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

// IWYU pragma: begin_exports
#include <units/bits/external/fixed_string.h>
#include <units/bits/basic_concepts.h>
// IWYU pragma: end_exports

#include <type_traits>

namespace units {

/**
 * @brief A dimension of a base quantity
 *
 * Base quantity is a quantity in a conventionally chosen subset of a given system of quantities, where no quantity
 * in the subset can be expressed in terms of the other quantities within that subset. They are referred to as
 * being mutually independent since a base quantity cannot be expressed as a product of powers of the other base
 * quantities.
 * 
 * Base unit is a measurement unit that is adopted by convention for a base quantity in a specific system of units.
 *
 * Pair of Symbol and Unit template parameters form an unique identifier of the base dimension. The same identifiers can
 * be multiplied and divided which will result with an adjustment of its factor in an Exponent of a DerivedDimension
 * (in case of zero the dimension will be simplified and removed from further analysis of current expresion). In case
 * the Symbol is the same but the Unit differs (i.e. mixing SI and CGS length), there is no automatic simplification but
 * is possible to force it with a quantity_cast.
 *
 * @tparam Symbol an unique identifier of the base dimension used to provide dimensional analysis support
 * @tparam U a base unit to be used for this base dimension
 */
template<basic_fixed_string Symbol, Unit U>
  requires U::is_named
struct base_dimension {
  static constexpr auto symbol = Symbol;  ///< Unique base dimension identifier
  using base_unit = U;                    ///< Base unit adopted for this dimension
};

// base_dimension_less
template<BaseDimension D1, BaseDimension D2>
struct base_dimension_less :
    std::bool_constant<(D1::symbol < D2::symbol) ||
                       (D1::symbol == D2::symbol && D1::base_unit::symbol < D1::base_unit::symbol)> {
};

}  // namespace units