"
#endif // HAVE_CONFIG_H

#include <opm/core/pressure/IncompTpfa.hpp>
#include <opm/core/pressure/FlowBCManager.hpp>

#include <opm/core/grid.h>
#include <opm/core/GridManager.hpp>
#include <opm/core/newwells.h>
#include <opm/core/WellsManager.hpp>
#include <opm/core/utility/ErrorMacros.hpp>
#include <opm/core/utility/initState.hpp>
#include <opm/core/utility/SimulatorTimer.hpp>
#include <opm/core/utility/StopWatch.hpp>
#include <opm/core/utility/Units.hpp>
#include <opm/core/utility/writeVtkData.hpp>
#include <opm/core/utility/miscUtilities.hpp>
#include <opm/core/utility/parameters/ParameterGroup.hpp>

#include <opm/core/fluid/IncompPropertiesBasic.hpp>
#include <opm/core/fluid/IncompPropertiesFromDeck.hpp>

#include <opm/core/linalg/LinearSolverUmfpack.hpp>
// #define EXPERIMENT_ISTL
#ifdef EXPERIMENT_ISTL
#include <opm/core/linalg/LinearSolverIstl.hpp>
#endif

#include <opm/core/transport/transport_source.h>
#include <opm/core/transport/CSRMatrixUmfpackSolver.hpp>
#include <opm/core/transport/NormSupport.hpp>
#include <opm/core/transport/ImplicitAssembly.hpp>
#include <opm/core/transport/ImplicitTransport.hpp>
#include <opm/core/transport/JacobianSystem.hpp>
#include <opm/core/transport/CSRMatrixBlockAssembler.hpp>
#include <opm/core/transport/SinglePointUpwindTwoPhase.hpp>

#include <opm/core/ColumnExtract.hpp>

#include <opm/polymer/PolymerState.hpp>
#include <opm/polymer/SinglePointUpwindTwoPhasePolymer.hpp>
#include <opm/polymer/GravityColumnSolverPolymer.hpp>
#include <opm/polymer/TransportModelPolymer.hpp>
#include <opm/polymer/PolymerProperties.hpp>
#include <opm/polymer/polymerUtilities.hpp>

#include <boost/filesystem/convenience.hpp>
#include <boost/scoped_ptr.hpp>
#include <boost/lexical_cast.hpp>

#include <cassert>
#include <cstddef>

#include <algorithm>
#include <tr1/array>
#include <functional>
#include <iostream>
#include <iomanip>
#include <fstream>
#include <iterator>
#include <vector>
#include <numeric>



class AdHocProps : public Opm::IncompPropertiesBasic
{
public:
    AdHocProps(const Opm::parameter::ParameterGroup& param, int dim, int num_cells)
        : Opm::IncompPropertiesBasic(param, dim, num_cells)
    {
        ASSERT(numPhases() == 2);
        sw_.resize(3);
        sw_[0] = 0.2;
        sw_[1] = 0.7;
        sw_[2] = 1.0;
        krw_.resize(3);
        krw_[0] = 0.0;
        krw_[1] = 0.7;
        krw_[2] = 1.0;
        so_.resize(2);
        so_[0] = 0.3;
        so_[1] = 0.8;
        kro_.resize(2);
        kro_[0] = 0.0;
        kro_[1] = 1.0;
    }

    virtual void relperm(const int n,
                         const double* s,
                         const int* /*cells*/,
                         double* kr,
                         double* dkrds) const
    {
        // ASSERT(dkrds == 0);
        // We assume two phases flow
        for (int i = 0; i < n; ++i) {
            kr[2*i] = krw(s[2*i]);
            kr[2*i+1] = kro(s[2*i+1]);
            if (dkrds != 0) {
                dkrds[2*i] = krw_dsw(s[2*i]);
                dkrds[2*i+3] = kro_dso(s[2*i+1]);
                dkrds[2*i+1] = -dkrds[2*i+3];
                dkrds[2*i+2] = -dkrds[2*i];
            }
        }
    }

    virtual void satRange(const int n,
                          const int* /*cells*/,
                          double* smin,
                          double* smax) const
    {
        const int np = 2;
        for (int i = 0; i < n; ++i) {
            smin[np*i + 0] = sw_[0];
            smax[np*i + 0] = sw_.back();
            smin[np*i + 1] = 1.0 - sw_[0];
            smax[np*i + 1] = 1.0 - sw_.back();
        }
    }

private:
    double krw(double s) const
    {
        return Opm::linearInterpolation(sw_, krw_, s);
    }

    double krw_dsw(double s) const
    {
        return Opm::linearInterpolationDerivative(sw_, krw_, s);
    }


    double kro(double s) const
    {
        return Opm::linearInterpolation(so_, kro_, s);
    }

    double kro_dso(double s) const
    {
        return Opm::linearInterpolationDerivative(so_, kro_, s);
    }

    std::vector<double> sw_;
    std::vector<double> krw_;
    std::vector<double> so_;
    std::vector<double> kro_;
};


// --------------- Types needed to define transport solver ---------------

class PolymerFluid2pWrappingProps
{
public:
    PolymerFluid2pWrappingProps(const Opm::IncompPropertiesInterface& props, const Opm::PolymerProperties& polyprops)
    : props_(props),
      polyprops_(polyprops),
      smin_(props.numCells()*props.numPhases()),
      smax_(props.numCells()*props.numPhases())
    {
        if (props.numPhases() != 2) {
            THROW("PolymerFluid2pWrapper requires 2 phases.");
        }
        const int num_cells = props.numCells();
        std::vector<int> cells(num_cells);
        for (int c = 0; c < num_cells; ++c) {
            cells[c] = c;
        }
        props.satRange(num_cells, &cells[0], &smin_[0], &smax_[0]);
    }

    double density(int phase) const
    {
        return props_.density()[phase];
    }

    template <class PolyC,
              class CAds,
              class DCAdsDc>

    void adsorption(const PolyC& c, const PolyC& cmax, CAds& cads, DCAdsDc& dcadsdc) {
        cads = polyprops_.adsorptionWithDer(c, cmax, &dcadsdc);
    }

    const std::vector<double> porosity() const {
        const int num_cells = props_.numCells();
        std::vector<double> porosity(num_cells, 0.);
        const double* poro = props_.porosity();
        for (std::vector<double>::iterator it = porosity.begin(); it != porosity.end(); ++it, ++poro) {
            *it = poro[0];
        }
        return porosity;
    }

    double rockdensity() const {
        return polyprops_.rockDensity();
    }

    template <class Sat,
              class PolyC,
              class Mob,
              class DMobDs,
              class DMobWatDc>
    void mobility(int cell, const Sat& s, const PolyC& c,
                  Mob& mob, DMobDs& dmobds, DMobWatDc& dmobwatdc) const
    {
        const double* visc = props_.viscosity();
        double relperm[2];
        double drelpermds[4];
	props_.relperm(1, &s[0], &cell, relperm, drelpermds);
        polyprops_.effectiveMobilities(c, visc, relperm, drelpermds, mob, dmobds, dmobwatdc);
    }

    template <class Sat,
    class Pcap,
    class DPcap>
    void pc(int c, const Sat& s, Pcap& pcap, DPcap& dpcap) const
    {
        double pc[2];
        double dpc[4];
        props_.capPress(1, &s[0], &c, pc, dpc);
        pcap = pc[0];
        ASSERT(pc[1] == 0.0);
        dpcap = dpc[0];
        ASSERT(dpc[1] == 0.0);
        ASSERT(dpc[2] == 0.0);
        ASSERT(dpc[3] == 0.0);
    }

    double s_min(int c) const
    {
        return smin_[2*c + 0];
    }

    double s_max(int c) const
    {
        return smax_[2*c + 0];
    }


    template <class PolyC,
              class Mc,
              class DMcDc>
    void mc(const PolyC& c,  Mc& mc,
            DMcDc& dmcdc) const
    {
        polyprops_.computeMc(c, mc, dmcdc);
    }

private:
    const Opm::IncompPropertiesInterface& props_;
    const Opm::PolymerProperties& polyprops_;
    std::vector<double> smin_;
    std::vector<double> smax_;
};

typedef PolymerFluid2pWrappingProps TwophaseFluidPolymer;
typedef Opm::SinglePointUpwindTwoPhasePolymer<TwophaseFluidPolymer> NewtonPolymerTransportModel;

using namespace Opm::ImplicitTransportDefault;

typedef NewtonVectorCollection< ::std::vector<double> >      NVecColl;
typedef JacobianSystem        < struct CSRMatrix, NVecColl > JacSys;

template <class Vector>
class MaxNorm {
public:
    static double
    norm(const Vector& v) {
        return AccumulationNorm <Vector, MaxAbs>::norm(v);
    }
};

typedef Opm::ImplicitTransport<NewtonPolymerTransportModel,
        JacSys        ,
        MaxNorm       ,
        VectorNegater ,
        VectorZero    ,
        MatrixZero    ,
        VectorAssign  > TransportSolver;



static void outputState(const UnstructuredGrid& grid,
                        const Opm::PolymerState& state,
                        const int step,
                        const std::string& output_dir)
{
    // Write data in VTK format.
    std::ostringstream vtkfilename;
    vtkfilename << output_dir << "/output-" << std::setw(3) << std::setfill('0') << step << ".vtu";
    std::ofstream vtkfile(vtkfilename.str().c_str());
    if (!vtkfile) {
        THROW("Failed to open " << vtkfilename.str());
    }
    Opm::DataMap dm;
    dm["saturation"] = &state.saturation();
    dm["pressure"] = &state.pressure();
    dm["concentration"] = &state.concentration();
    dm["cmax"] = &state.maxconcentration();
    std::vector<double> cell_velocity;
    Opm::estimateCellVelocity(grid, state.faceflux(), cell_velocity);
    dm["velocity"] = &cell_velocity;
    Opm::writeVtkData(grid, dm, vtkfile);

    // Write data (not grid) in Matlab format
    for (Opm::DataMap::const_iterator it = dm.begin(); it != dm.end(); ++it) {
        std::ostringstream fname;
        fname << output_dir << "/" << it->first << "-" << std::setw(3) << std::setfill('0') << step << ".dat";
        std::ofstream file(fname.str().c_str());
        if (!file) {
            THROW("Failed to open " << fname.str());
        }
        const std::vector<double>& d = *(it->second);
        std::copy(d.begin(), d.end(), std::ostream_iterator<double>(file, "\n"));
    }
}




class PolymerInflow
{
public:
    PolymerInflow(const double starttime,
                  const double endtime,
                  const double amount)
        : stime_(starttime), etime_(endtime), amount_(amount)
    {
    }
    double operator()(double time)
    {
        if (time >= stime_ && time < etime_) {
            return amount_;
        } else {
            return 0.0;
        }
    }
private:
    double stime_;
    double etime_;
    double amount_;
};



static void outputWaterCut(const Opm::Watercut& watercut,
                           const std::string& output_dir)
{
    // Write water cut curve.
    std::string fname = output_dir  + "/watercut.txt";
    std::ofstream os(fname.c_str());
    if (!os) {
        THROW("Failed to open " << fname);
    }
    watercut.write(os);
}


// ----------------- Main program -----------------
int
main(int argc, char** argv)
{
    std::cout << "\n================    Test program for incompressible two-phase flow with polymer    ===============\n\n";
    Opm::parameter::ParameterGroup param(argc, argv, false);
    std::cout << "---------------    Reading parameters     ---------------" << std::endl;

    // Reading various control parameters.
    const bool guess_old_solution = param.getDefault("guess_old_solution", false);
    const bool use_reorder = param.getDefault("use_reorder", true);
    const bool output = param.getDefault("output", true);
    std::string output_dir;
    int output_interval = 1;
    if (output) {
        output_dir = param.getDefault("output_dir", std::string("output"));
        // Ensure that output dir exists
        boost::filesystem::path fpath(output_dir);
        create_directories(fpath);
        output_interval = param.getDefault("output_interval", output_interval);
    }

    // If we have a "deck_filename", grid and props will be read from that.
    bool use_deck = param.has("deck_filename");
    boost::scoped_ptr<Opm::GridManager> grid;
    boost::scoped_ptr<Opm::IncompPropertiesInterface> props;
    boost::scoped_ptr<Opm::WellsManager> wells;
    Opm::SimulatorTimer simtimer;
    Opm::PolymerState state;
    Opm::PolymerProperties polyprop;
    double gravity[3] = { 0.0 };
    if (use_deck) {
        std::string deck_filename = param.get<std::string>("deck_filename");
        Opm::EclipseGridParser deck(deck_filename);
        // Grid init
        grid.reset(new Opm::GridManager(deck));
        // Rock and fluid init
        const int* gc = grid->c_grid()->global_cell;
        std::vector<int> global_cell(gc, gc + grid->c_grid()->number_of_cells);
        props.reset(new Opm::IncompPropertiesFromDeck(deck, global_cell));
        // props.reset(new AdHocProps(param, grid->c_grid()->dimensions, grid->c_grid()->number_of_cells));
        // Wells init.
        wells.reset(new Opm::WellsManager(deck, *grid->c_grid(), props->permeability()));
        // Timer init.
        if (deck.hasField("TSTEP")) {
            simtimer.init(deck);
        } else {
            simtimer.init(param);
        }
        // Gravity.
        gravity[2] = deck.hasField("NOGRAV") ? 0.0 : Opm::unit::gravity;
        // Init state variables (saturation and pressure).
        initStateTwophaseFromDeck(*grid->c_grid(), *props, deck, gravity[2], state);
        // Init polymer properties.
        polyprop.readFromDeck(deck);
    } else {
        // Grid init.
        const int nx = param.getDefault("nx", 100);
        const int ny = param.getDefault("ny", 100);
        const int nz = param.getDefault("nz", 1);
        const double dx = param.getDefault("dx", 1.0);
        const double dy = param.getDefault("dy", 1.0);
        const double dz = param.getDefault("dz", 1.0);
        grid.reset(new Opm::GridManager(nx, ny, nz, dx, dy, dz));
        // Rock and fluid init.
        // props.reset(new Opm::IncompPropertiesBasic(param, grid->c_grid()->dimensions, grid->c_grid()->number_of_cells));
        props.reset(new AdHocProps(param, grid->c_grid()->dimensions, grid->c_grid()->number_of_cells));
        // Wells init.
        wells.reset(new Opm::WellsManager());
        // Timer init.
        simtimer.init(param);
        // Gravity.
        gravity[2] = param.getDefault("gravity", 0.0);
        // Init state variables (saturation and pressure).
        initStateTwophaseBasic(*grid->c_grid(), *props, param, gravity[2], state);
        // Init polymer properties.
        // Setting defaults to provide a simple example case.
        double c_max = param.getDefault("c_max_limit", 5.0);
        double mix_param = param.getDefault("mix_param", 1.0);
        double rock_density = param.getDefault("rock_density", 1000.0);
        double dead_pore_vol = param.getDefault("dead_pore_vol", 0.15);
        double res_factor = param.getDefault("res_factor", 1.) ; // res_factor = 1 gives no change in permeability
        double c_max_ads = param.getDefault("c_max_ads", 1.);
        int ads_index = param.getDefault<int>("ads_index", Opm::PolymerProperties::NoDesorption);
        std::vector<double> c_vals_visc(2, -1e100);
        c_vals_visc[0] = 0.0;
        c_vals_visc[1] = 7.0;
        std::vector<double> visc_mult_vals(2, -1e100);
        visc_mult_vals[0] = 1.0;
        // polyprop.visc_mult_vals[1] = param.getDefault("c_max_viscmult", 30.0);
        visc_mult_vals[1] = 20.0;
        std::vector<double> c_vals_ads(3, -1e100);
        c_vals_ads[0] = 0.0;
        c_vals_ads[1] = 2.0;
        c_vals_ads[2] = 8.0;
        std::vector<double> ads_vals(3, -1e100);
        ads_vals[0] = 0.0;
        // polyprop.ads_vals[1] = param.getDefault("c_max_ads", 0.0025);
        ads_vals[1] = 0.0015;
        ads_vals[2] = 0.0025;
        polyprop.set(c_max, mix_param, rock_density, dead_pore_vol, res_factor, c_max_ads, 
                     static_cast<Opm::PolymerProperties::AdsorptionBehaviour>(ads_index),
                     c_vals_visc,  visc_mult_vals, c_vals_ads, ads_vals);
    }

    // Initialize polymer inflow function.
    double poly_start = param.getDefault("poly_start_days", 300.0)*Opm::unit::day;
    double poly_end = param.getDefault("poly_end_days", 800.0)*Opm::unit::day;
    double poly_amount = param.getDefault("poly_amount", polyprop.cMax());
    PolymerInflow poly_inflow(poly_start, poly_end, poly_amount);

    // Extra fluid init for transport solver.
    TwophaseFluidPolymer fluid(*props, polyprop);

    // Warn if gravity but no density difference.
    bool use_gravity = (gravity[0] != 0.0 || gravity[1] != 0.0 || gravity[2] != 0.0);
    if (use_gravity) {
        if (props->density()[0] == props->density()[1]) {
            std::cout << "**** Warning: nonzero gravity, but zero density difference." << std::endl;
        }
    }
    bool use_segregation_split = false;
    bool use_column_solver = false;
    bool use_gauss_seidel_gravity = false;
    if (use_gravity && use_reorder) {
        use_segregation_split = param.getDefault("use_segregation_split", use_segregation_split);
        if (use_segregation_split) {
            use_column_solver = param.getDefault("use_column_solver", use_column_solver);
            if (use_column_solver) {
                // use_gauss_seidel_gravity is not implemented for polymer.
                use_gauss_seidel_gravity = param.getDefault("use_gauss_seidel_gravity", use_gauss_seidel_gravity);
            }
        }
    }

    // Source-related variables init.
    int num_cells = grid->c_grid()->number_of_cells;
    std::vector<double> totmob;
    std::vector<double> omega; // Will remain empty if no gravity.
    // Extra rock init.
    std::vector<double> porevol;
    computePorevolume(*grid->c_grid(), *props, porevol);
    double tot_porevol_init = std::accumulate(porevol.begin(), porevol.end(), 0.0);

    // We need a separate reorder_sat, because the reorder
    // code expects a scalar sw, not both sw and so.
    std::vector<double> reorder_sat(num_cells);
    std::vector<double> src(num_cells, 0.0);

    // Initialising src
    if (wells->c_wells()) {
        Opm::wellsToSrc(*wells->c_wells(), num_cells, src);
    } else {
        const double default_injection = use_gravity ? 0.0 : 0.1;
        const double flow_per_sec = param.getDefault<double>("injected_porevolumes_per_day", default_injection)
            *tot_porevol_init/Opm::unit::day;
        src[0] = flow_per_sec;
        src[num_cells - 1] = -flow_per_sec;
    }

    TransportSource* tsrc = create_transport_source(2, 2);
    double ssrc[]   = { 1.0, 0.0 };
    double ssink[]  = { 0.0, 1.0 };
    double zdummy[] = { 0.0, 0.0 };
    for (int cell = 0; cell < num_cells; ++cell) {
        if (src[cell] > 0.0) {
            append_transport_source(cell, 2, 0, src[cell], ssrc, zdummy, tsrc);
        } else if (src[cell] < 0.0) {
            append_transport_source(cell, 2, 0, src[cell], ssink, zdummy, tsrc);
        }
    }
    std::vector<double> reorder_src = src;

    // Boundary conditions.
    Opm::FlowBCManager bcs;
    if (param.getDefault("use_pside", false)) {
        int pside = param.get<int>("pside");
        double pside_pressure = param.get<double>("pside_pressure");
        bcs.pressureSide(*grid->c_grid(), Opm::FlowBCManager::Side(pside), pside_pressure);
    }

    // Solvers init.
    // Pressure solver.
#ifdef EXPERIMENT_ISTL
    Opm::LinearSolverIstl linsolver(param);
#else
    Opm::LinearSolverUmfpack linsolver;
#endif // EXPERIMENT_ISTL
    const double *grav = use_gravity ? &gravity[0] : 0;
    Opm::IncompTpfa psolver(*grid->c_grid(), props->permeability(), grav, linsolver);
    // Reordering solver.
    const double nl_tolerance = param.getDefault("nl_tolerance", 1e-9);
    const int nl_maxiter = param.getDefault("nl_maxiter", 30);
    Opm::TransportModelPolymer::SingleCellMethod method;
    std::string method_string = param.getDefault("single_cell_method", std::string("Bracketing"));
    if (method_string == "Bracketing") {
        method = Opm::TransportModelPolymer::Bracketing;
    } else if (method_string == "Newton") {
        method = Opm::TransportModelPolymer::Newton;
    } else {
        THROW("Unknown method: " << method_string);
    }

    Opm::TransportModelPolymer reorder_model(*grid->c_grid(), props->porosity(), &porevol[0], *props, polyprop,
                                             method, nl_tolerance, nl_maxiter);

    if (use_gauss_seidel_gravity) {
        THROW("use_gauss_seidel_gravity option not yet implemented for polymer case.");
        // reorder_model.initGravity(grav);
    }
    // Non-reordering solver.
    NewtonPolymerTransportModel  model  (fluid, *grid->c_grid(), porevol, grav, guess_old_solution);
    if (use_gravity) {
        model.initGravityTrans(*grid->c_grid(), psolver.getHalfTrans());
    }
    TransportSolver tsolver(model);
    // Column-based gravity segregation solver.
    typedef std::pair<std::vector<int>, std::vector<std::vector<int> > > ColMap;
    ColMap columns;
    if (use_column_solver) {
        Opm::extractColumn(*grid->c_grid(), columns);
    }

    Opm::GravityColumnSolverPolymer<NewtonPolymerTransportModel> colsolver(model, *grid->c_grid(), nl_tolerance, nl_maxiter);


    // // // Not implemented for polymer.
    // // Control init.
    // Opm::ImplicitTransportDetails::NRReport  rpt;
    // Opm::ImplicitTransportDetails::NRControl ctrl;
    // if (!use_reorder || use_segregation_split) {
    //     ctrl.max_it = param.getDefault("max_it", 20);
    //     ctrl.verbosity = param.getDefault("verbosity", 0);
    //     ctrl.max_it_ls = param.getDefault("max_it_ls", 5);
    // }
    // // Linear solver init.
    // using Opm::ImplicitTransportLinAlgSupport::CSRMatrixUmfpackSolver;
    // CSRMatrixUmfpackSolver linsolve;

    // The allcells vector is used in calls to computeTotalMobility()
    // and computeTotalMobilityOmega().
    std::vector<int> allcells(num_cells);
    for (int cell = 0; cell < num_cells; ++cell) {
        allcells[cell] = cell;
    }

    // Warn if any parameters are unused.
    if (param.anyUnused()) {
        std::cout << "--------------------   Unused parameters:   --------------------\n";
        param.displayUsage();
        std::cout << "----------------------------------------------------------------" << std::endl;
    }

    // Write parameters used for later reference.
    if (output) {
        param.writeParam(output_dir + "/spu_2p.param");
    }

    // Main simulation loop.
    Opm::time::StopWatch pressure_timer;
    double ptime = 0.0;
    Opm::time::StopWatch transport_timer;
    double ttime = 0.0;
    Opm::time::StopWatch total_timer;
    total_timer.start();
    std::cout << "\n\n================    Starting main simulation loop     ===============" << std::endl;
    double init_satvol[2] = { 0.0 };
    double init_polymass = 0.0;
    double satvol[2] = { 0.0 };
    double polymass = 0.0;
    double polymass_adsorbed = 0.0;
    double injected[2] = { 0.0 };
    double produced[2] = { 0.0 };
    double polyinj = 0.0;
    double polyprod = 0.0;
    double tot_injected[2] = { 0.0 };
    double tot_produced[2] = { 0.0 };
    double tot_polyinj = 0.0;
    double tot_polyprod = 0.0;
    Opm::computeSaturatedVol(porevol, state.saturation(), init_satvol);
    std::cout << "\nInitial saturations are    " << init_satvol[0]/tot_porevol_init
              << "    " << init_satvol[1]/tot_porevol_init << std::endl;
    Opm::Watercut watercut;
    watercut.push(0.0, 0.0, 0.0);
    for (; !simtimer.done(); ++simtimer) {
        // Report timestep and (optionally) write state to disk.
        simtimer.report(std::cout);
        if (output && (simtimer.currentStepNum() % output_interval == 0)) {
            outputState(*grid->c_grid(), state, simtimer.currentStepNum(), output_dir);
        }

        // Solve pressure.
        if (use_gravity) {
            computeTotalMobilityOmega(*props, polyprop, allcells, state.saturation(), state.concentration(),
                                      totmob, omega);
        } else {
            computeTotalMobility(*props, polyprop, allcells, state.saturation(), state.concentration(),
                                 totmob);
        }
        pressure_timer.start();
        psolver.solve(totmob, omega, src, bcs.c_bcs(), state.pressure(), state.faceflux());
        pressure_timer.stop();
        double pt = pressure_timer.secsSinceStart();
        std::cout << "Pressure solver took:  " << pt << " seconds." << std::endl;
        ptime += pt;

        // Process transport sources (to include bdy terms).
        if (use_reorder) {
            Opm::computeTransportSource(*grid->c_grid(), src, state.faceflux(), 1.0, reorder_src);
        } else {
            clear_transport_source(tsrc);
            for (int cell = 0; cell < num_cells; ++cell) {
                if (src[cell] > 0.0) {
                    append_transport_source(cell, 2, 0, src[cell], ssrc, zdummy, tsrc);
                } else if (src[cell] < 0.0) {
                    append_transport_source(cell, 2, 0, src[cell], ssink, zdummy, tsrc);
                }
            }
        }

        // Find inflow rate.
        const double current_time = simtimer.currentTime();
        const double stepsize = simtimer.currentStepLength();
        const double inflowc0 = poly_inflow(current_time + 1e-5*stepsize);
        const double inflowc1 = poly_inflow(current_time + (1.0 - 1e-5)*stepsize);
        if (inflowc0 != inflowc1) {
            std::cout << "**** Warning: polymer inflow rate changes during timestep. Using rate near start of step.";
        }
        const double inflow_c = inflowc0;

        // Solve transport.
        transport_timer.start();
        if (use_reorder) {
            Opm::toWaterSat(state.saturation(), reorder_sat);
            reorder_model.solve(&state.faceflux()[0], &reorder_src[0], stepsize, inflow_c,
                     &reorder_sat[0], &state.concentration()[0], &state.maxconcentration()[0]);
            Opm::toBothSat(reorder_sat, state.saturation());
            Opm::computeInjectedProduced(*props, state.saturation(), src, simtimer.currentStepLength(), injected, produced);
            if (use_segregation_split) {
                if (use_column_solver) {
                    if (use_gauss_seidel_gravity) {
                        THROW("use_gauss_seidel_gravity option not implemented for polymer.");
                        // reorder_model.solveGravity(columns, simtimer.currentStepLength(), reorder_sat);
                        // Opm::toBothSat(reorder_sat, state.saturation());
                    } else {
                        colsolver.solve(columns, simtimer.currentStepLength(), state.saturation(), state.concentration(),
                                        state.maxconcentration());
                    }
                } else {
                    THROW("use_segregation_split option for polymer is only implemented in the use_column_solver case.");
                    // std::vector<double> fluxes = state.faceflux();
                    // std::fill(state.faceflux().begin(), state.faceflux().end(), 0.0);
                    // tsolver.solve(*grid->c_grid(), tsrc, simtimer.currentStepLength(), ctrl, state, linsolve, rpt);
                    // std::cout << rpt;
                    // state.faceflux() = fluxes;
                }
            }
        } else {
            THROW("Non-reordering transport solver not implemented for polymer.");
            // tsolver.solve(*grid->c_grid(), tsrc, simtimer.currentStepLength(), ctrl, state, linsolve, rpt);
            // std::cout << rpt;
            // Opm::computeInjectedProduced(*props, state.saturation(), src, simtimer.currentStepLength(), injected, produced);
        }

        transport_timer.stop();
        double tt = transport_timer.secsSinceStart();
        std::cout << "Transport solver took: " << tt << " seconds." << std::endl;
        ttime += tt;

        // Report volume balances.
        Opm::computeSaturatedVol(porevol, state.saturation(), satvol);
        polymass = Opm::computePolymerMass(porevol, state.saturation(), state.concentration(), polyprop.deadPoreVol());
        polymass_adsorbed = Opm::computePolymerAdsorbed(*props, polyprop, porevol, state.maxconcentration());
        Opm::computeInjectedProduced(*props, polyprop, state.saturation(), state.concentration(),
                                     src, simtimer.currentStepLength(), inflow_c,
                                     injected, produced, polyinj, polyprod);
        tot_injected[0] += injected[0];
        tot_injected[1] += injected[1];
        tot_produced[0] += produced[0];
        tot_produced[1] += produced[1];
        tot_polyinj += polyinj;
        tot_polyprod += polyprod;
        std::cout.precision(5);
        const int width = 18;
        std::cout << "\nVolume and polymer mass balance: "
            "   water(pv)           oil(pv)       polymer(kg)\n";
        std::cout << "    Saturated volumes:     "
                  << std::setw(width) << satvol[0]/tot_porevol_init
                  << std::setw(width) << satvol[1]/tot_porevol_init
                  << std::setw(width) << polymass << std::endl;
        std::cout << "    Adsorbed volumes:      "
                  << std::setw(width) << 0.0
                  << std::setw(width) << 0.0
                  << std::setw(width) << polymass_adsorbed << std::endl;
        std::cout << "    Injected volumes:      "
                  << std::setw(width) << injected[0]/tot_porevol_init
                  << std::setw(width) << injected[1]/tot_porevol_init
                  << std::setw(width) << polyinj << std::endl;
        std::cout << "    Produced volumes:      "
                  << std::setw(width) << produced[0]/tot_porevol_init
                  << std::setw(width) << produced[1]/tot_porevol_init
                  << std::setw(width) << polyprod << std::endl;
        std::cout << "    Total inj volumes:     "
                  << std::setw(width) << tot_injected[0]/tot_porevol_init
                  << std::setw(width) << tot_injected[1]/tot_porevol_init
                  << std::setw(width) << tot_polyinj << std::endl;
        std::cout << "    Total prod volumes:    "
                  << std::setw(width) << tot_produced[0]/tot_porevol_init
                  << std::setw(width) << tot_produced[1]/tot_porevol_init
                  << std::setw(width) << tot_polyprod << std::endl;
        std::cout << "    In-place + prod - inj: "
                  << std::setw(width) << (satvol[0] + tot_produced[0] - tot_injected[0])/tot_porevol_init
                  << std::setw(width) << (satvol[1] + tot_produced[1] - tot_injected[1])/tot_porevol_init
                  << std::setw(width) << (polymass + tot_polyprod - tot_polyinj + polymass_adsorbed) << std::endl;
        std::cout << "    Init - now - pr + inj: "
                  << std::setw(width) << (init_satvol[0] - satvol[0] - tot_produced[0] + tot_injected[0])/tot_porevol_init
                  << std::setw(width) << (init_satvol[1] - satvol[1] - tot_produced[1] + tot_injected[1])/tot_porevol_init
                  << std::setw(width) << (init_polymass - polymass - tot_polyprod + tot_polyinj - polymass_adsorbed)
                  << std::endl;
        std::cout.precision(8);

        watercut.push(simtimer.currentTime() + simtimer.currentStepLength(),
                      produced[0]/(produced[0] + produced[1]),
                      tot_produced[0]/tot_porevol_init);
    }
    total_timer.stop();

    std::cout << "\n\n================    End of simulation     ===============\n"
              << "Total time taken: " << total_timer.secsSinceStart()
              << "\n  Pressure time:  " << ptime
              << "\n  Transport time: " << ttime << std::endl;

    if (output) {
        outputState(*grid->c_grid(), state, simtimer.currentStepNum(), output_dir);
        outputWaterCut(watercut, output_dir);
    }

    destroy_transport_source(tsrc);
}