#ifndef DUNE_GFE_LOCALENERGY_HH
#define DUNE_GFE_LOCALENERGY_HH

#include <vector>

#include <dune/common/tuplevector.hh>

#include <dune/gfe/spaces/productmanifold.hh>

namespace Dune::GFE
{
  namespace Impl
  {
    /** \brief A class exporting container types for coefficient sets
     *
     * This generic template handles TargetSpaces that are not product manifolds.
     */
    template <class TargetSpace>
    struct LocalEnergyTypes
    {
      constexpr static bool isProductManifold = false;

      using Coefficients = std::vector<TargetSpace>;
      using CompositeCoefficients = TupleVector<std::vector<TargetSpace> >;
    };

    /** \brief A class exporting container types for coefficient sets -- specialization for product manifolds
     */
    template <class ... Factors>
    struct LocalEnergyTypes<ProductManifold<Factors...> >
    {
      constexpr static bool isProductManifold = true;

      using Coefficients = std::vector<ProductManifold<Factors...> >;
      using CompositeCoefficients = TupleVector<std::vector<Factors>... >;
    };
  }  // namespace Impl


  /** \brief Base class for energies defined by integrating over one grid element */
  template<class Basis, class TargetSpace>
  class LocalEnergy
  {
  public:
    using RT = typename TargetSpace::ctype;

    /** \brief Compute the energy
     *
     * \param localView Local view specifying the current element and the FE space there
     * \param coefficients The coefficients of a FE function on the current element
     */
    virtual RT
    energy (const typename Basis::LocalView& localView,
            const typename Impl::LocalEnergyTypes<TargetSpace>::Coefficients& coefficients) const = 0;

    /** \brief ProductManifolds: Compute the energy from coefficients in separate containers
     * for each factor
     */
    virtual RT
    energy (const typename Basis::LocalView& localView,
            const typename Impl::LocalEnergyTypes<TargetSpace>::CompositeCoefficients& coefficients) const = 0;

    /** Empty virtual default destructor
     *
     * To allow proper destruction of derived classes through a base class pointer
     */
    virtual ~LocalEnergy() = default;

  };

}  // namespace Dune::GFE

#endif  // DUNE_GFE_LOCALENERGY_HH