include(CMakeParseArguments) # cmake_parse_arguments

function(gen_toolchain_definitions)
  set(function_name "gen_toolchain_definitions")
  set(function_synopsis "${function_name}(OUTPUT output [DEFINITIONS def1 def2 ...])")

  # parse arguments
  set(parse_prefix x)
  set(optional_value_args "")
  set(one_value_args OUTPUT)
  set(multi_value_args DEFINITIONS)
  cmake_parse_arguments(${parse_prefix}
    ""
    "${one_value_args}"
    "${multi_value_args}"
    ${ARGV})

  # No free arguments allowed
  list(LENGTH x_UNPARSED_ARGUMENTS x_len)
  if(NOT x_len EQUAL 0)
    message(FATAL_ERROR
      "'${function_name}' incorrect usage,"
      " expected no free arguments '${x_UNPARSED_ARGUMENTS}'."
      " Synopsis: ${function_synopsis}"
    )
  endif()
  # option OUTPUT is mandatory
  string(COMPARE EQUAL "${x_OUTPUT}" "" is_empty)
  if(is_empty)
    message(FATAL_ERROR
      "'${function_name}' incorrect usage,"
      " option 'OUTPUT' with one argument is mandatory."
      " Synopsis: ${function_synopsis}"
    )
  endif()
  string(FIND "${x_OUTPUT}" " " x_OUTPUT_whitespace_position)
  if(NOT x_OUTPUT_whitespace_position EQUAL -1)
    message(FATAL_ERROR
      "'${function_name}' incorrect usage,"
      " definition '${x_OUTPUT}' with whitespaces not allowed."
    )
  endif()

  # option DEFINITIONS has default values
  string(COMPARE EQUAL "${x_DEFINITIONS}" "" is_empty)
  if(is_empty)
    # set default values for DEFINITIONS
    set(x_DEFINITIONS
      # architectures
      __amd64__
      _WIN64
      __i386__
      _WIN32
      _WIN32_WINNT
      __arm__
      __aarch64__
      # compiler: MINGW
      __MINGW32__
      __MINGW64__
      # compiler: gcc
      __GNUC__              #// major
      __GNUC_MINOR__        #// minor
      __GNUC_PATCHLEVEL__   #// patch
      # compiler: MSVC
      _MSC_BUILD
      _MSC_EXTENSIONS
      _MSC_FULL_VER
      _MSC_VER
    )
  endif()

  set(toolchain_working_dir "${CMAKE_BINARY_DIR}/_toolchain_definitions")
  set(toolchain_definitions_file "${toolchain_working_dir}/print_toolchain_definitions.cpp")
  # create temporary print_toolchain_definitions.cpp file
  file(WRITE ${toolchain_definitions_file}
    "// This file is automatically generated by '${function_name}'\n"
    "// do not edit!\n"
    "\n"
    "#define DEF_QUOTE(x) #x\n"
    "#define DEF_STRING(x) DEF_QUOTE(x)\n"
    "#define DEF_INFO(x) \\\n"
    "    \"__DEF_MACRO_CHECK_BEGIN__\" \\\n"
    "    \"#define \" #x \" \" DEF_STRING(x) \\\n"
    "    \"__DEF_MACRO_CHECK_END__\"\n"
    "\n"
    "#include <exception> // Check std library version\n"
    "\n"
    "#if defined(__ANDROID__)\n"
    "# include <android/api-level.h> // Header with __ANDROID_API__\n"
    "#endif\n"
    "\n"
    "#if defined(_MSC_VER)\n"
    "# include <SdkDdkVer.h> // Header with _WIN32_WINNT\n"
    "#endif\n"
    "\n"
  )

  foreach(def ${x_DEFINITIONS})
    file(APPEND ${toolchain_definitions_file}
      "#if defined(${def})\n"
      "# pragma message(DEF_INFO(${def}))\n"
      "#endif\n"
      "\n"
    )
  endforeach()
  # add main function to successfully compile
  file(APPEND ${toolchain_definitions_file}
    "int main() {\n"
    "}\n"
  )


  # compile toolchain-definitions file
  try_compile(
    try_compile_result
    "${toolchain_working_dir}"
    "${toolchain_definitions_file}"
    CMAKE_FLAGS "-DCMAKE_TOOLCHAIN_FILE=${CMAKE_TOOLCHAIN_FILE}"
    OUTPUT_VARIABLE outresult
  )

  if(NOT try_compile_result)
    message(FATAL_ERROR
      "Compilation of '${toolchain_definitions_file}' failed. Result: ${try_compile_result}\n"
      "Output:\n--- OUTPUT BEGIN ---\n${outresult}\n--- OUTPUT END ---"
    )
  endif()

  # split result string into list of strings
  set(string_in "${outresult}")
  set(list_of_strings "")

  while(TRUE)
    string(COMPARE EQUAL "${string_in}" "" is_empty)
    if(is_empty)
      break()
    endif()

    string(FIND "${string_in}" "\n" eol_pos)
    if(eol_pos EQUAL -1)
      list(APPEND list_of_strings "${string_in}")
      break()
    endif()

    string(SUBSTRING "${string_in}" 0 ${eol_pos} substring)
    list(APPEND list_of_strings "${substring}")
    math(EXPR eol_pos "${eol_pos} + 1") # Skip EOL character
    string(SUBSTRING "${string_in}" ${eol_pos} -1 string_in)
  endwhile()

  # convert list of strings to defines readable by check_toolchain_definition
  set(definitions "")
  foreach(x ${list_of_strings})
    string(
      REGEX
      MATCH
      "__DEF_MACRO_CHECK_BEGIN__.*__DEF_MACRO_CHECK_END__"
      result_x
      "${x}"
    )
    if(result_x)
      string(
        REGEX
        REPLACE
        ".*__DEF_MACRO_CHECK_BEGIN__\(.*\)__DEF_MACRO_CHECK_END__.*"
        "\\1"
        result_x
        "${x}"
      )
    set(definitions "${definitions}${result_x}\n")
    endif()
  endforeach()

  set(${x_OUTPUT} ${definitions} PARENT_SCOPE)
endfunction()