// author: Filip Roséen <filip.roseen@gmail.com>
// source: http://b.atch.se/posts/constexpr-meta-container

#ifndef ATCH_META_COUNTER_HPP
#define ATCH_META_COUNTER_HPP

#include <cstddef>

namespace atch { namespace {

  template<class Tag>
  struct meta_counter {
    using size_type = std::size_t;

    template<size_type N>
    struct ident {
      friend constexpr size_type adl_lookup (ident<N>);
      static constexpr size_type value = N;
    };

    // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 

    template<class Ident>
    struct writer {
      friend constexpr size_type adl_lookup (Ident) {
        return Ident::value;
      }

      static constexpr size_type value = Ident::value;
    };
    
    // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 

    template<size_type N, int = adl_lookup (ident<N> {})>
    static constexpr size_type value_reader (int, ident<N>) {
      return N;
    }

    template<size_type N>
    static constexpr size_type value_reader (float, ident<N>, size_type R = value_reader (0, ident<N-1> ())) {
      return R;
    }

    static constexpr size_type value_reader (float, ident<0>) {
      return 0;
    }

    // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 

    template<size_type Max = 64>
    static constexpr size_type value (size_type R = value_reader (0, ident<Max> {})) {
      return R;
    }

    template<size_type N = 1, class H = meta_counter>
    static constexpr size_type next (size_type R = writer<ident<N + H::value ()>>::value) {
      return R;
    }
  };
}}

#endif /* include guard */