message ("-- Configuring C++17")
message ("-- System: ${CMAKE_SYSTEM_NAME}")

include (CheckCXXCompilerFlag)

CHECK_CXX_COMPILER_FLAG("-std=c++17"   _HAS_CXX17)

if (_HAS_CXX17)
  set (CMAKE_CXX_STANDARD 17)
  set (CMAKE_CXX_EXTENSIONS OFF)
else (_HAS_CXX17)
 message (FATAL_ERROR "C++17 support missing. Try upgrading your C++ compiler. If you have a good reason for using an outdated compiler, please let us know at support@gothenburgbitfactory.org.")
endif (_HAS_CXX17)

if (${CMAKE_SYSTEM_NAME} MATCHES "Linux")
  set (LINUX true)
elseif (${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
  set (DARWIN true)
  set (_CXX14_FLAGS "${_CXX14_FLAGS} -stdlib=libc++")
elseif (${CMAKE_SYSTEM_NAME} MATCHES "kFreeBSD")
  set (KFREEBSD true)
elseif (${CMAKE_SYSTEM_NAME} MATCHES "FreeBSD")
  set (FREEBSD true)
elseif (${CMAKE_SYSTEM_NAME} MATCHES "OpenBSD")
  set (OPENBSD true)
elseif (${CMAKE_SYSTEM_NAME} MATCHES "NetBSD")
  set (NETBSD true)
elseif (${CMAKE_SYSTEM_NAME} MATCHES "DragonFly")
  set (DRAGONFLY true)
elseif (${CMAKE_SYSTEM_NAME} MATCHES "SunOS")
  set (SOLARIS true)
elseif (${CMAKE_SYSTEM_NAME} STREQUAL "GNU")
  set (GNUHURD true)
elseif (${CMAKE_SYSTEM_NAME} STREQUAL "CYGWIN")
  set (CYGWIN true)
  set (CMAKE_CXX_EXTENSIONS ON)
else (${CMAKE_SYSTEM_NAME} MATCHES "Linux")
  set (UNKNOWN true)
endif (${CMAKE_SYSTEM_NAME} MATCHES "Linux")

set (CMAKE_CXX_FLAGS "${_CXX14_FLAGS} ${CMAKE_CXX_FLAGS}")
set (CMAKE_CXX_FLAGS "-Wall -Wextra -Wsign-compare -Wreturn-type ${CMAKE_CXX_FLAGS}")