# Based on the Qt 5 processor detection code, so should be very accurate
# http://code.qt.io/cgit/qt/qtbase.git/tree/src/corelib/global/qprocessordetection.h
# Currently handles arm (v5, v6, v7, v8), x86 (32/64), ia64, and ppc (32/64)

# Regarding POWER/PowerPC, just as is noted in the Qt source,
# "There are many more known variants/revisions that we do not handle/detect."

set(archdetect_c_code "
#if defined(__arm__) || defined(__TARGET_ARCH_ARM) || defined(_M_ARM) \\
    || defined(__aarch64__) || defined(__ARM64__)
  #if defined(__aarch64__) || defined(__ARM64__)
    #define cmake_ARM_64
  #else
    #define cmake_ARM_32
  #endif
  #if defined(__ARM_ARCH) && __ARM_ARCH > 1
    #define cmake_ARM __ARM_ARCH
  #elif defined(__TARGET_ARCH_ARM) && __TARGET_ARCH_ARM > 1
    #define cmake_ARM __TARGET_ARCH_ARM
  #elif defined(_M_ARM) && _M_ARM > 1
    #define cmake_ARM _M_ARM
  #elif defined(__ARM64_ARCH_8__) \\
      || defined(__aarch64__) \\
      || defined(__ARMv8__) \\
      || defined(__ARMv8_A__)
    #define cmake_ARM 8
  #elif defined(__ARM_ARCH_7__) \\
      || defined(__ARM_ARCH_7A__) \\
      || defined(__ARM_ARCH_7R__) \\
      || defined(__ARM_ARCH_7M__) \\
      || defined(__ARM_ARCH_7S__) \\
      || defined(_ARM_ARCH_7) \\
      || defined(__CORE_CORTEXA__)
    #define cmake_ARM 7
  #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__)
    #define cmake_ARM 6
  #elif defined(__ARM_ARCH_5TEJ__) \\
      || defined(__ARM_ARCH_5TE__)
    #define cmake_ARM 5
  #else
    #define cmake_ARM 0
  #endif
  #if cmake_ARM >= 8
    #error cmake_ARCH armv8
  #elif cmake_ARM >= 7
    #error cmake_ARCH armv7
  #elif cmake_ARM >= 6
    #error cmake_ARCH armv6
  #elif cmake_ARM >= 5
    #error cmake_ARCH armv5
  #else
    #if defined(cmake_ARM_64)
      #error cmake_ARCH arm64
    #else
      #error cmake_ARCH arm
    #endif
  #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)
  if(APPLE AND CMAKE_OSX_ARCHITECTURES)
    # On OS X we use CMAKE_OSX_ARCHITECTURES *if* it was set
    # First let's normalize the order of the values

    # Note that it's not possible to compile PowerPC applications if you are using
    # the OS X SDK version 10.6 or later - you'll need 10.4/10.5 for that, so we
    # disable it by default
    # See this page for more information:
    # http://stackoverflow.com/questions/5333490/how-can-we-restore-ppc-ppc64-as-well-as-full-10-4-10-5-sdk-support-to-xcode-4

    # Architecture defaults to i386 or ppc on OS X 10.5 and earlier, depending on the CPU type detected at runtime.
    # On OS X 10.6+ the default is x86_64 if the CPU supports it, i386 otherwise.

    foreach(osx_arch ${CMAKE_OSX_ARCHITECTURES})
      if("${osx_arch}" STREQUAL "ppc" AND ppc_support)
        set(osx_arch_ppc TRUE)
      elseif("${osx_arch}" STREQUAL "i386")
        set(osx_arch_i386 TRUE)
      elseif("${osx_arch}" STREQUAL "x86_64")
        set(osx_arch_x86_64 TRUE)
      elseif("${osx_arch}" STREQUAL "ppc64" AND ppc_support)
        set(osx_arch_ppc64 TRUE)
      else()
        message(FATAL_ERROR "Invalid OS X arch name: ${osx_arch}")
      endif()
    endforeach()

    # Now add all the architectures in our normalized order
    if(osx_arch_ppc)
      list(APPEND ARCH ppc)
    endif()

    if(osx_arch_i386)
      list(APPEND ARCH i386)
    endif()

    if(osx_arch_x86_64)
      list(APPEND ARCH x86_64)
    endif()

    if(osx_arch_ppc64)
      list(APPEND ARCH ppc64)
    endif()
  else()
    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()
  endif()

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