#ifndef _C4_LANGUAGE_HPP_
#define _C4_LANGUAGE_HPP_

/** @file language.hpp Provides language standard information macros and
 * compiler agnostic utility macros: namespace facilities, function attributes,
 * variable attributes, etc.
 * @ingroup basic_headers */

#include "c4/preprocessor.hpp"
#include "c4/compiler.hpp"

/* Detect C++ standard.
 * @see http://stackoverflow.com/a/7132549/5875572 */
#ifndef C4_CPP
#   ifdef _MSC_VER
#       if _MSC_VER >= 1910  // >VS2015: VS2017, VS2019
#           if (!defined(_MSVC_LANG))
#               error _MSVC not defined
#           endif
#           if _MSVC_LANG >= 201705L
#               define C4_CPP 20
#               define C4_CPP20
#           elif _MSVC_LANG == 201703L
#               define C4_CPP 17
#               define C4_CPP17
#           elif _MSVC_LANG >= 201402L
#               define C4_CPP 14
#               define C4_CPP14
#           elif _MSVC_LANG >= 201103L
#               define C4_CPP 11
#               define C4_CPP11
#           else
#               error C++ lesser than C++11 not supported
#           endif
#       else
#           if _MSC_VER == 1900
#               define C4_CPP 14  // VS2015 is c++14 https://devblogs.microsoft.com/cppblog/c111417-features-in-vs-2015-rtm/
#               define C4_CPP14
#           elif _MSC_VER == 1800 // VS2013
#               define C4_CPP 11
#               define C4_CPP11
#           else
#               error C++ lesser than C++11 not supported
#           endif
#       endif
#   elif defined(__INTEL_COMPILER) // https://software.intel.com/en-us/node/524490
#       ifdef __INTEL_CXX20_MODE__ // not sure about this
#           define C4_CPP 20
#           define C4_CPP20
#       elif defined __INTEL_CXX17_MODE__ // not sure about this
#           define C4_CPP 17
#           define C4_CPP17
#       elif defined __INTEL_CXX14_MODE__ // not sure about this
#           define C4_CPP 14
#           define C4_CPP14
#       elif defined __INTEL_CXX11_MODE__
#           define C4_CPP 11
#           define C4_CPP11
#       else
#           error C++ lesser than C++11 not supported
#       endif
#   else
#       ifndef __cplusplus
#           error __cplusplus is not defined?
#       endif
#       if __cplusplus == 1
#           error cannot handle __cplusplus==1
#       elif __cplusplus >= 201709L
#           define C4_CPP 20
#           define C4_CPP20
#       elif __cplusplus >= 201703L
#           define C4_CPP 17
#           define C4_CPP17
#       elif __cplusplus >= 201402L
#           define C4_CPP 14
#           define C4_CPP14
#       elif __cplusplus >= 201103L
#           define C4_CPP 11
#           define C4_CPP11
#       elif __cplusplus >= 199711L
#           error C++ lesser than C++11 not supported
#       endif
#   endif
#else
#   ifdef C4_CPP == 20
#       define C4_CPP20
#   elif C4_CPP == 17
#       define C4_CPP17
#   elif C4_CPP == 14
#       define C4_CPP14
#   elif C4_CPP == 11
#       define C4_CPP11
#   elif C4_CPP == 98
#       define C4_CPP98
#       error C++ lesser than C++11 not supported
#   else
#       error C4_CPP must be one of 20, 17, 14, 11, 98
#   endif
#endif

#ifdef C4_CPP20
#   define C4_CPP17
#   define C4_CPP14
#   define C4_CPP11
#elif defined(C4_CPP17)
#   define C4_CPP14
#   define C4_CPP11
#elif defined(C4_CPP14)
#   define C4_CPP11
#endif

/** lifted from this answer: http://stackoverflow.com/a/20170989/5875572 */
#ifndef _MSC_VER
#  if __cplusplus < 201103
#    define C4_CONSTEXPR11
#    define C4_CONSTEXPR14
//#    define C4_NOEXCEPT
#  elif __cplusplus < 201402
#    define C4_CONSTEXPR11 constexpr
#    define C4_CONSTEXPR14
//#    define C4_NOEXCEPT noexcept
#  else
#    define C4_CONSTEXPR11 constexpr
#    define C4_CONSTEXPR14 constexpr
//#    define C4_NOEXCEPT noexcept
#  endif
#else  // _MSC_VER
#  if _MSC_VER < 1900
#    define C4_CONSTEXPR11
#    define C4_CONSTEXPR14
//#    define C4_NOEXCEPT
#  elif _MSC_VER < 2000
#    define C4_CONSTEXPR11 constexpr
#    define C4_CONSTEXPR14
//#    define C4_NOEXCEPT noexcept
#  else
#    define C4_CONSTEXPR11 constexpr
#    define C4_CONSTEXPR14 constexpr
//#    define C4_NOEXCEPT noexcept
#  endif
#endif  // _MSC_VER

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

#define _C4_BEGIN_NAMESPACE(ns) namespace ns {
#define _C4_END_NAMESPACE(ns)   }

// MSVC cant handle the C4_FOR_EACH macro... need to fix this
//#define C4_BEGIN_NAMESPACE(...) C4_FOR_EACH_SEP(_C4_BEGIN_NAMESPACE, , __VA_ARGS__)
//#define C4_END_NAMESPACE(...) C4_FOR_EACH_SEP(_C4_END_NAMESPACE, , __VA_ARGS__)
#define C4_BEGIN_NAMESPACE(ns) namespace ns {
#define C4_END_NAMESPACE(ns) }

#define C4_BEGIN_HIDDEN_NAMESPACE namespace /*hidden*/ {
#define C4_END_HIDDEN_NAMESPACE } /* namespace hidden */

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

#ifndef C4_API
#   if defined(_MSC_VER)
#       if defined(C4_EXPORT)
#           define C4_API __declspec(dllexport)
#       elif defined(C4_IMPORT)
#           define C4_API __declspec(dllimport)
#       else
#           define C4_API
#       endif
#   else
#       define C4_API
#   endif
#endif

#ifndef _MSC_VER  ///< @todo assuming gcc-like compiler. check it is actually so.
/** for function attributes in GCC,
 * @see https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#Common-Function-Attributes */
/** for __builtin functions in GCC,
 * @see https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html */
#   define C4_RESTRICT __restrict__
#   define C4_RESTRICT_FN __attribute__((restrict))
#   define C4_NO_INLINE __attribute__((noinline))
#   define C4_ALWAYS_INLINE inline __attribute__((always_inline))
/** force inlining of every callee function */
#   define C4_FLATTEN __atribute__((flatten))
/** mark a function as hot, ie as having a visible impact in CPU time
 * thus making it more likely to inline, etc
 * @see http://stackoverflow.com/questions/15028990/semantics-of-gcc-hot-attribute */
#   define C4_HOT __attribute__((hot))
/** mark a function as cold, ie as NOT having a visible impact in CPU time
 * @see http://stackoverflow.com/questions/15028990/semantics-of-gcc-hot-attribute */
#   define C4_COLD __attribute__((cold))
#   define C4_EXPECT(x, y) __builtin_expect(x, y) ///< @see https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html
#   define C4_LIKELY(x)   __builtin_expect(x, 1)
#   define C4_UNLIKELY(x) __builtin_expect(x, 0)
#   define C4_UNREACHABLE() __builtin_unreachable()
#   define C4_ATTR_FORMAT(...) //__attribute__((format (__VA_ARGS__))) ///< @see https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#Common-Function-Attributes
#   define C4_NORETURN __attribute__((noreturn))
#else
#   define C4_RESTRICT __restrict
#   define C4_RESTRICT_FN __declspec(restrict)
#   define C4_NO_INLINE __declspec(noinline)
#   define C4_ALWAYS_INLINE inline __forceinline
/** these are not available in VS AFAIK */
#   define C4_FLATTEN
#   define C4_HOT         /** @todo */
#   define C4_COLD        /** @todo */
#   define C4_EXPECT(x, y) x /** @todo */
#   define C4_LIKELY(x)   x /** @todo */
#   define C4_UNLIKELY(x) x /** @todo */
#   define C4_UNREACHABLE() /** @todo */
#   define C4_ATTR_FORMAT(...) /** */
#   define C4_NORETURN /** @todo */
#endif

#ifndef _MSC_VER
#   define C4_FUNC __FUNCTION__
#   define C4_PRETTY_FUNC __PRETTY_FUNCTION__
#else /// @todo assuming gcc-like compiler. check it is actually so.
#   define C4_FUNC __FUNCTION__
#   define C4_PRETTY_FUNC __FUNCSIG__
#endif

/** prevent compiler warnings about a specific var being unused */
#define C4_UNUSED(var) (void)var

#if C4_CPP >= 17
#define C4_STATIC_ASSERT(cond) static_assert(cond)
#else
#define C4_STATIC_ASSERT(cond) static_assert((cond), #cond)
#endif
#define C4_STATIC_ASSERT_MSG(cond, msg) static_assert((cond), #cond ": " msg)

/** @def C4_DONT_OPTIMIZE idea lifted from GoogleBenchmark.
 * @see https://github.com/google/benchmark/blob/master/include/benchmark/benchmark_api.h */
namespace c4 {
namespace detail {
#ifdef __GNUC__
#   define C4_DONT_OPTIMIZE(var) c4::detail::dont_optimize(var)
template< class T >
C4_ALWAYS_INLINE void dont_optimize(T const& value) { asm volatile("" : : "g"(value) : "memory"); }
#else
#   define C4_DONT_OPTIMIZE(var) c4::detail::use_char_pointer(reinterpret_cast< const char* >(&var))
void use_char_pointer(char const volatile*);
#endif
} // namespace detail
} // namespace c4

/** @def C4_KEEP_EMPTY_LOOP prevent an empty loop from being optimized out.
 * @see http://stackoverflow.com/a/7084193/5875572 */
#ifndef _MSC_VER
#   define C4_KEEP_EMPTY_LOOP { asm(""); }
#else
#   define C4_KEEP_EMPTY_LOOP { char c; C4_DONT_OPTIMIZE(c); }
#endif

/** @def C4_VA_LIST_REUSE_MUST_COPY
 * @todo <jpmag> I strongly suspect that this is actually only in UNIX platforms. revisit this. */
#ifdef __GNUC__
#   define C4_VA_LIST_REUSE_MUST_COPY
#endif

#endif /* _C4_LANGUAGE_HPP_ */
