Composer.hpp

#pragma once

#include <tuple>
#include <type_traits>

#include <amdis/common/Apply.hpp>
#include <amdis/common/Concepts.hpp>
#include <amdis/common/Logical.hpp>
#include <amdis/operations/Basic.hpp>

namespace AMDiS
{
  namespace Operation
  {

    template <class F, class... Gs>
    struct Composer
    {
      template <class F_, class... Gs_,
        REQUIRES( Concepts::Similar<Types<F,Gs...>, Types<F_,Gs_...>>) >
      constexpr Composer(F_&& f, Gs_&&... gs)
        : f_(FWD(f))
        , gs_(FWD(gs)...)
      {}

      template <class... Ts>
      constexpr auto operator()(Ts const&... args) const
      {
        auto eval = [&](auto const& g) { return g(args...); };
        return Ranges::apply([&,this](auto const&... gs) { return f_(eval(gs)...); }, gs_);
      }

      F f_;
      std::tuple<Gs...> gs_;
    };

#ifndef DOXYGEN
    template <class F, class... Gs>
    struct ComposerBuilder
    {
      using type = Composer<F, Gs...>;

      template <class F_, class... Gs_>
      static constexpr type build(F_&& f, Gs_&&... gs)
      {
        return type{FWD(f), FWD(gs)...};
      }
    };
#endif

    template <class F, class... Gs>
    constexpr auto compose(F&& f, Gs&&... gs)
    {
      return ComposerBuilder<TYPEOF(f), TYPEOF(gs)...>::build(FWD(f), FWD(gs)...);
    }

    // Polynomial order or composed function combines the orders of the sub-functions
    template <class F, class... Gs, class... Int,
      REQUIRES(Concepts::HasFunctorOrder<F,sizeof...(Gs)>
               && (Concepts::HasFunctorOrder<Gs,sizeof...(Int)> &&...))>
    int order(Composer<F,Gs...> const& c, Int... degrees)
    {
      auto deg = [&](auto const& g) { return order(g, int(degrees)...); };
      return Ranges::apply([&](auto const&... gs) { return order(c.f_, deg(gs)...); }, c.gs_);
    }

    template <int J, class F, class... Gs>
    auto partial(Composer<F,Gs...> const& c, index_t<J> _j);


#ifndef DOXYGEN
    // some specialization for the composer

    // id(g) => g
    template <class F>
    struct ComposerBuilder<Id, F>
    {
      using type = F;

      template <class F_>
      static constexpr F build(F_&& f)
      {
        return F{FWD(f)};
      }
    };
#endif

  } // end namespace Operation
} // end namespace AMDiS