format.h

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*
* This file contains private API, this might break at any time between releases.
* You have been warned!
*
*/
#ifndef ZYPP_NG_LOG_FORMAT_H_INCLUDED
#define ZYPP_NG_LOG_FORMAT_H_INCLUDED

#include <ostream>
#include <sstream>
#include <type_traits>

#include <zypp-core/ng/base/zyppglobal.h>
#include <zypp-core/ng/meta/type_traits.h>


namespace zyppng{

  ZYPP_FWD_DECL_TYPE_WITH_REFS(Context);

  namespace log {

    template <typename T, typename Enable = void>
    struct formatter;

    namespace detail {

      template <typename T>
      struct view_proxy {
          const T& obj;

          operator std::string() const {
              std::ostringstream ss;
              ss << *this;
              return ss.str();
          }

          friend std::ostream& operator<<(std::ostream& os, const view_proxy& v) {
              return formatter<T>::stream(os, v.obj);
          }
      };

      template <typename T>
      struct ctx_bound_view_proxy {
          const ContextWeakRef ctx;
          const T& obj;

          operator std::string() const {
              std::ostringstream ss;
              ss << *this;
              return ss.str();
          }

          friend std::ostream& operator<<(std::ostream& os, const ctx_bound_view_proxy& v) {
            auto ctxLock = v.ctx.lock();
            if ( ctxLock )
              return formatter<T>::stream(os, ctxLock, v.obj);
            else {
              return os << "<<Error: Context Required for streaming " << typeid(T).name() << ">>";
            }
          }
      };

        template <typename T, typename = void>
        struct has_view_proxy : std::false_type {};

        template <typename T>
        struct has_view_proxy<T, std::void_t<decltype(formatter<T>::stream(std::declval<std::ostream&>(), std::declval<const T&>()))>>
            : std::true_type {};
    }

    template <typename T>
    auto view(const ContextRef& ctx, const T& obj) {
      return detail::ctx_bound_view_proxy<T>{ ctx, obj };
    }

    template <typename T >
    auto view(const T& obj) {
      return detail::view_proxy<T>{ obj };
    }
  }

  template <typename T>
  auto operator<<(std::ostream& os, const T& obj)
      -> std::enable_if_t<log::detail::has_view_proxy<T>::value, std::ostream&>
  {
      return os << log::view<T>(obj);
  }
}

#endif