File ascomplexfield.h

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#ifndef COSMOINTERFACE_COMPLEXFIELDALGEBRA_ASCOMPLEXFIELD_H
#define COSMOINTERFACE_COMPLEXFIELDALGEBRA_ASCOMPLEXFIELD_H

/* This file is part of TempLat, available at https://cosmolattice.github.io/templat .
   Copyright 2021-2026 The TempLat authors, see AUTHORS.md.
   Released under the MIT license, see LICENSE.md. */

// File info: Main contributor(s): Franz R. Sattler, Year: 2026

#include "TempLat/lattice/algebra/operators/unaryoperator.h"
#include "TempLat/lattice/algebra/complexalgebra/helpers/complexfieldget.h"
#include "TempLat/lattice/algebra/complexalgebra/helpers/hascomplexfieldget.h"
#include "TempLat/lattice/algebra/helpers/getgetreturntype.h"
#include "TempLat/lattice/algebra/helpers/haseval.h"
#include "TempLat/lattice/algebra/helpers/iscomplextype.h"
#include "TempLat/lattice/algebra/helpers/isvariadicindex.h"
#include "TempLat/lattice/algebra/helpers/doeval.h"
#include "TempLat/lattice/algebra/helpers/getstring.h"
#include "TempLat/util/rangeiteration/tagliteral.h"
#include "TempLat/parallel/device.h"

// IMPORTANT: this header must NOT include real.h / imag.h. They include this header (to add their
// third overload), so including them back would form a cycle. Everything used here (UnaryOperator,
// complexfieldget.h) is verified not to reach real.h / imag.h.

namespace TempLat
{
  template <typename R, int N> class ComplexEvalComponent : public UnaryOperator<R>
  {
    static_assert(N == 0 || N == 1, "ComplexEvalComponent: N must be 0 (real) or 1 (imaginary).");

  public:
    using UnaryOperator<R>::mR;

    ComplexEvalComponent(const R &pR) : UnaryOperator<R>(pR) {}

    static constexpr size_t NDim = GetNDim::get<R>();

    template <typename... IDX>
      requires requires(std::decay_t<R> r, IDX... idx) {
        requires IsVariadicIndex<IDX...>;
        DoEval::eval(r, idx...);
      }
    DEVICE_INLINE_FUNCTION auto eval(const IDX &...idx) const
    {
      if constexpr (N == 0)
        return device::real(DoEval::eval(mR, idx...));
      else
        return device::imag(DoEval::eval(mR, idx...));
    }

    virtual std::string operatorString() const override { return N == 0 ? "Re " : "Im "; }
  };

  template <typename R> class AsComplexField : public UnaryOperator<R>
  {
  public:
    using UnaryOperator<R>::mR;

    AsComplexField(const R &pR) : UnaryOperator<R>(pR) {}

    static constexpr size_t NDim = GetNDim::get<R>();

    using ValueType = typename GetGetReturnType<std::decay_t<R>>::type; // complex<C>
    using ComponentType = typename ValueType::value_type;               // C

    auto ComplexFieldGet(Tag<0> t) const { return ComplexEvalComponent<R, 0>(mR); }
    auto ComplexFieldGet(Tag<1> t) const { return ComplexEvalComponent<R, 1>(mR); }

    template <int N> auto operator()(Tag<N> t) const
    {
      static_assert(N >= 0 && N <= 1, "Operator(): N must be 0 or 1 for AsComplexField");
      return ComplexFieldGet(t);
    }

    template <typename... IDX>
      requires requires(std::decay_t<R> r, IDX... idx) {
        requires IsVariadicIndex<IDX...>;
        DoEval::eval(r, idx...);
      }
    DEVICE_INLINE_FUNCTION auto eval(const IDX &...idx) const
    {
      const auto v = DoEval::eval(mR, idx...);
      device::array<ComponentType, 2> result;
      result[0] = device::real(v);
      result[1] = device::imag(v);
      return result;
    }

    std::string toString() const { return "asComplexField(" + GetString::get(mR) + ")"; }

    using Getter = ComplexFieldGetter;
    static constexpr size_t SHIFTIND = 0;
    static constexpr size_t size = 2;
  };

  template <typename T>
  concept HasComplexEval =
      HasEvalMethod<T> && !HasComplexFieldGet<T> && !IsComplexType<T> && GetGetReturnType<std::decay_t<T>>::isComplex;

  template <typename R>
    requires HasComplexEval<std::decay_t<R>>
  auto asComplexField(R &&r)
  {
    return AsComplexField<std::decay_t<R>>(std::forward<R>(r));
  }
} // namespace TempLat

#endif