module Celluloid
  module Internals
    module CPUCounter
      class << self
        def cores
          @cores ||= count_cores
        end

        private

        def count_cores
          result = from_env || from_sysdev || from_sysctl
          Integer(result.to_s[/\d+/], 10) if result
        end

        def from_env
          result = ENV["NUMBER_OF_PROCESSORS"]
          result if result
        end

        def from_sysdev
          ::IO.read("/sys/devices/system/cpu/present").split("-").last.to_i + 1
        rescue Errno::ENOENT
          result = Dir["/sys/devices/system/cpu/cpu*"].count { |n| n =~ /cpu\d+/ }
          result unless result.zero?
        end

        def from_sysctl
          result = `sysctl -n hw.ncpu`
          result if $CHILD_STATUS.success?
        rescue Errno::ENOENT
        end
      end
    end
  end
end