/*
 Copyright (c) 2003-2020 Andy Little.

 This program is free software: you can redistribute it and/or modify
 it under the terms of the GNU General Public License as published by
 the Free Software Foundation, either version 3 of the License or
 (at your option) any later version.

 This program is distributed in the hope that it will be useful,
 but WITHOUT ANY WARRANTY; without even the implied warranty of
 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 GNU General Public License for more details.

 You should have received a copy of the GNU General Public License
 along with this program. If not, see http://www.gnu.org/licenses./
*/

#include <units/physical/si/length.h>
#include <iostream>

/*
  get conversion factor from one dimensionally equivalent
  quantity type to another
*/

namespace {

template<units::Quantity Target, units::Quantity Source>
  requires units::equivalent_dim<typename Source::dimension, typename Target::dimension>
inline constexpr std::common_type_t<typename Target::rep, typename Source::rep> conversion_factor(Target, Source)
{
  // get quantities looking like inputs but with Q::rep that doesn't have narrowing conversion
  typedef std::common_type_t<typename Target::rep, typename Source::rep> rep;
  typedef units::quantity<typename Source::dimension, typename Source::unit, rep> source;
  typedef units::quantity<typename Target::dimension, typename Target::unit, rep> target;
  return target{source{1}}.count();
}

// get at the units text of the quantity, without its numeric value
inline auto constexpr units_str(const units::Quantity AUTO& q)
{
  typedef std::remove_cvref_t<decltype(q)> qtype;
  return units::detail::unit_text<typename qtype::dimension, typename qtype::unit>();
}

}  // namespace

namespace {

namespace length {

template<typename Rep = double>
using m = units::si::length<units::si::metre, Rep>;

template<typename Rep = double>
using mm = units::si::length<units::si::millimetre, Rep>;

}  // namespace length
}  // namespace

using namespace units::si::literals;

int main()
{
  std::cout << "conversion factor in mpusz/units...\n\n";

  constexpr length::m<> lengthA = 2.0q_m;
  constexpr length::mm<> lengthB = lengthA;

  std::cout << "lengthA( " << lengthA << " ) and lengthB( " << lengthB << " )\n"
            << "represent the same length in different units.\n\n";

  std::cout << "therefore ratio lengthA / lengthB == " << lengthA / lengthB << "\n\n";

  std::cout << "conversion factor from lengthA::unit of "
            << units_str(lengthA) << " to lengthB::unit of " << units_str(lengthB) << " :\n\n"
            << "lengthB.count( " << lengthB.count() << " ) == lengthA.count( " << lengthA.count()
            << " ) * conversion_factor( " << conversion_factor(lengthB, lengthA) << " )\n";
}