// The MIT License (MIT)
//
// Copyright (c) 2018 Mateusz Pusz
//
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#pragma once

#include <units/base_dimension.h>
#include <units/bits/external/downcasting.h>
#include <units/exp.h>

namespace units::detail {

/**
 * @brief A dimension of a derived quantity
 *
 * Expression of the dependence of a quantity on the base quantities (and their base dimensions) of a system of
 * quantities as a product of powers of factors corresponding to the base quantities, omitting any numerical factors.
 * A power of a factor is the factor raised to an exponent.
 * 
 * A derived dimension can be formed from multiple exponents (i.e. speed is represented as "exp<L, 1>, exp<T, -1>").
 * It is also possible to form a derived dimension with only one exponent (i.e. frequency is represented as just
 * "exp<T, -1>").
 * 
 * @note This class template is used by the library engine and should not be directly instantiated by the user.
 * 
 * @tparam E a first exponent of a derived dimension
 * @tparam ERest zero or more following exponents of a derived dimension
 */
template<Exponent E, Exponent... ERest>
  requires (BaseDimension<typename E::dimension> && ... && BaseDimension<typename ERest::dimension>)
struct derived_dimension_base : downcast_base<derived_dimension_base<E, ERest...>> {
  using exponents = exp_list<E, ERest...>;
};

template<typename T>
struct to_derived_dimension_base;

template<Exponent... Es>
struct to_derived_dimension_base<exp_list<Es...>> {
  using type = derived_dimension_base<Es...>;
};

}  // namespace units::detail