include(CheckCCompilerFlag)

option(ENABLE_WERROR "Turn compiler warnings into errors" OFF)
option(PICKY_COMPILER "Enable picky compiler options" ON)

if(ENABLE_WERROR)
  if(MSVC)
    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} /WX")
    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /WX")
  else()  # llvm/clang and gcc style options
    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Werror")
    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Werror")
  endif()
endif()

if(MSVC)
  # Use the highest warning level for visual studio.
  if(PICKY_COMPILER)
    if(CMAKE_CXX_FLAGS MATCHES "/W[0-4]")
      string(REGEX REPLACE "/W[0-4]" "/W4" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
    else()
      set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /W4")
    endif()
    if(CMAKE_C_FLAGS MATCHES "/W[0-4]")
      string(REGEX REPLACE "/W[0-4]" "/W4" CMAKE_C_FLAGS "${CMAKE_C_FLAGS}")
    else()
      set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} /W4")
    endif()
  endif()

  add_definitions(-D_CRT_SECURE_NO_WARNINGS)
elseif(CMAKE_COMPILER_IS_GNUCC OR CMAKE_COMPILER_IS_GNUCXX OR CMAKE_C_COMPILER_ID MATCHES "Clang")
  if(NOT CMAKE_CXX_FLAGS MATCHES "-Wall")
    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall")
  endif()
  if(NOT CMAKE_C_FLAGS MATCHES "-Wall")
    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall")
  endif()

  if(PICKY_COMPILER)
    foreach(_CCOPT -pedantic -W -Wpointer-arith -Wwrite-strings -Wunused -Wshadow -Winline -Wnested-externs -Wmissing-declarations -Wmissing-prototypes -Wfloat-equal -Wsign-compare -Wundef -Wendif-labels -Wstrict-prototypes -Wdeclaration-after-statement -Wstrict-aliasing=3 -Wcast-align -Wtype-limits -Wold-style-declaration -Wmissing-parameter-type -Wempty-body -Wclobbered -Wignored-qualifiers -Wconversion -Wvla -Wdouble-promotion -Wenum-conversion -Warith-conversion)
      # surprisingly, CHECK_C_COMPILER_FLAG needs a new variable to store each new
      # test result in.
      string(MAKE_C_IDENTIFIER "OPT${_CCOPT}" _optvarname)
      check_c_compiler_flag(${_CCOPT} ${_optvarname})
      if(${_optvarname})
        set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${_CCOPT}")
      endif()
    endforeach()
    foreach(_CCOPT long-long multichar format-nonliteral sign-conversion system-headers pedantic-ms-format)
      # GCC only warns about unknown -Wno- options if there are also other diagnostic messages,
      # so test for the positive form instead
      string(MAKE_C_IDENTIFIER "OPT${_CCOPT}" _optvarname)
      check_c_compiler_flag("-W${_CCOPT}" ${_optvarname})
      if(${_optvarname})
        set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wno-${_CCOPT}")
      endif()
    endforeach()
  endif()
endif()