/*---------------------------------------------------------------------------*\
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    \\  /    A nd           | Copyright (C) 2011-2026 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/>.

Class
    Foam::fixedGradientFvPatchField

Description
    This boundary condition supplies a fixed gradient condition, such that
    the patch values are calculated using:

        \f[
            x_p = x_c + \frac{\nabla(x)}{\Delta}
        \f]

    where
    \vartable
        x_p      | patch values
        x_c      | internal field values
        \nabla(x)| gradient (user-specified)
        \Delta   | inverse distance from patch face centre to cell centre
    \endvartable

Usage
    \table
        Property     | Description             | Required    | Default value
        gradient     | gradient                | yes         |
    \endtable

    Example of the boundary condition specification:
    \verbatim
    <patchName>
    {
        type            fixedGradient;
        gradient        uniform 0;
    }
    \endverbatim

SourceFiles
    fixedGradientFvPatchField.C

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

#ifndef fixedGradientFvPatchField_H
#define fixedGradientFvPatchField_H

#include "fvPatchField.H"

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

namespace Foam
{

/*---------------------------------------------------------------------------*\
                  Class fixedGradientFvPatchField Declaration
\*---------------------------------------------------------------------------*/

template<class Type>
class fixedGradientFvPatchField
:
    public fvPatchField<Type>
{
    // Private Data

        Field<Type> gradient_;


public:

    //- Runtime type information
    TypeName("fixedGradient");


    // Constructors

        //- Construct from patch and internal field
        fixedGradientFvPatchField
        (
            const fvPatch&,
            const DimensionedField<Type, fvMesh>&
        );

        //- Construct from patch, internal field and dictionary
        fixedGradientFvPatchField
        (
            const fvPatch&,
            const DimensionedField<Type, fvMesh>&,
            const dictionary&,
            const bool gradientRequired=true
        );

        //- Construct by mapping the given fixedGradientFvPatchField
        //  onto a new patch
        fixedGradientFvPatchField
        (
            const fixedGradientFvPatchField<Type>&,
            const fvPatch&,
            const DimensionedField<Type, fvMesh>&,
            const fieldMapper&,
            const bool mappingRequired=true
        );

        //- Disallow copy without setting internal field reference
        fixedGradientFvPatchField
        (
            const fixedGradientFvPatchField<Type>&
        ) = delete;

        //- Copy constructor setting internal field reference
        fixedGradientFvPatchField
        (
            const fixedGradientFvPatchField<Type>&,
            const DimensionedField<Type, fvMesh>&
        );

        //- Construct and return a clone setting internal field reference
        virtual tmp<fvPatchField<Type>> clone
        (
            const DimensionedField<Type, fvMesh>& iF
        ) const
        {
            return tmp<fvPatchField<Type>>
            (
                new fixedGradientFvPatchField<Type>(*this, iF)
            );
        }


    // Member Functions

        using fvPatchField<Type>::patch;
        using fvPatchField<Type>::patchInternalField;


        // Return defining fields

            //- Return gradient at boundary
            virtual Field<Type>& gradient()
            {
                return gradient_;
            }

            virtual const Field<Type>& gradient() const
            {
                return gradient_;
            }


        // Mapping functions

            //- Map the given fvPatchField onto this fvPatchField
            virtual void map(const fvPatchField<Type>&, const fieldMapper&);

            //- Reset the fvPatchField to the given fvPatchField
            //  Used for mesh to mesh mapping
            virtual void reset(const fvPatchField<Type>&);


        // Evaluation functions

            //- Return gradient at boundary
            virtual tmp<Field<Type>> snGrad() const
            {
                return gradient_;
            }

            //- Evaluate the patch field
            virtual void evaluate
            (
                const Pstream::commsTypes commsType =
                    Pstream::commsTypes::blocking
            );

            //- Return the matrix diagonal coefficients corresponding to the
            //  evaluation of the value of this patchField with given weights
            virtual tmp<Field<Type>> valueInternalCoeffs
            (
                const tmp<scalarField>&
            ) const;

            //- Return the matrix source coefficients corresponding to the
            //  evaluation of the value of this patchField with given weights
            virtual tmp<Field<Type>> valueBoundaryCoeffs
            (
                const tmp<scalarField>&
            ) const;

            //- Return the matrix diagonal coefficients corresponding to the
            //  evaluation of the gradient of this patchField
            virtual tmp<Field<Type>> gradientInternalCoeffs() const;

            //- Return the matrix source coefficients corresponding to the
            //  evaluation of the gradient of this patchField
            virtual tmp<Field<Type>> gradientBoundaryCoeffs() const;


        //- Write
        virtual void write(Ostream&) const;


    // Member Operators

        //- Inherit assignment
        using fvPatchField<Type>::operator=;
};


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

} // End namespace Foam

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

#ifdef NoRepository
    #include "fixedGradientFvPatchField.C"
#endif

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

#endif

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