// The MIT License (MIT)
//
// Copyright (c) 2018 Mateusz Pusz
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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// SOFTWARE.

#pragma once

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

namespace units {

/**
 * @brief The base for all prefix families
 *
 * Every prefix family should inherit from this type to satisfy PrefixFamily concept.
 */
struct prefix_family {};

/**
 * @brief No prefix possible for the unit
 *
 * This is a special prefix type tag specifying that the unit can not be scaled with any kind
 * of the prefix.
 */
struct no_prefix : prefix_family {};

namespace detail {

template<PrefixFamily PF, ratio R>
struct prefix_base : downcast_base<prefix_base<PF, R>> {
  using prefix_family = PF;
  static constexpr ::units::ratio ratio = R;
};

}  // namespace detail

/**
 * @brief A prefix used to scale units
 *
 * Data from a prefix class is used in two cases:
 * - when defining a prefixed_unit its ratio is used to scale the reference unit and its
 *   symbol is used to prepend to the symbol of referenced unit
 * - when printing the symbol of a scaled unit that was not predefined by the user but its
 *   factor matches ratio of a prefix from the specified prefix family, its symbol will be
 *   prepended to the symbol of the unit
 *
 * @tparam Child inherited class type used by the downcasting facility (CRTP Idiom)
 * @tparam PF a type of prefix family
 * @tparam Symbol a text representation of the prefix
 * @tparam R factor to be used to scale a unit
 */
template<typename Child, PrefixFamily PF, basic_symbol_text Symbol, ratio R>
  requires (!std::same_as<PF, no_prefix>)
struct prefix : downcast_dispatch<Child, detail::prefix_base<PF, R>, downcast_mode::on> {
  static constexpr auto symbol = Symbol;
};

}  // namespace units