/*---------------------------------------------------------------------------*\
  =========                 |
  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
   \\    /   O peration     | Website:  https://openfoam.org
    \\  /    A nd           | Copyright (C) 2011-2018 OpenFOAM Foundation
     \\/     M anipulation  |
-------------------------------------------------------------------------------
License
    This file is part of OpenFOAM.

    OpenFOAM 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.

    OpenFOAM 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 OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.

\*---------------------------------------------------------------------------*/

#include "springRenumber.H"
#include "addToRunTimeSelectionTable.H"
#include "decompositionMethod.H"

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

namespace Foam
{
    defineTypeNameAndDebug(springRenumber, 0);

    addToRunTimeSelectionTable
    (
        renumberMethod,
        springRenumber,
        dictionary
    );
}


// * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //

Foam::springRenumber::springRenumber(const dictionary& renumberDict)
:
    renumberMethod(renumberDict),
    dict_(renumberDict.optionalSubDict(typeName+"Coeffs")),
    maxCo_(readScalar(dict_.lookup("maxCo"))),
    maxIter_(readLabel(dict_.lookup("maxIter"))),
    freezeFraction_(readScalar(dict_.lookup("freezeFraction")))
{}


// * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //

Foam::labelList Foam::springRenumber::renumber
(
    const polyMesh& mesh,
    const pointField& points
) const
{
    CompactListList<label> cellCells;
    decompositionMethod::calcCellCells
    (
        mesh,
        identity(mesh.nCells()),
        mesh.nCells(),
        false,                      // local only
        cellCells
    );

    return renumber(cellCells(), points);
}


Foam::labelList Foam::springRenumber::renumber
(
    const labelListList& cellCells,
    const pointField& points
) const
{
    // Look at cell index as a 1D position parameter.
    // Move cells to the average 'position' of their neighbour.

    scalarField position(cellCells.size());
    forAll(position, celli)
    {
        position[celli] = celli;
    }

    labelList oldToNew(identity(cellCells.size()));

    scalar maxCo = maxCo_ * cellCells.size();

    for (label iter = 0; iter < maxIter_; iter++)
    {
        // Pout<< "Iteration : " << iter << nl
        //    << "------------"
        //    << endl;

        // Pout<< "Position :" << nl
        //    << "    min : " << min(position) << nl
        //    << "    max : " << max(position) << nl
        //    << "    avg : " << average(position) << nl
        //    << endl;

        // Sum force per cell.
        scalarField sumForce(cellCells.size(), 0.0);
        forAll(cellCells, oldCelli)
        {
            const labelList& cCells = cellCells[oldCelli];
            label celli = oldToNew[oldCelli];

            forAll(cCells, i)
            {
                label nbrCelli = oldToNew[cCells[i]];

                sumForce[celli] += (position[nbrCelli]-position[celli]);
            }
        }

        // Pout<< "Force :" << nl
        //    << "    min    : " << min(sumForce) << nl
        //    << "    max    : " << max(sumForce) << nl
        //    << "    avgMag : " << average(mag(sumForce)) << nl
        //    << "DeltaT : " << deltaT << nl
        //    << endl;

        // Limit displacement
        scalar deltaT = maxCo / max(mag(sumForce));

        Info<< "Iter:" << iter
            << "  maxCo:" << maxCo
            << "  deltaT:" << deltaT
            << "  average force:" << average(mag(sumForce)) << endl;

        // Determine displacement.
        scalarField displacement(deltaT*sumForce);

        // Pout<< "Displacement :" << nl
        //    << "    min    : " << min(displacement) << nl
        //    << "    max    : " << max(displacement) << nl
        //    << "    avgMag : " << average(mag(displacement)) << nl
        //    << endl;

        // Calculate new position and scale to be within original range
        // (0..nCells-1) for ease of postprocessing.
        position += displacement;
        position -= min(position);
        position *= (position.size()-1)/max(position);

        // Slowly freeze.
        maxCo *= freezeFraction_;
    }

    // writeOBJ("endPosition.obj", cellCells, position);

    // Move cells to new position
    labelList shuffle;
    sortedOrder(position, shuffle);

    // Reorder oldToNew
    inplaceReorder(shuffle, oldToNew);

    return invert(oldToNew.size(), oldToNew);
}


// ************************************************************************* //
