/*
 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>

/*
    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>
   constexpr inline
   std::common_type_t<
      typename Target::rep,
      typename Source::rep
   >
   conversion_factor(Target , Source)
   {
      // get quantities looking like inputs but with Q::rep that doesnt 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
   auto inline constexpr units_str( const units::Quantity & q)
   {
      typedef std::remove_cvref_t<decltype(q)> qtype;
      return units::detail::unit_text<typename qtype::dimension, typename qtype::unit>();
   }
}

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>;
   }
}

#include <iostream>

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

   constexpr length::m<>  lengthA = 2.0m;
   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";
}