# Based on the Qt 5 processor detection code, so should be very accurate
# https://qt.gitorious.org/qt/qtbase/blobs/master/src/corelib/global/qprocessordetection.h Currently handles arm (v5,
# v6, v7), x86 (32/64), ia64, and ppc (32/64)

set(archdetect_c_code
    "
#if defined(__arm__) || defined(__TARGET_ARCH_ARM)
    #if defined(__ARM_ARCH_7__) \\
        || defined(__ARM_ARCH_7A__) \\
        || defined(__ARM_ARCH_7R__) \\
        || defined(__ARM_ARCH_7M__) \\
        || (defined(__TARGET_ARCH_ARM) && __TARGET_ARCH_ARM-0 >= 7)
        #error cmake_ARCH armv7
    #elif defined(__ARM_ARCH_6__) \\
        || defined(__ARM_ARCH_6J__) \\
        || defined(__ARM_ARCH_6T2__) \\
        || defined(__ARM_ARCH_6Z__) \\
        || defined(__ARM_ARCH_6K__) \\
        || defined(__ARM_ARCH_6ZK__) \\
        || defined(__ARM_ARCH_6M__) \\
        || (defined(__TARGET_ARCH_ARM) && __TARGET_ARCH_ARM-0 >= 6)
        #error cmake_ARCH armv6
    #elif defined(__ARM_ARCH_5TEJ__) \\
        || (defined(__TARGET_ARCH_ARM) && __TARGET_ARCH_ARM-0 >= 5)
        #error cmake_ARCH armv5
    #else
        #error cmake_ARCH arm
    #endif
#elif defined(__i386) || defined(__i386__) || defined(_M_IX86)
    #error cmake_ARCH i386
#elif defined(__x86_64) || defined(__x86_64__) || defined(__amd64) || defined(_M_X64)
    #error cmake_ARCH x86_64
#elif defined(__ia64) || defined(__ia64__) || defined(_M_IA64)
    #error cmake_ARCH ia64
#elif defined(__ppc__) || defined(__ppc) || defined(__powerpc__) \\
      || defined(_ARCH_COM) || defined(_ARCH_PWR) || defined(_ARCH_PPC)  \\
      || defined(_M_MPPC) || defined(_M_PPC)
    #if defined(__ppc64__) || defined(__powerpc64__) || defined(__64BIT__)
        #error cmake_ARCH ppc64
    #else
        #error cmake_ARCH ppc
    #endif
#endif

#error cmake_ARCH unknown
")

# Set ppc_support to TRUE before including this file or ppc and ppc64 will be treated as invalid architectures since
# they are no longer supported by Apple

function(target_architecture output_var)
  file(WRITE "${CMAKE_BINARY_DIR}/arch.c" "${archdetect_c_code}")

  enable_language(C)

  # Detect the architecture in a rather creative way... This compiles a small C program which is a series of ifdefs that
  # selects a particular #error preprocessor directive whose message string contains the target architecture. The
  # program will always fail to compile (both because file is not a valid C program, and obviously because of the
  # presence of the #error preprocessor directives... but by exploiting the preprocessor in this way, we can detect the
  # correct target architecture even when cross-compiling, since the program itself never needs to be run (only the
  # compiler/preprocessor)
  try_run(
    run_result_unused
    compile_result_unused
    "${CMAKE_BINARY_DIR}"
    "${CMAKE_BINARY_DIR}/arch.c"
    COMPILE_OUTPUT_VARIABLE ARCH
    CMAKE_FLAGS CMAKE_OSX_ARCHITECTURES=${CMAKE_OSX_ARCHITECTURES})

  # Parse the architecture name from the compiler output
  string(
    REGEX MATCH
          "cmake_ARCH ([a-zA-Z0-9_]+)"
          ARCH
          "${ARCH}")

  # Get rid of the value marker leaving just the architecture name
  string(
    REPLACE "cmake_ARCH "
            ""
            ARCH
            "${ARCH}")

  # If we are compiling with an unknown architecture this variable should already be set to "unknown" but in the case
  # that it's empty (i.e. due to a typo in the code), then set it to unknown
  if(NOT ARCH)
    set(ARCH unknown)
  endif()

  set(${output_var}
      "${ARCH}"
      PARENT_SCOPE)
endfunction()