AngleLookup.h

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#ifndef INCLUDE_SYMMETRIES_CONSTEXPR_ANGLES_H
#define INCLUDE_SYMMETRIES_CONSTEXPR_ANGLES_H

#include "Molassembler/Temple/constexpr/UpperTriangularMatrix.h"

namespace Scine {
namespace Molassembler {
namespace Shapes {
namespace Detail {

template<unsigned long size>
constexpr double makeElement(
  const std::array<Temple::Vector, size>& positions,
  const size_t i
) {
  // Get i-j matrix indices from the linear index
  const auto indexPair = Temple::UpperTriangularMatrixImpl::index_conversion::toDoubleIndex<size>(i);

  // Calculate the angle
  return Temple::angle(
    positions[indexPair.first],
    positions[indexPair.second]
  );
}

template<unsigned long size, size_t... Inds>
constexpr std::array<double, size * (size - 1) / 2> makeArrayImpl(
  const std::array<Temple::Vector, size>& positions,
  std::integer_sequence<size_t, Inds...> /* inds */
) {
  // Expand the parameter pack for each individual linear index
  return {{ makeElement(positions, Inds)... }};
}

template<unsigned long size>
constexpr std::array<double, size * (size - 1) / 2> makeArray(
  const std::array<Temple::Vector, size>& positions
) {
  return makeArrayImpl(
    positions,
    std::make_index_sequence<size * (size - 1) / 2>{}
  );
}

} // namespace Detail
} // namespace Shapes
} // namespace Molassembler
} // namespace Scine

#endif